Biology
Given alongside is a diagrammatic sketch of the sectional view of a germinating pollen grain. Study the same and then answer the questions that follow:
(a) Name the parts labelled 1, 2, 3, 4 and 5.
(b) Where does the germination of the pollen grain take place and how?
(c) What is the function of the part labelled '4'?
(d) What happens to the part labelled '5' during the process?
Pollination
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Answer
(a) The parts labelled 1, 2, 3, 4 and 5 are:
- 1 → Exine
- 2 → Intine
- 3 → Pollen tube
- 4 → Tube nucleus
- 5 → Generative nucleus
(b) Germination of the pollen grain takes place only after it falls on the stigma of the same plant species. The pollen grain is stimulated to germinate due to the secretion of sugars by the stigma.
(c) The function of part '4' (tube nucleus) is to direct the growth of the pollen tube towards the ovary.
(d) During germination of the pollen grain, part '5' (generative nucleus) present at the tip of the pollen tube divides into two sperm nuclei. The pollen tube enters one of the synergids and releases its two sperm nuclei. Of these, one sperm nucleus enters the egg cell and fuses with its nucleus, while the other sperm nucleus moves towards the two polar nuclei in the central cell and fuses with them.
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