42.

(a) Name the parts labelled as A, B, C and D in the diagram given below:



(b) What is pollination? State its significance.

(c) How does fertilisation occur in flowers? Name the parts of the flower that develop into (i) seed, and (ii) fruit after fertilisation.

(a)
A - Pollen grain
B - Pollen tube
C - Ovary
D - Female germ cell

(b) Pollination is the process of transfer of pollen grains from anther to stigma of the flower.

Significance of pollination: Pollination is a significant event because it precedes fertilization. It brings the two types of gametes closer for the process of fertilization.
Pollination like cross pollination introduces variations in the plants due to mixing of
different genes which increases adaptability towards environment .

(c) Fertilisation in plants: In plants, pollination is followed by fertilisation. Once
the pollen grains are deposited on the stigma, they form pollen tubes. The pollen tubes grow through the ovules and reach the ovary where ovules are located. The pollen tube normally enters the ovule through a small opening called micropyle. Inside the ovule, the pollen tube releases two male gametes into the embryo sac.

The embryo sac of the ovule contains the egg. One male gamete fuses with the
egg. This fusion of male and female gamete is called syngamy and its product is
called zygote. The other male gamete fuse with two polar bodies and this
process is called triple fusion, where three nuclei are involved in the fusion
process, one male gamete and two polar nuclei. Thus, inside each embryo sac,
two fusions, syngamy and triple fusion, takes place. This mechanism of two
fusions occurring in an embryo sac is called double-fertilization.

After fertilization,
i. ovules develop into the seeds and
ii. ovary develops into the fruit.