TS Inter 1st Year Botany Study Material Chapter 11 Cell Cycle And Cell Division

Telangana TSBIE TS Inter 1st Year Botany Study Material 11th Lesson Cell Cycle And Cell Division Textbook Questions and Answers.

TS Inter 1st Year Botany Study Material 11th Lesson Cell Cycle And Cell Division

Very Short Answer Type Questions

Question 1.
Between a prokaryote and a eukaryote, which cell has a shorter cell division time?
Answer:

1. Prokaryotic cell, has a shorter cell division time due to shorter cell cycle.
2. For instance, bacterial cell cycle is 20 minutes as compared to 90 minutes of cell cycle in yeast.

Question 2.
Among prokaryotes and eukaryotes, which one has a shorter duration of cell cycle?
Answer:

1. Prokaryotes
2. Bacteria (prokaryote) cell cycle is 20 minutes and in human cells (Eukaryote) it is 24 hours.

Question 3.
Which of the phases of cell cycle is of longest duration?
Answer:

1. Interphase
2. In human cell cycle of 24 hours interphase lasts for 23 hours (about 95% of total duration).

Question 4.
Which tissue of animals and plants exhibits meiosis?
Answer:

1. Reproductive tissue – Gamete mother cells.
2. Diploid cells undergo meiosis to produce haploid sex cells.

Question 5.
Given that the average duplication time of E.coli is 20 minutes. How much time will two E.coli cells take to become 32 cells?
Answer:

1. 80 minutes.
2. It takes 4 cell divisions to form 32 cells from initial 2 cells.

Question 6.
Which part of the human body should one use to demonstrate stages in mitosis?
Answer:

1. The cells of the upper layer of epidermis, cells of the lining of the gut and blood cells (bone marrow).
2. The above cells of human body are being constantly replaced.

Question 7.
What attributes does a chromatid require to be classifed as a chromosome?
Answer:
Two chromatids attached at the centromere.

Question 8.
Which of the four chromatids of a bivalent at prophase -1 of meiosis can involve in cross over? [March – 2019]
Answer:

1. Non sister chromatids of the homologous chromosomes (a bivalent).
2. Crossing over occurs of pachytene stage of Prophase -1 in Meiosis.

Question 9.
If a tissue has at a given time 1024 cells, how many cycles of mitosis had the original parental single cell undergone? [Mar. ’20, May & mar. ’14]
Answer:

1. 10 cycles of mitosis.
2. Mitosis is equatorial cell division and doubling of cell number occur per each cell division.

Question 10.
An anther has 1200 pollen grains. How many pollen mother cells must have been there to produce them? [May ’17, Mar. ’17 A.P & T.S ; Mar. ’15 – A.P ; Mar. ’13]
Answer:

1. 300 pollen mother cells.
2. Due to meiosis each PMC produces 4 pollen grains.

Question 11.
At what stage of cell cycle does DNA synthesis occur? [Mar. – 2018]
Answer:

1. S or Synthetic phase of Interphase.
2. During S phase 2C DNA increases to 4C DNA.

Question 12.
It is said that one cycle of cell division in human cells (eukaryotic cells) take 24 hours. Which phase of the cycle, do you think occupies the maximum part of cell cycle?
Answer:

1. Interphase occupies the maximum time i.e., 23 hours.
2. It is about 95% of the total duration of cell cycle is human cells.

Question 13.
It is observed that heart cells do not exhibit cell division. Such cells do not divide further and exit phase to enter an inactive stage called of cell cycle. Fill in the blanks.
Answer:

1. G phase
2. Quiescent stage (G_o)

Question 14.
Identify the substages of prophase – I in Meiosis in which synapsis and desynapsis are formed.
Answer:

1. Synapsis (pairing of homologous chromosomes) occur in zygotene substage of prophase -1 in meiosis.
2. Desynapsis (separation of homologous chromosomes) occur in Diplotene substage of prophase -1 in meiosis.

Question 15.
Name the stage of meiosis in which actual reduction in chromosome number occurs. [Mar. ’15 – T.S]
Answer:

1. Anaphase – I in Meiosis I
2. During this stage homologous chromosome migrate to opposite poles.

Question 16.
Mitochondria and plastids have their own DNA (genetic material). What is their fate during nuclear division like mitosis?
Answer:

1. Mitochondria and plastids have no role during the nuclear division of mitosis.
2. At the time of cytoplasmic division, mitochondria and plastids get distributed between the two daughter cells.

Question 17.
A cell has 32 chromosomes. It undergoes mitotic division. What will be the chromosome number during metaphase? What would be the DNA content (C) during anaphase?
Answer:

1. The chromosome number in the cell at metaphase of mitosis is 32 only. But each chromosome consists of 2 sister chromatids.
2. In anaphase, two sister (daughter) chromatids of a chromosome are separated and move to opposite poles. Each of the separated chromatid consists of 2C DNA.

Question 18.
While examining the mitotic stage in a tissue, one finds some cells with 16 chromosomes and some with 32 chromosomes. What possible reasons could you give to this difference in chromosome number? Do you think cells with 16 chromosomes could have arisen from cells with 32 chromosomes or vice versa?
Answer:

1. In mitosis cells at prophase and metaphase consists of basic sets of chromosomes, i.e., in this case 2m = 16.
2. But at anaphase splitting of two sister (daughter) chromatids of a chromosome leads to doubling of number i.e., 32 that distribute equally (16 each) among two daughter cells formed from a mother cell.

Question 19.
The following events occurs during the various phases of the cell cycle. Fill the blanks with suitable answer against each.
a) Disintigration of nuclear membrane ………………
b) Appearance of nucleolus ………………
c) Division of centromere ………………
d) Replication of DNA ………………
Answer:
a) Prophase
b) Telophase and Interphase.
c) Anaphase
d) S (Synthesis) phase in Interphase.

Question 20.
Two key events take place during s-phase in animal cells – DNA replication and duplication of centriole. In which parts of the cell do thesfe events occur?
Answer:

1. DNA replication occurs in chromosomes present in nucleus during s-phase of Interphase.
2. Centriole duplication occurs in the cytoplasm.

Question 21.
Name a cell that is found arrested in diplotene stage for monthly and years. Comment in two or three sentences, how it completes cell cycle.
Answer:

1. Oocytes of some vertebrates, diplotene can last for months ‘or years.
2. Terminalization of chiasmata occurs in diakinesis and homologous chromosomes separated. Subsequently cell enters into other stages of Meiosis I for reduction of chromosome number.
3. Meiosis II results in formation of 4 daughter cells each with haploid chromosomes set.

Short Answer Questions

Question 1.
In which phase of meiosis are the following formed? Choose the answers from hint points given below.
a) Synaptonemal complex ………………
b) Recombination nodules ………………
c) Appearance / activation of ……………… Enzyme recombinase
d) Termination of chiasmata ………………
e) Interkinesis ………………
f) Formation, of dyad of cells ………………
Hints :
1) Zygotene, 2) Pachytene, 3) Pachytene, 4) Diakinesis, 5) After Telophase – I / Before Meiosis – II, 6) Telophase – I / After Meiosis – I
Answer:
a) Synaptonemal complex Zygotene
b) Recombination nodules Pachytene
c) Appearance / activation of Pachytene Enzyme recombinase
d) Termination of chiasmata Diakinesis
e) Interkinesis After Telophase – I / Before Meiosis – II
f) Formation of dyad of cells Telophase – I / After Meiosis – I

Question 2.
Mitosis results in producing two cells which are similar to each other. What would be the consequence if each of the following irregularities occurs during mitosis?
a) Nuclear membrane fails to disintegrate.
b) Duplication of DNA does not occur.
c) Centromeres do not divide.
d) Cytokinesis does not occur.
Answer:
a) If nuclear membrane fails to disintegrate chromosome cannot spread through the cytoplasm of the cell. Metaphase cannot take place.

b) If Duplication of DNA does not occur equal number of chromosomes cannot enter into daughter cells, results in variable number of chromosomes.

c) If centromeres do not divide chromatid cannot move to opposite poles, then daughter cells have same chromosome number with two chromatids.

d) If cytokinesis does not occur then after cell division each cell contains two nucleus. Resulting multinucleate condition.

Question 3.
Comment on the statement “Meiosis enables the conservation of specific chromosome number of each species even though the process per second, results in reduction of chromosome number.
Answer:

1. Meiosis is the mechanism, by which chromosome number is reduced to half in sexually reproducing organisms.
2. Meiosis produces 4 haploid daughter cells (sex cells or gametes) from a diploid mother cell.
3. Fertilization or union of sex cells again gives rise to diploid (2n) organism.
4. So, Meiosis is the mechanism, by which conservation of specific chromosome number of each species is achieved across generations.
5. It also increases the genetic variability in the population of organisms from one generation to the next, that leads to the evolution.

Question 4.
How does cytokinesis in plant cells differ from that in animal cells?
Answer:

1. Cytokinesis refers to division of a mother cell into 2 daughter cells. This occurs after the Karyokinesis, the division of a mother nucleus into 2 daughter nuclei.
2. In an animal cell, cytokinesis is achieved by the appearance of a furrow in the plasma membrane. The furrow gradually deepens and ultimately joins in the center, dividing the cell cytoplasm into two.
3. Plant cells are enclosed by a relatively in extensible (rigid) cell wall. So in those cells, wall formation starts in the centre of the cell and grows outward to meet the existing lateral walls.

Question 5.
Which division is necessary to maintain constant chromosome number in all body cells of multicellular organism and why? [May. ’14]
Answer:

1. Cell division Meiosis is necessary to maintain constant chromosome number in all body cells of multicellular organisms.
2. The reason is mitosis divide and forms two daughter cells which are similar to parent cell.
3. The chromosome number remains constant in all the cells.
4. Growth occurs due to mitosis.
5. Mitosis also helps in cell repair and growth.

Question 6.
Though redundantly described as a resting phase, interphase does not really involve rest. Comment. [Mar. ’20, ’19, ’18, ’17, ’15, ’13; May ’17]
Answer:

1. In cell cycle, the stage at which the nucleus is not in a state of division is called interphase. It occurs between two successive divisions.
2. During interphase, cell prepares for division by undergoing growth as well as DNA replication in an orderly manner, though considered as resting phase.
3. On the basis of biochemical studies, interphase is subdivided into 3 stages : G₁ phase, S phase and G₂ phase.

G₁ phase :
Cell increases in size. RNA and proteins are synthesised in large quantity.

S phase :
DNA replication occurs and its content increases to 4c from 2c.

G₂ phase :
Synthesis of proteins and RNA is continued. Various cell organelles are newly synthesised. The proteins and energy pools associated with the structure and movement of chromosomes are established.

Long Answer Type Questions

Question 1.
Discuss on the statement – Telophase is reverse of prophase.
Answer:

• The changes occurring in telophase are almost reverse to those which take place in prophase.
• The daughter chromosomes reach opposite poles.
• These daughter chromosomes lengthen and their visibility decreases due to decondensation of chromatin.
• The kinetochore fibres disappear.
• The nuclear membrane reappears.
• Nucleolus, golgi complex and ER reform.
• Thus at the end of telophase, two independent daughter nuclei are organised in the same mother cell.

Question 2.
What are the various stages of meiotic prophase – I? Enumerate the chromosomal events during each stage?
Answer:
Meiotic prophase I is longer and more complex when compared to prophase of mitosis. Prophase I is divided into 5 substages. They are –

1. Leptotene
2. Zygotene
3. Pachytene
4. Diplotene
5. Diakinesis.

1) Leptotene :
Nucleus enlarge in size. Chromosomes are visible. They are long and slender.

2) Zygotene :

1. Homologous chromosomes attract each other and form pairs. These are called bivalents.
2. The process of pairing is called synapsis.
3. Electron micrographs of this stage indicate that chromosome synapsis is accompanied by the formation of complex structure called synaptonemal complex

3) Pachytene :
It is most significant substage of Meiosis I.

1. Each chromosome divides into two chromatids. Thus in each bivalent, 4 chromatids can be seen. These are called pachytene tetrads.
2. In a bivalent, chromatids of the same chromosome are called sister chromatids and those of two different chromosomes are called non-sister chromatids.
3. Pachytene stage is characterised by the appearance of recombination nodules, the sites at which crossing over occurs between non-sister chromatids.
4. The non-sister chromatids exchange their parts mutually at one or two or more places. Such points where the non-sister chromatids physically contact each other are called chiasmata. Chiasmata appear as X – shaped structures.
5. Crossing over is also an enzyme mediated process and the enzyme involved is called recombinase.
6. By the end of pachytene, recombination between homlogous chromosomes is completed leaving the chromosome linked at the side of crossing one.

4) Diplotene :
The beginning of diplotene in recognised by the dissolution of the synaptonemal complex and the tendency of the homologous chromosomes of the bivalent separate from each other except at the site of chaismata.

5) Diakinesis:

1. Chaismata move towards the ends of chromosomes. This is called terminalisation.
2. Bivalents become very thick and short.
3. Nucleolus begins to disappear.
4. Nuclear membrane disappears.
5. Chromosomes are released into cytoplasm.

Question 3.
Differentiate between the events of mitosis and meiosis.
Answer:

Mitosis	Meiosis
1. In mitosis, chromosome doubling is followed by separation of daughter chromosomes. The cell divides only once.	1. in meiosis, there is doubling of chromosomes once but it is followed by two nuclear divisions. The cell divides twice.
2. In mitosis, nucleui divides first called Karyokinesis followed by division of cytoplasm called cytokinesis. It is completed in one sequence of stages. It is divided into following stages.	2. In meiosis it is divided into two major stages. They are Meiosis 1 and Meiosis II. Meiosis 1 has karyokinesis 1 followed by cytokinesis. Meiosis II has karyokinesis II followed by cytokinesis. It is divided into following stages.
Prophase: 3. Prophase of mitosis is of short duration and is without sub-stages.	3. Prophase 1 is of longer duration and completed in five substages : Leptotene, zygotene, pachytene, diplotene and diakinesis.
4. The homologous chromosome do not pair with each i.e., synapsis is absent.	4. In meiosis i, the homologous chromosomes which are in single state form pairs.
5. Duplication of chromosomes takes place in early prophase.	5. Duplication of chromosomes takes place in pachytene substage of Meiosis l.
6. Generally no chiasmata formation takes place. No crossing over takes place.	6. Chiasmata formation due to crossing over takes place in meiosis.
Metaphase: 7. Chromosome appears two stranded.	7. Chromosome appears in tetrad stage.
8. The centromere of each chromosome divides into two and thus the two chromatids of the chromosome become free from each other.	8. Centromere of the homologous chromosomes divides, thus their chromatids do not become free in Metaphase I.
Anaphase: 9. The two chromatids of each chromosome move towards the opposite poles of the spindle.	9. In meiosis, the two homologous chromosomes of each pair separate and move towards opposite poles of spindie during anaphase stage.
10. The chromosomes are long and thin.	10. The chromosomes are short and thick.

Question 4.
Write brief note on the following :
a) Synaptonemal complex
b) Metaphase plate
Answer:
a) Synaptonemal complex :
During the heptotene of prophase I, chromosome start pairing together and this process of association is called synapsis,

1. Such paired chromosomes are called homologous chromosome.
2. Electron micrographs of this stage indicate that chromosome synapsis is accompanied by the formation of complex structure called synoptonemal complex.
3. The complex formed by a pair of homologous synapsed homologous chromosomes is called a bivalent or a tetrad of chromatids.

b) Metaphase plate :
In Metaphase two important changes take place.

1. Formation of bipolar spindle fibres and attach the same to the kinetochores of chromosomes,
2. All the chromosomes lie at the equator.
3. The plane of alignment of the chromosomes at metaphase is referred to as the metaphase plate or equatorial plate.

Question 5.
Write briefly the significance of mitosis and meiosis in multicellular organism.
Answer:
Significance of mitosis :

1. Growth in organism is caused by mitosis and it restores the surface or volume ratio of the cell.
2. The daughter ceils formed by mitosis are identical with the mother cell. Hence it is important in conserving the genetic integrity of the organism.
3. In unicellular organisms, mitosis helps in reproduction.
4. Mitosis helps in wound healing and regeneration of lost plant parts.
5. Mitosis helps for grafting in vegetative reproduction.
6. It maintains a constant number of chromosomes in all the cells of the body.

Significance of meiosis:

1. It helps in the maintenance of a constant chromosome number from one generation to the next.
2. Due to crossing over, genetic recombinations are caused which help in genetic variation and origin of new species and leads to evolution.

Intext Question Answers

Question 1.
Name a stain commonly used to colour chromosome.
Answer:
Acetocarmine

Question 2.
Name the pathological condition when uncontrolled cell division occurs.
Answer:
Cancer

Question 3.
An organism has two pairs of chromosomes (i.e., chromosome number = 4). Diagrammatically represent the chromosomal arrangement during different phases of meiosis – II.
Answer:

Question 4.
Meiosis has events that lead to both gene recombinations as well as Mendelian recombinations. Discuss.
Answer:
Both chiasmata and crossing over occur between non-sister chromatids. Due to crossing over, genetic recombinations are caused. During Anaphase – I of meiosis – I Mendelian recombination takes place.

Question 5.
Both unicellular and multicellular organisms undergo mitosis. What are the differences, if any, observed between the two processes?
Answer:
In unicellular organisms, a cell divides into two halves by binary fission. Stages like Prophase, Metaphase, Anaphase, and Telophase are present in multicellular organisms. It’s not present in unicellular organisms.