Question

(a) What is meant by 'unisexual flowers' and 'bisexual flowers'? Give two examples of each.
(b) What is pollination? How does pollination occur?
(c) Describe the process of fertilisation in a flower with the help of labelled diagrams.
(d) What changes take place in the flower after fertilisation which lead to the formation of seeds and fruit?

Answer 1

(a) Unisexual flowers have only one kind of sex organ, either stamen or pistil, e.g., flowers of papaya and water melon. Bisexual flowers have both stamen and pistil, e.g., flowers of Hibiscus and mustard.

(b) Pollination is the transfer of pollen grains from the stamen to the stigma of the pistil. Pollination occurs when pollen grains are carried from the anther to the stigma by insects, birds, wind or water.

(c) Fertilisation occurs after pollen grains fall on the stigma. Upon falling on the stigma, the pollen grains burst and grow a pollen tube taht passes downwards from the style to the ovary containing the ovule. The male gamete present in the pollen moves downward through the pollen tube and reaches the ovule. This gamete fuses with the egg to form a zygote. This process is known as fertilisation.



(d) After fertilisation, the eggs in the ovule grow and develop into seeds. The ovule develops a thick coating and forms the seed, whereas the ovary develops into a fruit that contains the seed.