Govt. Exams
Entrance Exams
In microsporogenesis, all four microspores produced from meiosis are typically functional. In megasporogenesis, usually three of the four megaspores degenerate, leaving only one functional megaspore.
In Bryophyllum, small adventitious buds form at the margins of leaves, which can develop into new plants when they fall to the soil.
The mature female gametophyte (7-celled, 8-nucleate) contains: 1 egg cell, 2 synergids, 2 polar nuclei (in central cell), and 3 antipodal cells = 8 nuclei total.
A microspore undergoes mitosis to form the male gametophyte (2-celled or 3-celled pollen grain consisting of generative and vegetative cells). The pollen grain itself is the male gametophyte.
In typical monosporic development, the megaspore mother cell produces four megaspores through meiosis, but only one (usually the chalazal megaspore) survives and develops into the female gametophyte. The other three degenerate.
The primary endosperm nucleus is formed by the fusion of one sperm cell with the two polar nuclei (or secondary nucleus), making it triploid.
Meiosis reduces ploidy from diploid (2n) to haploid (n), while fertilization restores diploid (2n) condition.
Synergids guide the pollen tube towards the egg apparatus and help in pollen tube entry through the filiform apparatus.
Pollen grain (male gametophyte) and embryo sac (female gametophyte) represent the gametophytic phase in angiosperms.
Endosperm is triploid (3n), formed by fusion of one sperm nucleus (n) with two polar nuclei (2n).
