Biology · Sexual Reproduction in Flowering Plants · NEET
The pollen grain is the male gametophyte and it is haploid (n). It is made from a microspore, which the diploid anther produces by meiosis. Inside the pollen grain, cells divide by mitosis to form the vegetative cell and the generative cell (which later gives two male gametes). So the pollen grain is a tiny n gametophyte carried inside a 2n sporophyte (the anther).
The sporophyte (2n) is dominant. The whole visible plant - roots, stem, leaves, flowers - is the sporophyte. The gametophytes (pollen grain and embryo sac) are microscopic, short-lived, and never live on their own. This is the opposite of bryophytes, where the gametophyte is the dominant, green, independent plant.
No. This is a common trap. The gametophyte is already haploid, so it makes gametes by mitosis, not meiosis. Meiosis happens earlier, in the diploid sporophyte, to make haploid spores (microspores and megaspores). Rule to remember: sporophyte does meiosis to make spores; gametophyte does mitosis to make gametes.
In a diplontic life cycle the diploid sporophyte is the dominant, free-living, multicellular phase, and the haploid gametophyte is reduced to just a few cells that depend on the sporophyte. In angiosperms the pollen grain and embryo sac are only a handful of cells and are never independent, so the plant is diplontic. (Bryophytes are haplo-diplontic; most green algae like Chlamydomonas are haplontic.)
The diploid spore-producing phase (sporophyte, 2n) and the haploid gamete-producing phase (gametophyte, n) follow each other in a loop. Sporophyte -> meiosis -> spore -> mitosis -> gametophyte -> gametes -> fertilisation -> zygote -> sporophyte again. Fertilisation restores 2n and meiosis brings it back to n, so the two generations keep alternating.
The plant parts which consist of two generations one within the other: (a) Pollen grains inside the anther (b) Germinated pollen grain with two male gametes (c) Seed inside the fruit (d) Embryo sac inside the ovule
In angiosperm, the haploid, diploid and triploid structures of a fertilized embryo sac sequentially are:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The embryo sac (female gametophyte) is haploid (n). It develops from a single haploid functional megaspore by mitosis and holds the egg, synergids, antipodals and the central cell with two polar nuclei - all haploid nuclei until fertilisation happens.
The sporophyte is the whole visible plant - the roots, stem, leaves and flower parts like the anther, ovary and ovule wall. It is 2n and it produces haploid spores by meiosis, which then grow into the tiny gametophytes.
In a fern (pteridophyte) both sporophyte and gametophyte (the prothallus) are independent and free-living - this is haplo-diplontic. In an angiosperm the gametophytes are just a few cells that live inside the sporophyte and are never independent, making it diplontic.
Meiosis occurs in the diploid sporophyte: in the anther (microspore mother cell -> microspores) and in the ovule (megaspore mother cell -> megaspores). Each spore then grows by mitosis into a haploid gametophyte.
NEET regularly asks which structure is a gametophyte or sporophyte and its ploidy (n, 2n, 3n). Knowing that the pollen grain and embryo sac are haploid gametophytes inside a diploid sporophyte helps you solve 'two generations within one', double-fertilisation ploidy, and diplontic/haplo-diplontic questions quickly.
