Reproduction is common to all organisms. This ability to reproduce ensures the continuity and continuity of life. In organisms having a cellular structure, division is at the heart of reproduction.
Different scientists have proposed different classifications of types of reproduction. The main are three types of reproduction: vegetative, sexual and asexual.
In the latter case, the development of the body is carried out from one cell, sexually not differentiated. Vegetative reproduction is characterized by the development of an organism from multicellular primordia, sometimes difficult to differentiate.
Sexual reproduction of plants begins with the formation of germ 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 descendants.
Gametes are formed in the genitals - gametangia. Representatives of the flora, which are characterized by fertilization, have meiosis in their development cycle.
Sexual reproduction is not characteristic of blue-green algae, bacteria. Such a method of reproduction is not found in a number of fungi.
Types of sexual reproduction in the lower representatives of the flora are different. Thus, in some green algae, the reproduction process 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 chlamydomonas, for example), to some extent, themselves turn into the genitals, forming gametes. In multicellular representatives, single, non-different, cells become gametangia or gametangia are formed that have morphological differences (for example, in an ectocarpus).
Many isogamous algae are characterized by heterotallism (genetic and physiological sexual separation). In this case, physiologically different gametes merge.
Conjugation is characteristic of some algae: the protoplast of one cell flows into another.
The fusion of gametes with flagella of various sizes is called heterogamy. The combination of a flagless female gamete (egg) and a small male (sperm) flagellum (most often) is called oogamy. Such sexual reproduction is characteristic of many red, brown, diatoms, green algae, as well as a number of lower fungi.
Fertilization in gologamous, heterogamous, isogamous and most oogamous representatives of the flora is carried out in water. In a number of oogamous plants, the process of fusion occurs in oogonium (female gametangia). Sperm cells that have entered the water are actively moving towards them. Activity seems to be due to chemotaxis. In this case, spermatozoa of scarlet (red algae) are moved by a current of water - passively.
Higher plants are oogamous. However, fertilization occurs in different ways. For higher plants, typical are multicellular gametangia - archegonia (female) and anteridia (male). In the outer layer of the genital organs, the cells are sterile. In archegonia, the eggs are formed one at a time, in anteridia, spermatozoa are formed, as a rule, in large numbers.
Sexual reproduction of fern-like and bryophytes is carried out in water. Spermatozoa emerge from anteridia and move to archegonia. In turn, archegonias, which are ready for fertilization, attract spermatozoa by secreted mucus from the opening apex. Moving in the mucus, the sperm approach the ovum, but merges with it alone.