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Telangana TSBIE TS Inter 1st Year Zoology Study Material 8th Lesson Ecology and Environment Textbook Questions and Answers.

TS Inter 1st Year Zoology Study Material 8th Lesson Ecology and Environment

Very Short Answer Type Questions

Question 1.
Define the term ecology. (T.Q.)
Answer:
Ecology was defined as “the study of the relationship of organisms with their environment”.

Question 2.
What is autecology?
Answer:
Autecology is the ecology of a single species/population in relation to its environment. It is also known as species (population) ecology.

Question 3.
What do you call the study of interactions of organisms of a community?
Answer:
Synecology is a branch of ecology that deals with the structure, development and distribution of ecological communities.

Question 4.
What is an ecological population? (T.Q.)
Answer:
Population is a group of organisms of the same species, living in a specific area at a specific time.

Question 5.
Define a community. (T.Q.)
Answer:
Community is an association of the interacting members of populations of different autotrophic and heterotrophic species in a particular area.

Question 6.
What is an ecosystem? (T.Q.)
Answer:
Ecosystem is the next level of organisation above the level of biological community. An ecosystem is a functional unit of the biosphere in which members of the community interact among themselves and with surrounding environment.

Question 7.
Distinguish between ecosystem and biome.
Answer:

1. Ecosystem is a functional unit of biosphere in which members of the community interact among themselves and with surrounding environment.
2. A biome is a large community of plants and animals that occupies a vast region.

Question 8.
What is a biome? Name any two biomes you studied. (T.Q.)
Answer:
A biome is a large community of plants and animals that occupies a vast region.
eg : Tropical rain forest, desert, coniferous forest, tundra etc.

Question 9.
What is meant by ecosphere? (T.Q.)
Answer:
All the habitable zones on the Earth constitute the ecosphere or biosphere. It is the part of the Earth that supports life.

Question 10.
Define the term habitat.
Answer:
Habitat is the place in which an organism lives. It is comparable to the address of an organism.

Question 11.
Explain the difference between the ‘niche* of an organism and its ‘habitat’. (T.Q.)
Answer:

1. Niche : With in a community, each organism occupies a particular biological role or Niche. Niche is the functional role of an organism in an ecosystem.
2. Habitat is the place in which an organism lives.

Question 12.
A population has more genetically similar organisms than those on biotic community. Justify the statement. (T.Q.)
Answer:

1. Population is a group of organisms of the same species, living in a specific area at a specific time.
2. Community is an association of the interacting members of populations of different autotrophic and heterotrophic species in a particular area.

Question 13.
Among the red, green and brown algae that inhabit the sea, which is likely to be found in the deepest waters? Why?
Answer:
There are microbes like archaebacteria that flourish in hotsprings and in some parts of deep seas, where temperatures far exceed 100°C. Brown algae is likely to be found in the deepest waters as it is an alchea bacterium.

Question 14.
What is the source of energy for deep sea inhabitants?
Answer:
The source of energy for deep sea inhabitants is by the action of brown algae releasing energy during synthesis of their food. The spectral quality of solar radiation is also important in life. Also detritus food of sea bottom.

Question 15.
How do the fish living in Antarctic waters manage to keep their body fluids from freezing? (T.Q.)
Answer:
Many fish thrive in Antarctic waters where the temperature is always below zero. Many species have evolved a relatively constant internal environment. It permits all biochemical reactions and physiological functions to proceed with maximal efficiency and thus, enhance the overall fitness of the species.

Question 16.
How does your body solve the problem of altitude sickness, when you ascend tall mountains? (T.Q.)
Answer:
Altitude also causes variations in temperature. For instance, the temperature decreases gradually as we move to the top of the mountains we experience altitude sickness if we ever been to any high altitude place. Its symptoms include nausea, fatigue and heart palpitations. We can solve the problem because the body compensates low oxygen availability by increasing red blood cell production and increasing the rate of breathing.

Question 17.
Name the structural components of an ecosystem.
Answer:
The structural components of ecosystem are of two types: Abiotic and biotic factors. Abiotic factors are two types : physical and chemical.
Physical are light, temperature, soil, pressure etc.
Chemical are oxygen, carbondioxide, minerals of soil / water.

Question 18.
What is the effect of light on body pigmentation? (T.Q.)
Answer:
Light influences the colour of the skin. The animals which live in regions of low intensity of light have less pigmentation than that of the animals exposed to light.

Question 19.
Distinguish the terms phototaxis and photokinesis. (T.Q.)
Answer:

1. Phototaxis is oriented locomotor movement of an organism towards or away from the direction of light.
2. Photokinesis is the influence of light on non-directional movement of organisms as seen in the larvae of Pinnotheres macculatus-the mussel crab. Intensity of light influences the velocity of the movement of organism.

Question 20.
What is the primardial source of energy for all living organisms?
Answer:
The primardial source of energy for all living organisms is Sunlight.

Question 21.
What are biological rhythms?
Answer:
In the bodies of organisms, many behavioural activities are repeated at regular intervals and these are called biological rhythms.

Question 22.
What are circadian rhythms?
Answer:
Biological rhythms that occur in a time period of 24 hours are circadian rhythms.

Question 23.
What is photoperiodism? (T.Q.)
Answer:
The duration of the light hours / exposure to light in a day is known as photoperiod. The response of organisms for the photoperiod is called Photoperiodism.

Question 24.
Distinguish between photoperiod and critical photoperiod. (T.Q.)
Answer:
The duration of the light hours / exposure to light in a day is known as Photoperiod. The specific day length which is essential for the initiation of seasonal events is called ‘Critical Photoperiod’.

Question 25.
Explain Bioluminescence.
Answer:
Production of light by certain living organisms is called Bioluminestence. The light emitted by living organisms is devoid of infrared rays and so it is called cold light.

Question 26.
Mention the advantages of some UV rays to us. [March 2014] (T.Q.)
Answer:
UV radiation helps in the conversion of sterols present in the skin into vitamin D in mammals.

Question 27.
Distinguish between the terms heat and temperature.
Answer:
Temperature is a measure of the intensity of heat.

Question 28.
Distinguish between minimum effective temperature and maximum effective temperature.
Answer:

1. The lowest temperature at which an organism can live indefinitely is called minimum effective temperature.
2. The maximum temperature at which a species can live indefinitely in an active state is called maximum effective temperature.

Question 29.
What is optimum temperature?
Answer:
The temperature at which the metabolic activities occur at the climax level is called “optimum temperature”.

Question 30.
What is cyclomorphosis? Explain its importance in Daphnia. [March 2019] (T.Q.)
Answer:
The cyclic seasonal morphological variations among certain organisms is called cyclomorphosis. In Daphnia (water flea) the body may become elongated with hood or short with out hood depending upon seasons. Cyclomorphosis is a seasonal adaptation to changing densities of water in lakes based on seasons.

Question 31.
What are “regulators”? (T.Q.)
Answer:
Some organisms are able to maintain homeostasis by physiological (sometimes behavioural) means which ensures constant body temperature constant osmotic concentration. These are called regulators.

There are no perfect regulators. (Eg : Birds and Mammals)

Question 32.
What are ‘conformers’? (T.Q.)
Answer:
In aquatic animals, the osmotic concentration of the body fluids changes along with that of the surrounding water. Such animals are described as conformers. There are no perfect conformers.

Question 33.
Define commensalism. Give one example. [May 2017 – A.P.] (T. Q.)
Answer:
The interaction where one species is benefited and the other is neither benefited nor harmed is called “commensalism”.
Example : Barnacles growing on the back of a whale benefit while the whale derives no noticeable benefit.

Question 34.
Define mutualism. Give one example. [March 2015 – A.P.] (T. Q.)
Answer:
This type of interaction benefits both the interacting species.
Example: Lichens represent an intimate mutualistic relationship between a fungus and photosynthetic algae.

Question 35.
Define parasitism. Give one example.
Answer:
In parasitism only one species benefits and the interaction is detrimental to the other species. Parasite generally harms ho’st. Malarial parasite causes harm to the host man by causing malaria.

Question 36.
Define amensalism. Give one example. (T.Q.)
Answer:
In amensalism one species is harmed whereas the other is unaffected.

Question 37.
What is predation? Give one example.
Answer:
Predation :
Only one species benefits and the interaction is detrimental to the other species. Tiger predates upon a deer.

Question 38.
What is meant by interspecific competition? Give one example. (T.Q.)
Answer:
Interspecific competition is a potent force in the process of organic evolution, involving natural selection.
Example : In intertidal communities of the American Pacific Coast, the Starfish Pisaster is an important predator. In a field experiment, when all the starfish were removed from an enclosed intertidal area, more than 10 species of invertebrates became extinct within a year, because of increased inter-specific competition.

Question 39.
Distinguish between predation and parasitism.
Answer:
In both parasitism and predation only one species benefits (parasite and predator, respectively) and the interaction is detrimental to the other species (Host and Prey respectively). Sometimes predator controls over population of prey. Majority of parasites harm the host.

Question 40.
Distinguish between the interactions commensalism and amensalism.
Answer:
The interaction where one species is benefited and the other is neither benefited nor harmed is called “commensalism”.
Example: Barnacles growing on the back of a whale benefit while the whale derives no noticeable benefit.

In amensalism on the other hand one species is harmed whereas the other is unaffected.

Question 41.
In an ecological food chain, what types of interactions exist between trophic levels?
Answer:
Types of interactions exist between trophic levels are mutualism, commensalism, parasitism, amensalism, parasitism and predation.

Question 42.
What is camouflage? Give its significance. (T.Q.)
Answer:
Some species of insects and frogs are cryptically coloured (camouflaged) to avoid being detected easily by the predator.
Example : Stick insect.

Question 43.
What is Gause’s principle ? When is it applicable? (T.O.)
Answer:
Gause’s principle of competitive exclusion states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated in due course of time.

Question 44.
Name the association that exist in micorrhiza. (T.O.)
Answer:
Mycorrhizae are associations between fungi and the roots of higher plants. The fungi help the plant in the absorption of essential nutrients from the soil while the plant in turn provides the fungi with energy yielding carbohydrates. It is mutualism.

Question 45.
What are lichens?
Answer:
Lichens represent an intimate mutualistic relationship between a fungus and photosynthesising algae or cyanobacteria.

Question 46.
Name the major types of ecosystems.
Answer:
Major types of ecosystems are basically two types : Natural and Artificial. Natural ecosystems are aquatic and terrestrial ecosystems. Artificial ecosystems are agro-ecosystems like cropland ecosystems, aquaculture ponds and aquaria.

Question 47.
Distinguish between natural ecosystem and an artificial ecosystem.
Answer:
Natural Ecosystems :
These are naturally occurring ecosystems and these is no role of humans in the formation of such types of ecosystems.

Artificial ecosystems :
These are man made ecosystems such as agricultural or agro ecosystems. They include cropland ecosystems, aquaculture ponds and aquaria.

Question 48.
What is an estuary?
Answer:
Estuary is the zone where river joins the sea. Sea water ascends up into the river twice a day.

Question 49.
How does an estuarine ecosysterri differ from freshwater ecosystem?
Answer:
The Freshwater Ecosystem :
Is the smallest aquatic ecosystem. It includes rivers, lakes, ponds etc. Fresh water ecosystem is studied under Limnology.

Estuarine Ecosystem :
Estuary is the zone where river joins the sea. Sea water ascends up into the river twice a day. Estuarine organisms are capable of with standing the fluctuations in salinity.

Question 50.
Distinguish between lotic and lentic habitats. [March 2018 – A.P.] (T.Q.)
Answer:

1. The still water bodies like ponds, lakes, reservoirs, etc., fall under the category of lentic ecosystems.
2. Streams, rivers and flowing water bodies are called lotic ecosystems.

Question 51.
What is limnology?
Answer:
The study of freshwater ecosystem is called as Limnology.

Question 52.
What is euphotic zone?
Answer:
It is the shallow part of the lake closer to the shore. Light penetrates up to the bottom. It is Euphotic zone. It has rich vegetation and higher rate of photosynthesis, hence rich in oxygen.

Question 53.
What is zone of compensation in an aquatic ecosystem? (T.Q.)
Answer:
The imaginary line that separates the limnetic zone from the profundal zone is known as zone of compensation / compensation point / light compensation level.

Question 54.
Distinguish between phytoplankton and zooplankton. (T.Q.)
Answer:

1. Chlorophyll bearing floating micro organisms present in the water form the phytoplankton, eg : diatoms, volvox.
2. Small microscopic floating animals present in the surface waters form the zooplankton, eg: rotifers, copepods, Daphnia.

Question 55.
Distinguish between neuston and nekton. (T.Q.)
Answer:

1. The animals living at the air – water interface constitute the neuston.
2. The animals such as fishes, amphibians, water snakes which are capable of swimming constitute the nekton.

Question 56.
What is periphyton? (T.Q.)
Answer:
The animals that are attached to / creeping on the aquatic plants, such as the water snails, nymphs of insects, bryozoans, hydras constitute the periphyton.

Question 57.
What is benthos?
Answer:
The animals that rest on or move on the bottom of the lake constitute the ‘benthos’ eg: red annelids, chironomid larvae, crayfishes, some isopods, amphipods, clams, etc.

Question 58.
Write three examples for man-made ecosystems. (T.Q.)
Answer:
Examples for man-made ecosystems are 1) Cropland ecosystems 2) Aquaculture ponds 3) Aquaria.

Question 59.
What is meant by osmotrophic nutrition?
Answer:
Intake of pre-digested food material through the body surface is called osmotrophic nutrition.

Question 60.
Explain the process of ‘leaching’.
Answer:
By the process of leaching, water soluble inorganic nutrients go down into the soil and get precipitated as unavailable salts.

Question 61.
What is catabolism?
Answer:
Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called as catabolism.

Question 62.
What is humification? Name the organisms which act on it.
Answer:
Humification and mineralization occur during decomposition in the soil. Humification leads to accumulation of a dark coloured amorphous substance called humus. Microbes work on humus and make it further degraded.

Question 63.
What is PAR? (T.Q.)
Answer:
Sun is the only source of energy for all ecosystems on earth. Of the incident solar radiation less than 50 percent of it is photosynthetically active radiation(PAR). Plants capture only 2-10 percent of the PAR and this small amount of energy sustains the entire living world.

Question 64.
What is the percentage of PAR, in the incident solar radiation? (T.Q.)
Answer:
Of the incident solar radiation less than 50 percent of it is photosynthetically active radiation (PAR).

Question 65.
Define entropy. (T.Q.)
Answer:
Energy lost or not available for work in a system is called ENTROPY.

Question 66.
What is standing crop? (T.Q.)
Answer:
Each trophic level has a certain mass of living material at a particular time, and it is called the standing crop. The standing crop is measured as the mass of living organisms or the number of organisms per unit area.

Question 67.
If you were to count the number of insects feeding on a big tree, and asked to graphically represent the relation of structure and function between the tree and insects, what kind of pyramid does it form ?
Answer:
It forms an inverted pyramid of Numbers.

Question 68.
Explain the terms GPP, NPP. (T.Q.)
Answer:
1) Gross primary productivity (GPP) of an ecosystem is the rate of production of organic matter during photosynthesis.

2) Net primary productivity (NPP) :
Gross primary productivity minus respiratory loss (R) is the net primary productivity (NPP). On average about 20 – 25 percent of GPP is used for the catabolic (respiratory) activity.

Question 69.
Distinguish between GFC and DFC.
Answer:
a) GFC :
Grazing Food Chain also known as predatory food chain.

b) DFC :
Detritus Food Chain which begins with dead organic matter.
Some of the organisms of DFC may form the prey of GFC animals.

Question 70.
Name the trophic level(s) at which ‘decomposers’ feed.
Answer:
Decomposers break down complex organic matter into simple inorganic substances like CO₂, water and nutrients and the process is called decomposition. It occupies first trophic level.

Question 71.
Distinguish between production and decomposition.
Answer:
a) The green paints in the ecosystem terminology are called producers. They synthesize the food by using solar energy. They form main source of food for the organisms.

b) Breaking down of complex organic matter into simple inorganic substances like carbondioxide, water and nutrients by decomposess (microbes) and this process is called decomposition.

Question 72.
Distinguish between upright and inverted ecological pyramids. (T.Q.)
Answer:

1. In most ecosystems, all the pyramids of numbers, energy and biomass are upright i.e., produces are more in number and biomass than the herbivores, herbivores more in number and biomass than the carnivores.
2. In case of a parasitic food chain, the pyramid of numbers is inverted. Here in each trophic level from the bottom to the top, th’e numbers of organisms increase and form an inverted pyramid of numbers.

Question 73.
Distinguish between food chain and food web.
Answer:

1. When the path of food energy is ‘linear’ the components resemble the links of a chain and it is called food chain.
2. The natural interconnections of food chains form a network called food web.

Question 74.
Distinguish between litter and detritus. (T.Q.)
Answer:

1. Plant parts such as leaves, bark, flowers and dead remains of animals, including their faecal matter, constitute the detritus.
2. Litter contains only dead decayed plant material mixed with mud and soil.

Question 75.
Distinguish between primary and secondary productivity. (T.Q.)
Answer:

1. Primary productivity is defined as the amount of biomass or organic matter produced per unit area over a period of time by plants, during photosynthesis.
2. Secondary productivity is defined as the rate of formation of new organic matter by consumers.

Question 76.
What is the effect of Carbon monoxide pollution on human beings?
Answer:
CO interferes with O₂ transport. CO causes symptoms such as headache and blurred vision at lower concentrations. In higher concentrations. It leads to coma and death.

Question 77.
What is ‘Green House Effect’?
Answer:
The green house effect is a naturally occurring phenomenon that is responsible for heating of the Earth’s surface and atmosphere.

Question 78.
Which air pollutants are chiefly responsible for acid rains? (T.Q.)
Answer:
Sulphur dioxide and nitrogen oxides are the major causes of acid rains.

Question 79.
What is BOD? (T.Q.)
Answer:
BOD (biological oxygen demand) is a measure of the content of biologically degradable substances in sewage. Micro organisms involved in biodegradation of organic matter in water bodies consume a lot of oxygen, and as a result there is a sharp decline in dissolved oxygen causing death offish and other aquatic animals.

Question 80.
What is biological magnification? [March 2020, ’13] (T.Q.)
Answer:
Increase in the concentration of the pollutant or toxicant at successive trophic levels in an aquatic food chain is called Biological Magnification or Bio-magnification.

Question 81.
Distinguish between ‘Global warming’ and ‘Thermal pollution’?
Answer:

1. Increase in the level of green house gases has led to considerable heating of the earth leads to Global warming. Global warming is causing climatic changes.
2. Water pollution caused by hot water coming out from industries, thermal power plants which is harmful to aquatic organisms is called thermal pollution.

Question 82.
Why are incinerators used in hospitals? [May/June 2014] (T. Q.)
Answer:
Hospitals generate hazardous wastes that contain disinfectants, harmful chemicals and also pathogenic micro- organisms. Such wastes also require careful treatment and disposal. The use of incinerators (to burn wastes) is essential for disposal of hospital waste.

Question 83.
Why are catalytic converters used in automobiles?
Answer:
Fitting catalytic converters to the automobiles having expensive metals namely platinum, palladium and rhodium as catalysts which reduce emission of poisonous gases.

Short Answer Type Questions

Question 1.
Write about ecological hierarchy.
Answer:
Ecological Hierarchy :
Hierarchy means arrangement into a ‘graded series’. Ecological organization consists of eleven integrative levels, ranging from Cell to Ecosphere – cell, tissue, organ, organ – system, organism, population, community, ecosystem, landscape, biome and ecosphere (also called Biosphere).

Population :
Population is a group of organisms of the same species, living in a specific area at a specific time.

Community :
It is an association of the interacting members of populations of different autotrophic and heterotrophic species in a particular area. In a community, generally one or a few species dominate with reference to their numbers or size.

Ecosystem :
It is the next level of organization above the level of biological community. An ecosystem is a functional unit of the biosphere in which members of the community interact among themselves and with the surrounding environment, involving ‘flow of energy’ forming a well defined trophic structure.

Landscape :
It is the unit of land containing different ecosystems (mosaic of ecosystems) surrounded by natural boundaries. It is the level of organization higher than ‘ecosystem’.

Biome :
A ‘biome’ is a large community of plants and animals that occupies a vast region. There are ‘terrestrial biomes’ and ‘aquatic biomes’.

Ecosphere (Biosphere) :
All the habitable zones on the Earth constitute the ecosphere or biosphere. It is the part of the Earth that supports ‘life’.

Question 2.
Write a note on habitat and medium.
Answer:
Habitat and Medium: Ecologically, habitat is the place in which an organism lives. It is comparable to the ‘address’ of a person (as mentioned in the introduction page to ecology). For instance, the habitat of fish is a pond, lake, sea etc., the habitat of a lion is forest, the habitat of Ascaris is the ‘small intestine’ of man, and so on. The water surrounding the body of a fish is called the medium and the medium of a lion is the air around its body.

Question 3.
Considering the benefits of a constant internal environment to the organism, we tend to ask ourselves ‘why the conformers had not evolved to become regulators’? (T.Q.)
Answer:
Majority (99 percent) of animals cannot maintain a constant internal environment. Their body temperature changes with the ambient (surrounding) temperature. In aquatic animals the osmotic concentration of the body fluids changes along with that of the surrounding water. Such animals are described as conformers. Conformer means adapt from one condition to a new or different conditions.

Thermoregulation is energetically expensive for many organisms. (Animals such as camels can be conformers upto a particular range of temperature and regulator afterwards). Heat loss or heat gain is a function of the surface area.

During the course of evolution, the costs and benefits of maintaining a constant internal environment are taken into consideration.

Question 4.
The individuals who have fallen through the ice and been submerged under cold water for long periods can sometimes be revived – explain. (T.Q.)
Answer:
Many fish thrive in Antarctic waters where the temperature is always below zero. Having realized that the abiotic conditions of many habitats may vary over a time period. One would expect that during the course of millions of years of their existence, many species would have evolved a relatively constant internal environment. It permits all biochemical reactions and physiological functions to proceed with maximal efficiency and thus, enhance the overall fitness of the species. The familiar case of polar bears going into hibernation during winter is an example of escape in time. Some snails and fish go into aestivation to avoid summer related problems- heat and desiccation.

Question 5.
What is summer stratification? Explain. [March 2020] (T.Q.)
Answer:
Summer stratification :
During summer in temperate lakes, the density of the surface water decreases because of increase in its temperature (21-25°C). This ‘upper more warm layer’ of a lake is called epilimnion. Below the epilimnion there is a zone in which the temperature decreases at the rate of 1° C per meter in depth, and it is called thermocline or metalimnion. The bottom layer is the hypolimnion, where water is relatively cool, stagnant and with low oxygen content (due to absence of photosynthetic activity).

During autumn (also called Fall), the epilimnion cools down, and the surface water becomes heavy when the temperature is 4°C, and sinks to the bottom of the lake. Overturns bring about ‘uniform temperature’ in lakes during that period. This circulation during the autumn is known as the fall or autumn overturn. The upper oxygen rich water reaches the hypoliminion and the nutrient rich bottom water comes to the surface. Thus there is uniform distribution of nutrients and oxygen in the lake.

Question 6.
What is the significance of stratification in lakes? (T.Q.)
Answer:
Temperature variations occur with seasonal changes in the temperate regions. These differences in the temperature form ‘thermal layers’ in water. These phenomena are called thermal stratifications.

Water shows maximum density at 4°C. Rise or faII of temperatures above or below 4°C decreases its density. This anomalous property of water and the seasonal variations in temperature are responsible for the thermal stratification in temperate lakes.

Due to overturns, there is uniform distribution of nutrients and oxygen in the lake.

Question 7.
Explain van’t Hoff rule. (T.Q.)
Answer:
van’t Hoff’s rule :
van’t Hoff, a Nobel Laureate in thermochemistry, proposed that, with the increase of every 10°C, the rate of metabolic activities doubles. This rule is referred to as the van’t Hoff’s rule, van’t Hoff’s rule can also be stated in reverse saying that the reaction rate is halved with the decrease of every 10°C. The effect of temperature on the rate of a reaction is expressed in terms of temperature coefficient or Q₁₀ value. Q₁₀ values are estimated taking the ratio between the rate of a reaction at X°C and rate of reaction at (X – 10°C). In the ‘living systems’ the Q₁₀ value is about 2.0. If the Q₁₀ value is 2.0, it means, for every 10°C increase, the rate of metabolism doubles.

Question 8.
Unlike mammals the reptiles cannot tolerate environmental fluctuations in temperature. How do they adapt to survive in desert conditions? (T.Q.)
Answer:
Some organisms show behavioural responses to cope with variations in their environment. Desert lizards manage to keep their body temperature fairly constant by behavioural means. They ‘bask’ (staying in the warmth of sunlight) in the sun and absorb heat when their body temperature drops below the comfort zone, but move into shade when the temperature starts increasing. Some species are capable of burrowing into the soil to escape from the excessive heat above the ground level.

Question 9.
Write a short note on soil as an ecological abiotic factor.
Answer:
Soil :
The nature and properties of soil in different places vary depending on the climate, and the ‘weathering’ processes involved. Various characteristics of the soil such as soil composition, grain size and aggregation determine the percolation and water-holding capacity of the soils. These characteristics, along with the parameters such as pH, mineral composition etc., determine to a large extent the vegetation in any area. This in turn dictates the type of aninmals that can be supported. Similarly, in the aquatic environment, the sediment-characteristics often determine the type of benthic animals that can live there. ‘

Question 10.
How do terrestrial animals protect themselves from, the danger of dehydration of bodies? (T.Q.)
Answer:
In the absence of an external source of water, the kangaroo rat of the North American deserts is capable of meeting all its water requirements through oxidation of its internal fat (in which water is a by product – metabolic water). It also has the ability to concentrate its urine, so that minimal volume of water is lost in the process of removal of their excretory products.

Question 11.
How do marine animals adapt to hypertonic seawater? (T.Q.)
Answer:
Seawater is high in salt content compared to that of the body fluids. So, the marine animals continuously tend to lose water from their bodies by exosmosis and face the problem of dehydration. To overcome the problem of water loss, marine fishes have aglomerular kidneys with less numbers of nephrons. Such kidneys minimize the loss of water through urine. To compensate water loss the marine fish drink more water, and along with this water, salts are added to the body fluids and disturb the internal equilibrium.

To maintain salt balance (salt homeostasis) in the body, they have salt secreting chloride cells in their gills. Marine birds like sea gulls and penguins eliminate salts in the form of salty fluid that drips through their nostrils. In turtles the ducts of chloride secreting glands open near the eyes. Some cartilaginous fishes retain urea and trimethylamine oxide (TMO) in their blood to keep the body fluid isotonic to the sea water and avoid dehydration of the body due to exosmosis.

Question 12.
Discuss the various types of adaptations in freshwater animals. (T.Q.)
Answer:
Adaptations in freshwater habitat :
Animals living in freshwaters have to tackle the problem of endosmosis. The osmotic pressure of freshwater is very low and that of the body fluids of freshwater organisms is much higher. So water tends to enter into bodies by endosmosis. To maintain the balance of water in the bodies, the freshwater organisms acquired several adaptations such as, contractile vacuoles in the freshwater protozoans, large glomerular kidneys in fishes, etc. They send out large quantities of urine, along which some salts are also lost.

To compensate the ‘salt loss’ through urine, freshwater fishes have salt absorbing ‘chloride cells’ in their gills. The major problem in freshwater ponds is – in summer most of the ponds dry up. To overcome this problem most of the freshwater protists undergo encystment. The freshwater sponges produce asexual reproductive bodies, called gemmules, to tide over the unfavourable conditions of the summer. The ‘African lungfish’, Protopterus, burrows into the mud and forms a ‘gelatinous cocoon’ around it, to survive, in summer.

Question 13.
Compare the adaptations of animals with freshwater and seawater mode of life. (T.Q.)
Answer:
Seawater is high in salt content compared to that of the body fluids. So, the marine animals continuously tend to lose water from their bodies by exosmosis and face the problem of dehydration. To overcome the problem of water loss, marine fishes have aglomerular kidneys with less numbers of nephrons. Such kidneys minimize the loss of water through urine. To compensate water loss the marine fish drink more water, and along with this water, salts are added to the body fluids and disturb the internal equilibrium. To maintain salt balance (salt homeostasis) in the body, they have salt secreting chloride cells in their gills.

Marine birds like sea gulls and penguins eliminate salts in the form of salty fluid that drips through their nostrils. In turtles the ducts of chloride secreting glands open near the eyes. Some cartilaginous fishes retain urea and trimethylamine oxide (TMO) in their blood to keep the body fluid isotonic to the sea water and avoid dehydration of the body due to exosmosis.

Adaptations in freshwater habitat :
Animals living in freshwaters have to tackle the problem of endosmosis. The osmotic pressure of freshwater is very low and that of the body fluids of freshwater organisms is much higher. So water tends to enter into bodies by endosmosis. To maintain the balance of water in the bodies, the freshwater organisms acquired several adaptations such as, contractile vacuoles in the freshwater protozoans, large glomerular kidneys in fishes, etc. They send out large quantities of urine, along which some salts are also lost. To compensate the ‘salt loss’ through urine, freshwater fishes have salt absorbing ‘chloride cells’ in their gills.

The major problem in freshwater ponds is – in summer most of the ponds dry up. To overcome this problem most of the freshwater protists undergo encystment. The freshwater sponges produce asexual reproductive bodies, called gemmules, to tide over the unfavourable conditions of the summer. The ‘African lungfish’, Protopterus, burrows into the mud and forms a ‘gelatinous cocoon’ around it, to survive, in summer.

Question 14.
Distinguish between euryhaline and stenohaline animals. (T.Q.)
Answer:
For aquatic organisms the quality (chemical composition, pHr etc.,) of water becomes important. The salt concentration is less than 5 percent in inland, waters, and 30 – 35 percent in the sea water. Some organisms are tolerant to a wide range of salinities (euryhaline), but others are restricted to a narrow range (stenohaline). Many freshwater animals cannot live for long in sea water and vice versa because of the osmotic problems, they would face.

The animals of brackish water are adapted to withstand wide fluctuations in salinity. Such organisms are called euryhaline animals and those that can’t withstand are known as stenohaline.

Question 15.
How do the non migratory animals overcome the unfavourable climatic conditions?
Answer:
In bacteria, fungi and lower plants, various kinds of thick-walled spores are formed which help them survive unfavourable conditions. They germinate (come out of the spore wall and produce a normal active organism) on the return of suitable environmental conditions.

Some animals can avoid the stress by escaping in ‘time’ (migration is escaping in ‘space’). The familiar case of ‘polar bears’ going into hibernation during winter is an example of escape in time. Some snails and fish go into aestivation to avoid summer-related problems – heat and desiccation.

Diapause :
Certain organisms show delay in development, during periods of unfavourable environmental conditions and spend some period in a state of ‘inactiveness’ called ‘diapause’. This dormant period in animals is a mechanism to survive extremes of temperature, drought, etc. It is seen mostly in insects and embryos of some fish. Under unfavourable conditions many zooplankton species in lakes and ponds are known to enter diapause.

Question 16.
Many tribes living in high altitude of Himalayas normally have higher red blood cell count (or) total haemoglobin that the people living in the plains. Explain. (T.Q.)
Answer:
Pressure is another factor that changes dramatically with depth in the ocean. Organisms on land face less than one ‘atmosphere’ of pressure at the sea level. Since water is much heavier than air, marine organisms are under much more pressure than those pn land. The pressure in water increases at the rate of 1 atmosphere per 10m depth. The organisms living in such extreme environments show a wide range of biochemical adaptations. Some organisms possess adaptations that are physiological and allow them to respond quickly to a stressful situation. If you had ever been to any high altitude place (e.g. > 3,500m Rohtang Pass near Manali and Manasarovar, in Tibet) you must have experienced what is called altitude sickness.

Its symptoms include nausea (vomiting sense), fatigue (tiredness) and heart palpitations (abnormality in heart beat). This is because in the low atmospheric pressure of high altitudes, the body does not get enough oxygen. But, you gradually get acclimatized and overcome the altitude sickness. How did your body solve this problem ? The body compensates low oxygen availability by increasing red blood cell production and increasing the rate of breathing. (Note : decreasing the binding capacity of haemoglobin).

Question 17.
An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and mango tree? (T.Q.)
Answer:
This is an interaction called commensalism in which one species benefits and the other is neither harmed nor benefited. An orchid growing as an epiphyte on mango branch, gets the benefit of exposure to hight, while the mango tree does not derive any noticeable benefit.

Question 18.
Do you believe that an ideal parasite should be able to thrive within the host without harming it? Then why didn’t natural selection lead to the evolution of such totally harmless parasites?
Answer:
No. I don’t believe that an ideal parasite should be able to thrive within the host without harming it. It is not possible.

Considering that the parasitic mode of life ensures free ‘lodging’ and ‘meals’, it is not surprising that parasitism has evolved in so many taxonomic groups from plants to higher vertebrates. Many parasites have evolved to be host – specific (they can parasitize only a specific species of host) in such a way that both host and the parasite tend to co – evolve; that is, if the host evolves special mechanisms for rejecting or resisting the parasite, the parasite has to evolve mechanisms to ‘counteract’ and ‘neutralize1 them, in order to continue successful parasitic relationship with the same host species. In order to lead successful parasitic life, parasites evolved special adaptations, such as.

a) loss of sense organs b) loss of digestive system and presence of high reproductive capacity c) presence of adhesive organs such as suckers and hooks d) complex life cycle.

Question 19.
The female mosquito is not considered completely a parasite, although it needs our blood for reproduction. Can you explain why?
Answer:
Considering that the parasitic made of life ensures free lodging and meals, it is not surprising that parasitism has evolved in so many taxonomic groups from plants to higher vertebrates. Many parasites have evolved to be host specific (they can parasitize only a specific species of host) in such a way that both host and the parasite tend to co-evolve, that is, if the host evolves special mechanism for rejecting or resisting the parasite, the parasite has to evolve mechanism to counteract and neutralise them, in order to continue successful parasitic relationship with the same host species.

The female mosquito is not considered completely a parasite although it needs our blood for reproduction as warm conditions are necessary to stimulate the production of eggs, because it otherwise had a semi independent and free life as it is a temporary ecto parasite. It needs no shelter, no anaerobic respiration.

Question 20.
Predation is not an association. Support the statement. (T.Q.)
Answer:
Predation :
We think of predation as nature’s way of transferring the energy fixed by plants to higher trophic levels. When we think of predatorand prey, most probably it is the tiger and the deer that readily come to our mind, but a sparrow eating any seed is also a type of predator (a seed predator also called granivore). Although animals eating plants are categorized separately as herbivores, they are, in a broad ecological context, not very different from predators.

Besides acting as ‘conduits’ / ‘pipelines’ for energy transfer across trophic levels, predators play other important roles. They keep the prey populations under control. In the absence of predators, the prey species could achieve very high population densities and cause instability in the ecosystem. Predators have different types of functions to play in nature. They include :

a) Predator as ‘a biological control b) Predators maintain species diversity c) Predators are prudent pertaining to preys.

Question 21.
Assigning the sign ‘+’ for beneficial, for detrimental, and ‘O’ for neutral interactions. Explain the different types of interspecific interactions in an ecosystem.
Answer:
Inter-specific interactions arise from the interaction of populations of two different species. They could be beneficial, detrimental or neutral (neither harmful nor beneficial) to one of the species or both. Assigning a ‘+’ sign for beneficial interaction,’-‘ sign for detrimental and ‘O’ for neutral interaction, let us look at all the possible outcomes of inter-specific interactions.

Population Interactions – Types

Question 22.
Predation has a significant role in maintaining of species diversity – discuss.
Answer:
Predators maintain ‘species diversity’: Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species. In the rocky intertidal communities of the American Pacific Coast, the starfish Pisaster is an important predator. In a field experiment, when all the starfish were removed from an enclosed intertidal area, more than 10 species of invertebrates became extinct within a year, because of increased inter-specific competition.

Question 23.
What is the biological principle behind the biologiqal control method of managing pest insects? (T.Q.)
Answer:
Predator as a biological control: The prickly pear cactus introduced intcTAustralia in the early 1920s caused havoc by spreading rapidly into millions of hectares of rangeland (vast natural grass lands). Finally, the invasive cactus was brought under control only after a cactus feeding predator (a moth) was introduced into the country. Biological control methods adopted in agricultural pest control are based on the ability of the predators to regulate prey populations.

Question 24.
Name important defence mechanisms in plants against herbivory.
Answer:
For plants, herbivores are the predators. Nearly 25 percent of all insects are known to be phytophagous (feeding on plant sap and other parts of plants). The problem is particularly severe for plants because, unlike animals, they cannot escape from their predators. Plants therefore have evolved a variety of morphological and chemical defences against herbivores.

1. Thoms (Acacia, Cactus, etc.,) are the most common morphological means of defense. Many plants produce and store chemicals that make the herbivore sick when they are eaten, inhibit feeding or digestion, disrupt its reproduction or even kill it.
2. You must have seen the weed Calotropis growing in abandoned fields. The plant produces highly poisonous cardiac glycosides and that is why you never see any cattle or goats browsing on this plant.
3. A wide variety of chemical substances that we extract from plants on a commercial scale (nicotine, caffeine, quinine, strychnine, opium, etc.,) are produced by them actually as defences against grazers and browsers.

Question 25.
Discuss competitive release. (T.Q.)
Answer:
Competitive release :
Another evidence for the occurrence of competition in nature comes from what is called ‘competitive release’. Competitive release occurs when one of the two competing species is removed from an area, thereby releasing the remaining species from one of the factors that limited its population size. A species, whose distribution is restricted to a small geographical area because of the presence of a competitively superior species, is found to expand its distributional range dramatically when the competing species is experimentally removed. This is due to the phenomenon called ‘competitive release’.

Connell’s ‘field experiments’ showed that, on the rocky sea coasts of Scotland, the larger and competitively superior barnacle Balanus dominates the intertidal area, and excludes the smaller barnacle Chathamalus from that zone. When the dominant one is experimentally removed, the populations of the smaller ones increased. In general, herbivores and plants appear to be more adversely affected by competition than the carnivores.

Question 26.
Write a short note on the parasitic adaptations. (T.Q.)
Answer:
In order to lead successful parasitic life, parasites evolved special adaptations such as

1. Loss of sense organs (which are not necessary for most parasites).
2. Presence of adhesive organs such as suckers, hooks to cling on to the host’s body parts.
3. Loss of digestive system and presence of high reproductive capacity.
4. The life cycles of parasites are often complex, involving one or two intermediate hosts or vectors to facilitate parasitisation of their primary hosts.
   eg : 1 : The human liver fluke depends on two intermediate (secondary ) hosts (a snail and fish) to complete its life cycle.
   e.g. – 2 : The malaria parasite needs a vector (mosquito) to spread to other hosts.

Question 27.
Explain brood parasitism with a suitable example. (T.Q.)
Answer:
Brood parasitism :
Certain birds are fascinating examples of a special type of parasitism, in which the parasitic bird lays its eggs in the nest of its host and lets / allows the host incubates them. During the coruse of evolution, the eggs of the parasitic bird have evolved to resemble the host’s egg in size and colour to reduce the chances of the host bird detecting the foreign eggs and ejecting them from the nest, eg: Cuckoo (Koel) laying its eggs in crow’s nest.

Question 28.
How do predators act as biological control? (T.Q.)
Answer:
Predator as a biological control: The prickly pear cactus introduced into Australia in the early 1920s caused havoc by spreading rapdily into millions of hectares of rangeland (vast natural grass lands). Finally, the invasive cactus was brought under control only after a cactus feeding predator (a moth) was introduced into the country. Biological controlmethods adopted in agricultural pest control are based on the ability of the predators to regulate prey populations.

Question 29.
Explain the interaction mechanism between fig trees and wasps.
Answer:
In many species of fig trees, there is a one-to-one relationship with the pollinator species of wasp. It means that a given fig species can be pollinated only by its ‘partner’ wasp species and no other species. The female wasp uses the fruit not only as a site for oviposition (egg-laying site), but also uses the developing seeds within the fruit for nourishing its larvae. The wasp pollinates the flowers of the fig plant while searching for suitable egg-laying sites. In return for the favour of pollination the fig offers the wasp some of its developing seeds, as food for the developing wasp larvae.

Question 30.
Write notes on the structure and functioning of an ecosystem. (T.Q.)
Answer:
An ‘ecosystem’ is a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. Ecosystem varies greatly in size from a small pond to a large forest or a sea. Many ecologists regard the entire biosphere as a ‘global ecosystem’, as a composite of all local ecosystems on Earth. Since this system is too big and complex to be studied at one time, it is convenient to divide it into two basic categories, namely natural and artificial. The natural ecosystems include aquatic ecosystems of water and terrestrial ecosystems of the land. Both types of natural and artificial ecosystems have several subdivisions.

Question 31.
Explain the different types of aquatic ecosystems.
Answer:
Aquatic Ecosystems :
Based on the salinity of water, three types of aquatic ecosystems are identified marine, freshwater, and estuarine.

i) The Marine Ecosystem :
It is the largest of all the aquatic ecosystems. It is the most stable ecosystem.

ii) Estuarine Ecosystem :
Estuary is the zone where river joins the sea. Sea water ascends up into the river twice a day (effect of high tides and low tides). The salinity of water in an estuary also depends on the seasons. During the rainy season out flow of river water makes the estuary less saline and the opposite occurs during the summer. Estuarine organisms are capable of withstanding the ‘fluctuations’ in salinity.

iii) The Freshwater Ecosystem :
The freshwater ecosystem is the smallest aquatic ecosystem. It includes rivers, lakes, ponds, etc. It is divided into two groups – the lentic and lotic. The still water bodies like ponds, lakes, reservoirs, etc., fall under the category of lentic ecosystems. The communities of the above two types are called lentic and lotic communities respectively. The study of freshwater ecosystem is called as limnology.

Question 32.
Explain the different types of terrestrial ecosystems. (T.Q.)
Answer:
The Terrestrial Ecosystems: The ecosystems of land are known as terrestrial ecosystems.

Some examples of terrestrial ecosystems are the forest, grassland and desert.
i) The Forest Ecosystems :
The two important types of forests seen in India are i) tropical rain forest and ii) tropical deciduous forests.

ii) The Grassland Ecosystems :
These are present in the Himalayan region in India. They occupy large areas of sandy and saline soils in Western Rajasthan.

iii) Desert Ecosystems :
The areas having less than 25 cm rainfall per year are called deserts. They have characteristics flora and fauna. The deserts can be divided into two types – hot type and cold type deserts. Thar Desert in Rajasthan is the example for hot type of desert. Cold type desert is seen in Ladakh.

Question 33.
Draw a diagram of the lake ecosystem and its physical or ecological divisions.
Answer:

Question 34.
Write about the producers of the littoral zone with suitable examples.
Answer:
Producers of the littoral zone :
Littoral zone is rich with pedonic flora (especially up to the depth of the effective light penetration). At the shore proper emergent vegetation is abundant with firmly fixed roots in the bottom of the lake and shoots and leaves are exposed above the level of water. These are amphibious plants. Certain emergent rooted plants of littoral zone are the cattails (Typha), bulrushes (Scirpus), arrowheads (Sagittaria). Slightly deeper are the rooted plants with floating leaves, such as the water lilies (Nymphaea), Nelumbo, Trapa, etc. Still deeper are the submerged plants such as Hydrilla, Chara, Potamogeton, etc. The free floating vegetation includes Pistia, Wolffia, Lemna (duckweed), Azolla, Eichhornia, etc.

The phytoplankton of the littoral zone composed of diatoms (Coscinodiscus, Nitzschia, etc.), green algae (Volvox, Spirogyra, etc.), euglenoids (Euglena, Phacus, etc.), and dinoflagellates (Gymnodinium, Cystodinium, etc.).

Question 35.
Write a short note on the limnetic zone of a lake ecosystem.
Answer:
Limnetic zone :
It is the open water zone away from the shore. It extends up to the effective light penetration level, vertically. The imaginary line that separates the limnetic zone from the profundal zone is known as zone of compensation/ compensation point / light compensation level. It is the zone of effective light penetration. Here the rate of photosynthesis is equal to the rate of respiration. Limnetic zone has no contact with the bottom of the lake.

Biota of the limnetic zone :
Limnetic zone is the largest zone of a lake. It is the region of rapid variations of the level of the water, temperature, oxygen availability, etc., from time to time. The chief autotrophs of this region are the phytoplankton such as the euglenoids, diatoms, cyanobacteria, dinoflagellates and green algae. The consumers of the limnetic zone are the zooplanktonic organisms such as the copepods. Fishes, frogs, water snakes, etc., form the limnetic nekton.

Question 36.
Write a short note on the profundal zone of a lake ecosystem.
Answer:
Profundal zone :
It is the deep water area present below the limnetic zone and beyond the depth of effective light penetration. Light is absent. Photosynthetic organisms are absent and so the water is poor in oxygen content. It includes mostly the anaerobic organisms which feed on detritus.

The organisms living in lentic habitat are classified into pedonic forms, which live at the bottom of the lake and those living in the open waters of lakes, away from the shore vegetation are known as limnetic forms.

Biota of the profundal zone :
It includes the organisms such as decomposers (bacteria), chironomid larvae, Chaoborus (phantom larva), red annelids, clams, etc., that are capable of living in low oxygen levels. The decomposers of this zone decompose the dead plants and animals and release nutrients which are used by the biotic communities of both littoral and limnetic zones.

Question 37.
Give a brief account of a lake ecosystem.
Answer:
The lake ecosystem performs all the functions of any ecosystem and of the biosphere as a whole, i.e., conversion of inorganic substances into organic material, with the help of the radiant solar.energy by the autotrophs; consumption of the autotrophs by the heterotrophs; decomposition and mineralization of the dead matter to release them back for reuse by the autotrohs (recycling of minerals).

Question 38.
How is a lake ecosystem described as a ‘micro-model’ for the entire biosphere?
Answer:
Lake Ecosystem :
To understand the fundamentals of an aquatic ecosystem, let us take a ‘lake’ as an example. This is fairly a self-sustainable unit and rather a simple, example that explains even the complex interactions that exist in an aquatic ecosystem.

Lakes are large inland water bodies containing standing/still water (Recall: Lentic community). They are deeper than ponds (pond is not an ideal example as it is very shallow). Most lakes contain water throughout the year. In deep lakes, light cannot penetrate more than 200 meters, in depth. They are vertically stratified in relation to light intensity, temperature, pressure, etc., Deep water lakes contain three distinct zones namely, i) littoral zone, ii) limnetic zone, and iii) profundal zone. Hence lake ecosystem is described as a micro model for the entire biosphere.

Question 39.
In GFCs the number of trophic levels is restricted. Give reason.
Answer:
I. Grazing Food Chain (GFC) :
It is also known as predatory food chain. It begins with the green plants (producers) and the second, third and fourth trophic levels are occupied by the herbivores, primary carnivores and secondary carnivores respectively. In some food chains there is yet another trophic level – the climax carnivores. The number of trophic levels in food chains varies from 3 to 5 generally. Some examples for grazing food chain (GFC) are given below.

II. Parasitic food chain :
Some authors included the ‘Parasitic Food Chains’ as a part of the GFC. As in the case of GFCs, it also begins with the producers, the plants (directly or indirectly). However, the food energy passes from large organisms to small organisms in the parasitic chains. For instance, a tree which occupies the 1st trophic level provides shelter and food for many birds. These birds host many ectoparasites and endo-parasites. Thus, unlike in the predator food chain, the path of the flow of energy includes fewer, l^rge sized organisms in the lower trophic levels, and numerous, small sized organisms in the successive higher trophic levels.

Question 40.
What are the ecological limitations for ecological pyramids?
Answer:
Limitations of Ecological Pyramids :
There are certain limitations of ecological pyramids, such as-

1. It does not take into account the same species belonging to two or more trophic levels,
2. It assumes a simple food chain, something that almost never exists in nature,
3. It does not accommodate a food web,
4. moreover, saprophytes are not given any place in ecological pyramids even though they play a vital role in the ecosystem.

Question 41.
How is the second law of thermodynamics applicable to the functional part of an ecosystem?
Answer:
The ecosystems are not exempted from the Second Law of thermodynamics. It states that no process involving energy transformation will spontaneously occur unless there is degradation of energy. As per the second law of thermodynamics – the energy dispersed is in the form of unavailable heat energy, and constitutes the entropy (energy lost or not available for work in a system). The organisms need a constant supply of energy to synthesize the molecules they require. The transfer of energy through a food chain is known as energy flow.

A constant input of mostly solar energy is the basic requirement for any ecosystem to function. The important point to note is that the amount of energy available decreases at successive trophic levels. When an organism dies, it is converted to detritus or dead biomas that serves as a source of energy for the decomposers. Organisms at each trophic level depend on those at the lower trophic level, for their energy demands.

Question 42.
Discuss the main reason for the low productivity of ocean. (T.Q.)
Answer:
The element carbon constitutes 49 percent of the dry weight of organisms and is next only to water. Among the total carbon quantity present on the Earth, 71 percent is found dissolved in oceans. This ‘oceanic reservoir’ regulates the amount of carbon dioxide in the atmosphere. It will be interesting to know that the atmosphere only contains about 1 percent of the total global carbon. This is the main reason for the low productivity of ocean.

Question 43.
Explain the terms saprotrophs, detritivores, and mineralizers. (T.Q.)
Answer:
a) Saprotrophs :
The detritus food chain (DFC) begins with dead organic matter (such as leaf litter, bodies of dead organisms). It is made up of decomposers which are heterotrophic organisms, mainly the fungi and bacteria. They meet their energy and nutrient requirements by degrading dead organic matter or detritus. These are also known as saprotrophs.

b) Detritivores :
Plant parts such as leaves, bark, flowers and dead remains of animals, including their faecal matter, constitute the detritus. Detritus is the raw material for the decomposition.

Detritivores (eg : earthworm) break down detritus into smaller particles and this process is called fragmentation. Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called as catabolism.

c) Mineralizers :
It is important to note that all the steps in decomposition operate simultaneously on the detritus. Humification and mineralization occur during decompositon in the soil. Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decompositon at an extremely slow rate. Being colloidal in nature it serves as a reservoir of nutrients. The humus is further degraded by some microbes and release of inorganic nutrients occurs by the process known as mineralization. Hence the microbes are called mineralizers.

Question 44.
Discuss the factors that influence the process of decomposition.
(OR)
Question 45.
Define decomposition and describe the process and products of decomposition. (T.Q.)
Answer:
Decomposition :
Decomposition is largely an oxygen-requiring process. The rate of decomposition is controlled by chemical composition of the detritus and climatic factors. In a particular climatic condition, decomposition rate is slower if detritus is rich in lignin and chitin, and quicker, if detritus is rich in nitrogen and water-soluble substances like sugars. Temperature and soil moisture are the most important climatic factors that regulate decomposition through their effects on the activities of soil microbes.

Warm and moist environment favours decomposition whereas low temperature and anaerobic environment ‘inhibit’ the decomposition resulting in build up of organic materials. As most of the decomposers are very small microscopic forms, they are also called ‘micro-consumers’.

Question 46.
Explain GFC.
Answer:

Question 47.
Write a short notes on the various trophic levels in a typical ecosystem. [March 2013]
Answer:
Energy flows into biological systems (ecosystems) from the Sun. The biological systems of environment include several food levels called trophic levels. A trophic level is composed of those organisms which have the same source of energy and having the same number of steps away from the sun. Thus a plant’s trophic level is one, while that of a herbivore – two, and that of the first level carnivore – three.

The second and third levels of the carnivores occupy fourth and fifth trophic levels respectively.

A given organism may occupy more than one trophic level simultaneously. One must remember that the trophic level represents a functional level. A given species may occupy more than one trophic level in the same ecosystem at the same time; for example, a sparrow is a primary consumer when it eats seeds, fruits, and a secondary consumer when it eats insects and worms.
Trophic levels in an ecosystem

Question 48.
Give examples for GFCs with three, four and five trophic levels from your locality. Explain the parasitic food chain. How does it differ from GFC?
Answer:
Grazing food chain :

Question 49.
Write a note on DFC. Give its significance in a terrestrial ecosystem. (T.Q.) [March 2018 – A.P.]
Answer:
Detritus Food Chain (DFC): Dead organisms of the grazing food chain form a source of energy for other organisms. Similarly, waste materials passed from the bodies of living organisms are also a source of energy for some organisms called decomposers like saprotrophs, detritivores and mineralizers. Saprotrophs are microorganisms such as fungi and bacteria, which live on dead organic matter. Detritivores ingest small fragments of decomposing organic materials, termed detritus. Mineralisers effect the mineralisation of humus.

Detritivores may be eaten by the carnivores, which may then be consumed by other carnivores, thus building up a food chain based on detritus. This is termed detritus food chain. Those feeding directly on the dead bodies or detritus are primary detritus feeders and those preying on these organisms are secondary detritus feeders.

Two typical detritus food chains of the woodland ecosystem are :

Question 50.
What is primary productivity? Give a brief description of the factors that affect primary productivity. (T.Q.)
Answer:
The rate of production of biomass is called productivity. It can be divided into primary and secondary productivities.

I. Primary productivity is defined as the amount of biomass or organic matter produced per unit area over a period of time by plants, during photosynthesis. It can be divided into gross primary productivity (GPP) and net primary productivity (NPP).

a) Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilized by plants for their catabolic process (respiration).

b) Net primary productivity Gross primary productivity minus respiratory loss (R), is the net primary productivity (NPP). On average about 20 – 25 percent of GPP is used for the catabolic (respiratory) activity.
GPP-R = NPP

The net primary productivity is the biomass available for the consumption of the heterotrophs (herbivores and decomposers).

II. Secondary productivity is defined as the rate of formation of new organic matter by consumers.

Question 51.
Define ecological pyramids and describe with examples, pyramids of numbers and biomass. (T.Q.)
Answer:
Ecological Pyramids (Eltonian pyramids) :
You must be familiar with the shape of a pyramid. The base of a pyramid is broad and it narrows down towards the apex. The trophic relationship is expressed in terms of numbers; biomass or energy arranged one on the top of its lower trophic level, resulting in a pyramidal shape. It is a graphical representation of the trophic structure and function of an ecosystem.

The base of each pyramid represents the producers or the first trophic level, while the apex represents the tertiary or top level / top order consumer. The three types of ecological pyramids that are usually studied are (a) pyramid of number, (b) pyramid of biomass and (c) pyramid of energy. These pyramids were first represented by Elton, hence the name ELTONIAN pyramids / Ecological pyramids.

Any calculations of energy content, biomass, or numbers has to include all organisms at that trophical evel. No generalizations we make will be true if we take only a few individuals of any trophic level into account. In most ecosystems, all the pyramids – of numbers, energy and biomass are upright i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores. Also energy (available) at a lower trophic level is always more than that at a higher level.

There are exceptions to this generalization. In the case of a parasitic food chain, the pyramid of numbers is inverted.

Question 52.
Can you work out the number of trophic levels at which human beings can function in a food chain?
Answer:
Man occupies 3^rd trophic level being represented by secondary consumer. Some times man also occupies 2^nd tropic level as he becomes primary consumer feeding only on producers.

If he feeds on animals like fish, goat, prawns etc., he becomes secondary consumer in a food chain. But never goes to 4^th trophic level of tertiary consumer.

So total number of trophic levels at which human beings can function in a food chain are two or three levels.

Question 53.
Measurement of biomass in terms of dry weight is more accurate. Justify.
Answer:
Each trophic level has a certain mass of living material at a particular time, and it is called the standing crop. The standing crop is measured as the “mass” of living organisms (biomass) or the number of organisms per unit area. The biomass of a species is expressed in terms of fresh or dry weight (dry weight) is more accurate because water contains no usable energy.

Question 54.
What are the deleterious effects of depletion of ozone in the stratosphere? [March 2020, ’19, May/June 2014] (T.Q.)
Answer:
The depletion of ozone is particularly marked over the Antarctic region. This has resulted in the formation of a large area of thinned ozone layer, commonly called as the ‘ozone hole’.

UV radiation with wavelengths shorter than that of UV-B, are almost completely absorbed by Earth’s atmosphere, provided that the ozone layer is intact. But UV-B damages DNA and may induce mutations. It causes ageing of skin, damage to skin cells and various types of skin cancers. In human eye, cornea absorbs UV-B radiation, and a high dose of UV-B causes inflammation of cornea, called snow blindness, cataract, etc. Such exposure may permanently damage the cornea.

Question 55.
Write a note on ‘algal blooms’.
Answer:
Algal blooms: Presence of large amounts of nutrients in waters also causes excessive growth of planktonic algae and the phenomenon is commonly called ‘algal blooms’. Algal blooms impart distinct colour to the water bodies and deteriorate the quality of water. It also causes mortality of fish. Some algae which are involved in algal blooms are toxic to human beings and animals.

Excessive growth of aquatic plants such as the common water hyacinth (Eichhornia crassipes), the world’s most problematic aquatic weed which is also called ‘Terror of Bengal’ causes blocks in our water ways. They grow faster than our ability to remove them. They grow abundantly in eutrophic water bodies (water bodies rich in nutrients) and lead to imbalance in the ecosystem dynamics of the water body.

Question 56.
Describe ‘Greenhouse Effect’. [May 17; Mar. 2020, 17, 14] (T.Q)
Answer:
The greenhouse effect is a naturally occurring phenomenon that is responsible for heating of the Earth’s surface and atmosphere. It would be surprising to know that without greenhouse effect the average temperature of the Earth’s surface would have been a chilly – 18° C rather than the present average of 15° C.

When sunlight reaches the outermost layer of the atmosphere, clouds and gases reflect about one-fourth of the incoming solar radiation, and absorb some of it. Almost half of the incoming solar radiation falls on the Earth’s surface and heats it up, while a small proportion is reflected back. The Earth’s surface re-emits heat in the form of infrared radiation but part of this does not escape into space as atmospheric gases (e.g., carbondioxide, methane, etc.,) absorb a major fraction of it. The molecules of these gases radiate heat energy, and a major part of which again comes back to the Earth’s surface, thus heating it up once again.The above – mentioned gases – carbon dioxide and methane – are commonly known as greenhouse gases, because they are responsible for the greenhouse effect.

Increase in the level of greenhouse gases has led to considerable heating of the Earth leading to global warming.

Question 57.
Write notes on the following.
a) Radioactive waste disposal
b) e-wastes management
Answer:
Radioactive wastes :
Initially, nuclear energy was hailed as a non-polluting way for generating electricity. Later on, it was realised that the use of nuclear energy has two very serious inherent problems. The first is accidental leakages, as occurred in the Three Mile Island (USA) and Chernobyl (Russia) and the second is the safe disposal of radioactive wastes.

Radiation, that is released from nuclear waste is extremely dangerous to biological organisms, because it induces mutations. Exposure to high doses of nuclear radiation is lethal as it can lead to cancers (e.g. leukemia). Therefore, nuclear waste is an extremely potent pollutant and has to be dealt with utmost caution. Storage of nuclear wastes should be done in suitably shielded containers and buried deep in the soil or oceans (about 500 meters). Even when done so, geological upheavals can bring them up, some day and cause radiation.

Electronic wastes (e-wastes) :
Irreparable computers and other electronic goods constitute the modern day pollutants called electronic wastes (e-wastes), wases). E-wastes are buried in landfills or incinerated. Over half of the e-wastes generated in the developed world are exported to developing countries, mainly to China, India and Pakistan, where metals like copper, iron, silicon, nickel and gold are recovered during recycling process.

Unlike developed countries, which have specifically built facilities for recycling of e-wastes, recycling in developing countries often invovles manual participation thus exposing workers to toxic substances present in e-wastes. Eventually recycling is the only solution for the treatment of e-wastes provided it is carried out in an environmental friendly manner.

Question 58.
Discuss the role of women and communities in protection and conservation of forests in India.
Answer:
People’s participation in ‘protecting forests’ has a long history in India. In 1731, the king of Jodhpur in Rajasthan asked one of his ministers to arrange wood for constructing a new palace. The minister and workers went to a forest near a village, inhabited by Bishnois, to cut down trees. The Bishnoi community is known for its peaceful co-existence with nature. The effort to cut down trees by the king was thwarted by the Bishnois. A Bishnoi woman Amrita Devi showed exemplary courage lost their lives in their effort to save trees.

Nowhere in history do we find a commitment of this magnitude when human beings sacrificed their lives for the cause of the environment. The Government of India has recently instituted the “Amrita Devi Bishnoi Wildlife Protection Award” for individuals or communities from rural areas that have shown extraordinary courage and dedication in protecting wildlife.

The Chipko Movement of Garhwal Himalayas :
In 1974, local women showed enormous bravery in protecting trees from the axe of contractors by hugging the trees. People all over the world have acclaimed the Chipko movement. Realising the significance of participation by local communities the Governemnt of India in 1980s has introduced the concept of Joint Forest Management (JFM) so as to work closely with the local communities for protecting and managing forests. In return for their services to the forest, the communities get benefit of various forest products (e.g. frutis, gum, rubber, medicine, etc.).

Question 59.
Discuss briefly the following : (T.Q.)
a) Greenhouse gases
b) Noise pollution
c) Organic farming
d) Municipal solid wastes
Answer:
a) Greenhouse gases :
Carbon dioxide and methane are commonly known as greenhouse gases, because they are responsible for the greenhouse effect.

b) Noise pollution :
In India, Air (Prevention and control of pollution) Act came into force in 1981. In 1987 it was amended to include noise also as an air pollutant. Undesirably high sound constitute NOISE POLLUTION. Sound is measured in units called decibels (dB). The human ear is sensitive to sounds ranging from 0 to 180 dB. 0 dB is threshold limit of hearing and 120 dB is threshold limit for sensation of pain in the ear. Any noise above 120 dB is considered to be a noise pollution.

A brief exposure to extremely high sound level, 150 dB or more generated by jet planes while taking-off may damage eardrums causing permanent hearing impairment. Even long term exposure to a relatively lower level of noise of cities may also cause hearing impariment. Noise also causes auditory fatigue, anxiety, sleeplessness (insomnia), increased heart beat, altered breathing pattern thus causing considerable stress to humans.

c) Organic farming :
Integrated organic farming is a zero-waste procedure, where recycling of waste products is efficiently carried out. Wastes originated from one process are used as nutrients for other processes. This allows the maximum utilisation of resource and increases the efficiency of production. A method practised by Ramesh Chandra Dagar, a farmer in Sonipat, Haryana, is a very good example for this. He integrated bee-keeping, dairy management, water harvesting, composting and agriculture in a chain of processes.

All these processes support one another and allow an extremely economical and substainable venture. Crop waste and cattle excreta (dung) are used to create compost, which can be used as a natural fertilizer. Natural bio-gas generated in the process can be used for meeting the energy needs of the farm. Enthusiastic about spreading information and helping in the practice of integrated organic farming, Dagar has created by Haryana Kisan Welfare Club.

d) Municipal solid wastes :
Any thing (substance/ material / articles / goods) that is thrown out as waste in solid form is referred to as solid waste. Municipal solid wastes are wastes from homes, offices, institutions, shops, hotels, restaurants etc., in towns and cities.

The municipal solid wastes generally consist of paper, food wastes, plastics, glass, metals, rubber, leather, textile, etc. The wastes are burnt to reduce the volume of the wastes. But generally wastes are not completely burnt and left as open dumps which often serve as the breeding grounds for rats and flies. As the substitute for open-burning dumps, sanitary landfills are adopted. In a sanitary landfill, wastes are dumped in a depression or trench after compaction, and covered with dirt everyday. These is a danger of seepage of chemicals and pollutants from these landfills, which may contaminate the underground water resources.

Question 60.
Discuss the causes and effects of global warming. What measures need to be taken to control ‘Global Warming’? [March 2015 – T.S. & A.P.] (T.Q.)
Answer:
Increase in the level of greenhouse gases has led to considerable heating of the earth leading to global warming. During the past century, the temperature of the earth has increased by 0.6°C. Most of it during the last three decades. Scientists believe, that this rise in temperature is leading to severe changes in the environment. Global warming is causing climate changes and is also responsible for the melting of polar ice. caps and other snow caps of mountains such as the Himalayas. Over many years, this will result in a rise in sea levels all over the world that can sub-merge many coastal areas. The total spectrum of changes that gldbal warming can bring about is a subject that is still under active research.

Global warming – Control measures :

1. The measures include cutting down use of fossil fuels
2. Improving efficiency of energy usage
3. Planting of trees, and avoiding deforestation
4. Slowing down the growth of human population.

Question 61.
Write critical notes on the following : (T.Q.)
a) Eutrophication
b) Biological magnification
c) Ground water depletion and ways for its replenishment.
Answer:
a) Eutrophication :
Natural ageing of a lake by nutrient enrichment of its water is known as eutrophication. In a young lake, the water is cold and clear, supporting little life. Gradually nutrients, such as nitrates and phosphates are carried into the lake via streams, in course of time. This encourages the growth of aquatic algae and other plants. Consequently, the animal life proliferates, and organic matter gets deposited on the bottom of the lake. Over centuries, as silt and organic debris piles up, the lake grows shallower and warmer. As a result, the aquatic organisms thriving in the cold environment are gradually replaced by warm-water organisms.

Marsh plants appear by taking root in the shallow regions of the lake. Eventually, the lake gives way to large masses of floating plants (bog) and finally converted into land.

b) Biomagnification :
Increase in the concentration of the pollutant or toxicant at successive trophic levels in an aquatic food chain is called Biological Magnification or Biomagnification. This happens in the instances where a toxic substance accumulated by an organism is not metabolized or excreted and thus passes on to the next higher trophic level. This phenomenon is well known regarding DDT and mercury pollution.

As shown in the above example, the concentration of DDT is increased at successive trophic levels starting at a very low concentration of 0.003 ppb (ppb = parts per billion) in water, which ultimately reached an alarmingly high concentration of 25 ppm (ppm = parts per million) in fish-eating birds, through biomagnification. High concentrations of DDT disturb calcium metabolism in birds, which causes thinning of egg shell and their premature breaking, eventually causing decline in bird populations.

c) Ground water depletion and ways for its replenishment :
Sewage arising from homes and hospitals may contain undesirable pathogenic microorganisms. If it is released untreated into water courses, there is a likelihood of outbreak of serious diseases, such as dysentery, typhoid, jaundice, cholera etc.

Untreated industrial effluents released into water bodies pollute most of the rivers, fresh water streams, etc. Effluents contain a wide variety of both inorganic and organic pollutants such as oils, greases, plastics, metallic wastes, suspended solids and toxins. Most of them are non-degradable. Arsenic, Cadmium, Copper, Chromium, Mercury, Zinc, and Nickel are the common heavy metals discharged from industries.

Effects :
Orgnic substanes present in the water deplete the dissolved oxygen content in water by increasing the BOD (Biological Oxygen Demand) and COD (Chemical Oxygen Demand). Most of the inorganic substances render the water unfit for drinking.

Removal of dissolved salts such as nitrates, phosphates and other nutrients and toxic metal ions and organic compounds is much more difficult. Domestic sewage primarily contains biodegradable organic matter, which will be readily decomposed by the action of bacteria and other microorganisms.

Water-logging and soil salinity :
Irrigation without proper drainage of water leads to water-logging in the soil. Besides affecting the crops, water-logging draws salt to the surface of the soil (salinisation of the top soil). The salt then is deposited as a thin crust on the land surface or starts collecting at the roots of the plants. This increased salt content is inimical (unfavourable) to the growth of crops and is extremely damaging to agriculture. Water-logging and soil salinity are some of the problems that have come in the wake of the Green Revolution.

Essay Answer Type Questions

Question 1.
Write an essay on temperature as an ecological factor. (T.Q.)
Answer:
Temperature :
Temperature is a measure of the intensity of heat. The temperature on land or in water is not uniform. On land the temperature variations are more pronounced when compared to the aquatic medium, because land absorbs or loses heat much quicker than water. The temperature on land depends on seasons and the geographical area on this planet. Temperature decreases progressively when we move from the equator to the poles. Altitude also causes variations in temperature. For instance, the temperature decreases gradually as we move to the top of the mountains.

The Effects of Temperature in Lakes :
Thermal Stratification :
Temperature variations occur with seasonal changes in the temperature regions. These differences in the temperature form ‘thermal layers’ in water. These phenomena are called thermal stratifications.

Water shows maximum density at 4°C. Rise or fall of temperatures above or below 4°C decreases its density. This anomalous property of water and the seasonal variations in temperature are responsible for the thermal stratification in temperate lakes.

Summer stratification :
During summer in temperate lakes, the density of the surface water decreases because of increase in its temperature (21-25° C). This ‘upper more warm layer’ of a lake is called epilimnion. Below the epilimnion there is a zone in which the temperature decreases at the rate rate of 1°C per meter in depth, and it is called thermocline or metalimnion. The bottom layer is the hypolimnion, where water is relatively cool, stagnant and with low oxygen content (due to absence of photosynthetic activity).

During autumn (also called fall), the epilimnion cools down, and the surface water becomes heavy when the temperature is 4° C, and sinks to the bottom of the lake. Overturns bring about ‘uniform temperature’ in lakes during that period. This circulation during the autumn is known as the fall or autumn overturn. The upper oxygen rich water reaches the hypoliminion and the nutrient rich bottom water comes to the surface. Thus there is uniform distribution of nutrients and oxygen in the lake.

Winter stratification / stagnation :
The ‘Fall’ is followed by ‘Winter’. In this season the surface water cools down. The upper water freezes when the temperature reaches 0°C. Below the upper icy layer, the cool (4° C) water occupies the lake. The aquatic animals continue their life below the icy layer. At lower temperatures the activity of bacteria and the rate of oxygen consumption by aquatic animals decrease. Hence, organisms can survive below the frozen upper water without being subjected to ‘hypoxia’ (low oxygen availability).

In the ‘Spring season’ the temperatures start rising. When it reaches 4°C, the water becomes more dense and heavy and sinks to the bottom, taking ‘oxygen rich water’ to the bottom. The upper oxygen rich water sinks down and the bottom ‘nutrient rich water’ reaches the surface. It is called ‘spring overturn’. The lakes which show overturns twice a year are called ‘dfmictic lakes’. Thus ‘stratifications’ and ‘overturns’ help survival of organisms at all levels in deep lakes.

Biological effects of Temperature :
Temperature Tolerance :
A few organisms can tolerate and thrive in a wide range of temperatures they are called eurythermal, but, a vast majority of organisms are restricted to a narrow range of temperatures (such organisms are called stenotherma. The levels of thermal tolerance of different species determine their geographical distribution.

Temperature and Metabolism :
Temperature affects the working of enzymes and through it, the basal metabolism, and other physiological functions of organism. The temperature at which the metabolic activities occur at the climax level is called the ‘optimum temperature. The lowest temperature at which an organism can live indefinitely is called minimum effective temperature. If an animal or plant is subjected to a temperature below the minimum effective limit, it enters into a condition of inactiveness called chilLcoma. The metabolic rate increases with the rise of temperature from the minimum effective temperature to optimum temperature.

The maximum temperature at which a species can live indefinitely in an active state is called maximum effective temperature. If the temperature is raised above the maximum effective temperature, the animals enter into ‘heat coma’. The maximum temperature varies much in different animals.

van’t Hoff’s rule :
van’t Hoff, a Nobel Laureate in thermochemistry, proposed that, with the increase of every 10°C, the rate of metabolic activities doubles. This rule is referred to as the van’t Hoff’s rule, van’t Hoffs rule can also be stated in reverse saying that the reaction rate is halved with the decrease of every 10°C. The effect of temperature on the rate of a reaction is expressed in terms of temperature coefficient or Q₁₀ value. Q₁₀ values are estimated taking the ratio between the rate of a reaction at X°C and rate of reaction at (X – 10°C). In the ‘living systems’ the Q₁₀ value is about 2.0. If the Q₁₀ value is 2.0, it means, for every 10° C increase, the rate of metabolism doubles.

Cyclomorphosis :
The cyclic seasonal morphological variations among certain organisms is called cyclomorphosis. This phenomenon has been demonstrated in the cladoceran (a sub group of Crustacea) Daphnia (water flea). In the winter season the head of Daphnia is ’round’ in shape (typical or non-helmet morph). With the onset of the spring season, a small ‘helmet’/ ‘hood’ starts developing on it. The helmet attains the maximum size in summer. In ‘autumn’ the helmet starts receding. By the winter season, the head becomes round. Some scientists are of the opinion that cylomorphosis is a seasonal adaptation to changing densities of the water in

lakes – in summer as the water is less dense Daphnia requires a larger body surface to keep floating easily. During winter the water is more dense, and so it does not require a larger surface area of the body to keep floating. Others believe that these cyclic changes are adaptations to ‘stabilize the movement’ in water. Compared to the ’typical morphs’, the ‘helmeted morphs’ can resist the water currents better to stay in the water rich in food materials.

Temperature adaptations :
Temperature adaptations in animals can be dealt under three heads a) Behavioural adaptations, b) Morphological and Anatomical adaptations and c) Physiological adaptations.

a) Behavioural adaptations :
Some organisms show behavioural responses to cope with variations in their environment. Desert lizards manage to keep their body temperature fairly constant by behavioural means. They ‘bask’ (staying in the warmth of sunlight) in the sun and absorb heat when their body temperature drops below the comfort zone^ but move into shade when the temperature starts increasing. Some species are capable of burrowing into the soil to escape from the excessive heat above the ground level.

b) Morphological and anatomical adaptations :
In the polar seas, aquatic mammals such as the seals have a thick layer of fat (blubber) that acts as an insulatpr and reduces the loss of body heat, underneath their skin.

The animals which inhabit the colder regions have larger body size with greater mass. The body mass is useful to generate more heat. As per Bergmann’s rule mammals and other warm blooded animals living in colder regions have less surface area to body volume ratio’, than their counterparts living in the tropical regions.

The small surface area helps to conserve heat. For instance, the body size of American moose/Eurasian elk (Alces alces), increases with the latitudes in which they live. Moose of northern part of Sweden shows 15-20% more body mass than the same species (counterparts) living in the southern Sweden.

Mammals from colder climates generally have shorter earlobes and limbs (extremities of the body) to minimize heat loss. Large earlobes and long limbs increase the surface.area without changing the body volume. This is known as Allen’s rule. For instance, the polar fox, Vulpes lagopus (formerly called Alopex lagopus), has short extremities to minimize the heat loss from the body. In contrast, the desert fox, Vulpes zerda, has large earlobes and limbs to facilitate better ‘heat loss’ from the body.

c) Physiological adaptations :
In most animals, all the physiological functions proceed ‘optimally’ in a narrow temperature range (in humans, it is 37° C). But there are microbes (archaebacteria) that flourish in hot springs and in some parts of deep seas, where temperatures far exceed 100° C. Many fish thrive in Antarctic waters where the temperature is always below zero. Having realized that the abiotic conditions of many habitats may vary over a time period, we now ask – How do the organisms living in such habitats manage with stressful conditions? One would expect that during the course of millions of years of their existence, many species would have evolved a relatively constant internal (within the body) environment.

It permits all biochemical reactions and physiological functions to proceed with maximal efficiency and thus, enhance the over all’ fitness’ of the species. This constancy, could be chiefly in terms of optimal temperature and osmotic concentration of body fluids. So the organism should try to maintain the constancy of its internal environment (homeostasis) despite varying external environmental conditions that tend to upset its homeostasis. This is achieved by the processes described below.

(i) Regulate :
Some organisms are able to maintain homeostasis by physiological (sometimes behavioural also ) means which ensures constant body temperature, constant osmotic concentration, etc. All birds and mammals, and a very few lower vertebrate and invertebrate species are indeed capable of such regulation (thermoregulation and osmoregulation). Evolutionary biologists believe that the ‘success’ of mammals is largely due to their ability to maintain a constant body temperature and thrive whether they live in Antarctica or in the Sahara desert.

The mechanisms used by most mammals to regulate their body temperature are similar to the one that we, the humans use. We maintain a constant body temperature of 37°C. In summer, when outside temperature is more than our body temperature, v.e sweat profusely. The resulting ‘evaporative cooling’ brings down the body temperature. In winter when the temperature is much lower than 37°C, we start to shiver (a kind of exercise which produces heat and raises the body temperature – a type of body’s own defence mechanism against low temperature). Plants, on the other hand, do rvot have such mechanisms to maintain internal temperatures.

ii) Conform :
Majority (99 percent) of animals cannot maintain a constant internal environment. Their body temperature changes with the ambient (surrounding) temperature. In aquatic animals, the osmotic concentration of the body fluids changes along with that of the surrounding water. Such animals are described as ‘conformers’.

(iii) Partially regulate :
Animals such as ‘camels’ can be ‘conformers’ up to a particular range of temperature and ‘regulator’ afterwards. So, they are described as ‘partial regulators’ or ‘partial conformers’.

Thermoregulation is energetically ‘expensive’ for many organisms. This is particularly true in small animals like shrews and humming birds. Heat loss or heat gain is a function of the surface area. Since small animals have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; then they have to spend much energy to generate Body heat through metabolism. This is the main reason why very small animals are rarely found in the ‘polar regions’. During the course of evolution, the costs and benefits of maintaining a constant internal environment are taken into consideration. Some species have evolved the ability to regulate, but only over a limited range of environmental conditions, beyond which they simply conform.

If the stressful external conditions are localized or remain only for as short duration, the organism has two other alternatives.

(iv) Migrate :
The organism can move away temporarily from the ‘stressful habitat’ to a more ‘hospitable’ (comfortable) area and return when the stressful period is over. In human analogy (comparison), this strategy is comparable a person moving from Delhi to Shimla for the duration of summer. Many animals, particularly birds, during winter undertake long-distance migrations to more hospitable areas. Every winter, many places in India including the famous Keoladeo or Keoladeo Ghana National park (Formerly – Bharatpur bird sanctuary) in Rajasthan and Pulicat Lake in Andhra Pradesh host thousands of ‘migratory birds’ coming from Siberia and other extremely cold northern regions.

(v) Suspend life activities :
In bacteria, fungi and lower plants, various kinds of thick-walled spores are formed which help them survive unfavoruable conditions. They germinate (come out of the spore wall and produce a normal active organisms) on the return of suitable environmental conditions.

Some animals can avoid the stress by escaping in ‘time’ (migration is – escaping in space’). The familiar case of ‘Polar bears’ going into hibernation during winter is an example of escape in time. Some snails and fish go into aestivation to avoid summer-related problems – heat and desiccation.

Diapause :
Certain organisms show delay in development, during periods of unfavourable environmental conditions and spend some period in a state of ‘inactiveness’ called ‘diapause’. This dormant period in animals is a mechanism to survive extremes of temperature, drought, etc. It is seen mostly in insects and embryos of some fish. Under unfavourable conditions many zooplankton species in lakes and ponds are known to enter diapause.

Question 2.
Write an essay on water as an ecological factor. (T.Q.)
Answer:
Water :
Water is another important factor influencing the life of organisms. Life is unsustainable without water. Its availability is so limited in deserts that only certain special adaptations make it possible for them to live there. You might think that organisms living in oceans, lakes and rivers should not face any water-related problems, but it is not true. For aquatic organisms the quality (chemical composition, pH, etc.,) of water becomes important.

The salt concentration is less than 5 percent in inland waters, and 30 – 35 percent in the seawater. Some organisms are tolerant to a wide range of salinities (euryhaline), but others arerestricted to a narrow range (stenohaline). Many freshwater animals cannot live for long in sea water and vice versa because of the osmotic problems, they would face.

Adaptations in freshwater habitat: Animals living in freshwaters have to tackle the problem of endosmosis. The osmotic pressure of freshwater is very low and that of the body fluids of freshwater organisms is much higher. So water tends to enter into bodies by endosmosis. To maintain the balance of water in the bodies, the freshwater organisms acquired several adaptation such as, contractile vacuoles in the freshwater protozoans, large glomerular kidneys in fishes, etc. They send out large quantities of urine, along which some salts are also lost.

To compensate the ‘salt loss’ through urine, freshwater fishes have ‘salt absorbing’ ‘chloride cells’ in their gills. The major problem in freshwater ponds is – in summer most of the ponds dry up. To overcome this problem most of the freshwater protists undergo encystment. The freshwater sponges produce asexual reproductive bodies, called gemmules, to tide over the unfavourable conditions of the summer. The ‘African lungfish’, Protopterus, burrows into the mud and forms a ‘gelatinous cocoon’ around it, to survive, in summer.

Adaptations in marine habitat :
Seawater is high in salt content compared to that of the body fluids. So, the marine animals continuously tend to lose water from their bodies by exosmosis and face the problem of dehydration. To overcome the problem of water loss, marine fishes have aglomerular kidneys with less number of nephrons. Such kidneys minimize the loss of water through urine. To compensate water loss the marine fish drink more water, and along with this water, salts are added to the body fluids and disturb the internal equilibrium.

To maintain salt balance (salt homeostasis) in the body, they have salt secreting chloride cells in their gills. Marine birds like sea gulls and penguins eliminate salts in the form of salty fluid that drips through their nostrils. In turtles the ducts of chloride secreting glands open near the eyes. Some cartilaginous fishes retain urea and trimethylamine oxide (TMO) in their blood to keep the body fluid isotonic to the sea water and avoid dehydration of the body due to exosmosis.

Water related adaptations in brackish water animals :
The animals of brackish water are adapted to withstand wide fluctuations in salinity. Such organisms are called euryhaline animals and those that can’t withstand are known as stenohaline. The migratory fishes such as salmon and Hilsa are anadromous fishes i.e., they migrate from the sea to freshwater, for breeding; Anguilla bengalensis is a catadromous fish i.e., it migrates from the river to sea, for breeding. In these fishes their glomerular kidneys are adjusted to changing salinities.

The chloride cells are adapted to excrete or absorb salts depending on the situation. On entering the river salmon drinks more freshwater to maintain the concentration of body fluids equal to that of the surround water.

Water related adaptations for terrestrial life :
In the absence of an external source of water, the kangaroo rat of the North American deserts is capable of meeting all its water requirements through oxidation of its internal fat (in which water is a by product – metabolic water). It also has the ability to concentrate its urine, so that minimal volume of water is lost in the process of removal of their excretory products.

Question 3.
Give an account of various types of interactions among the animal species of an ecosystem.
Answer:
Inter – specific Interactions :
Inter – specific interactions arise from the interaction of populations of two different species. They could be beneficial, detrimental or neutral (neither harmful nor beneficial) to one of the species or both. Assigning a V sign for beneficial interaction, sign for detrimental and ‘O’ for neutral interaction, let us look at all the possible outcomes of inter-specific interactions.

The interactions between species are grouped into four types. They are mutualism, commensalism, parasitism and amensalism. Both the species benefit in mutualism and both lose in competition in their interactions with each other. The interaction where one species is benefited and the other is neither benefited nor harmed is called commensalism. In amensalism on the other hand one species is harmed whereas the other is unaffected. In both parasitism and ‘predation’only one species benefits (parasite and predator, respectively) and the interaction is detrimental to the other species (host and prey, respectively). Predation, parasitism and commensalisms share a common characteristic – the interacting species live closely together.

Population Interactions – Types

Predation :
What would happen to all the energy fixed by autotrophic organisms if the community has no animals to eat the plants? We can think Of predation as nature’s way of transferring the energy fixed by plants to higher trophic levels. When we think of predator and prey, most probably it is the tiger and the deer that readily come to our mind, but a sparrow eating any seed is also a type of predator (a seed predator also called granivore). Although animals eating plants are categorized separately as herbivores, they are, in a broad ecological context, not very different from predators.

Besides acting as ‘conduits’ / ‘pipelines’ for energy transfer across trophic levels, predators play other important roles. They keep the prey populations under control. In the absence of predators, the prey species could achieve very high population densities and cause instability in the ecosystem. Predators have different types of functions to play in nature. They include :

A. Predator as a biological control :
The prickly pear cactus introduced into Australia in the early 1920s caused havoc by spreading rapidly into millions of hectares of rangeland (vast natural grass lands). Finally, the invasive cactus was brought under control only after a cactus feeding predator (a moth) was introduced into the country. Biological control methods adopted in agricultural pest control are based on the ability of the predators to regulate prey populations.

B. Predators maintain ‘species diversity’ :
Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species. In the rocky intertidal communities of the American Pacific Coast, the starfish Pisaster is an important predator. In a field experiemnt, when all the starfish were removed from an enclosed intertidal area, more than 10 species of invertebrates became extinct within a year, because of increased inter-specific competition.

C. Predators are prudent (practical) pertaining to preys :
If a predator is too efficient and overexploits its prey, then the prey might become extinct and following it, the predator will also become extinct due to lack of food. This is the reason why predators in nature are ‘prudent’.

Prey species have evolved various defenses to lessen the impact of predation they include :

a) Preys fool (deceive) or avoid their predators :
Some species of insects and frogs are cryptically – coloured (camouflaged) to avoid being detected easily by the predator. Some are poisonous and therefore avoided by the predators.

b) Preys defend by becoming distasteful to predators :
The Monarch butterfly is highly distasteful to its predator (bird) because of a special chemical present in its body. Interestingly, the butterfly acquires this chemical during its caterpillar stage by feeding on a poisonous weed.

c) Plants too have their defensive mechanisms :
For plants, herbivores are the predators. Nearly 25 percent of all insects are known to be phytophagous (feeding on plant sap and other parts of plants). The problem is particularly severe for plants because, unlike animals, they cannot escape from their predators. Plants therefore have evolved a variety of morphological and chemical defences against herbivores.

i) Thorns (Acacia, Cactus, etc.,) are the most common morphological means of defense. Many plants produce and store chemicals that make the herbivore sick when they are eaten, inhibit feeding or digestion, disrupt its reproduction or even kill it.

ii) We must have seen the weed Calotropis growing in abandoned fields. The plant produces highly poisonous cardiac glycosides and that is why we never see any cattle or goats browsing on this plant.

iii) A wide variety of chemical substances that we extract from plants on a commercial scale (nicotine, caffeine, quinine, strychnine, opium, etc.,) are produced by them actually as defences against grazers and browsers. Competition: When Darwin spoke of the struggle for existence and survival of the fittest in nature, he was convinced that interspecific competition is a ’potent force’ in the process of organic evolution, involving Nature Selection. It is generally believed that competition occurs when closely related species compete for the same resources that are limited, but this is not entirely true.

Parasitism :
Considering that the parasitic mode of life ensures free ‘lodging’ and ‘meals’, it is not surprising that parasitism has evolved in so many taxonomic groups from plants to higher vertebrates. Many parasites have evolved to be host-specific (they can parasitize only a specific species of host) in such a way that both host and the parasite tend to co-evolve; that is, if the host evolves special mechanisms for rejecting or resisting the parasite, the parasite has to evolve mechanisms to ‘counteract’ and ‘neutralize’ them, in order to continue successful parasitic relationship with the same host species. In order to leacl successful parasitic life, parasites evolved special adaptations, such as :
In order to lead successful parasitic life, parasites evolved special adaptations such as.

1. Loss of sense organs (which are not necessary for most parasites).
2. Presence of adhesive organs such as suckers, hooks tq cling on to the host’s body parts.
3. Loss of digestive system and presence of high reproductive capacity.
4. The life cycles of parasites are often complex, involving one or two intermediate hosts or vectors to facilitate parasitisation of their primary hosts.

e.g : 1: The human liver fluke depends on two intermediate (secondary ) hosts (a snail anda fish)to complete its life cycle.

e.g : 2 : The malaria parasite needs a vector (mosquito) to spread to otehr hosts. Majority of the parasites harm the host. They may reduce the survival, growth and reproduction of the host and reduce its population density. They might render the host more vulnerable to predation by making it physically weak.

Commmensalism :
This is the interaction in which one species benefits and the other is neither harmed nor benefited. Barnacles growing on the back of a whale benefit while the whale derives no noticeable benefit.

Mutualism :
This type of interaction benefits both the interacting species.

The most common examples of mutualism are found in plant-animal relationships. Plants need the help of animals for pollinating their flowers and dispersing their seeds. Animals obviously have to be paid ‘fees’ for the services that plants derive from them. Plants offer rewards in the form of pollen and nectar for pollinators and juicy and nutritious fruits for seed dispersing animals.

Question 4.
Describe lake as an ecosystem giving examples for the various zones and the biotic components in it. [March 2015 – T.S ; March 2013] (T.Q.)
Answer:
Lake Ecosystem :
To understand the fundamentals of an aquatic ecosystem, let us take a ‘lake’ as an example. This is fairly a self-sustainable unit and rather a simple example that explains even the complex interactions that exist in an aquatic ecosystem.

Lakes are large inland water bodies containing standing/still water (Recall: Lentic community). They are deeper than ponds (pond is not an ideal example as it is very shallow). Most lakes contain water throughout the year. In deep lakes, light cannot penetrate more than 200 meters, in depth. They are vertically stratified in relation to light intensity, temperature, pressure, etc. Deep water lakes contain three distinct zones namely, i) littoral zone, ii) limnetic zone, and iii) profundal zone.

Littoral zone :
It is the shallow part of the lake closer to the shore. Light penetrates up to the bottom. It is ‘euphoric’ (having good light), has rich vegetation and higher rate of photosynthesis, hence rich in oxygen.

Limnetic zone :
It is the open water zone away from the shore. It extends up to the effective light penetration level, vertically. The imaginary line that separates the limnetic zone from the profundal zone is known as zone of compensation/ compensation point / light compensation level. It is the zone of effective light penetration. Here the rate of photosynthesis is equal to the rate of respiration. Limnetic zone has no contact with the bottom of the lake.

Profundal zone :
It is the deep water area present below the limnetic zone and beyond the depth of effective light penetration. Light is absent. Photosynthetic organisms are absent and so the water is poor in oxygen content. It includes mostly the anaerobic organisms which feed on detritus.

The organisms living in lentic habitat are classified into pedonic forms, which live at the bottom of the lake and those living in the open waters of lakes, away from the shore vegetation are known as limnetic forms.

Biota (animal and plant life of a particular region) of the littoral zone :
Littoral zone is rich with pedonic flora (especially up to the depth of the effective light penetration.) At the shore proper emergent vegetation is a abundant with firmly fixed roots in the bottom of the lake and shoots and leaves are exposed above the level of water. These are amphibious plants. Certain emergent rooted plants of littoral zone are the cattails (Typha), bulrushes (Scirpus), arrowheads (Sagittaria). Slightly deeper are the rooted plants with floating leaves, such as the water lilies (Nymphaea), Nelumbo, Trapa, etc. Still deeper are the submerged plants such as Hydrilla, Chara, Potamogeton, etc. The free floating vegetation includes Pistia, Wolffia, Lemna (duckweed), Azolla, Eichhornia, etc.

The phytoplankton of the littoral zone composed of diatoms (Coscinodiscus, Nitzschia, etc.), green algae (Volvox, Spirogyra, etc.), euglenoids (Euglena, Phacus, etc.), and dinoflagellaes (Gymnodinium, Cystodinium, etc.)

Animals, the consumers of the littoral zone, are abundant in this zone of the lake. These are categorized into zooplankton, neuston, nekton, periphyton, and benthos. The zooplankton of the littoral zone consists of ‘water fleas’ such as Daphnia rotifers and ostracods.

The animals living at the air – water interface constitute the ‘neuston’. They are of two types, the epineuston and hyponeuston. Water striders (Gerris), beetles, water bugs (Dineutes) form the epineustone / supraneuston and the hyponeuston/ infraneuston includes the ‘larvae of mosquitoes’.

The animals such as fishes, amphibians, water snakes, terrapins, insects like ‘water scorpion’ (Ranatra), ‘back swimmer’ (Notonecta), ‘dividing beetles’ (Dytiscus), capable of swimming constitute the nekton.

The animals that are attached to / creeping on the aquatic plants such as the ‘water snails’, ‘nymphs of insects’, ‘bryozoans’, ‘turbellarians’, etc., constitute the ‘periphyton’.

The animals that rest on or move on the bottom of the lake constitute the ‘benthos’ e.g. red annelids, chironomid larvae, cray fishes, some isopods, amphipods, clams, etc.

Biota of the limnetic zone :
Limnetic zone is the largest zone of a lake. It is the region of rapid variations of the level of the water, temperature, oxygen availability, etc., from time to time. The limnetic zone has autotrophs (photosynthetic plants) in abundance. The chief autotrophs of this region are the phytoplankton such as the euglenoids, diatoms, cyanobacteria, dinoflagellates and green algae. The consumers of the limnetic zone are the zooplanktonic organisms such as the copepods. Fishes, frogs, water snakes, etc., form the limnetic nekton.

Biota of the profundal zone :
It includes the organisms such as decomposers (bacteria), chironomid larvae, Chaoborus (Phantom larva), red annelids, clams, etc., that are capable of living in low oxygen levels. The decomposers of this zone decompose the dead plants and animals and release nutrients which are used by the biotic communities of both littoral and limnetic zones.

The lake ecosystem performs all the functions of any ecosystem and of the biosphere as a whole, i.e., conversion of inorganic substances into organic material, with the help of the radiant solar energy by the autotrophs; consumption of the autotrophs by the heterotrophs; decomposition and mineralization of the dead matter to release them back for reuse by the autotrophs (recycling of minerals).

Question 5.
Give an account of the various types of ecosystems on the Earth.
Answer:
An ‘ecosystem’ is a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. Ecosystem varies greatly in size from a small pond to a large forest or a sea. Many ecologists regard the entire biosphere as a ‘global ecosystem’, as a composite of all local ecosystems on Earth. Since this system is too big and complex to be studied at one time, it is convenient to divide it into two basic categories, namely natural and artificial. The natural ecosystems include aquatic ecosystems of water and terrestrial ecosystems of the land. Both types of natural and artificial ecosystems have several subdivisions.

The Natural Ecosystems :
These are naturally occurring ecosystems and there is no role of humans in the formation of such types of ecosystems. These are categorized mainly into two types – aquatic and terrestrial ecosystems.

Aquatic Ecosystems :
Based on the salinity of water, three types of aquatic ecosystems are identified marine, freshwater, and estuarine.

i. The Marine Ecosystem :
It is the largest of all the aquatic ecosystems. It is the most stable ecosystems.

ii. Estuarine Ecosystem :
Estuary is the zone where river joins the sea. Sea water ascends up into the river twice a day (effect of high tides and low tides). The salinity of water in an estuary also depends on the seasons. During the rainy season out flow of river water makes the estuary less saline and the opposite occurs during the summer. Estuarine organisms are capable of withstanding the ‘fluctuations’ in salinity.

iii. The Freshwater Ecosystem :
The freshwater ecosystem is the smallest aquatic ecosystem. It includes rivers, lakes, ponds, etc. It is divided into two groups – the lentic and lotic. The still water bodies like ponds, lakes, reservoirs, etc., fall under the category of lentic ecosystems, whereas, streams, rivers and flowing water bodies are called lotic ecosystems. The communities of the above two types are called lentic and lotic communities respectively. The study of freshwater ecosystem is called as limnology.

The Terrestrial Ecosystems :
The ecosystems of land are known as terrestrial ecosystems. Some examples of terrestrial ecosystems are the forest, grassland and desert.

i. The forest Ecosystems :
The two important types of forests seen in India are i) tropical rain forest and ii) tropical deciduous forests.

ii. The Grassland Ecosystems :
These are present the Himalayan region in India. They occupy large areas of sandy and saline soils in Western Rajasthan.

iii. Desert Ecosystems :
The areas having less than 25 cm rainfall per year are called desert. They have characteristics flora and fauna. The deserts can be divided into two types – hot type and cold type deserts. Thar Desert in Rajasthan is the example for hot type of desert. Cold type desert is seen in Ladakh.

Artificial Ecosystems :
These are man-made ecosystems such as agricultural or agro-ecosystems. They include cropland ecosystems, aquaculture ponds and aquaria.

Question 6.
Describe different types of food chains that exist in an ecosystem. [March 2019, May 2017 – A.P.; May/June, Mar. 2014] (T.Q.)
Answer:
Energy flows into biological systems (ecosystems) from the Sun. The biological systems of environment include several food levels called trophic levels. A trophic level is composed of those organisms which have the same source of energy and having the same number of steps away from the sun. Thus a plant’s trophic level is one, while that of a herbivore – two, and that of the first level carnivore – three. The second and third levels of the carnivores occupy fourth and fifth trophic levels respectively.

A given organism may occupy more than one trophic level simultaneously. One must remember that the trophic level represents a functional level. A given species may occupy more than one trophic level in the same ecosystem at the same time; for example, a sparrow is a primary consumer when it eats seeds, fruits, and a secondary consumer when it eats insects and worms.

The food energy passes from one trophic level to another trophic level mostly from the lower to higher trophic leves. When the ‘path of food energy is ‘linear’, the components resemble the ‘links’ of a chain, and it is called ‘food chain’. Generally a food chain ends with decomposers. The three major types of food chains in an ecosystem are Grazing Food Ghain, Parasitic Food Chain and Detritus Food Chain.

I. Grazing Food Chain (GFC) :
It is also known as predatory food chain. It begins with the green plants (producers) and the second, third and fourth trophic levels are occupied by the herbivores, primary carnivores and secondary carnivores respectively. In some food chains there is yet another trophic level – the climax carnivores. The number of trophic levels in food chains varies from 3 to 5 generally. Some examples for grazing food chain (GFC) are given below.

II. Parasitic food chain :
Some authors included the ‘parasitic Food Chains’ as a part of the GFC. As in the case of GFCs, it also begins with the producers, the plants (directly or indirectly). However, the food energy passes from large organisms to small organisms in the parasitic chains. For instance, a tree which occupies the 1^st trophic level provides shelter and food for many birds. These birds host many ecto-parasites and endo-parasites. Thus, unlike in the predator food chain, the path of the flow of energy includes fewer, large sized organisms in the lower trophic levels, and numerous, small sized organisms in the successive higher trophic levels.

III. Detritus Food Chain :
The detritus food chain (DFC) begins with dead organic matter (such as leaf litter, bodies of dead organisms). It is made up of Decomposers which are heterotrophic organisms, mainly the ‘fungi’ and ‘bacteria’. They meet their energy and nutrient requirements by degrading dead organic matter or detritus. These are also known as saprotrophs (sapro : to decompose)

Decomposers secrete digestive enzyme that breakdown dead and waste materials (such as faeces) into simple absorbable substances. Some examples of detritus food chains are :

1. Detritus (formed from leaf litter) – Earthworms – Frogs – Snakes.
   Dead animals – Flies and maggots – Frogs – Snakes.

In an aquatic ecosystem, GFC is the major ‘conduit’ for the energy flow. As against this, in a terrestrial ecosystem, a much larger fraction of energy flows through the detritus food chain than through the GFC. Detritus food chain may be connected with the grazing food chain at some levels. Some of the organisms of DFC may form the prey of the GFC animals. For example, in the detritus food chain given above, the earthworms of the DFC may become the food of the birds of the GFC. It is to be understood that food chains are not ‘isolated’ always.

Question 7.
Write an essay on productivity of an ecosystem.
Answer:
The rate of production of biomass is called productivity. It can be divided into primary and secondary productivities.

I. Primary productivity is defined as the amount of biomass or organic matter produced per unit area over a period of time by plants, during photosynthesis. It can be divided into gross primary productivity (GPP) and net primary productivity (NPP).

a) Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilized by plants for their catabolic process (respiration).

b) Net primary productivity Gross primary productivity minus respiratory loss (R), is the net primary productivity (NPP). On average about 20 – 25 percent of GPP is used for the catabolic (respiratory) activity.

GPP – R = NPP
The net primary productivity is the biomass available for the consumption of the heterotrophs (herbivores and decomposers).

II. Secondary productivity is defined as the rate of formation of new organic matter by consumers.

Question 8.
Give an account of flow of energy in an ecosystem. [March 2015 – A.P.] (T.Q.)
Answer:
Energy Flow :
Except for the deep sea hydro-thermal ecosystem, sun is the only source of energy for all ecosystems on Earth. Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR). We know that plants and photosynthetic bacteria (autotrophs), fix Sun’s radiant energy to synthesise food from simple inorganic materials. Plants capture only 2-10 percent of the PAR and this small amount of energy sustains the entire living world. So, it is very important to know how the solar energy captured by plants flows through different organisms of an ecosystem.

All heterotrophs are dependent on the producers for their food, either directly or indirectly. The law of conservation of energy is the first law of thermodynamics. It states that energy may transform from one form into another form, but it is neither created nor destroyed. The energy that reaches earth is balanced by the energy that leaves the surface of the earth as invisible heart radiation.

The energy transfers in an ecosystem are essential for sustaining life. Without energy transfers there could be no life and ecosystems. Living beings are the natural proliferations that depend on the continuous inflow of concentrated energy.

Further, ecosystems are not exempted from the Second Law of thermodynamics. It states that no process involving energy transformation will spontaneously occur unless there is degradation of energy. As per the second law of thermodynamics – the energy dispersed is in the form of unavailable heat energy, and constitutes the entropy (energy lost or not available for work in a system). The organisms need a constant supply of energy to synthesize the molecules they require. The transfer of energy through a food chain is known as energy flow.

A constant input of mostly solar energy is the basic requirement for any ecosystem to function. The important point to note is that the amount of energy available decreases at successive trophic levels. When an organism dies, it is converted to detritus or dead biomass that serves as a source of energy for the decomposers. Organisms at each trophic level depend on those at the lower trophic level, for their energy demands.

Each trophic level has a certain mass of living material at a particular time, and it is called the standing crop. The standing crop is measured as the mass of living organisms (biomass) or the number of organisms per unit area. The biomass of a species is expressed in terms of fresh or dry weight (dry weight is more accurate because water contains no usable energy).

The 10 percent Law :
The 10 percent law for the transfer of energy from one trophic level to the next was introduced by Lindeman (the Founder of the modern Ecosystem Ecology).

According to this law, during the transfer of energy from one trophic level to the next, only about 10 percent of the energy is stored / converted as body mass / biomass. The remaining is lost during the transfer or broken down in catabolic activities (Respiration).

Lindeman’s rule of trophic efficiency /Gross ecological efficiency is one of the earliest and most widely used measures of ecological efficiency. For example, if the NPP (Net primary production) in a plant is 100 kJ, the organic substance converted into body mass of the herbivores which feeds on it is 10 kJ only. Similarly the body mass of the carnivore -1 is 1 kJ only.

Question 9.
List out the major air pollutants and describe their effects on human beings. [March 2018, 17 – A.P.] (T.Q.)
Answer:
The major air pollutants :
1. Carbon monoxide (CO) :
It is produced mainly due to incomplete combustion of fossil fuels. Automobiles are a major cause of CO pollution in larger cities and towns. Automobile exhausts, fumes from factories, emissions from power plants, forest fires and even burning of fire-wood contribute to CO pollution. Haemoglobin has greater affinity for CO and so CO competitively interferes with oxygen transport. Co causes symptoms such as headache and blurred vision at lower concentrations. In higher concentrations, it leads to coma and death.

2. Carbon Dioxide (CO₂) :
Carbon dioxide is the main pollutant that is leading to global warming. Plants utilize CO₂ for photosynthesis and all living organisms emit carbon dioxide in the process of respiration. With rapid urbanization, automobiles, aeroplanes, power plants, and other human activities that involve the burning of fossil fuels such as gasoline, carbon dioxide is turning out to be an important pollutant of concern.

3. Sulphur Dioxide (SO₂) :

It is mainly produced by burning of fossil fuels. Melting of sulphur ores is another important source for SO₂ pollution. Metal smelting and other industrial processes also contribute to SO₂ pollution. Sulphur dioxide and nitrogen oxides are the major causes of acid rains, which cause acidification of soils, lakes and streams, and also accelerated corrosion of buildings and monuments. High concentrations of sulphur dioxide (SO₂) can result in breathing problems in asthmatic children and adults. Other effects associated with long – term exposure to sulphur dioxide, include respiratory illness, alterations in the lungs’ defenses and aggravation of existing cardiovascular problems.

To control SO₂ pollution, the emissions are filtered through scrubbers. Scrubbers are devices that are used to clean the impurities in exhaust gases. Gaseous pollutants such as SO₂ are removed by scrubbers.

4. Nitrogen Oxides :
Nitrogen oxides are considered to to be major primary pollutants. The source is mainly automobile exhaust. The air polluted by nitrogen oxides is not only harmful to humans and animals, but also dangerous for the life of plants. Nitrogen oxide pollution also results in acid rains and formation of photochemical smog. The effect of nitrogen oxides on plants include the occurrence of necrotic spots on the surface of leaves. Photosynthesis is affected in crop plants and they yield is reduced. Nitrogen oxides combine with volatile organic compounds by the action of sunlight to form secondary pollutants called Peroxyacetyl nitrate (PAN) which are found especially in photochemical smog. They are powerful irritants to eyes and respiratory tract.

5. Particulate matter/Aerosols :
Tiny particles of solid matter suspended in a gas or liquid constitute the ‘particulate matter’. ‘Aerosols’ refer to particles and / or liquid droplets and the gas together (a system of colloidal particles dispersed in a gas). Combustion of ‘fossil fuels’ (petrol, diesel, etc.,), fly ash produced in thermal plants, forest fires, cement factories, asbestos mining and manufacturing units, spinning and ginning mills etc., are the main sources of particulate matter pollution. According to the Central Pollution Control Board (CPCB) particles of 2.5 micrometers or less in diameter are highly harmful to man and other air breathing organisms.

Question 10.
What are the causes of water pollution and suggest measures for control of water pollution?
Answer:

Inferior quality of water, caused by pollution of natural waters is a major problem world is facing today. It is posing all the rivers in India are grossly polluted either by sewage or discharge of industrial effluents.

The major water pollutants :
1. Domestic Sewage :
Sewage is the major source of water pollution in large cities and towns. It mainly consists of human and animal excreta and other waste materials. It is usually released into freshwater bodies or sea directly. As per the regulations the sewage has to be passed through treatment plants before it is released into the water courses. Only 0.1 percent of impurities from domestic sewage are making these water sources unfit for human consumption. In the treatment of sewage, solids are easy to remove. Removal of dissolved salts such as nitrates, phosphates and other nutrients and toxic metal ions and organic compounds is much more difficult. Domestic sewage primarily contains biodegradable organic matter, which will be readily decomposed by the action of bacteria and other microorganisms.

Effect of sewage discharge on some important characteristics of a river
Biological Oxygen Demand (BOD) :
BOD is measure of the content of biologically degradable substances in sewage. The organic degradable substances are broken-down by microorganisms using oxygen. The demand of oxygen is measured in terms of the oxygen consumed by microorganisms over a period of 5 days (BOD 5) or seven days (BOD 7). BOD forms an index for measuring pollution load in the sewage. Microorganisms involved in biodegradation of organic matter in water bodies consume a lot of oxygen, and as a result there is a sharp decline in dissolved oxygen causing death offish and other aquatic animals.

Algal blooms :
Presence of large amounts of nutrients in waters also causes excessive growth of planktonic algae and the phenomenon is commonly called ‘algal blooms’. Algal blooms impart distinct colour to the water bodies and deteriorate the quality of water. It also causes mortality of fish. Some algae which are involved in algal blooms are toxic to human beings and animals.

Excessive growth of aquatic plants such as the common water hyacinth (Eichhornia crassipes), the world’s most problematic aquatic weed which is also called ‘Terror of Bengal’ causes blocks in our water ways. They grow faster than our ability to remove them. They grow abundantly in eutrophic water bodies (water bodies rich in nutrients) and lead to imbalance in the ecosystem dynamics of the water body.

Sewage arising from homes and hospitals may contain undesirable pathogenic microorganisms. If it is released untreated into water resources, there is a likelihood of outbreak of serious diseases, such as dysentery, typhoid, jaundice, cholera etc.

2. Industrial Effluents :
Untreated industrial effluents released into water bodies pollute most of the rivers, fresh water streams, etc. Effluents contain a wide variety of both inorganic and organic pollutants such as oils, greases, plastics, metallic wastes, suspended solids and toxins. Most of them are non-degradable. Arsenic, Cadmium, Copper, Chromium, Mercury, Zinc, and Nickel are the common heavy metals discharged from industries.

Effects :
Organic substances present in the water deplete the dissolved oxygen content in water by increasing the BOD (Biological oxygen demand) and COD (Chemical oxygen demand). Most of the inorganic substances render the water unfit for drinking. Outbreaks of dysentery, typhoid, jaundice, cholera etc., are caused by sewage pollution.

b) Biomagnification :
Increase in the concentration of the pollutant or toxicant at successive trophic levels in an aquatic food chain is called Biological Magnification or Bio – magnification. This happens in the instances where a toxic substance accumulated by an organism is not metabolized or excreted and thus passes on to the next higher trophic level. This phenomenon is well known regarding DDT and mercury pollution.

As shown in the above example, the concentration of DDT is increased at successive trophic levels starting at a very low concentration of 0.003 ppb (ppb – parts per billion) in water, which ultimately reached an alarmingly high concentration of 25 ppm (ppm – parts per million) in fish-eating birds, through bio-magnification. High concentrations of DDT disturb calcium metabolism in birds, which causes thinning of egg shell and their premature breaking, eventually causing decline in bird populations.

Eutrophication :
Natural ageing of a lake by nutrient enrichment of its water is known as eutrophication. In a young lake, the water is cold and clear, supporting little life. Gradually nutrients such as nitrates and phosphates are carried into the lake via streams, in course of time. This encourages the growth of aquatic algae and other plants. Consequently the animal life proliferates, and organic matter gets deposited on the bottom of the lake. Over centuries, as silt and organic debris piles up, the lake grows shallower and warmer. As a result, the aquatic organisms thriving in the cold environment are gradually replaced by warm-water organisms. Marsh plants appear by taking root in the shallow regions of the lake. Eventually, the lake gives way to large masses of floating plants (bog) and finally converted into land.

Depending upon the climatic conditions, size of the lake and other factors, the natural ageing of a lake may span thousands of years. However, pollutants from human ativity (anthropogenic) radically accelerate the aging process. This phenomenon is called ‘Cultural or Accelerated eutrophication’.

During the past century, lakes in many parts of the earth have been severey eutrophied by sewage, agricultural and industrial wastes. The prime contaminants are nitrates and phosphates, which are the ’chief plant nutrients’. The dissolved oxygen which is vital to other aquatic clife is depleted. At the same time, other pollutants flowing into the lake may poison the whole population of fish, whose decomposing remains further deplete the dissolved oxygen content in the water.

Thermal pollution :
Water is used as a coolant in Thermal power plants and other industries. Hot water flowing out of industries also constitute an important category of pollutants. Thermal waste water eliminates sensitive organisms (Stenothermal organisms such as fish – especially the juveniles) downstream and may enhance the growth of plants and fish in extremely cold areas but, only after causing damage to the indigenous flora and fauna.

Ecological Sanitation – ’Ecosan Toilets’ :
Generally it is assumed that removal of wastes requires water, which means creation of sewage. If water is not used to dispose off human waste like excreta, and if one didn’t have to flush the tiolet after its use, a large amount of water can be saved. This is already a reality. Ecological sanitation is a substainable system for handling human excreta, using ‘dry composting toilets’. This is a practical, hygienic, efficient and cost-effective solution to human waste disposal. The key point to note here is that, with this composting method, human excreta can be recycled into a resource (as natural fertiliser), which reduces the need for chemical fertilizers. ‘EcoSan’ toilets are in use in many parts of Kerala and Sri Lanka.

Question 11.
Write an essay on soil pollution and measures to control soil pollution.
Answer:
Solid Wastes :
Any thing (substance/ material / articles / goods) that is thrown out as waste in solid form is referred to as solid waste. Municipal solid wastes are wastes from homes, offices, institutions, shops, hotels, restaurants etc., in towns and cities.

The municipal solid wastes generally consist of paper, food wastes, plastics, glass, metals, rubber, leather, textile, etc. The wastes are burnt to reduce the volume of the wastes. But generally wastes are not completely burnt and left as open dumps which often serve as the breeding grounds for rats and flies. As the substitute for open-burning dumps, sanitary landfills are adopted. In a sanitary landfill, wastes are dumped in a depression or trench after compaction, and covered landfill, wastes are dumped in a depression or trench after compaction, and covered with dirt everyday. These is a danger of seepage of chemicals and pollutants from these landfills, which may contaminate the underground water resources.

The best solution is to develop awareness in the society on these environmental issues. All wastes that we generate can be categorized into three types (a) biodegradable, (b) recyclable and (c) non-biodegradable. It is important that all garbage generated should be sorted out category wise. The reusable or recyclable material has to be separated out and utilised. (Rag-pickers in the streets are doing a great job of separation of materials for recycling.) The biodegradable materials can be put into deep pits in the ground and be left for natural breakdown. The remaining non-biodegradable waste left over is to be disposed off properly.

The prime goal should be to reduce our garbage generation. But we are increasing the use of non-biodegradable products. We are packaging products of our daily use such as milk and water also in polythene bags. In cities and towns, many purchased things are packed in polystyrene and plastic packets. Thus we are contributing heavily to environmental pollution. State Governments across the country are trying to educate people on the reduction in use of plastic and use of eco-friendly packaging. We can do our bit by using carry-bags made of cloth or other natural fibres when we go for shopping and by refusing polythene bags.

i) Hospital wastes :
Hospitals generate hazardous wastes that contain disinfectants, harmful chemicals and also pathogenic micro-organisms. Such wastes also require careful treatment and disposal. The use of incinerators (to burn wastes) is essential for disposal of hospital waste.

ii) Electronic wastes (e-wastes) :
Irreparable computers and other electronic goods constitute the modern day pollutants called electronic wastes (e-wastes), e – wastes are buried in landfills or incinerated. Over half of the e-wastes generated in the developed world are exported to developing countries, mainly to China, India and Pakistan, where metals like copper, iron, silicon, nickel and gold are recovered during recycling process.

Unlike developed countries, which have specifically built facilities for recycling of e-wastes, recycling in developing countries often involves manual participation thus exposing workers to toxic substances present in e – wastes. Eventually recycling is the only solution for the treatment of e – wastes provided it is carried out in an environmental friendly manner.

iii) Agro – chemicals and their effects :
In the wake of the Green Revoltuion, use of inorganic fertilisers and pesticides has increased many times, for enhancing crop production. Pesticides, herbicides, fungicides, etc., are being increasingly used. They are also toxic to non-target organisms such as earthworms, nitrogen fixing bacteria, etc., that are important components of soil eco-system. Moreover due to bio-magnification, the harmful chemicals pose a great threat to human health. Indiscriminate use of fertilizers will lead to increased drain of nutrients into the nearby aquatic ecosystems causing eutrophication and the consequent effects.

iv) Radioactive wastes :
Initially, nuclear energy was hailed as a non-polluting way for generating electricity. Later on, it was realised that the use of nuclear energy has two very serious inherent problems. The first is accidental leakages, as occurred in the Three Mile Island (USA) and Chernobyl (Russia) and the second is the safe disposal of radioactive wastes.

Radiation, that is released from nuclear waste is extremely dangerous to biological organisms, because it induces mutations. Exposure to high doses of nuclear radiation is lethal as it can lead to cancers (e.g. leukemia). Therefore, nuclear waste is an extremely potent pollutant and has to be dealt with utmost caution. Storage of nuclear wastes should be done in suitably shielded containers and buried deep in the soil or oceans (about 500 meters). Even when done so, geological upheavals can bring them up, some day and cause radiation.

Telangana TSBIE TS Inter 1st Year Zoology Study Material 7th Lesson Type Study of Periplaneta Americana (Cockroach) Textbook Questions and Answers.

TS Inter 1st Year Zoology Study Material 7th Lesson Type Study of Periplaneta Americana (Cockroach)

Very Short Answer Type Questions

Question 1.
Why do you call cockroach a pest? (U).
Answer:
Cockroach is commonly found in kitchen and contaminates our food with its excreta. It can transmit a number of bacterial diseases by contaminating food. Hence it is called a pest.

Question 2.
Name the terga of thoracic segments of cockroach. (K)
Answer:
The terga of thoracic segments are one large pronotum covering prothorax. The terga on the mesothorax and metathorax are called mesonotum and metanotum.

Question 3.
What are the structures with which cockroach walks on smooth surfaces and on rough surfaces respectively? (U)
Answer:
The claws and the arolium help in locomotion on rough surfaces whereas plantulae are useful on smooth surfaces.

Question 4.
Name the chitinous tubes that support the wings of cockroach. (K)
Answer:
The wings of cockroach contain a network of hollow veins or nervures.

Question 5.
What is tegmen? What is its function? (KJ
Answer:
The fore wings are thick, opaque and leathery. They donot help in flight, but cover and protect the hind wings when they are not in use. They are called tegmina (singular: tegmen).

Question 6.
Why is the head in cockroach called hypognathous? (U)
Answer:
The head of cockroach is called hypognathous because it lies hanging almost at right angles to the body with the posterior wider part upwards and the mouth parts directed downwards.

Question 7.
How is a tripod formed with reference to locomotion in cockroach? (U)
Answer:
Each tripod is formed by fore leg and hind leg of one side and the middle leg of the other side in cockroach.

Question 8.
Name the muscles that help in elevating and depressing the wings of a cockroach. (K)
Answer:
Wings are elevated by the contraction of dorsoventral muscles. Contraction of the dorso – longitudinal muscles depresses the wings.

Question 9.
Name the different blood sinuses in cockroach. (K)
Answer:
The blood sinuses are a) Pericardial haemocoel or the dorsal sinus b) Perivisceral haemocoel or the middle sinus, c) Sternal haemocoel or ventral sinus.

Question 10.
How are the fat bodies similar to the liver of the vertebrates? (A)
Answer:
The haemocoel of cockroach contains many large sized fat bodies called corpora adiposa. These are similar to the liver of the vertebrates in certain function like storing of food, secrete lipids, store uric acid and contain symbiotic bacteria.

Question 11.
What are the three regions of the alimentary canal in cockroach? (K)
Answer:
The three regions are foregut or stomodaeum, midgut or mesenteron and hindgut or proctodaeum.

Question 12.
How many denticulate plates are present in the gizzard of cockroach? (K)
Answer:
The chitinous inner lining of the gizzard of cockroach has six powerful teeth, which form an efficient grinding apparatus.

Question 13.
Which part of the gut secretes the peritrophic membrane in cockroach? (U)
Answer:
The ‘bolus’ of food in the mesenteron is enveloped by a chitinous and porous membrane called peritrophic membrane, which is secreted by the funnel like stomodeal valve of the gizzard.

Question 14.
Which parts of cockroach help in locating the food? (U)
Answer:
Cockroach locates the food by the olfactory sensillae of antenna, labial palps and maxillary palps.

Question 15.
In which part of the gut of cockroach, water is reabsorbed? (K)
Answer:
The undigested food is passed into the ileum, colon and then reaches the rectum, where water is reabsorbed by rectal papillae.

Question 16.
Write the names of mouthparts in cockroach that help in biting and tasting the food. (K).
Answer:
Mandibles help in biting and chewing of food. Labrum helps in tasting the food.

Question 17.
What are alary muscles? [K)
Answer:
There is a series of paired triangular muscles, called “Alary muscles.” Every segment has one pair of these muscles. These are attached to the pericardial septum by their broad bases and to the terga by their pointed ends.

Question 18.
What is haemocoel? (K)
Answer:
The body cavity of an arthropod or a mollusk filled with haemolymph : derived from the blastocoels of the embryo, also called the “Primary body cavity.”

Question 19.
The three sinuses in a cockroach are not equal in size. Why? (U)
Answer:
The middle sinus is very large as it contains most of the viscera. The dorsal and ventral sinuses are small as they have only heart and nerve cord, respectively.

Question 20.
Why is the blood of Periplaneta called haemolymph? (U)
Answer:
The blood of periplaneta is colourless and is called haemolymph. It consists of a fluid called plasma and free blood corpuscles or haemocytes which are phagocytic.

Question 21.
What is the function of haemocytes found in the blood of Periplaneta? (K)
Answer:
Haemocytes are phagocytic. They are large in size and can ingest foreign particles such as bacteria. Hence defensive in function.

Question 22.
Why does not the blood of Periplaneta help in respiration ? (A)
Answer:
There is no respiratory pigment in the blood and so it plays no major role in respiration.

Question 23.
Write important functions of blood in Periplaneta. (K)
Answer:
Blood functions

1. It absorbs digested food from alimentary canal and distributes it to the rest of the body.
2. It brings nitrogenous wastes from all parts of the body to the excretory organs for their elimination.
3. Phagocytes of blood are defensive in function.
4. It transports secretions of the ductless glands to the target organs.

Question 24.
The blood of Periplaneta is not red. Which pigment, do you think, is absent in it? (U)
Answer:
The blood of periplaneta is not red. There is no respiratory pigment called haemoglobin in the blood and so it plays no major role in respiration.

Question 25.
How many spiracles are present in cockroach? Mention their locations. (K)
Answer:
There are ten pairs of openings called stigmata or spiracles. The first two pairs of spiracles are present in the thoracic segments (2^nd and 3^rd). Remaining eight pairs are present in the first eight abdominal segments.

Question 26.
What are trichomes? Write their functions. (K)
Answer:
All spiracles bear small hair like structures called ‘trichomes’ to filter the dust particles.

Question 27.
Why is the respiratory system of cockroach called polypneustic and holopneustic system? (U)
Answer:
The spiracles of cockroach are polypneustic (as they are more than 3 pairs) and holopneustic (as all of them are functional).

Question 28.
Name the chitinous ring that encircles the spiracle of cockroach. (K)
Answer:
All spiracles are valvular and each of them is surrounded by a chitinous ring called peritreme.

Question 29.
What is intima? (K)
Answer:
Trachea in cockroach is made up of three layers, outer basement membrane, a middle one cell thick epithelium and an inner layer of cuticle called intima. The intima is produced into spiral thickenings called taenidia.

Question 30.
Name the protein that lines the tracheole of the cockroach. (K)
Answer:
Tracheoles are formed of a protein called trachein.

Question 31.
During inspiration which spiracles are kept open and which are kept closed? (K)
Answer:
During inspiration the thoracic spiracles are kept open and the abdominal spiracles are kept closed.

Question 32.
Which factors regulate the opening of the spiracles? (U)
Answer:
Opening and closing or spiracles is influenced by C02 tension in haemolymph and oxygen tension in the tracheae.

Question 33.
Inspiration in cockroach is a passive process and expiration is an active process. Justify. (U)
Answer:
During inspiration air is drawn in due to the relaxation of the muscles, the process is a “passive process”. Expiration involves the contraction of muscles, hence is described as ‘active process.’

Question 34.
The nitrogenous wastes in Periplaneta are removed from the body through alimentary canal. Why? (U)
Answer:
The removal of nitrogenous waste material through the alimentary canal helps in complete reabsorption of water from the wastes and formation of dry uric acid. It is an adaptation for conservation of water.

Question 35.
How does the cuticle of a cockroach help in excretion? (A)
Answer:
Some nitrogenous waste materials are deposited on the cuticle and eliminated during moulting.

Question 36.
How do fat bodies help in excretion? (A)
Answer:
Fat bodies absorb and store uric acid throughout the life. This is called storage excretion as they remain stored in the cells of the corpora adiposa.

Question 37.
What is ‘storage excretion’? (U)
Answer:
Fat bodies absorb and store uric acid throughout the life. This is called storage excretion as they remain stored in the cells of the corpora adiposa.

Question 38.
In which part of the alimentary canal of Periplaneta more water is reabsorbed? (K)
Answer:
The part of the alimentary canal of Periplaneta more water is reabsorbed in rectum containing rectal papillae.

Question 39.
List out the organs associated with excretion in Periplaneta. (K)
Answer:
The organs associated with excretion are
1) Malpighian tubules of anterior end of hind gut 2) Fat bodies 3) Uricose glands 4) Cuticle.

Question 40.
Which part of malpighian tubules extract water, salts and nitrogenous wastes from the haemolymph? (K)
Answer:
The distal portion of malpighian tubules containing glandular cells absorb salts, water and nitrogenous wastes from the haemolymph.

Question 41.
Which structure of cockroach acts as sensory and endocrine centre? (K)
Answer:
Brain or cerebral ganglia is mainly a sensory and an endocrine centre.

Question 42.
Distinguish between scolopidia and sensillae. (U)
Answer:

1. Sensillae are the units of cuticular receptors and chemoreceptors.
2. Scolopidia are the subcuticular units of mechanoreceptors of chordo-tonal organs.

Question 43.
How is the ommatidium of cockroach different from that of a diurnal insect? (A]
Answer:
In cockroach a nocturnal insect ommatidia form superposition image in which overlapping of images occur and it is a blurred image.

In diurnal insects the image is called apposition image as it is formed by the juxtaposition of small parts of the visual field. This type of vision is called mosaic vision.

Question 44.
How many segmental ganglia are present on the ventral nerve cord of cockroach? (K)
Answer:
On the ventral nerve cord segmental ganglia show 3 + 6 arrangement. 3 thoracic ganglia and 6 abdominal ganglia in first 7 segments except 5^th segment.

Question 45.
Which of the abdominal ganglia is the largest and why? (U)
Answer:
The last or the 6^th abdominal ganglion is the largest of all the abdominal ganglia. It is formed by the fusion of the ganglia of the 7^th, 8^th, 9^th and 10^th abdominal segments.

Question 46.
Name the structural and functional unit of compound eye of cockroach. How many such units are present in a single compound eye ? (K)
Answer:
Structural and functional unit of compound eye is ommatidium. In a single compound eye of cockroach 2000 ommatidia are present.

Question 47.
Why is the brain called the principal sensory centre in cockroach? (U)
Answer:
In brain protocerebrum receives sensory impulses from compound eyes through optic nerves, deutero cerebrum receives sensory impulses from antennae through antennel nerves and tritocerebrum receives sensory impulses from the labrum. Hence brain in principally sensory in nature.

Question 48.
Which parts of an ommatidium constitute dioptric region? (K)
Answer:
The region containing the cornea and crystalline cone constitute the dioptrical or focussing region of the ommatidium. ,

Question 49.
Distinguish between apposition image and superposition image. (U)
Answer:
In cockroach a nocturnal insect ommatidia form superposition image in which overlapping of images occur and it is a blurred image. In diurnal inserts the image is called apposition image as it is formed by the juxtaposition of small parts of the visual field. This type of vision is called mosaic vision.

Question 50.
List out the characters that help in understanding the difference between male and female cockroaches. (K)
Answer:
The female is different from the male in respect of short and broad abdomen, presence of brood pouches and absence of anal styles.

Question 51.
What is the function of mushroom gland in cockroach? (K)
Answer:
A characteristic mushroom shaped gland is present in the 6th and 7th abdominal segments which functions as an accessory reproductive gland.

Question 52.
Compare the utriculi majores and utriculi breviores of the mushroom gland functionally. (U)
Answer:
Secretion of utriculi majores forms the inner layer of the spermatophore while that of utriculi breviores nourishes the sperms.

Question 53.
How many ovarioles are present in a single ovary of Periplaneta and what are the two parts of a single ovariole? (U)
Answer:
Each ovary consists of eight tubules called ovarioles. Each ovariole consists of a tapering anterior filament called germarium and a posterior wider vitellarium.

Question 54.
What are phallomeres? (K)
Answer:
Surrounding the male genital opening there are chitinous and asymmetrical structures called phallic organs or gonapophyses or phallomeres which help in copulation. These are the male external genitalia.

Question 55.
What are gonapophyses? (K)
Answer:
Three pairs of plate like chitinous structures called gonapophyses are present around the female genital aperture. These gonapophyses guide the ova into ootheca as ovipositors. These are female external genitalia.

Question 56.
How is colleterial gland helpful in reproduction of Periplaneta? (A)
Answer:
Secretion of the two collateral glands forms a hard egg case called ootheca around the eggs.

Question 57.
What is paurometabolous development ? (U)
Answer:
Cockroach is paurometabolous, which means the development is gradual through nymphal stages.

Short Answer Type Questions

Question 1.
Draw a neat labelled diagram of the mouth parts of cockroach. (S)
Answer:

Question 2.
Describe the physiology of digestion in cockroach. (K)
Answer:
Digestion :
After swallowing, the food passes through the pharynx and oesophagus, and reaches the crop. In the crop, food is mixed with digestive juices that are regurgitated into it through the grooves of the gizzard. Hence, most of the food is digested in the crop. The partly digested food is filtered by the bristles of the gizzard and later it passes through the stomodeal valve into the ventriculus.

The enzyme amylase of the salivary juice converts starches into disaccharides. Invertase or sucrase digests sucrose into glucose and fructose. Maltase converts maltose into glucose. The enzyme lipase digests lipids into fatty acids and glycerol. Proteases digest proteins into amino acids. Cellulose of the food is digested by the enzyme cellulase secreted by the microorganisms present in the hindgut of cockroach. Cellulose in converted into glucose.

In the ventriculus, the digested food is absorbed. The undigested food is passed into the ileum, colon, and then reaches the rectum, where water is reabsorbed by rectal papillae. Then the remaining material is finally defaecated as dry pellets, through the anus.

Question 3.
Draw a neat labelled diagram of the salivaary apparatus of cock roach. (S)
Answer:

Question 4.
What is haemocoel? Describe it with reference to Periplaneta. (U)
Answer:
The blood filled body cavity of an organism is called Haemocoel.
Haemocoel in Periplaneta :
The haemocoel of cockroach is divided in to three sinuses by two muscular, horizontal membranes, called dorsal diaphragm or ‘pericardial septum’ and ventral diaphragm. Both the diaphragms have pores. There is a series of paired triangular muscles, called alary muscles. Every segment has one pair of these muscles situated on the lateral sides of the body.

These are attached to the pericardial septum by their broad bases and to the terga by their pointed ends or apices. The three sinuses of the haemocoel are known as pericardial haemocoel or the ‘dorsal sinus’, the perivisceral haemocoel or the ‘middle sinus’ and sternal haemocoel or ‘venral sinus’ or ‘perineural sinus’. The middle sinus is very large as it contains most of the viscera. The dorsal and ventral sinuses are small as they have only heart and nerve cord, respectively.

Question 5.
Describe the structure and function of the heart in Periplaneta. (K)
Answer:
Heart :
The heart lies in the pericardial haemocoel or dorsal sinus. It is a long, muscular, contractile tube found along the mid dorsal line, beneath the terga of the thorax and abdomen. It consists of 13 chambers. Every chamber opens into the other present in front of it. Three of the thirteen chambers are situated in the thorax and ten in the abdomen. Its posterior end is closed while the anterior end is continued forward as the anterior aorta. At the posterior side of each chamber, except the last, there is a pair of small apertures called ‘ostia’ one on each side. Ostia have valves which allow the blood to pass only into the heart from the dorsal sinus.

Question 6.
Describe the process of blood circulation in Periplaneta. (K)
Answer:
Circulation of blood :
The blood flows forward in the heart by the contractions of its chambers. At the anterior end of the heart, the blood flows into the aorta and from there it enters the sinus of the head. From the head sinus, the blood flows into the perivisceral and sternal sinuses. On contraction of the alary muscles the pericardial septum is pulled down. This increases the volume of the pericardial sinus.

Hence blood flows from the perivisceral sinus into the pericardial sinus through the appertures of the pericardial septum. On relaxation of the alary muscles, the pericardial septum moves upwards to its original position. This forces the blood, to enter the chambers of the heart through the ostia from the pericardial sinus.

Question 7.
How do contraction and relaxation of alary muscles help in circulation? (A)
Answer:
On contraction of the alary muscles the pericardial septum is pulled down. This increases the volume of the pericardial sinus. Hence blood flows from the perivisceral sinus into the pericardial sinus through the appertures of the pericardial septum. On relaxation of the alary muscles, the pericardial septum moves upwards to its original position. This forces the blood, to enter the chambers of the heart through the ostia from the pericardial sinus.

Question 8.
Describe the structure of trachea of cockroach. (K)
Answer:
Structure of Trachea :
The wall of the tracheae is made of three layers. They are an outer basement membrane, a middle one cell thick epithelium and an inner layer of cuticle called intima. It has protein / chitin layer and epicuticle towards lumen. The intima is produced into spiral thickenings called taenidia. In taenidia, protein / chitin layer is differentiated as exocuticle. The taenidia keep the tracheae always open.

Question 9.
Explain the structure of malpighian tubules. (U)
Answer:
Malpighian tubule :
The malpighian tubules are long, unbranched yellowish tubules, attached at the extreme anterior end of the hindgut, lying freely in the haemolymph, but do not open into it, being blind at the free ends. They are 100 – 150 in number arranged in 6 – 8 bundles, each bundle having 15-25 tubules. Marcello Malpighi, described these tubules and called them vasa varicosa Meckel called them Malpighian tubules. Each tubule is lined by a single layer of glandular epithelium with a brush border on the inner surface. The ‘distal portion’ of the tubule is secretory and the ‘proximal part’ is absorptive in nature.

Question 10.
What are different excretory organs in Periplaneta? Describe the process of excretion in detail. (K)
Answer:
The structures associated with excretory function are
a) Malpighian tubules b) Fat bodies c) Uricose glands d) Cuticle.

Malpighian tubules :
The glandular cells of the malpighian tubules absorb water, salts, CO₂ and nitrogenous wastes from the haemohymph and secrete them into the lumen of the tubules. The cells of the proximal part of the tubules reabsorb water and certain inorganic salts. By the contraction of the tubules urine is pushed into the ileum. More water is reabsorbed from it, when it moves in to the rectum and almost solid uric acid is excreted along with faecal matter.

The removal of nitrogenous waste material through the alimentary canal helps in complete reabsorption of water from the wastes and formation of dry uric acid. It is an adaptation for conservation of water as it is very important in terrestrial organisms.

Fat bodies :
Fat body is a lobed white structure. Urate cells present in these bodies are associated with excretion in a way. These cells absorb and store uric acid throughout the life. This is called storage excretion as they remain stored in the cells of the corpora adiposa.

Uricose glands :
Uric acid is stored in uricose gland or utriculi majores of the mushroom gland in male cockroach. It is discharged during copulation.

Cuticle :
Some nitrogenous waste materials are deposited on the cuticle and eliminated during moulting.

Question 11.
How does Periplaneta conserve water? Explain it with the help of excretion in it. (A)
Answer:
The removal of nitrogenous waste material through the alimentary canal helps in complete reabsorption of water from the wastes and formation of dry uric acid. It is an adaptation for conservation of water as it is very important in terristrial organisms.

Fat bodies :
Fat body is a lobed white structure. Urate cells present in these bodies are associated with excretion in a way. These cells absorb and store uric acid throughout the life. This is called storage excretion as they remain stored in the cells of the corpora adiposa.

Question 12.
Describe the structure of an ommatidium and label its parts. (K)
Answer:
Structure of an Ommatidium :
Each typical ommatidium is an elongated sub unit of the compound eye, consisting of the following parts.

1. Cornea :
It is the outermost part of an ommatidium and corresponds to a ‘hexagonal facet’ of the compound eye. It is a biconvex, transparent part of the cuticle and allows light to pass through it. Cornea is secreted by specialized cells of epidermis. Cornea is the ‘refractive* 1 2 3 region of ommatidium.

2. Corneagen cells or lenticular cells :
These are two transparent specialized epidermal cells that secrete cornea. These cells later form the ‘primary pigment sheath’ or iris pigment sheath.

3. Vitrellae or cone cells (Semper cells) :
These are four transparent more or less conical cells that lie below the corneagen cells. They surround the transparent crystalline cone. Crystalline cone is secreted by the cone cells.

4. Crystalline cone :
It is the transparent conical structure that is secreted by the vitrellae and is surrounded by them. Light absorbing dark primary pigment cells surround the vitrellae. The region containing the cornea and crystalline cone constitute the dioptrical or focussing region of the ommatidium. Crystalline cone focuses the light on to the next part of the ommatidium.

5. Retinulae :
These are the innermost and elongated cell of an ommatidium. They are seven in number. They rest on the basement membrane. Each cell bears microvilli towards the inner surface. Microvilli of each retinular cell collectively form a rhabdomere that contains photoreceptor pigments. These rhabdomeres fuse along the axis of the ommatidium to form the rhabdome in the centre. Retinulae are the nerve cells from which sensory nerve fibres leave as the optic nerve to the protocerebrum. They are the photoreceptor cells of the ommatidium. Rhabdome and retinulae form the retinal or receptor region. Receptor region is surrounded by seven secondary pigment cells, which absorb light and serve to isolate each ommatidium from the rest (retinal pigment sheath).

Question 13.
Draw a neat and labelled diagram of ommatidium. (S)
Answer:

Question 14.
How can you identify the male and female cockroaches? Explain it describing the chief features of the external and internal genetalia. (U)
Answer:
The sexual dimorphism is evident both externally and internally. The female is different from the male in respect of short and broad abdomen, presence of brood pouches and absence of anal styles.

Male :
Internally male reproductive system contains a pair of testes, vas deferens, ductus ejaculatorius, mushroom shaped gland, conglobate gland.

Surrounding the male genital opening there are chitinous and asymmetrical structures called phallic organs or phallomeres which help in copulation. These are the male external genitalia.

Female :
Internally female reproductive system consists of a pair of ovaries, a pair of oviducts, vagina, spermathecae, spermathecal papilla and colleteral glands.

Three pairs of plate like chitinous structures called gonopophyses are present around the female genital aperture. These gonopophyses guide the ova into ootheca as ovipositors. These are the female external genitalia.

Question 15.
Describe the male reproductive system of cockroach. (K)
Answer:
Male Reproductive System :
The male reproductive system .consists of a pair of testes. These are elongated and lobed structures lying one on each lateral side in the fourth to sixth abdominal segments. They are embedded in the fat bodies. From the posterior end of each testis, there starts a thin duct, the vas deferens. The two vasa deferntia run backwards and inwards to open into a wide median duct, the ductus ejaculatorius in the seventh segment.

A characteristic mushroom shaped gland is present in the 6^th and 7^th abdominal segments which functions as an accessory reproductive gland. The gland consists of two types of tubules, i) long slendertubules, the utriculi majores or ‘peripheral tubules’ ii) Short tubules, the utriculi breviores. Secretion of utriculi majores forms the inner layer of the spermatophore while that of utriculi breviores nourishes the sperms. These tubules open into the anterior part of the ejaculatory duct.

The seminal vesicles are present on the ventral surface cf the ejaculatory duct. These sacs store the sperms in the form of bundles called spermatophores. The ejaculatory duct is a muscular tube that extends posteriorly and opens at the gonopore or the ‘male genital pore’. The duct of phallic or conglobate gland also opens near the gonopore. Its function is still not known. Surrounding the male genital opening there are chitinous and asymmetrical structures called phallic organs or gonapophyses or phallomeres which help in copulation. These are the male external genitalia.

Question 16.
Describe the female reproductive system of cockroach. (K)
Answer:
Female Reproductive System :
The female reproductive system of Periplaneta consists of a pair of ovaries, a pair of oviducts, vagina, spermathecae, spermathecal papilla, and colleterial glands.

Ovaries :
A pair of large ovaries lies laterally in 2 to 6 abdominal segments. They are light yellow in colour surrounded by fat bodies. Each ovary consists of eight tubules called ovarian tubules or ovarioles. Each ovariole consists of a tapering anterior filament called germarium and a posterior wider vitellarium. The germarium contains various stages of developing ova, and the vitellarium contains mature ova with yolk. The tapering ends of the ovarioles of each ovary unite to form a single thread which attaches to the dorsal body wall. The ovarioles, at their posterior end unite to form a short wide oviduct.

The oviducts unite to form a very short median vagina. The vertical opening of the vagina is called female genital pore. It opens into a large genital pouch on the eighth sternum. A spermatheca or ‘receptaculium seminis’. consisting of a left-sac like and a right filamentous caecum, is present in the 6th segment which opens by a median aperture on a small spermathecal papilla in the dorsal wall of the genital pouch on the ninth sternum. In a fertile female, the spermatheca contains spermatophores, obtained during copulation.

A pair of branched colleterial glands is present behind the ovaries. These glands open into the genital pouch separately, just above the spermathecal aperture. Secretion of the two collaterial glands forms a hard egg case called ootheca around the eggs.

Genital pouch is formed by 7^th, 8^th, and 9^th abdominal sterna. The sternum of the seventh segment is boat shaped and forms the floor and side walls of the genital pouch. The sterna of the eighth and ninth segments, which are tucked into the seventh segment, constitute the anterior wall and the roof of the genital pouch, respectively. The genital pouch has two chambers the anterior ‘gynatrium’ or genital chamber and posterior ‘vestibulum’ or oothecal chamber.

Three pairs of plate like chitinous structures called gonapophyses are present around the female genital aperture. These gonapophyses guide the ova into ootheca as ovipositors. These are the female external genitalia.

Essay Answer Type Questions

Question 1.
Descirbe the structure of the head of cockroach, with the help of a neat labelled diagram. (K & S)
Answer:
Heat :
The head of cockroach is small and triangular. It is called hypognathous because it lies hanging almost at right angles to the body with the posterior wider part upwards, and the mouthparts directed downwards.

The head of cockroach is formed by the fusion of six embryonic segments. It is movably attached to the thorax by a short neck or cervicum. it is covered by a number of sclerites which fuse to form a capsule. The top of the head between the eyes is called vertex. The vertex has two sclerites called ‘epicranial plates’ connected by an ‘epicranial suture’. Below the vertex, the sclerites covering the’ head in front are a large frons, a narrow rectangular clypeus and a movable labrum. Covering the sides of the head, below the compound eyes are.the ‘cheek sclerities’ or ‘genae. At the back of the head capsule there is a large opening called occipital foramen.

It is bordered by a sclerite called occiput. The occipital foramen forms a passage for the oesophagus, aorta; nerve cord and tracheae. At the base of each antenna, a small whitish speck called fenestra or ‘ocellar spot’ or ‘simple eye’ is present. Appendages are absent in the first and third segments of the head. The second segment bears a pair of long, slenife^ and segmented antennae, one on each side of the head. The antennae are tactile and olfactory in function. The fourth segment bears a pair of mandibles. The fifth segment has a pair of ‘first maxillae’. The sixth segment bears a pair of ‘second maxillae’, which fuse to form the labium (also called ‘lower lip’)

Question 2.
Describe the abdomen of cockroach. (K)
Answer:
Abdomen :
The abdomen consists of ten segments. Each segment is covered by the dorsal tergum, the ventral sternum and the two lateral pleura or pleurites. There are ten terga but only nine sterna as the tenth sternum is absent. The eighth tergum in the male and both eighth and ninth terga in the female are not visible as they are overlapped by the seventh tergum. The tenth tergum extends beyond the posterior end of the body and has a deep notch/groove in the middle of its free end. In the male nine sterna are visible whereas in the female, only seven sterna are visible. The seventh, eighth and ninth sterna together form a brood pouch. The brood pouch has two parts the anterior genital chamber or gynatrium and posterior oothecal chamber.

The posterior end of the abdomen has a pair of anal cerci, a pair of anal styles and gonapophyses in the males. Anal cerci are jointed and arise from the lateral sides of the tenth tergum and are found in both the sexes. The anal styles are without joints and arise from the ninth sternum (seen only in the males). The gonapophyses are small chitinous processes arising from the ninth sternum in the males and eighth and ninth sterna in the females. They are the external genital organs. The anus is at the posterior end of the abdomen. The genital aperture in male is present just below the anus on one of the gonapophyses and in female it is located on the eighth sternum.

Question 3.
Describe the digestive system of cockroach with the help of a neat labelled diagram. (K & S)
Answer:
The digestive system of cockroach consists of an alimentary canal and the associated glands. The preoral cavity, surrounded by the mouth parts, is present in front of the mouth. The hypopharynx divides it into two chambers called cibarium (anterior) and salivarium (posterior)

Alimentary canal :
The alimentary canal of cockroach is a long tube and is coiled at some places. It extends between the mouth and the anus. It is divided into three regions, namely, foregut or stomodaeum, midgut or mesenteron and hindgut or proctodaeum. The foregut and hindgut are internally lined by ectoderm. The mesenteron is lined by the endodermal cells.

Foregut of stomodaeum :
The foregut includes pharynx, oesophagus, crop, and gizzard. It is internally lined by a chitinous cuticle. Mouth opens into the pharynx, which in turn leads into a narrow tubular oesophagus. The oesophagus opens behind into a thin walled distensible sac called crop. The crop serves as a reservoir for storing food. Its outer surface is covered by a network of tracheae.

Behind the crop there is a thick walled muscular proventriculus, or gizzard. The chitinous inner lining of the gizzard has six powerful teeth, which form an efficient grinding apparatus. Behind each tooth is a hairy pad, which bears backwardly directed bristles. Among these plates, food is thoroughly ground into fine particles. These food particles are filtered by the bristles. The gizzard thus acts both as a grinding mill and also as a sieve. There is a membranous projection of the gizzard into the mesenteron in the form of a funnel called stomodeal valve. This valve prevents the entry (regurgitation) of food from the mesenteron back into the gizzard.

Midgut (mesenteron or ventriculus) :
The midgut is a short and narrow tube behind the gizzard. It is also called mesenteron or ventriculus. Between the ventriculus and the gizzard, arising from ventriculus, there are six to eight finger like diverticula called hepatic caecae. They are helpful in digestion and absorption of the digested t food materials. Ventriculus is functionally divided into an anterior secretory part and a posterior absorptive part.

The secretory part of the ventriculus has many gland cells and it secretes several enzymes. The ‘bolus’ of food in the mesenteron is enveloped by a chitinous and porous membrane called peritrophic membrane, which is secreted by the funnel like stomodeal valve of the gizzard.

Digested food is absorbed into the blood through the peritrophic membrane in the posterior absorptive region of the ventriculus. The peritrophic membrane protects the wall of the ventriculus from hard food particles in the food. The opening of the ventriculus into the hindgut is controlled by a sphincter muscle. It prevents entry of undigested food and uric acid from the hindgut into the midgut.

Hindgut or proctodaeum :
The hindgut is a long coiled tube, consisting of three regions namely ileum, colon and rectum, it is internally lined by chitinous cuticle. The ileum that lies behind the mesenteron is a short tube. Six bundles of fine yellow, blind tubules called malpighiari tubules open into the ileum near the junction of mesenteron and ileum. Malpighian tubules are excretory in function.

Ileum collects uric acid from the malpighian tubules and undigested food from the mesenteron. Ileum opens behind into a long coiled tube called colon. Colon leads into a short and wide rectum, which opens out through the anus. Rectum bears on its inner side six longitudinal chitinous folds called rectal papillae. They are concerned with the reabsorption of water from the undigested food.

Digestive glands :
The digestive glands associated with the alimentary canal of cockroach are salivary glands, hepatic caecae and glandular cells of the mesenteron. Salivary glands : There is a pair of salivary glands attached to the ventrolateral sides of the crop, one on each side. Each salivary gland has two lobes. Each lobe of salivary gland has many lobules called acini. Each acinus is a group of secretory cells called zymogen cells with a small ductule. The ductules of both the lobes of a salivary gland unite to form a common salivary duct on each side.

The two common salivary ducts are joined to form the median salivary duct. Between the two lobes of a salivary gland of each side is a sac called salivary receptacle that stores saliva. It leads into a receptacular duct, or ‘reservoir duct’. The receptacular ducts of both the sides are united to form a common receptacular duct, or ‘common reservoir duct’. The median salivary duct opens into the common receptacular duct. Later these two form an efferent salivary duct. The efferent salivary duct opens at the base of the hypopharynx. Acinar cells secrete saliva, which contains starch digesting enzymes such as amylase.

Question 4.
Describe the blood circulatory system of Periplaneta in detail and draw a neat labelled diagram of it. (K & S)
Answer:
Circulatory system of Periplaneta :
The circulatory system helps in the transportation of digested food, hormones etc., from one part to another in the body. Periplaneta has an open type of circulatory system as the blood, or haemohymph, flows freely within the body cavity or haemocoel. Blood vessels are poorly developed and open into spaces. Visceral organs located in the haemocoel are bathed in the blood. The three main parts associated with the blood circulatory system of Periplaneta are the haemocoel, heart, and blood.

Haemocoel :
The haemocoel of cockroach is divided into three sinuses by two muscular, horizontal membranes, called dorsal diaphragm or ‘pericardial septum1 and ventral diaphragm. Both the diaphragms have pores. There is a series of paired triangular muscles, called alary muscles. Every segment has one pair of these muscles situated on the lateral sides of the body. These are attached to the pericardial septum by their broad bases and to the terga by their pointed ends or apices.

The three sinuses of the haemocoel are known as pericardial haemocoel or the ‘dorsal sinus’, the perivisceral haemocoel or the ‘middle sinus’ and sternal haemocoel or ‘vental sinus’ or ‘perineural sinus’. The middle sinus is very large as it contains most of the viscera. The dorsal and ventral sinuses are small as they have only heart and nerve cord, respectively.

Heart :
The heart lies in the pericardial haemocoel or dorsal sinus. It is along, muscular, contractile tube found along the mid dorsal line, beneath the terga of the thorax and abdomen. It consists of 13 chambers. Every chamber opens into the other present in front of it. Three of the thirteen chambers are situated in the thorax and ten in the abdomen. Its posterior end is closed while the anterior end is continued forward as the anterior aorta. At the posterior side of each chamber, except the labt, there a pair of small apertures called ostia’ one on each side. Ostia have valves which allow the blood to pass only into the heart from the dorsal sinus.

Blood :
The blood of Periplaneta is colourless and is called haemolymph. it consists of a fluid called plasma, and free blood corpuscles or haemocytes, which are ‘phagocytic1. The phagocytes are large in size and can’ingest1 foreign particles such as bacteria. There is no respiratory pigment in the blood and so it plays no major role in respiration. The important functions of the blood are :

1. It absorbs digested food from the alimentary canal and distributes it to the rest of the body.
2. It brings nitrogenous wastes from all parts of the body to the excretory organs for their elimination.
3. It carries defensive phagocytes to the places of infection where they engulf the germs and disintegrating tissue parts.
4. It transports secretions of the ductless glands to the target organs.

Circulation of blood :
The blood flows forward in the heart by the contractions of its chambers. At the anterior end of the heart, the blood flows into the aorta and from there it enters the sinus of the head. From the head sinus, the blood flows into the perivisceral and sternal sinuses. On contraction of the alary muscles, the pericardial septum is pulled down. This increases the volume of the pericardial sinus. Hence blood flows from the perivisceral sinus into the pericardial sinus through the appertures of the pericardial septum. On relaxation of the alary muscles, the pericardial septum moves upwards to its original position. This forces the blood, to enter the chambers of the heart through the ostia from the pericardial sinus.

Question 5.
The blood circulatory system of Periplaneta is of open type. Illustrate the statement describing the course of circulation in it. (U)
Answer:
The circulatory system helps in the transportation of digested food, hormones etc. from one part to another in the body. Periplaneta has an open type of circulatory system as blood or haemolymph flows freely with in the body cavity or haemocoel.

Circulation of blood :
The blood flows forward in the heart by the contraction of its chambers. At the anterior end of the heart, the blood flows into the aorta and from there it enters the sinus of the head. From the head sinus, the blood flows into the perivisceral and sternal sinuses. On contraction of the alary muscles the pericardial septum is pulled down. This increases the volume of the pericardial sinus. Hence blood flows from the perivisceral sinus into the pericardial sinus through the appertures of the pericardial septum. On relaxation of the alary muscles, the pericardial septum moves upwards to its original position. This forces the blood, to enter the chambers of the heart through the ostia from the pericardial sinus.

Question 6.
Describe the respiratory system of cockroach with the help of neat and labelled diagrams. (K & S)
Answer:
Respiratory System of Periplaneta :
Due to the absence of respiratory pigment, the blood of cockroach is colourless and it cannot carry oxygen to different tissues. Therefore a tracheal system is developed to carry the air directly to the tissues. The respiratory system of cockroach consists of stigmata, tracheae and tracheoles.

Stigmata or spiracles :
The tracheal system communicates with the exterior by ten pairs of openings called stigmata or spiracles. The first two pairs of spiracles are present in the thoracic segments, one pair in mesothorax and one pair in the metathorax. The remaining eight pairs are present in the first eight abdominal segments. Spiracles are located in the pleura of their respective segments. The respiratory system in insects is classified on the basis of number and nature of spiracles.

The spiracles of cockroach are polypneustic (as they are more than 3 pairs) and holopneustic (as all of them are functional). All spiracles are valvular and each of them is surrounded by a chitinous ring called peritreme. All spiracles bear small hair like structures called trichomes to filter the dust particles. Each spiracle opens into a small chamber called atrium.

Tracheae :
From the atrium of each thoracic spiracle several horizontal tracheae run inside. They join with each other in the thorax to form many tracheal trunks like dorsal cephalic, ventral cephalic trunks and their branches. These branches enter all organs of the head. The thoracic region also contains lateral longitudinal trunks. The abdominal spiracles lead into atria. From the atrium of each abdominal spiracle three tracheal tubes arise. All these tracheal tubes of one side open into three separate longitudinal tracheal trunks.

They are lateral, dorsal and ventral longitudinal trunks. Lateral longitudinal trunks are the longest tracheal trunks. The three pairs of longitudinal tracheal trunks of both the sides are interconnected by many commissural tracheae. From all the tracheal trunks several branches are given out, which enter different organs. All tracheal branches entering into an organ end in a special cell called tracheole cell.

The wall of the tracheae is made of three layers. They are an outer basement membrane, a middle one cell thick epithelium and an inner layer of cuticle called intima. The intima is produced into spiral thickenings called taenidia. The taenidia keep the tracheae always open and prevent it from collapsing.

Tracheoles :
The terminal cell of trachea is called tracheoblast or tracheole cell. It has several intracellular tubular extensions called tracheoles. Tracheoles are devoid of intima and taenidia. They are formed of a protein called trachein. Tracheolar fluid is present inside the tracheoles. The level of the tracheolar fluid varies with the metabolic activity of the insect. It is more when the insect is inactive and completely reabsorbed into the tissues, when the insect is more active. Tracheoles penetrate the cell and are intimately associated with mitochondria (to supply oxygen to them).

Mechanism of respriation :
Respiration includes two events, viz., inspiration and expiration. The muscles helpful are dorsoventral muscles and ventral longitudinal musdes. Dorsoventral muscles are the principal muscles of respriation.

Inspiration :
Taking in of air is inspiration. lifts effected by the relaxation of the dorsoventral muscles and ventral longitudinal muscles. Due to the relaxation of the dorsoventral muscles, tergal plates are elevated and the volume of the body cavity increases. Due to the relaxation of the ventral longitudinal muscles, the telescoped segments come to the normal position. So the volume of the body cavity increases in the longitudinal axis. As air is drawn in due to the relaxation of the muscles, the process is a ‘passive’ process. During inspiration the thoracic spiracles are kept open and the abdominal spiracles are kept closed.

Expiration :
Sending out air from the body is called expiration. On contraction the dorsoventral muscles depress the tergal plates. Body cavity decreases in size and pressure increases. Due to the contraction of the ventral longitudinal muscles, the segments are telescoped and the volume of the body cavity decreases in the longitudinal axis increasing the pressure further. As this process involves the contraction of muscles, expiration is described as active process. During expiration thoracic spiracles are closed and abdominal spiracles are kept open.

Exchange of gases :
As air enters the tracheoles, oxygen from the air is taken into the cells and CO₂ is released into haemolymph. The CO₂ from the haemolymph mostly goes out through the inter-segmental membranes of the body wall. Cockroach and some other insects such as grasshoppers and beetles exhibit the phenomenon of discontinuous ventilation. In this mode of respiration continuous exchange of gases is interrupted by extended periods during which spiracles remain closed. The expulsion of CO₂ from the body occurs in bursts, when the spiracles are open.

The exchange of gases depends on the metabolic rate and temperature. When air enters the tracheoles, oxygen diffuses faster into the tissues due to its high partial pressure. At the same time the carbon dioxide of tissues, instead of passing into the tracheal system, goes into the haemolymph. Carbon dioxide is carried more quickly into the haemolymph due to its greater solubility in it. This CO₂ accumulates near the spiracles and diffuses into the artial chambers near the spiracles and goes o.ut in bursts through the abdominal spiracles. Opening and closing of spiracles is influenced by CO₂ tension in haemolymph and oxygen tension in the trachea.

Question 7.
Describe the nervous system of Periplaneta and draw a labelled diagram of it. (K & S)
Answer:
The nervous sytem of cockroach consists of central nervous system, peripheral nervous system and autonomous nervous system.

Central Nervous System :
It consists of a nerve ring, and a ganglionated double ventral nerve cord.

Nerve ring :
The nerve ring, which is present around the oesophagus, is formed by the following.

Brain :
Brain lies above the oesophagus. The brain is mainly a sensory and an endocrine centre. Three lobes of the brain are protocerebrum,deutocerebrum and tritocerebrum. the protocerebrum receives sensory impulses from the compound eyes through optic nerves; deutocerebrum receives sensory impulses from antennae through antennal nerves; and tritocerebrum receives sensory impulses from the labrum. Hence brain is principally ‘sensory’ in nature.

Sub-oesophageal ganglion :
It lies below the oesophagus. It is the motor center that controls the movements of mouthparts, legs and wings, it is formed by the fusion of paired ganglia of mandibular, maxillary and labial segments of the head. Circum-oesophageal connectives : A pair of circum-oesophageal connectives is present around the oesophagus, connecting the tritocerebrum with the sub – oesophageal ganglion/ sub oesophageal ganglia.

Ventral nerve cord :
The two ventral nerve cords are solid and ganglionated. They arise from the sub-oesophageal ganglion and extend upto the 7^th abdominal segment. The two nerve cords remain separate except at the ganglia. Three thoracic ganglia are present, one in each thoracic segment. In addition, there are six abdominal ganglia. The first to the fourth abdominal segments have one abdominal ganglion each. The 5^th abdominal segment has no ganglion . The serially 5^th abdominal ganglion is present in the 6^th segment. The serially 6^th abdominal ganglion is present in the 7^th segment. The last or the 6^th abdominal ganglion is the largest of all the abdominal ganglia. It is formed by the fusion of the ganglia of the 7^th, 8^th, 9^th, and 10^th abdominal segments.

Peripheral Nervous System :
It consists of nerves arising from the central nervous system. It receives a pair of optic nerves, from the compound eyes, a pair of antennal nerves, from the antennae and a pair of labral nerves from the labrum. Motor neurons of the frontal nerve to the frontal ganglion join the sensory neurons of the labral nerve to form the larbro frontal nerve arising from the tritocerebrum. Sub – oesophageal ganglion gives off motor nerves to the mandibles, maxillae, labium, wings and legs. It is the principal ‘motor centre’ in the body. Thoracic ganglia supply nerves to the parts of their respective segments. Metathoracic ganglia send nerves to the first abdominal segment also.

Nerves from the first four abdominal ganglia supply to the organs of the segments 2 – 6 serially (the 1^st to the 4^th ganglia innervate segments 2^nd to 5^th respectively). The 5^th ganglion present in the 6^th segment innervates the organs of the 6th segment. All organs present in 7^th to 10^th segments receive nerves from the last abdominal ganglion (present in the 7^th segment.) The organs include the reproductive organs, copulatory appendages besides anal cerci.

Autonomous Nervous System :
This system is also called stomatogastric nervous system or ‘visceral nervous system’. It controls the visceral organs, particularly the muscles of the alimentary canal, and the heart. Autonomous nervous system includes four ganglia, a frontal ganglion on the dorsal wall of the pharynx, in front of the brain, hypocerebral ganglion or occipital ganglion above the oesophagus, behind the brain, a visceral ganglion or ingluvial ganglion on the wall of the crop and a proventricular ganglion on the gizzard.

These ganglia contain the ‘somata’ of the post ganglionic motor neurons. Pregaglionic motor neurons of tritocerebrum go to the frontal ganglion as labrofrontal and frontal nerve. Frontal ganglion is connected to the hypocerebral ganglion by a ‘recurrent nerve’. Hypocerebral ganglion is connected to the visceral ganglion and in turn the visceral ganglion is connected to proventricular ganglion.

Question 8.
Describe the reproductive system of Periplaneta and draw neat and labelled diagrams of it. (K & S)
Answer:
Reproductive System of Periplaneta :
Periplaneta is dioecious, or unisexual, and both the sexes have well developed reproductive organs. The sexual dimorphism is evident both externally and internally. The female is different from the male in respect of short and broad abdomen, presence of brood pouches and absence of anal styles.

Male Reproductive System :
The male reproductive system consists of a pair of testes. These are elongated and lobed structures lying one on each lateral side in the fourth to sixth abdominal segments. They are embedded in the fat bodies. From the posterior end of each testis, there starts a thin duct, the vas deferens. The two vasa deferentia run backwards and inwards to open into a wide median duct, the ductus ejaculatorius ip the seventh segment. A characteristic mushroom shaped gland is present in the 6th and 7^th abdominal segments which functions as an accessory reproductive gland. The gland consists of two types of tubules, i) long slender tubules. The utriculi majores or ‘peripheral tubules’ ii) Short tubules, the utriculi breviores. Secretion of utriculi majores forms the inner layer of the spermatophore while that of utriculi breviores nourishes the sperms. These tubules open into the anterior part of the ejaculatory duct.

The seminal vesicles are present on the ventral surface of the ejaculatory duct. These sacs store the sperms in the form of bundles called spermatophores. The ejaculatory duct is a muscular tube that extends posteriorly and opens at the gonopore or the ‘male genital ‘pore’. The duct of phallic or conglobate gland also opens near the gonopore. Its function is still not known. Surrounding the male genital opening there are chitinous and asymmetrical structures called phallic organs or gonapophyses or phallomeres which help in copulation. These are the male external genitalia.

Female Reproductive System :
The female reproductive system of Periplaneta consists of a pair of ovaries, a pair of oviducts, vagina, spermathecae, spermathecal papilla, and colleterial glands.

Ovaries :
A pair of large ovaries lies laterally in 2 to 6 abdominal segments. They are light yellow in colour surrounded by fat bodies. Each ovary consists of eight tubules called ovarian tubules or ovarioles. Each ovariole consists of a tapering anterior filament called germarium, and a posterior wider vitellarium. The germarium contains various stages of developing ova, and the vitellarium contains mature ova with yolk. The tapering ends of the ovarioles of each ovary unite to form a single thread which attaches to the dorsal body wall. The ovarioles, at their posterior end unite to form a short wide oviduct. The oviducts unite to form a very short median vagina.

The vertical opening of the vagina is called female genital pore. It opens into a large genital pouch on the eighth sternum. A spermatheca or receptaculum seminis, consisting of a left-sac like and a right filamentous caecum, is present in the 6th segment which opens by a median aperture on a small spermathecal papilla in the dorsal wall of the genital pouch on the ninth sternum. In a fertile female, the spermatheca contains spermatophores, obtained during copulation.

A pair of branched colleterial glands is present behind the ovaries. These glands open into the genital pouch separately, just above the spermathecal aperture. Secretion of the two collaterial glands forms a hard egg case called ootheca around the eggs.

Genital pouch is formed by 7^th, 8^th, and 9^th abdominal sterna. The sternum of the seventh segment is boat shaped and forms the floor and side walls of the genital pouch. The sterna of the eighth and ninth segments, which are tucked into the seventh segment, constitute the anterior wall and the roof of the genital pouch, respectively. The genital pouch has two chambers the anterior ‘gynatrium’ or genital chamber and posterior ‘vestibuium’ or oothecal chamber.

Three pairs of plate like chitinous structures called gonapophyses are present around the female genital aperture. These gonapophyses guide the ova into ootheca as ovipositors. These are the female external genitalia.

Telangana TSBIE TS Inter 1st Year Zoology Study Material 6th Lesson Biology in Human Welfare Textbook Questions and Answers.

TS Inter 1st Year Zoology Study Material 6th Lesson Biology in Human Welfare

Very Short Answer Type Questions

Question 1.
Define parasitism and justify this term.
Answer:
An intimate association between two organisms of different species in which, one is benefited and the other one is often adversely affected is called parasitism. The organism that obtains nourishment is called parasite and the organism from which the nourishment is obtained is called host.

Question 2.
Distinguish between facultative parasite and obligatory parasite.
Answer:
a) Facultative Parasite :
They lead parasitic life on host if available or may lead free living life in its absence.
Example : (Mycobacterium tuberculosus), Ascaris lumbricoides is facultative anaerobe.

b) Obligatory parasite :
They lead total parasitic life on host and in its absence, they die.
Example : (Blood fluke) Taenia solium is an obligatory anaerobe.

Question 3.
Distinguish between definitive host and intermediate host.
Answer:
Definitive host :
It is the host that harbours the adult stage or sexually mature stage of a parasite or the host in which the parasite undergoes sexual reproduction.

Intermediate host :
It is the host that harbours the developing larval or immature or asexual stages of a parasite or the host in which the parasite undergoes asexual reproduction.

Question 4.
Distinguish between vector and a reservoir host.
Answer:
a) Reservoir host :
It is the host that lodges the infective stages of a parasite in its body when the main host is not available. In the reservoir host, the parasite neither undergoes development nor causes any disease.

b) Vector :
It is an organism which transfers the infective stages of a parasite from one main host to another.

Question 5.
Distinguish between mechanical vector and biological vector.
Answer:
a) Mechanical vector :
It is the vector, which merely transfers the infective stages of a parasite but no part of the parasitic development takes place in it.

b) Biological vector :
It is the vector in which the parasite undergoes a part of the development before it gets transferred to another host.

Question 6.
What is a hyper-parasite? Mention the name of one hyper-parasite.
Answer:
Hyperparasite :
It is a parasite which lives in /on the body of another parasite.
eg : Nosema notabilis (cnidosporan parasite) lives in Sphaerospora polymorpha (also a cnidosporan parasite) which lives in the urinary bladder of toad fish.

Question 7.
What do you mean by parasitic castration? Give one example. [March 2020, 17]
Answer:
Parasitic castration :
Some parasites cause the degeneration of gonads of the host, making it sterile. This effect is called parasitic castration, eg : Sacculina (a crustacean) causes degeneration of ovaries in the crab carcinus.

Question 8.
What are the parasitic adaptations observed in Ascaris lumbricoides?
Answer:

1. Developed protective cuticle to withstand the action of digestive enzymes of the host.
2. Reproductive potential is high due to risky lifecycle. Ascaris female lays 2 lakhs of eggs per day.
3. It is a facultative anaerobe.

Question 9.
What are the endo-parasitic adaptations observed in Fasciola hepatica?
Answer:
Life cycle of Fasciola hepatica is very complex involving many developmental stages and two intermediate hosts to increase the chances of reaching a new definitive host.

Question 10.
Define neoplasia. Give one example.
Answer:
Neoplasia :
Some cause an abnormal growth of the host cells in a tissue to form . new structures. This effect is called Neoplasia which leads to cancers, eg : Some viruses.

Question 11.
Define the most accurate definition of the term ‘health’ and write any two factors that affect the health.
Answer:
Health is a state of complete physical, mental and social well-being and not merely ‘absence of any disease’ or ‘absence of physical fitness’. Two factors that affect the health are 1) contaminated water 2) pollution of air.

Question 12.
Distinguish between infectious and non-infectious diseases. Give two examples each.
Answer:
a) Infectious diseases :
The diseases which are easily transmitted from one person to another are called infectious diseases. Eg. Amoebic dysentery, Malaria,

b) Non – infectious diseases :
The diseases which are not transmitted from one person to another and are not caused by pathogens are called non-infectious diseases.
eg : Kidney problems, genetic disorders, heart problems.

Question 13.
When can you diagnose a healthy person as unhealthy?
Answer:
When the functioning of one or more organs or systems of the body is adversely affected characterized by various signs and symptoms, we say that we are not healthy or we are unhealthy.

Question 14.
Write any two diagnostic features of trophozoite of Entamoeba histolytica.
Answer:
a) Cartwheel shaped nucleus.
b) Single blunt finger like pseudopodium called lobopodium.
c) Presence of RBC in food vacuole.

Question 15.
‘Entamoeba histolytica is an obligatory anaerobe.’ Justify.
Answer:
The absence of mitochondria indicates the obligate anaerobic nature of Entamoeba histolytica.

Question 16.
Distinguish between precystic stage and cystic stage of E. histolytica.
Answer:
Precystic stage :
It is the non-feeding and non-pathogenic stage of Entamoeba histolytica. It is a small, spherical or oval, non-motile form.

Cystic stage :
It is round in shape and is surrounded by a thin, delicate, and highly resistant cyst wall. This is infective stage.

Question 17.
What is the reserve food in the precystic and early cyst stages of Entamoeba histolytica?
Answer:
The reserve food in the precystic and early cyst stages of Entamoeba histolytica are glycogen granules and chromatoid bars (made up of ribonucleo protein).

Question 18.
What is a metacystic form with reference to Entamoeba histolytica?
Answer:
When the tetranucleate cysts of entamoeba histolytica enter a new human host, they pass into small intestine where the cyst wall gets ruptured by the action of the enzyme trypsin, releasing the tetranucleate amoebae. Such tetranucleate excystic amoebae are called metacysts.

Question 19.
A person is suffering from bowel irregularity, abdominal pain, blood and mucus in stool /etc. Based on these symptoms, name the disease and its causative organism.
Answer:
The disease is Amoebic dysentery or Amoebiasis. The causative organism is Entamoeba histolytica.

Question 20.
On the advice of a doctor, a patient has gone to a clinical laboratory for the examination of a sample of faeces. The lab technician, on observing the stool of the patient diagnosed that the patient was suffering from amoebiasis. Write any two characteristic features based on which the technician came to that conclusion.
Answer:

1. Stools with blood and mucous.
2. Stools containing the tetranucleate cysts.

Question 21.
Define ‘asymptomatic cyst passers’ with reference to Entamoeba histolytica.
Answer:
Some people do not exhibit any symptoms of amoebic dysentery or intestinal amoebiasis or tropical amoebiasis. Such people are called carriers or ‘asymptomatic cyst passers’ as their stool contains the tetranucleate cysts.

Question 22.
Distinguish between primary amoebiasis and secondary amoebiasis.
Answer:

1. Stools with blood and mucous with acute abdominal pair is generally referred to as primary amoebiasis.
2. When trophozoites rupture the wall of capillaries, enter the blood stream, and primarily reach the liver where they may cause abscesses – some call it secondary amoebiasis.

Question 23.
What are the stages of Plasmodium vivax that infect the hepatocytes of man?
Answer:
The stages of plasmodium vivax that infect the hepatocytes of man are

1. Sporozoites primarily
2. Cryptozoites Secondarily (They are also referred to as I generation merozoites)

Question 24.
What are the stages of Plasmodium vivax that infect the RBC of the intermediate host?
Answer:
The stages of Plasmodium vivax that infect the RBc of the intermediate host are a) Cryptozoites b) Micro-metacryptozoites.

Question 25.
Define prepatent period. What is its duration in the life cycle of Plasmodium vivax?
Answer:
The interval between the first entry of plasmodium into the blood in the form of sporozoites and the second entry of plasmodium into the blood in the form of cryptozoites is called “Prepatent period”. In Plasmodium vivax it is 8 days.

Question 26.
Define incubation period. What is its duration in the life cycle of Plasmodium vivax? [March 2018 – A.P.]
Answer:
The period between the entry of plasmodium into the blood in the form of sporozoites and the first appearance of symptoms of malaria in man is called incubation period. It is approximately 10 to 14 days in Plasmodium vivax.

Question 27.
What are Schuffner’s dots? What is their significance?
Answer:
In the signet ring stage’of malarial parasite small red coloured dots appear in the cytoplasm of the RBC known as Schuffner’s dots. These are believed to be the antigens released by the parasite.

Question 28.
What are haemozoin granules ? What is their significance?
Answer:
The malaria parasite digests the globin part of the ingested haemoglobin and converts the soluble haem into an insoluble crystalline haemozoin granules. It is called the malaria pigment which is a disposable product.

Question 29.
Distinguish between schizogony and sporogony.
Answer:

1. In man the plasmodium reproduces by asexual reproduction called Schizogony. It occurs in liver cells as well as in RBC.
2. The formation of sporozoites in the oocysts seen in the stomach wall of female Anopheles mosquito is called SPOROGONY.

Question 30.
What is exflagellation and what are the resultant products called?
Answer:
The formation of male gametes or microgametes by lashing movements like flagella from micro gametocyte is called exflagellation.

Question 31.
Why is the syngamy found in Plasmodium called anisogamy?
Answer:
In plasmodium the male and female gametes are dissimilar in size, the process of union or syngamy is called Anisogamy.

Question 32.
What is ookinete? Based on the ‘sets of chromosomes’ how do you describe it?
Answer:
The zygote remains inactive for some time and then transforms into a long, slender, motile, vermiform ookinete or vermicule within 18 – 24 hours. The ookinete is diploid.

Question 33.
What is tertian fever, with reference to the types of malaria you have learnt about? Give the name of the causative species of the pathogen concerned.
Answer:
Four species of Plasmodium cause four types of malaria in man. They are
a) Plasmodium vivax – benign tertian malaria.
b) Plasmodium falciparum – malignant tertian malaria or cerebral malaria.
c) Plasmodium ovale – mild tertian malaria.
d) Plasmodium malariae-quartan malaria.
Recurrent fever of Malaria is called tertian fever.

Question 34.
What is the significance of hypnozoites, with reference to malaria fever?
Answer:
Some of the stages of macro-metacryptozoites may survive for a long period in liver as dormant stages called HYPNOZOITES. Reactivation of these hypnozoites leads to the initiation of fresh erythrocytic cycles resulting in the new attacks of malaria. This is referred to as relapse of malaria.

Question 35.
A person is suffering from chills and shivering and high temperature. These symptoms arp cyclically followed by profuse sweating and return to normal body temperature. Based on these symptoms, name the disease and its causative organism.
Answer:
a) Malaria is the disease; b) Causative organism Plasmodium.

Question 36.
Describe the methods of biological control of mosquitoes.
Answer:
Biological control of mosquitoes :
Introduction of larvivorous fishes like Gambusia, insectivorous plants like utricularia into the places where mosquitoes breed.

Question 37.
The eggs of Ascaris are called ‘mammillated eggs’. Justify.
Answer:
In Ascaris each egg is surrounded by a protein coat with rippled surface. Hence the eggs of Ascaris are described as “mammillated eggs”.

Question 38.
Write the route of extra intestinal migration followed by the juveniles of Ascaris lumbricoides.
Answer:
Extra intestinal migration exhibited by 2nd stage larva of Ascaris.

Question 39.
Write any two differences between male and female worms of Wuchereria bancrofti.
Answer:
Wuchereria bancrofti male and female differences.
a) Male worm :
Its posterior end is curved with a cloacal aperture. A pair of unequal, chitinous pineal spicules or copulatory spicules is present in the cloacal region.

b) Female worm :
Its posterior end is straight. Anus is present near the posterior end. The female genital pore or vulva is present mid ventrally at about one third the length from the mouth. It is ovi viviparous.

Question 40.
What is meant by nocturnal periodicity with reference to the life history of a nematode parasite you have studied?
Answer:
The microfilaria larvae of Wuchereria bancrofti in man move in the peripheral blood circulation during the night time between 10 pm and 4 am. This tendency is referred to as NOCTURNAL PERIODICITY.

Question 41.
Distinguish between lymphadenitis and lymphangitis.
Answer:

1. Inflammation in the lymph vessels is called lymphangitis.
2. Inflammation in the lymph glands is called lymphadenitis. Both are caused by filarial worm injection.

Question 42.
‘Elephantiasis is the terminal condition of filariasis.’ Justify.
Answer:
Fibroblasts accumulate in these tissues and form the fibrous tissue. In severe cases, the sweat glands of the skin in the affected regions disintegrate and the skin becomes rough. This terminal condition is referred to as Elephantiasis.

Question 43.
Mention the pathogens that cause ringworm.
Answer:
Ringworm is one of the most common infectious diseases in man. It is caused by many fungi belonging to the genera Microsporum, Trichophyton and Epidermophyton.

Question 44.
Explain any three preventive measures to control microbial infections.
Answer:

1. The immunization programmes by the use of vaccines have enabled us to completely eradicate a deadly disease like smallpox.
2. Biotechnology is at the verge of making available newer and safer vaccines.
3. Discovery of antibiotics and various other drugs has also enabled us to treat infectious diseases effectively.

Question 45.
“Maintenance of personal and public hygiene is necessary for prevention and control of many infectious diseases.” Justify the statement giving suitable examples.
Answer:
The following hygienic habits help prevent spread of this disease.
a) Using boiled and filtered water
b) Washing hands, fruits and vegetables properly
c) Using septic tank toilets
These habits prevent diseases like Amoebiasis and Ascariasis.

Question 46.
Diseases like amoebic dysentery, ascariasis, typhoid etc., are more common in overcrowded human settlements. Why?
Answer:
In overcrowded human settlements, poor sanitation facilities are seen. No septic toilets for defecation. Drinking water is only from available water sources like tanks, lakes and ponds where cleaning of cattle, washing of clothes is also done. Due to these conditions the contaminated water, food and air spread the diseases like typhoid, amoebic dysentery and ascariasis.

Question 47.
In which way does tobacco affect the respiration? Name the alkaloid found in tobacco : [May 2017 – A.P.]
Answer:
Tobacco is smoked or chewed as gutkha or used in the form of snuff. Smoking increases the carbon monoxide level and reduces the oxygen level in the blood. Alkaloid found in tobacco is NICOTINE.

Question 48.
Define drug abuse.
Answer:
When drugs are taken for a purpose other than the medicinal use or in excess amounts that impair one’s physical or psychological functions, it constitutes “drug abuse”.

Question 49.
From which substances ‘Smack’ and ‘Coke’ are obtained?
Answer:
Smack and coke are obtained from :
Smack is chemically diacetylmorphine obtained by the acetylation of morphine extracted from dried latex of unripe seed capsule of poppy plant. Coke or crack is obtained from coca plant Erythroxylum coca, commonly called cocaine.

Question 50.
‘Many secondary metabolites of plants have medicinal properties. It is their misuse that creates problems.’ Justify the statement with an example.
Answer:
Benzodiazepines (tranquilizers), Lysergic acid diethyl amides (LSD) and other similar drugs, normally used as medicines to treat patients with mental illnesses like depression are often abused.

Question 51.
Write the scientific names of any two plants with hallucinogenic properties.
Answer:

Question 52.
Why are cannabinoids and anabolic steroids banned in sports and games?
Answer:
Cannabinoids and anabolic steroids (AAS) increase protein synthesis within cells which result in the build up of cellular tissues, especially in muscles. Cannabinoids show their effects on cardio-vascular system of the body. Hence they are banned in sports and games (DOPING TEST). They give tremendous energy temporarily.

Question 53.
Mention the names of any four drugs which are used as medicines to treat patients with mental illness like depression, insomnia, etc.’ that are often abused.
Answer:

1. Lysergic acid diethyl amides (LSD)
2. Barbiturates (sleeping pills)
3. Amphetamines
4. Benzodiazepines (tranquilizers)

Short Answer Type Questions

Question 1.
What is the need for parasites to develop special adaptations? Mention some special adaptations developed by the parasites. [May 2017 – A.P.]
Answer:
Parasites have evolved special adaptations to meet the requirements and lead successful life in the hosts.

1. In order to live in the host, some parasites have developed structures like hooks, suckers, rostellum, etc., for anchoring, e.g. Taenia solium.
2. Some intestinal parasites have developed protective cuticle to withstand the action of the digestive enzymes of the host. e.g. Ascaris lumbricoides.
3. Some intestinal parasites produce anti enzymes to neutralize the effect of host’s digestive enzymes, e.g. Taenia solium.
4. Some parasites live as obligatory anaerobes as the availability of oxygen is very rare for them. e.g. Entamoeba histolytica, Taenia solium, etc.
5. Some intestinal parasites live as facultative anaerobes i.e., if oxygen is not available, they live anaerobically and if oxygen is available, they respire aerobically, e.g. Ascaris lumbricoides.
6. The morphological and anatomical features are greatly simplified while emphasizing their reproductive potential. For example, an Ascaris lays nearly two lakh eggs per day. In Taenia solium the body is divided into 700 to 900 proglottids of which each proglottid acts as a unit of reproductive system and releases approximately 35,000 eggs.
7. The life cycles of endoparasites are more complex because of their extreme specialization. For example, life cycle of certain parasites like Fasciola hepatica (sheep liver fluke) is very complex involving many developmental stages and two intermediate hosts to increase the chances of reaching a new definitive host.
8. Certain parasites like Entamoeba develop cysts to tide over the unfavourable conditions like desiccation while reaching the new host.
9. Some parasites elude production of vaccines against them (smart parasites!) as they keep changing their surface antigens form time to time.
   e.g. Plasmodium, HIV, etc.

Question 2.
Describe the effects of parasites on the host.
Answer:
Effects of parasites on hosts :
In general, the parasites cause weakening of the body of their hosts by causing the deprivation of nutrients, fluids and metabolites as they compete with their hosts for the same. They may also cause pathological effects in their hosts suchas

1) Parasitic castration :
Some parasites cause the degeneration of gonads of the host, making it sterile. This effect is called parasitic castration.
e.g. Sacculina (root headed barnacle, a crustacean) causes the degeneration of ovaries in the crab Carcinus maenas.

2) Neoplasia :
Some cause an abnormal growth of the host cells in a tissue to form new structures. This effect is called neoplasia which leads to cancers, e.g. Some viruses

3) Gigantism :
Some parasites cause an abnormal increase in the size of the host. This effect is called gigantism, e.g. The larval stages of Fasciola hepatica cause gigantism in snail (an intermediate host).

4) Hyperplasia :
Some parasites cause an increase in the number of cells. This effect is called hyperplasia, e.g. Fasciola hepatica in the bile ducts of sheep.

5) Hypertrophy :
Some parasites cause an abnormal increase in the volume / size of the infected host cells. This effect is called hypertrophy, e.g. RBC of man infected by Plasmodium.

6) Most of the parasites cause various types of diseases like

1. African sleeping sickness by Trypanosoma gambiense
2. Delhi boils / Tashkent ulcers / Oriental sores by Leishmania tropica
3. Kala azar/ Dum dum fever/Visceral leishmaniasis by Leishmania donovani
4. Malaria by Plasmodium sps
5. Elephantiasis by Wuchereria bancrofti.

Question 3.
Distinguish between hypertrophy and hyperplasia with an example [March 2020]
Answer:
Hyperplasia :
Some parasites cause an increase in the number of cells. This effect is called hyperplasia, e.g. Fasaola hepatica in the bile ducts of sheep Hypertrophy: Some parasites cause an abnormal increase in the volume / size of the infected host cells. This effect is called hypertrophy, e.g. RBC of man infected by Plasmodium

Question 4.
Write any four types of parasitic diseases. Mention the primary and secondary hosts of these parasites.
Answer:

1. Malaria caused by Plasmodium. Primary host – female Anopheles mosquito. Secondary host-man.
2. Elephantiasis caused by wuchereria bancrofti. Primary host – man. Secondary host – female culex mosquito.
3. Amoebic dysentery or Anoebiasis caused by Entamoeba histolytica. Single host -man.
4. Ascariasis caused by Ascaris lumbricoides. Single host – man.

Question 5.
Describe the structure of a trophozoite of Entamoeba histolytica.
Answer:

Trophozoite stage :
It is the most active, motile, feeding and pathogenic stage that lives in the mucosa and sub-mucosa membranes of the large intestine. It moves with the help of a single blunt finger like pseudopodium called lobopodium which is produced anteriorly. The body of the trophozoite is surrounded by plas- malemma. Its cytoplasm is differentiated into an outer clear, viscous, non-granular ectoplasm and the inner fluid like, granular endoplasm. Ribosomes, food vacuoles and a vesicular, cartwheel shaped nucleus are present in the endoplasm. However contractile vacuoles, endoplasmic reticulum, Golgi apparatus and mitochondria are absent.

The absence of mitochondria indicates the ‘obligate anaerobic nature’ of Entamoeba histolytica. It produces the proteolytic enzyme called histolysin due to which the species name histolytica’ was assigned to it. Due to the effect of this enzyme, the mucosa and sub-mucosa of the gut wall are dissolved releasing some amount of blood, tissue debris which are ingested by the trophozoites. Hence, the food vacuoles are with erythrocytes, fragments of epithelial cells and bacteria. The mode of nutrition is holozoic. Presence of ‘RBC in food vacuoles’ and cartwheel shaped nucleus are the characteristic features of the trophozoites of Entamoeba histolytica.

Question 6.
Explain the life cycle of Entamoeba histolytica.
Answer:
Life cycle :
The trophozoites undergo binary fissions in the wall of the large intestine and produce a number of daughter entamoebae. They feed upon the bacteria and the host’s tissue elements, grow in size and again multiply. After repeated binary fissions, when the trophozoites increase in number, some of the young ones enter the lumen of the large intestine and transform into precystic stages. Here, the precystic stages transform into cystic stages which in turn develop into tetranucleate cysts.

The entire process is completed only in a few hours. These tetranucleate cysts come out along with the faecal matter and can remain alive for about 10 days. These cysts reach new host through contaminated food and water. They pass into the small intestine of a new human host where the cyst wall gets ruptured by the action of the enzyme trypsin, releasing the tetranucleate amoebae. Such tetranucleate excystic amoebae are called metacysts.

The four nuclei of the metacyst undergo mitotic divisions and produce eight nuclei. Each nucleus gets a bit of the cytoplasm and thus eight daughter entamoebae or ‘metacystic trophozoites’ are produced. These young ones develop into feeding stages called trophozoites. They invade the mucous membrane of the large intestine and grow into mature trophozoites.

Question 7.
Write a short note on the pathogenicity of Entamoeba histolytica.
Answer:
The trophozoites ‘dissolve’ the mucosal lining by histolysin, go deep into sub¬mucosa and cause ulcers. These ulcers contain cellular debris, lymphocytes, blood corpuscles and bacteria. It leads to the formation of abscesses in the wall of large intestine. Ultimately it results in stool with blood and mucous. This condition is called amoebic dysentery or intestinal amoebiasisor tropical amoebiasis. Some people do not exhibit any symptoms. Such people are called ‘carriers or asymptomatic cyst passers’ as their stool contains the tetranucleate cysts. They help in spreading the parasites to other persons.

Extra-intestinal amoebiasis:
Sometimes, the trophozoites may rupture the wall of capillaries, enter the blood stream and primarily reach the liver where they may cause ‘abscesses’ (some call it ‘secondary amoebiasis’). From there, they may go to lungs, heart, brain, kidneys, gonads, etc., and cause abscesses in those parts leading to severe pathological conditions.

Question 8.
Describe the structure of sporozoite of Plasmodium vivax.
Answer:

Structure of sporozoite :
It is sickle shaped with a swollen middle part and pointed at both ends of its body. It measures about 15 microns in length and one micron in width. The body is covered by an elastic pellicle with microtubules which help in the wriggling movements of the sporozoite. The cytoplasm contains cell organelles such as Golgi complex, endoplasmic reticulum, mitochondria and a nucleus. Cytoplasm also shows many convoluted tubules of unknown function throughout the length of the body. It contains a cup like depression called apical cup at the anterior end into which a pair of secretory organelles opens. They secrete a cytolytic enzyme, which helps in the penetration of sporozoite into the liver cells.

Question 9.
What do you know about the exo-erythrocytic cycle of plasmodium vivax?
Answer:
This is a part of the life cycle of Plasmodium taking place in the liver of man. This starts after the liberation of cryptozoites from ruptured liver cells. Exo-erythrocytic cycle: If the cryptozoites enter the fresh liver cells, they undergo the changes similar to that of the pre-erythrocytic cycle and produce the second generation merozoites called metacryptozoites. These are of two types – the smaller micro-metacryptozoites and larger macro-metacryptozoites. This entire process is completed approximately in two days. The macro-metacryptozoites attack fresh liver cells and continue another exo-erythrocytic cycle, whereas the micro- metacryptozoites always enter blood stream and attack fresh RBC to continue erythrocytic cycle.

Question 10.
Describe the cycle of Golgi in the life history of Plasmodium vivax.
Answer:
Erythrocytic cycle :
Itwas first described by Camillo Golgi. Hence it is also called Golgi cycle. This cycle is initiated either by the cryptozoites of pre-erythrocytic cycle or the micro-metacryptozoites of exo-erythrocytic cycle. In the fresh RBC, these stages assume spherical shape and transform into trophozoites. It develops a small vacuole which gradually enlarges in size, pushing the cytoplasm and nucleus to the periphery. Now the Plasmodium looks like a finger ring. Hence this stage is called signet ring stage. Soon it loses the vacuole, develops pseudopodia and becomes amoeboid stage. With the help of pseudopodia, it actively feeds on the contents of the RBC and increases in size. As a result, the RBC grows almost double the size, this process is called hypertrophy.

The malaria parasite digests the globin part of the ingested haemoglobin and converts the soluble haem into an insoluble crystalline haemozoin. It is called the ‘malaria pigment’ which is a disposable product. During this stage, small red coloured dots appear in the cytoplasm of the RBC known as Schuffner s dots. These are believed to be the antigens released by the parasite. Now the Plasmodium loses the pseudopodia, further increases in size, occupies the entire RBC and becomes a schizont. It undergoes schizogony similar to that of the pre-erythrocytic cycle and produces 12 to 24 erythrocytic merozoites. They are arranged in the form of the petals of a rose in the RBC. Hence, this stage is called the rosette stage. Finally the erythrocyte bursts and releases the merozoites along with haemozoin into the blood. This cycle is completed approximately in 48 hours.

Question 11.
Describe the process of sporogony in the life cycle of Plasmodium vivax. What is the significance of sporozoites?
Answer:

Sporogony :
The formation of sporozoites in the oocysts is called sporogony. According to Bano, the nucleus of the oocyst first undergoes reduction division followed by repeated mitotic divisions resulting in the formation of about 1,000 daughter nuclei. Each bit of nucleus is surrounded by a little bit of the cytoplasm and transforms into a sickle shaped sporozoite. Oocyst with such sporozoites is called sporocyst. When this sporocyst ruptures, the sporozoites are liberated into the haemocoel of the mosquito. From there, they travel into the salivary glands and are ready for infection. The life cycle of Plasmodium in mosquito is completed in about 10 to 24 days.

Question 12.
Explain the pathogenicity of Wuchereria bancrofti in man.
Answer:
Pathogenicity of Wuchereria bancrofti in man :
Light infection causes filarial fever which is characterised by headache, mental depression and increase in the body temperature. In general, the infection of filarial worm causes inflammatory effect in lymph vessels and lymph glands. Inflammation in the lymph vessels is called lymphangitis and that of lymph glands is called lymphadenitis.

In the case of heavy infection, the accumulation of dead worms blocks the lymph vessels and lymph glands resulting in immense swelling. This condition is called lymphoedema which is noticed in the extremities of limbs, scrotum of males and mammary glands in females. Fibroblasts accumulate in these tissues and form the fibrous tissue. In severe cases, the sweat glands of the skin in the affected regions disintegrate and the skin becomes rough. This terminal condition is referred to as elephantiasis.

Question 13.
Write short notes on typhoid fever and its prophylaxis.
Answer:
Typhoid fever :
It is caused by Salmonella typhi which is a Gram negative bacterium. It mainly lives in the small intestine of man and then migrates to other organs through blood. It can be confirmed by Widal test.

Mode of infection :
Contamination through food and water.

Symptoms :
Sustained fever with high temperature upto 104 F, weakness, stomach pain, constipation, headache and loss of appetite. Intestinal perforation and death may also occur in severe cases.

Prophylaxis :
The immunization programmes by the use of vaccines have enabled us to completely eradicate a deadly disease like smallpox. Biotechnology is at the verge of making available newer and safer vaccines. Discovery of antibiotics and various other drugs has also enabled us to treat infectious diseases effectively.

Question 14.
Write short notes on pneumonia and its prophylaxis.
Answer:
Pneumonia :
It is caused by Gram positive bacteria such as streptococcus pneumoniae and Haemophilus influenzae. They infect the alveoli of lungs in human beings.

Mode of infection :
Contamination by inhaling the droplets / aerosols released by an infected person or even by sharing the utensils with an infected person.

Symptoms :
The alveoli get filled with fluid leading to severe problems in respiration. In severe cases, the lips and finger nails may turn gray to bluish in colour.

Prophylaxis :
The immunization programmes by the use of vaccines have enabled us to completely eradicate a deadly disease like smallpox. Biotechnology is at the verge of making available newer and safer vaccines. Discovery of antibiotics and various other drugs has also enabled us to treat infectious diseases effectively.

Question 15.
Write short notes on common cold and its prophylaxis.
Answer:
Common cold :
It is caused by Rhino virus group of viruses. They infect nose and respiratory passage but not lungs.

Mode of infection :
Contamination by direct inhalation of the droplets resulting from cough or sneezes of an infected person or indirectly through contaminated objects such as pens, books, cups, door-knobs, computer keyboard or mouse etc. Generally all the medicines that are used against cold cause drowsiness.

Symptoms :
Nasal congestion, discharge from nose, sore throat, hoarseness, cough, headache, tiredness, etc., which usually last for 3 – 7 days.

Prophylaxis :
The immunization programmes by the use of vaccines have enabled us to completely eradicate a deadly disease like smallpox. Biotechnology is at the verge of making available newer and safer vaccines. Discovery of antibiotics and various other drugs has also enabled us to treat infectious diseases effectively.

Question 16.
Write short notes on ‘ringworm’ and its prophylaxis.
Answer:
Ringworm :
It is one of the most common infectious diseases in man. It is caused by many fungi belonging to the genera Microsporum, Trichophyton, and Epidermophyton. Heat and moisture help these fungi grow in the skin folds such as those in the groin or between the toes.

Mode of infection :
Contamination by using towels, clothes or combs of the infected persons or even from soil.

Symptoms :
Appearance of dry, scaly, usually round lesions accompanied by intense itching on various parts of the body such as skin, nails and scalp.

Prophylaxis :
Using of antifungal drugs like Griesoven orally, and antifungal creams like Zole, Itchguard. Ring guard for external tise’cures the disease. Hygiene habits prevent the disease.

Question 17.
What are the adverse effects of tobacco?
Answer:
Tobacco has been used by human beings for more than 400 years. It contains a large number of chemical substances including nicotine, an alkaloid. While buying cigarettes one cannot miss the statutory warning present on the packet Smoking is injurious to health.

Mode of abuse :
It is smoked or chewed as gutkha or used in the form of snuff.

Effect :
Smoking increases the carbon monixide (CO) level and reduces the oxygen level in the blood. Nicotine stimulates the adrenal gland to release adrenaline and nor-adrenaline into blood. These hormones raise the blood pressure and increase the heart rate. Smoking is associated with bronchitis, emphysema, coronary heart disease, gastric ulcer and increases the incidence of cancers of throat, lungs, urinary bladder etc. Smoking also paves the way to hard drugs. Yet, smoking is very prevalent in society, both among young and old. Tobacco chewing is associated with increased risk of cancer of the oral cavity.

Question 18.
Write short notes on opioids.
Answer:
Opioids :
These are the drugs obtained from opium poppy plant Papaver somniferum (vernacular name : Nallamandu mokka).

They bind to specific opioid receptors present in our central nervous system and gastrointestinal tract. Some of them are morphine, heroin, etc.

i) Morphine :
It is extracted from the dried latex of the unripe seed capsule (pod) of poppy plant. It occurs as colourless crystals or a white crystalline powder.

Mode of abuse :
Generally it is taken orally or by injection.

Effect :
It is a very effective sedative and painkiller. It is very useful in patients who have undergone surgery.

ii) Heroin :
It is a white, bitter, odourless and crystalline compound, obtained by the acetylation of morphine. Chemically it is diacetylmorphine. It is commonly called ‘smack’.

Mode of abuse :
Generally it is taken by snorting and injection.

Effect :
Heroin is a depressant and slows down the body functions.

Question 19.
Write short notes on Cannabinoids.
Answer:
Cannabinoids :
These are a group of chemicals obtained from Indian hemp plant Cannabis sativa (vernacular name: Ganjai mokka). They interact with cannabinoid receptors present in the brain. The flower tops, leaves and the resin of this plant are used in various combinations to produce marijuana, hashish, charas and ganja. These days, cannabinoids are being abused by even some sports-persons (doping).

Mode of abuse :
These are generally taken by inhalation and oral ingestion.

Effect :
Show their effects on cardiovascular system of the body.

Question 20.
Write short notes on Cocaine.
Answer:
Coca alkaloid or Cocaine :
It is a white, crystalline alkaloid that is obtained from the leaves of Coca plant Erythroxylum coca, native to South America. It is commonly called coke or crack.

Mode of abuse :
It is usually snorted.

Effect :
It has a potent stimulating action on the central nervous system as it interferes with the transport of the neuro transmitter dopamine. Hence it produces a sense of euphoria and increased energy. Its excessive dosage causes hallucinations. Other well-known plants with hallucinogenic properties are Atropa belladonna and Datura. Certain drugs like ‘Barbiturates (sleeping pills), Amphetamines (cause sleeplessness), Benzodiazepines (tranquilizers), Lysergic acid diethyl amides (LSD) and other similar drugs, normally used as medicines to treat patients with mental illnesses like depression, insomnia, etc.,1 are often abused.

Question 21.
Why is adolescence considered vulnerable phase?
Answer:
Adolescence :
It is the time period between the beginning of puberty and the beginning of adulthood. In other words, it is the bridge linking childhood and adulthood. The age between 12 -18 years is considered adolescence period. It is both ‘a period and a process’ during which a child becomes mature. It is accompanied by several biological and behavioural changes. Thus, adolescence is a very vulnerable phase of mental and psychological development of an individual.

Question 22.
Why do some adolescents start taking drugs? How can this be avoided?
Answer:
Curiosity, desire for adventure and excitement, experimentation, are the common causes for the motivation of youngsters towards the use of tobacco, drugs. The first use of drugs or alcohol may be out of curiosity or experimentation, but later the person starts using them to escape facing problems. Recently ‘stress from the pressure to excel in academics or examination’s has played a significant role in alluring the youngsters to try certain drugs. Television, movies, newspapers and internet also help promoting this wrong perception. Other factors that are associated with tobacco, drug and alcohol abuse among adolescents are unstable or unsupportive family structures and peer pressure.

A lot of help is available in the form of highly qualified psychologists, psychiatrists and de-addiction and rehabilitation programmers. Educating and counselling the adolescents to face problems, stress and failures as a part of life.

Question 23.
Distinguish between addiction and dependence. [March 2017 -A.P.]
Answer:
Addiction :
It is a psychological attachment to certain effects such as euphoria. The most important thing one fails to realise is, the inherent addictive nature of tobacco, drugs and alcohol. With the repeated use of TDA, the tolerance level of the receptors present in our body increases. Consequently the receptors respond only to higher doses leading to greater intake and addiction.

However it should be clearly borne in mind that use of TDA even once, can be a fore-runner to addiction. Thus, the addictive potential of tobacco, drugs’and alcohol pull the users into a vicious circle leading to their regular use (abuse) from which they may not be able to get out. In the absence of any guidance or counseling, people get addicted and become dependent on them.

Dependence :
It is the tendency of the body to manifest a characteristic and unpleasant condition (withdrawal syndrome) if the regular dose of drugs or alcohol is abruptly discontinued. The withdrawal syndrome is characterised by anxiety, shakiness (tremors), nausea and sweating which may be relieved when the regular use is resumed again. Dependence leads the patients to ignore all social norms.

Question 24.
“Prevention is better than cure.” Justify with regard to TDA abuse. [March 2018 – A.P.]
Answer:
Prevention and Control: The age-old adage of Prevention is better than cure holds true here also. Some of the measures useful for prevention and control of TDA abuse among the adolescents are :

i) Avoid undue parental pressure :
Every child has his / her own choice, capacity and personality. The parents should not force their children to perform beyond their capacity by comparing them with others in studies, games, etc.

ii) Responsibility of parents and teachers :
They should look for the danger signs and counsel such students who are likely to get into the ‘trap’.

iii) Seeking help from peers :
If peers find some one abusing drugs or alcohol, immediately it should be brought to the notice of their parents or teachers so that they can guide them appropriately.

iv) Education and counselling :
Educating and counselling the children to face problems, stress and failures as a part of life.

v) Seeking professional and medical help :
A lot of help is available in the form of highly qualified psychologists, psychiatrists and de-addiction and rehabilitation programmers.

Essay Answer Type Questions

Question 1.
Explain the structure and life cycle of Entamoeba histolytica with the help of neat and labelled diagrams.
Answer:
Structure: Entamoeba histolytica passes through three distinct stages in its life cycle, namely:

1. Trophozoite stage
2. Precystic stage and
3. Cystic stage

Trophozoite stage :
It is the most active, motile, feeding and pathogenic stage that lives in the mucosa and sub-mucosa membranes of the large intestine. It moves with the help of a single blunt finger like pseudopodium called lobopodium which is produced anteriorly. The body of the trophozoite is surrounded by plasmalemma. Its cytoplasm is differentiated into an outer clear, viscous, non-granular ectoplasm and the inner fluid like, granular endoplasm. Ribosomes, food vacuoles and a vesicular, cartwheel shaped nucleus are present in the endoplasm. However contractile vacuoles, endoplasmic reticulum, Golgi apparatus and mitochondria are absent.

The absence of mitochondria indicates the ‘obligate anaerobic nature’ of Entamoeba histolytica. It produces the proteolytic enzyme called histolysin due to which the species name histolytica’ was assigned to it. Due to the effect of this enzyme, the mucosa and sub-mucosa of the gut wall are dissolved releasing some amount of blood, tissue debris which are ingested by the trophozoites. Hence, the food vacuoles are with erythrocytes, fragments of epithelial cells and bacteria. The mode of nutrition is holozoic. Presence of ‘RBC in food vacuoles’ and cartwheel shaped nucleus are the characteristic features of the trophozoites of Entamoeba histolytica.

Precysticstage :

It is the non-feeding and non-pathogenic stage of Entamoeba histolytica that is found in the lumen of the large intestine. It is a small, spherical or oval, non- motile form. The cytoplasm of the precystic stage stores glycogen granules and chromatoid bars (made of ribonucleo protein) which act as reserve food.

Cystic stage :

It is round in shape and is surrounded by a thin, delicate and highly resistant cyst wall. It is found in the lumen of the large intestine. The process of development of cyst wall is called encystation which is a means to tide over the unfavourable conditions that the parasite is going to encounter while passing to a new host. Soon after the encystation, the nucleus undergoes two successive mitotic divisions to form four daughter nuclei. This type of cystic stage is called tetra nucleate cyst or mature cyst which is ‘the stage infective to man’.

Life cycle :
The trophozoites undergo binary fissions in the wall of the large intestine and produce a number of daughter entamoebae. They feed upon the bacteria and the host’s tissue elements, grow in size and again multiply. After repeated binary fissions, when the trophozoites increase in number, some of the young ones enter the lumen of the large intestine and transform into precystic stages. Here, the precystic stages transform into cystic stages which in turn develop into the tetranucleate cysts.

The entire process is compelted only in a few hours. These tetranucleate cysts come out along with the faecal matter and can remain alive for about 10 days. These cysts reach new host through contaminated food and water. They pass into the small intestine of a new human host where the cyst wall gets ruptured by the action of the enzyme trypsin, releasing the tetranucleate amoebae. Such tetranucleate excystic amoebae are called metacysts.

The four nuclei of the metacyst undergo mitotic divisions and produce eight nuclei. Each nucleus gets a bit of the cytoplasm and thus eight daughter entamoebae or ‘metacystic trophozoites’ are produced. These young ones develop into feeding stages called trophozoites. They invade the mucous membrane of the large intestine and grow into mature trophozoites.

Pathogenicity :
The trophozoites ‘dissolve’ the mucosal lining by histolysin, go deep into sub¬mucosa and cause ulcers. These ulcers contain cellular debris, lymphocytes, blood corpuscles and bacteria. It leads to the formatjon of abscesses in the wall of large intestine . Ultimately it results in stool with blood and mucous. This condition is called amoebic dysentery or intestinal amoebiasis or tropical amoebiasis. Some people do not exhibit any symptoms. Such people are called ‘carriers or asymptomatic cyst passers’ as their stool contains the tetranucleate cysts. They help in spreading the parasites to other persons.

Extra-intestinal amoebiasis :
Sometimes, the trophozoites may rupture the wall of capillaries, enter the blood stream, and primarily reach the liver where they may cause ‘abscesses’ (some call it ‘secondary amoebiasis’). From there, they may go to lungs, heart, brain, kidneys, gonads, etc., cause abscesses in those parts leading to severe pathological conditions.

Question 2.
Describe the life cycle of Plasmodium vivax in man. [March 2017 – A.P.]
Answer:
Life cycle of Plasmodium in man (The human phase): In man, the Plasmodium reproduces by asexual reproduction called schizogony. It occurs in liver cells (hepatocytes) as well as in RBC. In liver cells, it is called hepatic schizogony and in RBC it is called erythrocytic schizogony.

Hepatic schizogony :
This was discovered by Shortt and Garnham. Whenever, a mosquito infected by Plasmodium bites a man, nearly 2000 sporozoites are released into the blood of man through its saliva. Within half an hour, they reach the hepatocytes where they undergo pre-erythrocytic and exo-erythrocytic cycles.

Pre-erythrocytic cycle :
Whenever the sporozoites reach the liver cells, they transform into trophozoites. They feed on the contents of the hepatic cells, assume spherical shape and attain the maximum size. This stage is called schizont stage. Its nucleus divides several times mitotically, followed by the cytoplasmic divisions resulting in approximately 12,000 daughter individuals called cryptozoites or the regeneration merozoites. They enter the sinusoids of the liver by rupturing the cell membrane of the schizont and the liver cells. This entire process is completed approximately in 8 days. Now these first generation merozoites have two options i.e., they can enter either fresh liver cells and continue exo-erythrocytic cycle or they can enter RBC and continue erythrocytic cycle.

Exo-erythrocytic cycle :
If the cryptozoites enter the fresh liver cells, they undergo the changes similar to that of the pre-erythrocytic cycle and produce the second generation merozoites called metacryptozoites. These are of two types -the smaller micro-metacryptozoites and larger macro-metacryptozoites. This entire process is completed approximately in two days. The macro-metacryptozoites attack fresh liver cells and continue another exo – erythrocytic cycle, whereas the micro- metacryptozoites always enter blood stream and attack fresh RBC to continue erythrocytic cycle.

Prepatent period :
The interval between ‘the first entry of Plasmodium into the blood in the form of sporozoites and the second entry of Plasmodium into the blood in the form of cryptozoites is called prepatent period. It lasts approximately 8 days. During this period, the host does not show any clinical symptoms of the disease. It is only a means of multiplication.

Erythrocytic cycle :
It was first described by Camillo Golgi. Hence it is also called Golgi cycle. This cycle is initiated either by the cryptozoites of pre-erythrocytic cycle or the micro-metacryptozoites of exo – erythrocytic cycle. In the fresh RBC, these stages assume spherical shape and transform into trophozoites. It develops a small vacuole which gradually enlarges in size, pushing the cytoplasm and nucleus to the periphery. Now the Plasmodium looks like a finger ring. Hence this stage is-” called signet ring stage. Soon it loses the vacuole, develops pseudopodia and becomes amoeboid stage.

With the help of pseudopodia, it actively feeds on the contents of the RBC and increases in size. As a result, the RBC grows almost double the size. This process is called hypertrophy. The malaria parasite digests the globin part of the ingested haemoglobin and converts the soluble haem into an insoluble crystalline haemozoin. It is called the ‘malaria pigment’ which is a disposable product. During this stage, small red coloured dots appear in the cytoplasm of the RBC known as Schuffner s dots.

These are believed to be the antigens released by the parasite. Now the Plasmodium loses the pseudopodia, further increases in size, occupies the entire RBC and becomes a schizont. It undergoes schizogony similar to that of the pre-erythrocytic cycle and produces 12 to 24 erythrocytic merozoites. They are arranged in the form of the petals of a rose in the RBC. Hence, this stage is called the rosette stage. Finally the erythrocyte bursts and releases the merozoites along with haemozoin into the blood. This cycle is completed approximately in 48 hours.

Incubation Period :
The period between ‘the entry of Plasmodium into the blood in the form of sporozoite and the first appearance of symptoms of malaria in man’ is called incubation period. It is approximately 10 to 14 days.

Formation of gametocytes :
After repeated cycles of erythrocytic schizogony, when the number of fresh RBC decreases, some merozoites enter the RBC and transform into gametocytes instead of continuing the erythrocytic cycle. This process generally takes place when the RBCs are present in spleen and bone marrow.

The gametocytes are of two types namely, smaller microgametocytes or male gametocytes and larger macrogametocytes or female gametocytes. The gametocytes cannot undergo further development in man as the temperature and pH of the blood of man are not suitable for further development. These gametocytes reach the blood circulation and wait to reach the next host. They degenerate and die if they are not transferred to mosquito within a week.

Question 3.
Describe the life cycle of Plasmodium vivax in mosquito.
Answer:
Life cycle of Plasmodium in mosquito (The mosquito phase)- Ross cycle: When a female Anopheles mosquito bites and sucks the blood of a malaria patient, the gametocytes along with the other stages of the erythrocytic cycle reach the crop of mosquito. Here all the stages are digested except the gametocytes. Further part of the life cycle consists of:

1. Gametogony
2. Fertilization
3. Formation of Ookinete & Oocysts
4. Sporogony

i) Gametogony :
The formation of male and female gametes from the gametocytes is called gametogony. It occurs in the lumen of the crop of mosquito.

Formation of male gametes :
During this process, the nucleus of microgametocyte divides into eight daughter nuclei called pronuclei which reach the periphery. The cytoplasm is pushed out in the form of eight flagella like processes. Into each flagellum like process, one pronucleus enters and forms a micro gamete or male gamete. These male gametes show lashing movements like flagella and get separated from the cytoplasm of microgametocyte. This process is called exflagellation.

Formation of female gamete :
The female gametocyte undergoes a few changes and transforms into a female gamete. This process is called maturation. The nucleus of the female gamete moves towards the periphery and the cytoplasm at that point forms a projection. This projected region is called the fertilization cone.

ii) Fertilization :
The fusion of male and female gametes is called fertilization. It also occurs in the lumen of the crop of the mosquito. When an actively moving male gamete comes into contact with the fertilization cone of the female gamete, it enters it. The pronuclei and cytoplasm of these two gametes fuse with each other, resulting in the formation of a synkaryon. Since the two gametes are dissimilar in size, this process is known as anisogamy. The female gamete that bears the synkaryon is called the zygote which is round and non – motile.

iii) Formation of ookinete and oocysts :
The zygote remains inactive for some time and then transforms into a long, slender, motile, vermiform ookinete or vermicide within 18 to 24 hours. It pierces the wall of the crop and settles beneath the basement membrane. It becomes round and secretes a cyst around its body. This encysted ookinete is now called oocyst. About 50 to 500 oocysts are formed on the wall of the crop and appear in the form of small nodules. (Sir Ronald Ross identified these oocysts for the first time).

iv) Sporogony :

The formation of sporozoites in the oocysts is called sporogony. According to Bano, the nucleus of the oocyst first undergoes reduction division followed by repeated mitotic divisions resulting in the formation of about 1,000 daughter nuclei. Each bit of nucleus is surrounded by a little bit of the cytoplasm and transforms into a sickle shaped sporozoite. Oocyst with such sporozoites is called sporocyst. When this sporocyst ruptures, the sporozoites are liberated into the haemocoel of the mosquito. From there, they travel into the salivary glands and are ready for infection. The life cycle of Plasmodium in mosquito is completed in about 10 to 24 days.

Question 4.
Describe the structure and life cycle of Ascaris lumbricoides with the help of a neat and labelled diagram.
Answer:

Structure :
Sexes are separate and the sexual dimorphism is distinct. In both males and females, the body is elongated and cylindrical. Mouth is present at the extreme anterior end and is surrounded by three chitinous lips. Close to the mouth mid ventrally, there is a small aperture called excretory pore.

Male :
It has a curved posterior end which is considered the tail. The posterior end possesses a cloacal aperture and a pair of equal sized chitinous ‘pineal spicules or ‘pineal setae which serve to transfer the sperms during copulation.

Female :
It has a straight posterior end, the tail. The female genital pore or vulva is present mid ventrally at about one third the length from mouth. The anus is present a little in front of the tail end.

Life history :
Copulation takes place in the small intestine of man. After copulation, the female releases approximately two lakh eggs per day. Each egg is surrounded by ‘a protein coat with rippled surface. Hence the eggs of Ascaris are described as mammillated eggs. The protein coat is followed by a chitinous shell and a lipid layer internally. These eggs come out along with faecal matter. In the moist soil, development takes place inside the egg so that the 1^st stage rhabditiform larva is produced. It undergoes the 1^st moulting and becomes the 2nd stage rhabditiform larva which is considered ‘the stage infective to man’. They reach the alimentary canal of man through contaminated food and water.

In the small intestine, the shell gets dissolved so that the 2^nd stage larva is released. Now it undergoes extra intestinal migration. First it reaches the liver through the hepatic portal vein. From there it reaches the heart through the post caval vein. It goes to the lungs through the pulmonary arteries. In the alveoli of lungs it undergoes the 2^nd moulting to produce the 3^rd stage larva. It undergoes the 3^rd moulting so that the 4^th stage larva is produced in the alveoli only. It leaves the alveoli and reaches the small intestine again, through bronchi, trachea, larynx, glottis, pharynx, oesophagus and stomach. In the small intestine, it undergoes the 4^th and final moulting to become a young one which attains sexual maturity within 8 to 10 weeks.

Pathogenicity :
The disease caused by Ascaris lumbricoides is called ascariasis. The disease is asymptomatic if the number of worms is less. A heavy infection causes nutritional deficiency and severe abdominal pain. It also causes stunted growth in children.

Question 5.
Describe the life cycle of Wuchereria bancrofti.
Answer:
Life Cycle :
Wuchereria bancrofti completes its life cycle in two hosts namely man and female culex mosquito.

In man :
Both male and female worms are found coiled together in the lymphatic vessels of man. After copulation the female releases the sheathed microfilaria larvae into the lymph of man. Each sheathed microfilaria larva measures 0.2 to 0.3 mm in length. It is surrounded by a loose cuticular sheath which is supposed to be the modified shell. They migrate to the blood circulation and reside in the deeper blood vessels during the day time. They move to the peripheral blood circulation during the night time between 10.00 pm and 4.00 am. This tendency is referred to as nocturnal periodicity. When a female Culex mosquito sucks the blood of an infected person, they enter the gut of mosquito. They die if they are not transferred to mosquito with in 70 days.

In mosquito :
In the mid gut of mosquito, the sheath of the larva is dissolved within 2 to 6 hours of the infection. The ex-sheathed microfilaria larva penetrates the gut wall and reaches the haernocoel of mosquito. From there, it reaches the thoracic muscles and transforms into a ‘sausage shaped larva within two days. It is called the first stage larva or first stage microfilaria. This undergoes two moultings within 10 to 20 days and transforms into a long, infective 3^rd stage microfilaria. It reaches the labium of the mosquito.

In man after the infection :
When an infected mosquito bites a man, the 3^rd stage microfilaria larvae enter the blood circulation of man and finally reach the lymphatic vessels. Here they undergo the 3^rdand the 4^th moultings to produce young filarial worms. They attain sexual maturity within 5 to 18 months.

Question 6.
Write an essay on adolescence and TDA abuse.
Answer:
Adolescence and TDA abuse:
Adolescence :
It is the time period between the beginning of puberty and the beginning of adulthood. In other words, it is the bridge linking childhood and adulthood. The age between 12 -18 years is considered adolescence period. It is both ‘a period and a process’ during which a child becomes mature. It is accompanied by several biological and behavioural changes. Thus, adolescence is a very vulnerable phase of mental and psychological development of an individual.

TDA abuse :
Curiosity, desire for adventure and excitement, experimentation, are the common causes for the motivation of youngsters towards the use of tobacco, drugs and alcohol. The first use of drugs or alcohol may be out of curiosity or experimentation, but later the person starts using them to escape facing problems. Recently ‘stress from the pressure to excel in academics or examinations’ has played a significant role in alluring the youngsters to try certain drugs. Television, movies, newspapers and internet also help promoting this wrong perception. Other factors that are associated with tobacco, drug and alcohol abuse among adolescents are unstable or unsupportive family structures and peer pressure.

Addiction and Dependence :
The TDA abuse leads to addiction and dependence.

Addiction :
It is a psychological attachment to certain effects such as euphoria. The most important thing one fails to realise is, the inherent addictive nature of tobacco, drugs and alcohol. With the repeated use of TDA, the tolerance level of the receptors present in our body increases. Consequently the receptors respond only to higher doses leading to greater intake and addiction. However it should be clearly borne in mind that use of TDA even once, can be a fore-runner to addiction. Thus, the addictive potential of tobacco, drugs and alcohol pull the users into a vicious circle leading to their regular use (abuse) from which they may not be able to get out. In the absence of any guidance or counselling, people get addicted and become dependent on them.

Dependence :
It is the tendency of the body to manifest a characteristic and unpleasant condition (withdrawal syndrome) if the regular dose of drugs or alcohol is abruptly discontinued. The withdrawal syndrome is characterised by anxiety, shakiness (tremors), nausea and sweating which may be relieved when the regular use is resumed again. Dependence leads the patients to ignore all social norms.

Adverse effects of drugs and alcohol abuse :
The immediate adverse effects of drugs and alcohol abuse are manifested in the form of reluctant behaviour, vandalism and violence. Excessive doses of drugs may lead to coma and death due to respiratory or heart failure or cerebral haemorrhage. A combination of drugs or their intake along with alcohol generally results in overdosing and even death. The most common warning signs of drug and alcohol abuse among the youth include drop in academic performance, lack of interest in personal hygiene, depression, fatigue, aggressive behaviour, loss of interest in hobbies, change in sleeping and eating habits, fluctuations in weight, appetite, etc.

Those who take drugs intravenously are much more likely to acquire serious infections such as HIV, HBV (Hepatitis – B virus) etc., as the viruses are transferred from one person to another by the sharing of infected needles and syringes. The chronic use of drugs and alcohol damages nervous system and liver. The use of drugs and alcohol during pregnancy is also known to affect the foetus adversely.

Some sports-persorTs take drugs such as anabolic steroids to enhance their performance. The side-effects of the use of these drugs in females include masculinisation, increased aggressiveness, mood swings, depression, abnormal menstrual cycles, excessive hair growth on the face and body and the enlargement of clitoris. In males it includes acne (pimples), increased aggressiveness, mood swings, depression, reduction in the size of testicles, decreased sperm production, kidney and liver dysfunction, enlargement of breasts, premature baldness and the enlargement of the prostate gland.

Prevention and Control :
The age-old adage of Prevention is better than cure holds true here also. Some of the measures useful for prevention and control of TDA abuse among the adolescents are :
i) Avoid undue parental pressure :
Every child has his / her own choice, capacity and personality. The parents should not force their children to perform beyond their capacity by comparing them with others in studies, games, etc.

ii) Responsibility of parents and teachers :
They should look for the danger signs and counsel such students who are likely to get into the ‘trap’.

iii) Seeking help from peers :
If peers find someone abusing drugs or alcohol, immediately it should be brought to the notice of their parents or teachers so that they can guide them appropriately.

iv) Education and counselling :
Educating and counselling the children to face problems, stress and failures as a part of life.

v) Seeking professional and medical help:
A lot of help is available in the form of highly qualified psychologists, psychiatrists and de-addiction and rehabilitation programmers.

Telangana TSBIE TS Inter 1st Year Zoology Study Material 5th Lesson Locomotion and Reproduction in Protozoa Textbook Questions and Answers.

TS Inter 1st Year Zoology Study Material 5th Lesson Locomotion and Reproduction in Protozoa

Very Short Answer Type Questions

Question 1.
Draw a labelled diagram of T.S. of flagellum. [March 2018-A.P.]
Answer:

Question 2.
List any two differences between a flagellum and a cilium. [Mar. 2020, ’19, 17 – A.P ; May/June, Mar. 2014]
Answer:

Question 3.
What are dynein arms? What is their significance? [May 2017 – A.P.]
Answer:
In cross section of flagellum / cilium Dynein arms are seen. The ‘A’ tubule of flagellum/ cilium of each peripheral doublet bears paired arms along its length, called dynein arms

Bending movement of a flagellum is brought about by the sliding of microtubules past each other due to the functioning of ‘dynein arms’.

Question 4.
What is a Kinety? [March 2014]
Answer:
A longitudinal row of kinetosomes together with Kinetodesmata constitute a unit called ‘Kinety’.

Question 5.
Distinguish between synchronous and metachronous movements.
Answer:
1) Synchronous movement :
Cilia in a transverse row beat simultaneously in one direction. It is called synchronous movement.

2) Metachronous movement :
The sequential movement of Cilia, in a longitudinal row, one after the other in one direction is called metachronous movement.

Question 6.
Why do we refer to the offspring, formed by asexual method of reproduction, a clone? [March 2020, 19]
Answer:
The term clone is used to describe morphologically and genetically similar daughter individuals formed from single parent by asexual reproduction. They are not only identical to one another but also exact copies of their parent.

Question 7.
Distinguish between proter and opisthe. [Mar. 2017, 13 – A.P ; Mar. 2015 A.P & T.S]
Answer:
During Transverse binary fission of paramecium, two daughter paramecia are formed. The upper or anterior one is proter which receive upper contractile vacuole, cytopharynx and cytostome of its parent. The lower or posterior daughter is opisthe which receives the posterior contractile vacuole only.

Question 8.
How is sexual reproduction advantageous in evolution?
Answer:
Because of the fusion of male and female gametes, sexual reproduction results in offspring that are not identical to the parents or amongst themselves. This leads gradually to origin of new species in course of evolution.

Question 9.
Distinguish between lobopodium and filopodium. Give an example to each of them. [May ’17 ; March 2015 – A.P.]
Answer:
a) Blunt finger like pseudopodia are called lobopodium and are seen in Amoeba and Entamoeba.
b) Fibre like pseudopodia are called filopodiurn and are seen in Euglypha.

Question 10.
Define conjugation with reference to ciliates. Give two examples. [March 2018 – A.P.; March 2015 – T.S ; May/June 2014]
A. Conjugation is a temporary union between two senile ciliates that belong to two different mating types for the exchange of nuclear material and its reorganization. This is observed in Paramecium and Vorticella.

Short Answer Type Questions

Question 1.
Name the system that controls the fastest swimming movement of protozoans and write its components.
Answer:
The system that controls the fastest swimming movement of protozoans is infraciliary system.

It is located just below the pellicle in the ectoplasm of a ciliate. It includes kinetosomes, kinetodesmal fibrils and kinetodesmata. The kinetosomes are present at the bases of cilia in transverse and longitudinal rows. The kinetodesmal fibrils are connected to the kinetosomes and run along the right side of each row of kinetosomes as a ‘cord of fibres’ called kinetodesmata. A longitudinal row of kinetosomes together with kinetodesmata constitute a unit called ‘kinety’.

All the kineties together form an infraciliary system, which is connected to a ‘motorium’, located near the cytopharynx. The infraciliary system and motorium form the ‘neuromotor system’ that controls and coordinates the movement of cilia.

Question 2.
Write the mechanism of bending of flagellum and explain effective and recovery strokes.
Answer:
Bending movement of flagella: Dynein arms show a complex cycle of movements using energy provided by ATP (dynein arms are the sites of ATPase activity in the cilia and flagella). The dynein arms of each doublet attach to an adjacent doublet and pull the neighbouring doublet. So the doublets slide past each other in opposite directions. The arms release and reattach a little farther on the adjacent doublet and again ‘puli’. As the doublets of a flagellum or cilium are physically held in place by the radial spokes, the doublets cannot slide past much. Instead they curve and cause bending of flagellum or cilium. Such bending movements of flagella and cilia play an important role in the flagellar and ciliary locomotion.

i) Effective stroke :
Flagellum becomes rigid and starts bending to one side beating against the water. This beating against water is at right angles to the body axis and the organism moves forwards.

ii) Recovery stroke :
Flagellum becomes comparatively soft so as to offer least resistance to water and moves backwards to its original position. It is called ‘recovery stroke’.

Question 3.
What are lateral appendages? Based on their presence and absence, write the various types of flagella giving at least one example for each type. [Mar. 17 – A.P ; Mar. 15 – A.P & T.S]
Answer:
Lateral appendages :
Some flagella bear one or two or many rows of short, lateral hair like fibrils called lateral appendages. They are of two types namely ‘mastigonemes’ and ‘flimmers’.

Types of Flagella :
Based on the presence or absence and / or the number of rows of lateral appendages, five types of flagella are recognised.

a. Stichonematic :
This flagellum bears one row of lateral appendages on the axoneme. Eg : Euglena and Astasia.

b. Pantonematic :
This flagellum has two or more rows of lateral appendages on the axoneme. Eg: Peranema and Monas.

c. Acronematic :
This type of flagellum does not bear lateral appendages and the terminal part of the axoneme is naked without the outer sheath at its tip.
Eg: Chlamydomonas and Polytoma.

d. Pantacronematic :
This type of flagellum is provided with two or more rows of lateral appendages and the axoneme ends in a terminal naked filament.
Eg. Urceolus.

e. Anematic or simple :
In this type of flagellum, lateral appendages and terminal filament are absent. Hence, it is called anematic (a – no; nematic – threads).
Eg: Chilomonas and Cryptomonas.

Question 4.
Describe the process of transverse binary fission in paramecium. [May 2017 – A.P.; May/June 2014]
Answer:

During favourable conditions, Paramecium stops feeding after attaining its maximum growth. At first the micronucleus divides by mitosis and the macronucleus divides into two daughter nuclei by amitosis. The oral groove disappears. After karyokinesis, a transverse constriction appears in the middle of the body, which deepens and divides the parent cell into two daughter individuals, the anterior proter and the posterior opisthe. The proter receives the anterior contractile vacuole, cytopharynx and cytosome from its parent individual.

It develops posterior contractile vacuole and a new oral groove. The opisthe receives the posterior contractile vacuole of its parent. It develops a new anterior contractile vacuole, cytopharynx, cytostome and a new oral groove. Binary fission is completed in almost two hours, in favourable conditions and paramecium can produce four generations of daughter individuals by binary fission in a day.

The transverse binary fission is also called homothetogenic fission, because the plane of fission is at right angles to the longitudinal axis of the body. As it occurs at right angles to the kineties, it is also called perkinetai fission.

Question 5.
Describe the process of longitudinal binary fission in Euglena. [March 2018 – A.P.; March 2014]
Answer:
During the process of binary fission, the nucleus, basal granules, chromatophores, cytoplasm undergo division. The nucleus divides by mitosis into two daughter nuclei. Then the kinetosomes and the chromatophores also divide. At first, a longitudinal groove develops in the middle of the anterior end. This groove extends gradually towards the posterior end until the two daughter individuals are separated.

One daughter Euglena retains the parental flagella. The other daughter individual develops new flagella from the newly formed basal granules. The stigma, paraflagellar body and contractile vacuole of the parent disappear. They develop afresh in both the daughter euglenae. The longitudinal binary fission is known as symmetrogenic division, because the two daughter euglenae resemble each other like ‘mirror images’.

Question 6.
Write a short note on multiple fission.
Answer:
Multiple Fission :
It is the division of the parent body into many smaller individuals (Multi – many; Fission – splitting). Normally multiple fission occurs during unfavourable conditions. During the multiple fission, the nucleus first undergoes repeated mitotic divisions without cytokinesis. This causes the formation of many daughter nuclei. Then the cytoplasm also divides into as many-number of bits as there are nuclei. Each cytoplasmic bit encircles one daughter nucleus. This results in the formation of many smaller individuals from a single parent organism.

There are different types of multiple fissions in protozoans such as schizogony, male gametogony, sporogony in Plasmodium, sporulation in Amoeba, etc.

Question 7.
Give an account of pseudopodia.
Answer:
Pseudopodia :
These are found in rhizopods. The pseudopodia are temporary extensions of cytoplasm that develop in the direction of the movement. These temporary structures are useful to move on the substratum as our legs do, hence the name ‘pseudopodia’. There are four kinds of pseudopodia namely lobopodia (blunt finger-like) as in Amoeba and Entamoeba, filopodia (fibre-like) as in Euglypha, reticulopodia (net-like) as in Elphidium and axopodia or heliopodia (sun ray-like) as in Actionophrys.

The Pseudopodium is formed by the conversion of gel (viscous outer endoplasmic part) to sol (fluid-like inner endoplasmic part) and vice-versa. There are different theories on the formation of pseudopodium. The sol-gel transformation theory is the most accepted theory. Pseudopodial movement is performed by Amoeba, Polystomella, Actionophrys.

Question 8.
Give an account of the ultra structure of an axoneme.
Answer:
The structural components of a typical flagellum include axoneme, microtubules, dynein arms, inner sheath, outer sheath, radial spokes, lateral appendages (such as mastigonemes or flimmers) and a basal granule (kinetosome).
i) Axoneme / axial filament :
It is the central, longitudinal, microtubular structure of cilium and flagellum. It is surrounded by a membrane which is continuous with plasma membrane. All the components of the axoneme are embedded within the matrix.

ii) Microtubules :
An axoneme is made up of 2 central ‘singlets’ and 9 peripheral ‘doublets (9+2 array)’. These are formed by the protein, tubulin. Each peripheral doublet consists of an outer ‘A’ (alpha) and the inner ‘B’ (beta) tubules, so, the peripheral tubules are actually 9 microtubular doublets. (The microtubule ‘A’ is smaller but complete whereas ‘B’ is larger and incomplete). The peripheral doublets are interconnected by linkers called nexins.

iii) Dynein arms :
The ‘A’ tubule of each peripheral doublet bears paired arms along its length, called dynein arms (Dyne – pulling like a dynamo). The dynein arms of ‘A’ tubule face the tubule ‘B’ of the adjacent doublet. They are oriented in the same direction (clockwise) in all microtubules, when the axoneme is viewed from the base to the top. The dynein arms are considered ‘protein motor molecules’. They are made of the protein, dynein.

iv) Inner and outer sheaths :
The two central singlets are enclosed by a fibrous inner sheath and the peripheral doublets are enclosed by an outer sheath (an extension of plasma membrane). The central singlets do not reach below the level of the pellicle or plasmalemma.

v) Radial spokes :
They are elastic fibres that connect the inner sheath, with the ‘A’ tubule of each doublet. They resemble the spokes that connect the rim of a bicycle wheel with the centre, hence the name ‘radial spokes / radial bridges’. The nine radial spokes limit the extent of sliding past of the doublets, during bending movements.

Question 9.
Draw a neat labelled diagram of Euglena.
Answer:

Question 10.
Draw a neat diagram of Paramecium and label its important structures/components.
Answer: