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Which organisms consist of a single cell? Examples, classification

All animals and plants that we meet in everyday life are multicellular organisms. However, there is also a microcosm, where invisible creatures dwell in our eyes. Sometimes they consist of one cell. Therefore, they can be seen only under a microscope. What features can be distinguished from unicellular organisms?

The structure of the cell: a scheme of a typical prokaryotic and eukaryotic cell

Living organisms in nature can be unicellular or multicellular, eukaryotic or prokaryotic. Each individual group has its own peculiarities in structure, physiology, biochemistry. What are the signs of a prokaryotic cell? First of all, this is the simplicity of the organization. This type of cells lacks a nucleus, and genetic information is contained in DNA. And in this form it "floats" in the cytoplasm. Another characteristic feature is that such cells lack any organelles. Their functions replace the protrusions of the cytoplasmic membrane, which are called mesosomes. In most cases, they are responsible for breathing or photosynthesis.

In prokaryotic cells, the surface apparatus is rather complicated, because it is represented by several layers. The first of these - the cytoplasmic membrane - plays a crucial role in the transport of substances between the cell and the environment. The CPM is represented by a bilipid layer in which various proteins are anchored. Further, the prokaryotic cell is covered with a membrane that has a protective and adaptive character. The second layer prevents the penetration of toxic substances. It protects against the effects of damaging factors, although this shell has its limits.

The last layer of the surface device may not always be present. It is a slimy cover. First, it helps the cell in the process of movement, reducing friction. Secondly, the mucous cover contains the products of metabolism and secretion of these cells. These substances can be used for protective purposes or, conversely, to attack their victim. All prokaryotic organisms consist of a single cell. These include, first of all, bacteria.

Features of eukaryotes

Eukaryotic cells differ in their complexity of organization. They have a large number of formations and structures, and numerous biochemical processes require the presence of a variety of specific enzymes and formations. What is the living cell of eukaryotes? In its structure, the following elements are distinguished:

  • Core.
  • Organelles and cytoplasm.
  • Membrane and cytoskeleton.

The nucleus is the central structure of any eukaryotic cell in which hereditary information is stored. It contains chromosomes and nucleoli. They are responsible for the transfer and implementation of genetic information. Among the organelles, the cells are isolated:

  1. Two-membrane structures (mitochondria and plastids).
  2. Single-membrane structures (lysosomes, Golgi apparatus, endoplasmic reticulum, vacuoles, peroxisomes, etc.).
  3. Non-membrane structures (ribosomes, cytoskeleton).

The membrane of eukaryotes is similar in structure to that of prokaryotes. However, it is distinguished by a more complex organization. The eukaryotic cell consists of parts, which are called compartments. This system of organization greatly simplifies the course of all biochemical processes, since the cell is divided into different compartments.

Protists - unicellular eukaryotic organisms

Among the whole variety of eukaryotic organisms, which we also belong to, exist also less visible to the human eye creatures. They are called protists. They constitute a separate kingdom in the systematics. All protists consist of a single cell, so the size does not exceed 250 microns. They are divided into several groups, among which are sarcodic, flagellate, and infusoria.

Sarcode type

These include amoeba, which consist of a single cell. These creatures live in soil, fresh or salt water. Their body does not have a permanent shape, which allows them to form the so-called legs, by which these protists seize their food.

Type Flagellate

Flagellates received their name because of the presence of flagella at the end of the body. It allows such cells to move quickly. This makes the flagellates excellent hunters. Among them, a large number of parasites of higher multicellular organisms are isolated. The body of such creatures has a constant shape because of the sweaty cellular membrane.

Type of Infusoria

Infusoria consist of a single cell. Despite this, they are considered evolutionarily the most developed among the simplest. There was even a theory of the formation of multicellular animals, according to which they originated from infusorians. These creatures have a dense cell wall. They have two nuclei in the cytoplasm: generative, which controls reproduction, and vegetative, which is responsible for vital processes. The entire body of the ciliates is covered with cilia. The metabolic products are removed through a special hole - powder.

Human cells: a variety of forms and structural features

Our body is a multicellular formation, in which the cells are connected with each other. They transmit information using synthesized signaling substances. Form tissues, organs and systems, which differ from each other functionally and morphologically.

What does the human cell consist of? If we consider the cells of any tissue of the body, then they have all the signs of eukaryotes: the nucleus, organelles, the cytoskeleton, the complexity of the organization of metabolism. However, among them you can find exceptions, which give the uniqueness of this or that fabric.

For example, red blood cells do not have a nucleus. This allows them to bind more oxygen or carbon dioxide. The ovum can reach 0.12-0.15 cm in diameter, which is a very large value even for a eukaryotic cell. Human neurons also have their own characteristics. They form numerous outgrowths, among which there are short dendrites and long axons.

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