Sexual Reproduction in Flowering Plants — Class 12 Biology

This chapter examines how flowering plants reproduce sexually through the flower, the reproductive structure of angiosperms. The androecium produces microspores in the anther through microsporogenesis, yielding pollen grains that carry the male gametophyte. The gynoecium, with ovary, style and stigma, develops ovules in which a megaspore mother cell undergoes megasporogenesis to form the embryo sac (female gametophyte), typically an 8-nucleate, 7-celled structure with an egg, two synergids, three antipodals and a central cell with two polar nuclei. Pollination transfers pollen to the stigma and may be self (autogamy, geitonogamy) or cross (xenogamy), aided by wind, water, insects and other agents, with floral devices like dichogamy and self-incompatibility promoting outcrossing. After pollination the pollen tube grows through the style to the embryo sac, where double fertilisation occurs: one male gamete fuses with the egg (syngamy) forming the zygote, and the other fuses with the central cell forming the triploid primary endosperm nucleus. The zygote develops into an embryo, the ovule into a seed and the ovary into fruit. The chapter also covers apomixis, polyembryony and pollen-pistil interaction, linking these to plant breeding and crop improvement.