All multicellular organisms necessarily have alternating haploid and diploid phases, and their reproduction occurs by a sexual way. In plants, the di

Gametogenesis in plants [Gametophyte, Spermatogenesis oogenesis, Formation]

All multicellular organisms necessarily have alternating haploid and diploid phases, and their reproduction occurs by a sexual way. In plants, the diploid phase of the life cycle — is a sporophyte. At this stage occurs meiosis, resulting in formation of haploid spores, from which under favorable conditions develops gametophyte — a haploid stage. At this stage occurs gametogenesis — formation of gametes by mitosis. In the evolution process of plants the diploid stage was gaining growing importance. In flowering plants, unlike ferns and moss, gametophyte just became a part of the sporophyte.

Male gametophyte (spermatogenesis)

Male gametophyte of flowering plants is pollen grains. This is where the sperm forms (diagram 10). It produces in the anthers, which have a large amount of pollen mother cells. These cells undergo meiosis, turning in tetrads, and in some, in fact, form pollen grains. At first, the pollen grains are unicellular. After the first mitotic division, they become two-celled. One cell, which is called autonomic (or vegetative), stops dividing. Pollen tube produces from it. In the second cell — a generative — there goes another mitosis; two nuclei form therein. The result is a mature pollen grain consisting of two cells, one of which — binuclear. Taken from http://worldofschool.org

Diagram 10. Formation of male gametes in flowering plants (spermatogenesis): 1 — microspore mother; 2 — metaphase-1; 3 — telophase-1; 4 — metaphase-2; 5 — stage four spores; 6 — first mitosis in microspores; 7 — bicellular pollen grains; 8 — vegetative cell; 9 — generative cell, 10 — mature pollen grains; 11 — nucleus of the pollen tube, 12 — sperm
Diagram 11. Formation of female gametes in flowering plants (oogenesis): 1 — parent macrospore; 2 — metaphase-1; 3 — telophase-1; 4 — metaphase-2; 5 — stage of four macrospores; 6 — degeneration of three macrospores; 7 — three mitotic divisions of the embryo sac, leading to the formation of a mature female gamete; 8 — egg; 9 — nuclei, forming a centrosome

Female gametophyte (oogenesis)

Female sporophyte develops in the ovule, where the maternal cells are — the macrospores (diagram 11). From each of them form four macrospores by meiosis, three of which die. The remaining macrospore that is called the embryo sac is the female gametophyte. It undergoes three mitoses. As a result, in the embryo sac form eight nuclei. They are collected in three groups: two polar each containing three nuclei (in one of them there is the egg), and one center, consisting of two central nuclei, which, after merging, give a diploid centrosome.

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Questions:
  • What the male gametes of flowering plants are different from the sperm of animals?

  • Because of what divisions occurs formation of plants’ gametes?