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Question

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

A
1
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B
3
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C
5
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D
7
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E
4
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Solution

The correct options are
A 1
B 3
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.

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