Cell division provides the most important processes in living nature:
- reproduction of unicellular organisms;
- growth and development of multicellular organisms;
- constant renewal of tissues and organs;
- restoration of tissues and organs after damage.
There are four main methods of cell division:
- direct binary division;
Direct binary fission is typical for prokaryotes (bacteria and cyanobacteria).
A bacterial cell contains one circular DNA molecule. DNA doubles before cell division.
The formed identical DNA molecules are attached to the cytoplasmic membrane (CPM). During division, the CPM grows between two DNA molecules and divides the cell in half. Each daughter cell contains one identical DNA molecule.
Amitosis, or direct division, is the division of the nucleus by constriction, which proceeds without spiraling chromosomes.
This division occurs:
- in highly specialized cells with low activity (cells of cartilage, cornea of the eye, liver, endosperm of seeds, walls of the ovary of the pistil),
- in degenerated plant and animal cells doomed to death.
In amitosis, only nuclear fission is often observed, and cytoplasm separation does not occur. As a result, multinucleated cells can form. If the cytoplasm is divided, then the distribution of cellular components, like DNA, occurs arbitrarily.
Amitosis is the most economical method of division, proceeding with minimal energy consumption.
Mitosis is an indirect division of eukaryotic somatic cells, as a result of which the chromosome set is transmitted unchanged. Mitosis underlies the growth of organisms, the regeneration of damaged parts, and vegetative reproduction.
Meiosis is the division of eukaryotic cells, leading to the formation of haploid cells, i.e., a halving of the chromosome set. Meiosis leads to the formation of gametes in animals and spores in plants. In this case, four haploid cells with different chromosomal sets are formed from one maternal diploid cell.