All living organisms are divided into precellular and cellular. Pre-cellular viruses and phages. The second group, cellular, is divided into prokaryotes and eukaryotes, which are pre-nuclear and nuclear organisms.
Prokaryotes
The first cellular, prokaryotes, arose on Earth more than 3 billion years ago. This was the greatest leap in the development of life. Prokaryotes are bacteria. Their structure is relatively simple. The hereditary information, DNA, is in their primitive, low protein ring-shaped chromosome. It is located in a special area of the cytoplasm, the nucleoid, which is not separated from the rest of the cell by the membrane. The main thing that distinguishes prokaryotes and eukaryotes from each other is that in the cells of the first type there is no real nucleus.
The cytoplasm of the pre-nucleated cells has much less cellular structures. Of these, ribosomes are known that are smaller in comparison with ribosomes of eukaryoid cells. The role of mitochondria in prokaryotes belongs to simple membrane structures. Chloroplast is also absent in them. Prokaryotes have a plasma membrane over which the cell membrane is located. They differ from eukaryotes in significantly smaller sizes. In some cases, in prokaryotes, there may be so-called plasmids - small, in the form of a ring, DNA molecules.
Eukaryotes
All nuclear cells differ in their general plan of structure and common origin. They arose from pre-nucleated cells 1.2 billion years ago. Their structure is much more complicated. Both prokaryotes and eukaryotes have a cell membrane. But otherwise, their structural and biochemical features are very different. The most important difference is that in nuclear cells there is a true nucleus in which their genetic information is stored.
The nucleus is delimited from the cytoplasm by a special membrane consisting of the outer and inner layers. It is similar to a plasma membrane, but contains pores. Thanks to them, an exchange is carried out between the cytoplasm and the nucleus. The genome of the cell consists of a whole set of chromosomes, this prokaryotes and eukaryotes also differ from each other. DNA in eukaryotic chromosomes is associated with histone proteins.
In the cell nucleus are the nucleoli in which ribosomes are formed. Unstructured mass, karyoplasm, surrounds the chromosomes and nucleoli. Each type of animal and plant has its own, strictly defined set of chromosomes. During cell division, they double and then are distributed among daughter cells.
If we consider prokaryotes and eukaryotes, the differences in them are also visible in the cytoplasm of the cells.
The presence of large central vacuoles and plastids is characteristic of plant cells. This vacuole can move the nucleus to the periphery of the cell. The plant cell’s nutritional reserve carbohydrate is starch. Outside, plant cells are coated with a cell wall consisting of cellulose. There is no centriole in the cell center, which can only be seen in algae.
Animal cells do not have a central vacuole, plastid, and dense cell wall. In the center of the cell is centriole. The reserve carbohydrate in animal cells is glycogen.
In fungal cells, centriole is not always the case. The cell wall consists of chitin, there are no plastids in the cytoplasm, but there is a central vacuole in the center of the cell. The carbohydrate reserve in them is also glycogen.
In the cytoplasm of eukaryotes, there are mitochondria, the Golgi apparatus, lysosomes, the endoplasmic reticulum, and organelles of movement. Their ribosomes are much larger than the ribosomes of prokaryotes. The cytoplasm of the cell is divided into separate compartments, compartments, using special membranes consisting of lipids. Each of them has its own biochemical processes. It is almost not found in prokaryotes.
In general, prokaryotes and eukaryotes express the laws of evolution, which are characterized by a movement from simpler to more complex forms.
However, pre-nucleated cells are characterized by greater plasticity and a variety of metabolic processes. Many bacteria can receive energy through light or chemical reactions, exist in an environment devoid of oxygen (anaerobic bacteria). Thanks to this, they fit into the picture of the modern world.