All gametes of higher plants (Embryophytes) greatly differ in appearance and are divided into male and female. They form in gametangia those in highe

Fertilization in higher plants [Embryophytes]

All gametes of higher plants (Embryophytes) greatly differ in appearance and are divided into male and female. They form in gametangia those in higher plants, in contrast to algae, are multicellular.

Male sex organs are as well as in algae — antheridia. In antheridia of mosses and ferns forms a lot of sperm. As the sperm of animals, they have flagella and are mobile. In seed plants male gametes develop in pollen grains. They are immobile and called spermatozoa.

Female reproductive organ of higher plants — is archegonium (from Greek “arche” — “the beginning” and “gonium”). Only one egg produces in it. Archegonium is inherent only in the lower spore plants. They are still stored in the gymnosperms, but completely reduced in angiosperms. In the latter, the eggs develop in the embryo sac.

Fertilization in bryophytes

Fertilization in bryophytes takes place in water. Got out of the antheridium, sperm swims to opened archegonia and there merge with the egg, giving rise to the sporophyte.

Fertilization in ferns

In ferns fertilization, which is also necessary for the aquatic environment occurs on prothallia (gametophyte). In some species, prothallia are only bisexual, while in others are either female or male.

Diagram 84. Scheme of double fertilization in flowering plants: a — longitudinal cut of the pistil; b — the germination of pollen grains; c — the penetration of the pollen tube in the embryo sac; d — the penetration of the two sperm cells in the embryo sac; e — the embryo sac after fertilization: 1 — germinating pollen grain; 2 — pollen tube; 3 — ovary; 4 — mature embryo sac; 5 — sperm; 6 — egg; 7 — polar nuclei, forming the polar body; 8 — a zygote; 9 — triploid nucleus of endosperm

Fertilization in seed plants

Fertilization in seed plants occurs due to pollination — the transfer of pollen grains in the pollen chamber ovule (in gymnosperms) or stigma (angiosperms). In seed plants prothallia are only bisexual.

Fertilization in flowering plants

Immobile sperm of flowering plants get to the egg, located in the middle of the embryo sac, via the pollen tubes, which are outgrowths of cytoplasm of male prothallia. Taken from http://worldofschool.org

In flowering plants, pollen tube grows between pistil cells and enters the cavity of the ovary, grows into the embryo sac (diagram 84). Sperm gets out from the pollen tube. One of them merges with the egg to form a diploid zygote, the second — with the central diploid cell of embryo sac, which as a result becomes triploid.

From zygote develops embryo, from the central cell — endosperm (from Greek “endon” — “inside” and “spermatos”) — a nutrient that is used by the embryo during its development. The embryo and endosperm together form a seed.

Thus, fertilization in flowering plants — a very peculiar process. It is called a double fertilization. This type of fertilization does not occur in any other group of living organisms. It was first described in 1898 by a professor of Kiev University Sergei Navashin.

Categories:
Questions:
  • Why fertilization in plants is called double?