Question

3.a) Discuss the stages in the development of the embryo in the Capsella plant

3.b) Describe the development of a microspore mother cell into a pollen grain.

3.c)Define pollination as it takes place in the Angiosperms.

Answer 1

Ans:

3. a) The embryo development of Capsella sp. is crucifer type where the basal cell doesn't play any or minor role in the embryo development. At first, the oospore transversely divided into large basal cell which is again transversely divided into two cell and a small terminal cell that is also divided longitudinally to form two cells. This four cell stage is called proembryo.

The two basal cells undergo repeated transverse division to form 5-10 cell suspensor. The lower most basal cells becomes swollen to form haustorial cell and the upper most cell of suspensor is called hypophysis.

The two terminal cells further longitudinally divided at right angle of first longitudinal division to form quadrant and this quadrant again transversely divided to form octant. This octant periclinally divided to form outer and inner layer.

1. The terminal four cells of the octant form plumule and two cotyledons.

2.The basal four cells of the octant forms hypocotyl and the core of the radicle.

3. The hypophysis further differentiated into cortex and epidermis of radicle and root cap.

Further development by cell division gives horse shoe-shaped hypocotyl and cotyledon and further development of embryo in the lower portion of octant give rise a cordate structure.

3. b) Microspore or pollen grain is the unicellular, haploid and spherical structure that develops from microspore mother cell in the following ways-

1. The sporogenous tissues formed from archesporial cells, either directly function as spore mother cells or mitotically divided into a number of cells that function as spore mother cells.

2. This spore mother cell undergo meotic division to forms four haploid microspore or pollen grains mostly arranged tetrahedrally. This is also called microspore tetrad.

3.c) Pollination: The transfer of pollen grains from an anther to the stigma of a pistol of same or different flower is called pollination. In angiosperms, the pollination is of two types which are as follows-

1. Self-pollination: when pollen grains are transferred to the stigma of same flower. e.g. Commelina benghalensis of Commelinaceae.

2. Cross-pollination: when pollen grains are transferred to the stigma of another flower of different plant of same or different species. e.g. Michelia champaca of Magnoliaceae.