Here students can locate TS Inter 1st Year Botany Notes 7th Lesson Sexual Reproduction in Flowering Plants to prepare for their exam.
TS Inter 1st Year Botany Notes 7th Lesson Sexual Reproduction in Flowering Plants
→ The branch which deals with the study of flowers is called Floriculture.
→ The two most important units of sexual reproduction in a flower are Androecium and Gynoecium.
→ Embryology is the study of formation of gametes, fertilization and embryo development.
→ Each stamen has two parts filament and anther.
→ Each dithecous anther has four microsporangia whereas monothecous anther has two microsporangia.
→ Each microsporangium is generally surrounded by four wall layers – epidermis, endothecium, middle layers and tapetum.
→ The sporogenous cells of microsporangium produce microspore mother cells.
→ These cells produce tetrads of haploid microspores or pollen grains by meiosis.
→ Microspore or pollen grain represents male gametophyte.
→ Pollen grain contains two cells
- Vegetative cell
- Generative cell.
→ Ovules are present in the ovary of gynoecium. Ovule is the megasporangium.
→ Ovule has integuments, nucellus, chalaza, stalk or funiculus and microphyle.
→ Orthotropous ovule – Micropyle, funiculus and chalaza are in the a straight line,
→ Anatropous ovule – Ovule inverted. Funiculus and micropyle lie side by side.
→ Campylotropous ovule – Body of the ovule is at right angles to the funicules.
→ One cell of the nucellus develops into megaspore mother cell.
→ Development of megaspore from megaspore mother cell is called megasporogenesis.
→ Megaspore mother cell produces 4 haploid megaspores by meiosis. Upper degenerate and lower one develops into embryo sac.
→ Embryosac represents female gametophyte. It is 7 celled and 8 nucleated.
→ The process of transfer of pollen grain from anther to stigma is called pollination, It is of two types.
(a) Self pollination : Pollen grains transferred to stigma of same flower,
(b) Cross pollination : Pollination between 2 flowers – 2 kinds.
- Geitonogamy : Cross pollination between 2 flowers of same plant.
- Xenogamy: Cross pollination between 2 flowers of different plants of same species.
→ Contrivances of cross pollination
(a) Dichogamy – Androecium and gynoecium of a bisexual flower mature at different timings.
(b) Herkogamy – Male and female parts of a bisexual flower arranged at different levels.
(c) Heterostyly – Presence of styles in different lengths in the flower of the same species.
(d) Self sterile – Pollen fail to germinate on the stigma of the same flower.
(e) Decliny – Flowers unisexual.
→ External agents that help in pollination i.e. transfer of pollen to the stigma are called ‘agents’.
→ Water and wind are abiotic agents.
→ Pollination that occurs through wind is called anaemophily. Eg : Rice.
→ Pollination that occurs in hydrophytes with the help of water is called Hydrophily. – They are Epihydrophily & Hypohydrophily.
→ Pollination favoured by animals is called zoophily. Based on animals they are – Ornithophiiy, Chiropterophily, Entamophily, Malacophily.
→ The fusion of male and female gamete is called fertilisation.
→ Entry of pollen tube into the ovule is 3 types – They are
- porogamy,
- chalazogamy and
- mesogamy.
→ Pollen tube reaches the embryosac only through micropylar end by destroying one of the synergids.
→ Pollen tube releases two male gametes.
(a) One male gamete (x) + egg (x) → Zygote (2x) – Syngamy.
(b) Second male gamete (x) + secondary nucleus (2x) → Primary endosperms jj nucleus (PEN) (3x) – Triple fusion.
→ As two fusion processes are occuring in angiousperms it is called – Double fertilisation.
→ All the floral parts except ovary wither and fail off.
→ Ovary forms fruit. Ovule forms seeds. Zygote develops into embryo. Integuments becomes seed coats.
→ Primary endosperm nucleus develops into nutritive tissue – Endosperm.
→ In some seeds some amount of nucellus is left out, it is called perisperm.
→ Many fruits have evolved mechanisms for seed dispersal.
→ Seeds without fertilisation is called Apomixis.
→ Fruits without fertilisation is called parthenocarpy.
→ Occurrence of more than one embryo in a seed is referred on polyembryony.