Question

Describe the stages of embrayosac formation in angiosperm with suitable diagram.

Answer 1

Solution :

The functional megaspore grows in size.

The functional megaspore grows in size.

Each nucleus at the poles undergoes two mitotic divisions to form four nuclei in each pole or a total of 8 nuclei.

Two nuclei from each pole move to the centre to form the polar nuclei. The other nuclei, three at each pole get surrounded by bit of cytoplasm to form cells.

The female gametophyte or the embryo sac thus has 7 cells and eight nuclei.



or

Depending on the source of pollen, pollination can be of three types namely:

a. Autogamy

b. Geitonogamy

c. Xenogamy

Autogamy: Transfer of pollen grains from the anther to the stigma of the same flower. In autogamous flower, pollen release and stigma receptivity should be simultaneous. Autogamy is seen in both cleistogamous flowers and chasmogamous flowers. Cleistogamous flowers never open and hence autogamy or self pollination is the only option. Chasmogamous flowers can undergo both autogamy and xenogamy. (Self pollination or cross pollination)

Geitonogamy: Transfer of pollen grains from the anther to the stigma of another flower of the same plant. Though it is functionally a cross pollination involving a pollinating agent, genetically it is similar to autogamy since pollen grains come from the same plant.

Xenogamy: Transfer of pollen grains from the anther to the stigma of another flower of a different plant. This brings different kinds of pollen grains to stigma.