Alternation of generations in ferns

why is alternation of generations important

For example, in flowering plants, microspores ultimately produce microgametes sperm and megaspores ultimately produce megagametes eggs.

Spores are released into the air and can travel on the slightest breezes to other habitats. Gametophyte of the fern Onoclea sensibilis the flat thallus at the bottom of the picture with a descendant sporophyte beginning to grow from it the small frond at the top of the picture.

The zygote grows via mitosis into the diploid sporophyte, completing the life cycle.

Alternation of generations in ferns

A megaspore often but not always develops at the expense of the other three cells resulting from meiosis, which abort. Life Cycle: The Gametophyte Generation The tiny spores swirl out into the night, diaspora of the human vegetable mimics. Seed Plants gymnosperms and angiosperms ALL of these diverse plants undergo a life cycle that includes an Alternation of Generations. Diagram of alternation of generations in ferns. Fusion of the gametes creates the new diploid sporophyte, completing the life cycle. The more derived the plant group, the more reduced the gametophyte. Microspores germinate producing microgametophytes; at maturity one or more antheridia are produced. Eggs develop within the archegonia. This is another method that permits quick reproduction. At last it rained!

If there is enough moisture, the gametophyte is fertilized and grows into a diploid sporophyte. Archegonia produce ova eggs. It is called the prothallus or gametophyte.

sporophyte generation

Each spore grows into a photosynthetic prothallus gametophyte via mitosis. The life cycle of ferns is different from other land plants as both the gametophyte and the sporophyte phases are free living.

life cycle of fern summary

An archegonium develops within the megagametophyte and produces an egg. If the sperm do manage to get to an egg, fertilisation occurs, and that is where the two — the sperm and egg — come together.

Alternation of generation in pteridophytes

A megaspore often but not always develops at the expense of the other three cells resulting from meiosis, which abort. The egg is produced within a similar structure called an archegonium. It is a green, photosynthetic structure that is one cell thick, usually heart or kidney shaped, 3—10 mm long and 2—8 mm broad. The entire gametophyte generation, with the sole exception of pollen grains microgametophytes , is contained within the sporophyte. At maturity, these structures become the seed. While the sporophyte consisted of fronds and rhizomes, the gametophyte has leaflets and rhizoids. Eggs develop within the archegonia. Antheridia and archegonia occur on the same gametophyte, which is then called monoicous. In liverworts, mosses and hornworts, the dominant form is the haploid gametophyte. The larger sessile megagametes are eggs ova , and smaller motile microgametes are sperm spermatozoa, spermatozoids. On the undersurface of its fronds or leaves, its cells undergo meiosis to create haploid cells. The zygote undergoes mitosis to grow and develop into a new diploid 2n sporophyte plant. The whole pollen grain is moved e.
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Fern life cycle