Sexual reproduction among the higher and lower representatives of the flora

Reproduction is characteristic of all organisms. This ability to reproduce provides continuity and continuity of life. In organisms that have a cellular form of structure, division is the basis of reproduction.

Different scientists have proposed different classifications of reproduction types. Three types of reproduction are considered basic : vegetative, sex and asexual.

In the latter case, the development of the organism is carried out from one cell, not sexually differentiated. For vegetative reproduction is characteristic of the development of the organism from multicellular embryos, sometimes difficult to differentiate.

Sexual reproduction of plants begins with the formation of sex cells (gametes). Reproduction itself boils down to the fusion of gametes into a zygote. This process is called fertilization and ensures the transfer of genetic data from parents to offspring.

Gametes are formed in the genital organs - gametangia. Representatives of the flora, which is characterized by fertilization, have a meiosis in their development cycle.

Sexual reproduction is not typical for blue-green algae, bacteria. This method of reproduction is not found in a number of fungi.

Types of sexual reproduction in the lower representatives of the flora are different. So, for some green algae, the process of reproduction can occur without the formation of gametes. In this case, two unicellular organisms merge.

The fusion of gametes that have flagella is called isogamy. Such sexual reproduction is characteristic of many algae.

Unicellular algae (some chlamydomonads, for example) to some extent themselves turn into genital organs, forming gametes. Multicellular representatives of gametangiae become separate cells, not differing from others, or gametangia are formed, which have morphological differences (for example, in the ectocarpus).

For many isogamous algae is characterized by heterothallism (genetic and physiological sexual separation). In this case, a fusion of physiologically different gametes occurs.

For some algae, conjugation is characteristic: a "flow" of protoplast from one cell to another takes place.

The fusion of gametes having different flagella is called heterogamy. The connection of an unbuttoned female gamete (egg) and having flagella (most often) of a small male (sperm) is called oogamy. Such sexual reproduction is characteristic for many red, brown, diatomaceous, green algae, as well as a number of lower fungi.

Fertilization in the hologram, heterogamous, isogamous and most ooham representatives of the flora is carried out in the water. In a number of oogamous plants, the fusion process occurs in oogonia (female gametangia). They are actively promoted sperm, released into the water. Activity, apparently, is due to chemotaxis. In this case, spermation of red squids (red algae) is moved by a current of water - passively.

Higher plants are oogamous. However, their fertilization takes place in different ways. For higher plants, multicellular gametangia are typical - archegonia (female) and antheridia (male). In the outer layer of the genital organs, the cells are sterile. In the archegonium, egg cells are formed one by one, in antheridia, spermatozoa are usually formed in large numbers.

Sexual reproduction of fern-like and bryophytes takes place in water. Spermatozoa leave antheridia and move towards archegonium. In turn, ready-to-fertilize archegonia attract spermatozoa by excreting mucus from the exposed apex. Moving on in the mucus, the spermatozoa approach the egg, but merges with it alone.