Question

meiotic and mitotic divisions are required for the development of 7-celled, 8-nucleate embryo sac.

• A. 1
• B. 3
• C. 5
• D. 7
• E. 4

Answer 1

Answer: (A), (B), (D)

7

• In the ovule, megaspore mother cell divides meiotically and produces four megaspores.
• Out of these only one towards the chalazal end is functional. As the functional megaspore grows, its nucleus undergoes first mitotic division to form two nuclei separated by a central vacuole.
• As the vacuole enlarges one of the two daughter nuclei is pushed to the micropylar end and the other to the chalazal end to form a 2-nucleate structure. Both of these nuclei now undergo two more mitotic divisions each to form four nuclei at both the ends.
• At the micropylar end, three nuclei develop cell walls to form the egg apparatus while in the chalazal end the three nuclei develop cell wall to form the antipodals.
• The remaining one nuclei at each end migrates towards the center of the embryo sac forming the polar nuclei. Therefore, there is one meiotic and three mitotic divisions.