Write 7-celled 8nucleate stage in plants?
Answers
Answer:
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Explanation:
The eight nucleate female gametophytes of flowering plants have an egg apparatus made of one egg cell and two flanking cells at the micropylar end. The flanking cells are known as synergids and have finger-like projections on the wall which forms filiform apparatus. Three cells present at the chalazal end of embryo sac are called as antipodals. The large central cell has two polar nuclei. This makes embryo sac 7 celled and 8 nucleate structure.
The female gametophyte (embryo sac) develops from a single functional mega spore. This mega spore undergoes three successive mitotic divisions to form eight nucleate embryo sacs.
The first mitotic division in the mega spore forms two nuclei. One nucleus moves towards the micro pylar end while the other nucleus moves towards the chalazal end. Then, these nuclei divide at their respective ends and re-divide to form eight nucleate stages. As a result, there are four nuclei each at both the ends i.e., at the micro pylar and the chalazal end in the embryo sac. At the micro pylar end, out of the four nuclei only three differentiate into two synergids and one egg cell. Together they are known as the egg apparatus. Similarly, at the chalazal end, three out of four nuclei differentiates as antipodal cells. The remaining two cells (of the micro pylar and the chalazal end) move towards the center and are known as the polar nuclei, which are situated in a large central cell. Hence, at maturity, the female gameto phyte appears as a 7-celled structure, though it has 8 nucleate.
