Propagation is the ability of organisms to form their own kind. Play is one of the most important properties of life and is possible thanks to the overall ability of organisms to produce offspring. But not always direct descendants like the parent individuals. For example, a dispute fern grows numerous offspring represented prothallia not resemble the parent spore-bearing plant. On prothallia, in turn, occurs unlike him plant – sporophyte. This phenomenon is called alternation of generations.
If the formation is accompanied by the increase in the number of offspring of the species, the process is a reproduction. Reproduction – this reproduction of genetically similar individuals of the species, which is characterized by an increase in the number of individuals in the child generation in comparison with their parents.
When reproduction is ensured continuity and continuity of life. Continuity is that during reproduction is transmitted all the genetic information incorporated in the parent generation, the child generation. Due to the change of generations of certain species and their populations can exist indefinitely, because the decline in their numbers due to the natural death of animals compensated by continuously reproducing organisms and replacement of dead born (the continuity of life).
Types of organisms being presented mortal individuals, due to the change of generations, not only preserve and transmit the descendants of the main features of its structure and functioning, but also changed. Hereditary changes in breeding organisms observed in some algae and protozoa (foraminifers, Sporozoa).
Spore formation occurs in algae, protozoa (Sporozoa) and some groups of bacteria. This type of reproduction is associated with the formation of spores. The spore is a cell covered by a dense shell. The latter protects the inner contents of the cells from the effects of adverse conditions. Bacterial spores, for example, are very resistant to high temperatures. In Sporozoa disputes are a particular stage of the life cycle, enables “worry” of unfavorable environmental factors. Once in favorable conditions, spores germinate and develop into a new organism.
Asexual reproduction of multicellular organisms. Vegetative reproduction – a form of asexual reproduction in plants, in which the beginning of a new body to give vegetative organs – root, stem, leaf, or a specialized modified shoots – tubers, bulbs, rhizomes, brood buds, etc…
At the heart of fragmentation, as in the case of vegetative reproduction, is the body’s ability to restore the missing parts of the body (regeneration). In this method of breeding new individuals arise from fragments of the maternal organism. Fragmentation can breed, for example, filamentous algae, fungi, some flat (ciliary) and annelid worms.
Budding characteristic of sponges, some coelenterates (hydras) and tunicates (sea squirts), in which a group of cells at the expense of reproduction formed on the body protrusions (kidney). Bud grows in size, then it has appeared the rudiments of all the structures and organs characteristic of the mother’s body. Then there is a separation (budding), a subsidiary of individuals, which grows and reaches the mother’s body size. If the individual subsidiaries are not separated from the parent, then the colonies formed (coral polyps).
Some coelenterates occur strobilation reproduction. This polyp is growing rapidly, and then in the upper part is divided by transverse constrictions on the individual subsidiaries (strobila). At this time polyp resembles a stack of plates. The resulting individual subsidiaries – jellyfish – detached from the parent and start an independent existence.
Asexual reproduction of single-celled organisms. Bacteria and protozoa (amoeba, Euglena, ciliates, and others.) Reproduce by dividing into two cells. Bacteria are divided into simple binary fission; simple – mitosis. After dividing daughter cells grow and reached the value of the maternal organism, divided again.
In nature, there are cases when cells divide not into equal parts. In this case, the smaller the cell as it buds from the big. This type of division (heteroatoms) found in yeast and certain bacteria, and it is called budding.
Multiple division (schizogony) is characterized by the fact that at such reproduction observed multiple nuclear fission without division of the cytoplasm. Further, around each of the cores segregated small portion of cytoplasm and cell division is completed the formation of many subsidiaries of individuals. This type of series of generations led to change the form or appearance of new species.
Typically, there are two basic types of reproduction: asexual and sexual. Sexual reproduction is associated with the formation of sex cells – gametes; they merge (fertilization), zygote formation and its further development. Asexual reproduction is not associated with the formation of gametes.