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Answer the Following Question. Where Does the Process of Megasporogenis Start in an Angiosperm? Describe the Process up to the Formation of an Embryo Sac. - Biology

Answer in Brief

Answer the following question.
Where does the process of megasporogenis start in an angiosperm? Describe the process up to the formation of an embryo sac.

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Solution

Megasporogenesis is the process of formation of megaspores from megaspore mother cells (MMC). The megaspore mother cell (MMC) undergoes meiosis and forms a linear tetrad of 4 haploid megaspores. The process of meiotic formation of haploid megaspores from diploid megaspore mother cell is called megasporogenesis. Commonly the chalazal megaspore remains functional while the other 3 degenerates.
The functional megaspore is the first cell of the female gametophyte. The cell enlarges and undergoes three free nuclear mitotic divisions. The first division produces two nucleate embryo sac. The two nuclei shift to the two ends and divide there twice forming four nucleate and then eight nucleate structures.
One nucleus from each side moves to the middle. They are called polar nuclei. The remaining three nuclei from cells at the two ends, 3 celled egg apparatus at the micropylar end and three antipodal cells at the chalazal end.
The middle bi-nucleate part organizes itself into a central cell. Embryo sac developed from a single megaspore is called monosporic.

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