Question Bank [2022] — BIOLOGY STD 12 Science — Question

i. Nuclear Type:

1. It is the most common type of endosperm found in 161 angiospermic families.
2. In this, the primary endosperm nucleus repeatedly divides mitotically without wall formation. Due to which the a large number of free nuclei are formed.
3. A big central vacuole appears in the centre of the cell which pushes the nuclei towards the periphery.
4. Later, wall formation occurs between the nuclei, hence multicellular endosperm is formed.
5. But in several cases, cell wall formation remains incomplete. e.g. wheat, sunflower, and coconut.
6. Coconut has multicellular endosperm in the outer part and free nuclear as well as vacuolated endosperm in the centre.

ii. Cellular Type:

1. In some plants, a division of the triploid primary endospermic nucleus is immediately followed by wall formation.
2. So that the endosperm is cellular right from the beginning.
3. It is mostly observed in 72 families of dicots as in members - Balsam, Petunia, Adoxa, etc.

iii. Helobial Type:

1. It occurs in the order Helobiales of monocotyledons.
2. In this case, the first division of the primary endosperm nucleus is followed by a transverse wall, which divides the cell unequally.
3. The smaller cell is called the chalazal cell and the larger cell is the micropylar cell.
4. The nuclei in each cell divide by free nuclear divisions and then walls develop between nuclei in the micropylar chamber.
5. It is intermediate between cellular and nuclear type endosperm e.g. Asphodelus.