(a) Explain the post-pollination events leading to seed production in angiosperms.
(b) List the different types of pollination depending upon the source of pollen grains.

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

i. When the pollen grains fall on the stigma, the pollen tube enters one of the synergids and releases two male gametes.

ii. One of the male gametes moves towards the egg cell and fuses with it to form zygote.

iii. The other male gamete fuses with the two polar nuclei and forms the primary endosperm nucleus. This is termed as triple fusion.

iv. After the triple fusion, the central cell becomes the primary endosperm cell (PEC). The primary endosperm nucleus gives rise to endosperm, while the zygote develops into an embryo.

v. Seeds are the fertilised ovules that are developed inside a fruit.

vi. The integuments of ovules harden to form the seed coat, and the micropyle facilitates the entry of oxygen and water into the seed.


b) Depending on the source of pollen grains, pollination can be divided as follows:

i. Autogamy - When the pollen grains are transferred from anther to stigma of the same flower. Autogamy requires the anther and the stigma to in lie close proximity and also requires synchrony between the pollen release and the stigma receptivity. For example - plants like Viola and Oxalis produce two kinds of flowers: Chasmogamous flowers (with exposed anther and stigma) and cleistogamous flowers (plants that do not open at all and in which only autogamy occurs).

Geitonogamy - It is the transfer of pollen grains from the anther of one flower to the stigma of another flower on the same plant. Genetically, it is similar to autogamy, but it requires pollinating agents like winds, water or insects.

Xenogamy - It is the transfer of pollen grains from the anther to the stigma of a different plant.