Question

Trace the development of a mature ovule from a megaspore mother cell.

Answer 1

The diploid megaspore mother cell in the nucellus undergoes meiosis to form four haploid megaspores. Usually three degenerate, while the functional megaspore undergoes three mitotic divisions to form eight nuclei. These organise into a seven-celled embryo sac: three antipodals at the chalazal end, an egg flanked by two synergids at the micropylar end, and a central cell with two polar nuclei. After fertilisation, the zygote forms the embryo, the primary endosperm nucleus forms endosperm, the integuments become the seed coats and the ovule matures into a seed.