Prokaryotic and eukaryotic cells
All cells are divided into two large groups: prokaryotic and eukaryotic.
All prokaryotic organisms (about 3000 species of bacteria and blue-green (cyanobacteria)) are currently united in the Kingdom of Drobyanka.
In prokaryotic cells, there is no formed nucleus. The surface apparatus of the cell consists of the cytoplasmic membrane and the cell wall.
The structure of the cytoplasmic membrane is the same as that of eukaryotes. Inside the cell, numerous folds – mesosomes – extend from the membrane. The cell wall of prokaryotes resembles the cell wall of plant cells, but it is formed not by fiber, but by pectin and murein.
The cells of prokaryotes have ribosomes, but no membrane organelles. Their functions are performed by mesosomes.
Prokaryotes often have organelles of movement – flagella and cilia.
Bacterial (prokaryotic, prokaryotic) cells have the following characteristic structures – a dense cell wall, one circular DNA molecule (nucleoid), ribosomes.
Many prokaryotes are anaerobes, that is, they do not need oxygen in the air.
Many prokaryotes are able to capture and use nitrogen from the air (nitrogen-fixing nodule bacteria that develop on the roots of legumes), which eukaryotic organisms cannot.
Those types of prokaryotes that receive energy through photosynthesis contain a special type of chlorophyll, which can be located on the mesosomes.
Many prokaryotes, such as bacteria, are capable of forming spores under unfavorable conditions (the contents of the bacterial cell contract, and a dense membrane is released around it).
Prokaryotes often reproduce asexually (by dividing the cell in two).
Sexual reproduction in prokaryotes is observed much less frequently than asexual reproduction, but it is very important, since when bacteria exchange genetic information, they transfer resistance to each other to adverse effects (for example, to drugs). During the sexual process, bacteria can exchange both sections of the bacterial chromosome and special small circular double-stranded DNA molecules – plasmids. The exchange can take place through a cytoplasmic bridge between two bacteria or with the help of viruses that assimilate sections of the DNA of one bacterium and transfer them to other bacterial cells that they infect.
Eukaryotic (eukaryotic) cells contain a nucleus that coordinates the vital activity of the cell, which contains the hereditary apparatus of the body, and numerous organelles that perform various functions.
Most eukaryotes are aerobes, that is, they use atmospheric oxygen in energy metabolism.