Question

explain the formation of embryo sac with diagram? 5marks​

Answer 1

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The embryo sac or female gametophyte is an oval structure present in the ovule of flowering plants. An embryo sac is said to form when the haploid megaspore nucleus divides. It possesses two haploid nuclei and six haploid cells which do not have cell walls.

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Answer 2

Formation of Embryo Sac
The embryo sac formation occurs in two stages:

Stage 1:
In the first stage, megasporogenesis occurs, where the haploid megaspore tetrad forms due to the meiosis of a single diploid mother cell.
Out of this, three disintegrates, and one sustains, which later develops into the embryo sac.
Stage 2:
The second stage is the megagametogenesis, where the embryo sac is formed due to mitosis of the functional haploid megaspore to produce 8-nucleate, 7-celled gametophyte.
The polar nuclei move to the centre out of all the eight nuclei, to combine and generate a single diploid cell at that location (centre).
This single diploid cell then fuses with the sperm to generate the triploid endosperm.
The other three nuclei grow into antipodal cells while two modify into synergid cells which degenerate gradually.