Define the terms pollination and fertilisation. Draw a diagram of a pistil showing pollen tube growth into the ovule and label the following : pollen grain, male gamete, female gamete, ovary.

Or

Describe in brief the role of (i) testis (ii) seminal vesicle, (iii) vas deferens, (iv) ureter and (v) prostate gland in human male reproductive system.

Pollination: The transfer of pollen grains from the anther (of the stamen) to the stigma (of the pistil) of a flower is called pollination. It is of two types:

• Self-pollination — when pollen is transferred from the anther to the stigma of the same flower (or another flower of the same plant).
• Cross-pollination — when pollen is transferred from the anther of one flower to the stigma of a different flower of the same species. Agents like wind, water, insects (e.g., bees), birds and bats help in cross-pollination.

Fertilisation: The fusion of the male gamete (present inside the pollen grain) with the female gamete (present inside the ovule in the ovary) is called fertilisation. After the pollen grain lands on a suitable stigma, a pollen tube grows out of it, passes through the style and reaches the ovary. The male gamete travels through this pollen tube and fuses with the female gamete in the ovule to form a zygote, which then develops into an embryo.

Diagram of a pistil showing pollen tube growth into the ovule:

Labelled parts of the diagram:

1. Pollen grain — present on the stigma; it contains the male gamete.
2. Male gamete — travels through the pollen tube to reach the ovule.
3. Female gamete — present inside the ovule; fuses with the male gamete to form the zygote.
4. Ovary — the swollen basal part of the pistil that contains ovules; it later develops into the fruit after fertilisation.