BIOLOGY CLASS: VIII TOPIC: Life Processes: Growth, Reproduction & Development (plants) Difference between self-pollination & cross pollination

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Bridget Merritt
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BIOLOGY CLASS: VIII TOPIC: Life Processes: Growth, Reproduction & Development (plants) Difference between self-pollination & cross pollination Self -Pollination 1.

No new varieties are formed. Cross-pollination 1. It is transfer of pollen grains from anther of one flower to the stigma of another flower. 2. External agents (wind, insects, water) are required 3.

1 BIOLOGY CLASS: VIII TOPIC: Life Processes: Growth, Reproduction & Development (plants) Difference between self-pollination & cross pollination Self -Pollination 1. It is transfer of pollen grains from anther to the stigma of same flower or same plant. 2. No external agents are required 3. Male & female parts mature at the same time. 4. No new varieties are formed. Cross-pollination 1. It is transfer of pollen grains from anther of one flower to the stigma of another flower. 2. External agents (wind, insects, water) are required 3. Anthers and stigma mature at different time. 4. New varieties are formed. Fertilization Fertilization is the union of male and female gamete to form a zygote. In flowering plants: The pollen grain carries the male gamete. Hence the androecium is called the male part of the flower. The ovule inside the ovary contains the female gamete. Hence the gynoecium is called the female part of the flower. ( 1 )

2 A:POLLEN GRAINS GERMINATING ON STIGMA. ONE POLLEN TUBE HAS ENTERED THE OVULE. B: A MATURE POLLEN GRAIN C: POLLEN GRAIN BEGINNING TO GERMINATE ( 2 )

D. D:GERMINATED POLLEN GRAIN E: OVULE SHOWING THE EMBRYO SAC IN ITAND THE EVENTS OCCURING THERE Structure of the pollen grain: - The mature pollen grain is a cell with a double wall--- outer exine

3 D. D:GERMINATED POLLEN GRAIN E: OVULE SHOWING THE EMBRYO SAC IN ITAND THE EVENTS OCCURING THERE Structure of the pollen grain: - The mature pollen grain is a cell with a double wall--- outer exine and the inner intine - It has two nuclei. A tube nucleus and a generative nucleus. - Further changes in pollen grain occur only if it has fallen on the stigma of a flower of the same species Structure of the ovule: - Ovule is found in the inner part of the ovary. - Ovule is destined to become a seed and the ovary becomes the fruit. - Single ovule produces single seeded fruit and many ovules produce a many seeded fruit - Each ovule has one or two protective coverings the integuments - A minute opening or pore through which the pollen tube enters is called the micropyle. - The nutritive tissue lining the inside of the ovule is the nucellus ( a mass of food laden cells) - In the centre of the nucellus is the embryo sac. - The embryo sac contains seven cells(3+3+1) o 3 cells towards the micropyle. ( 1 egg cell and 2 synergids) o 3 cells at the opposite end are called antipodal cells o 1 large central cell called the secondary nucleus. It is formed by the fusion of two nuclei called the polar nuclei. ( 3 )

4 Germination of pollen grain: - Pollen grain germinates only if it has fallen on the stigma of the same plant species, otherwise it gets decomposed - Stigma of the flower provides a solution of sugars to feed the pollen cell. - A pollen tube grows out of the pollen grain by breaking through its exine. - The generative nucleus divides into two male nuclei (male gamete nuclei or sperm nuclei) - Thus there are three nuclei which share a common cytoplasm- they are the 2 male nuclei and the tube nucleus. - The pollen tube grows through the stigma and style and reaches the ovary by dissolving the tissues with the help of the enzymes. - In the ovary the pollen tube pushes through the micropyle and reaches the embryo sac - The tube nucleus which had directed the growth of pollen tube all the way down, now disintegrates - The pollen tube releases its two sperm nuclei - Of the two sperm nucleus, one sperm nucleus enters the egg cell and fuses with its nucleus. - While the other sperm nucleus moves towards the secondary nucleus and fuses with it to form the endosperm nucleus. (Thus 3 nuclei together produce endosperm nucleus. This is called triple fusion.) Double Fertilization: - One of male nuclei unites with the egg cell forming the fertilized egg or zygote. - The other male cell combines with the secondary nucleus to form endosperm nucleus. - Since there are two sets of fertilization taking place, it is called Double Fertilization. Fate of floral parts & parts of the ovary after fertilization: Part Ovary Ovule Outer integument Inner integument Secondary nucleus Egg cell Petals, Stamen, Style & Stigma Calyx Fruit Seed Testa Tegmen Endosperm Embryo Wither & fall off What it becomes May fall off or remain intact in dried or shrivelled form as in chillies and capsicum. ( 4 )

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Sexual Reproduction in Flowering Plants

Sexual Reproduction in Flowering Plants Question 1: Name the parts of an angiosperm flower in which development of male and female gametophyte take place. Answer :- The male gametophyte or the pollen grain