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The development of the three celled male gametophyte prior to dehiscing has evolved multiple times and is present in about a third of angiosperm species allowing for faster fertilization after pollination. [20] Once pollination occurs, the tube cell grows in size and if the male gametophyte is only 2 cells at this stage, the single sperm cell ...
The male gametophyte gives rise to sperm cells, which are used for fertilization of an egg cell to form a zygote. Megaspores are structures that are part of the alternation of generations in many seedless vascular cryptogams , all gymnosperms and all angiosperms .
The pollen grains, which are the male gametophytes, are reduced to only a few cells (just three cells in many cases). Here the notion of two generations is less obvious; as Bateman & Dimichele say "sporophyte and gametophyte effectively function as a single organism". [8] The alternative term 'alternation of phases' may then be more appropriate ...
The gametophyte produces male or female gametes (or both), by a process of cell division, called mitosis. In vascular plants with separate gametophytes, female gametophytes are known as mega gametophytes (mega=large, they produce the large egg cells) and the male gametophytes are called micro gametophytes (micro=small, they produce the small ...
The male gametophyte is produced inside a pollen grain within the anther and is non-motile, but can be distributed by wind, water or animal vectors. When a pollen grain lands on a mature stigma of a flower it germinates to form a pollen tube that grows down the style into the ovary of the flower and then into the ovule.
A microsporangium (pl. microsporangia) is a sporangium that produces microspores that give rise to male gametophytes when they germinate. Microsporangia occur in all vascular plants that have heterosporic life cycles, such as seed plants , spike mosses and the aquatic fern genus Azolla .
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There are two key differences between mammalian and plant gametogenesis. First, there is no predetermined germline in plants. Male or female gametophyte-producing cells diverge from the reproductive meristem, a totipotent clump of developing cells in the adult plant that creates all the flower's features (both sexual and asexual structures).