All animals and plants that we meet in everyday life are multicellular organisms. However, there is also a microcosm, where creatures invisible to our eyes live. Sometimes they consist of one cell. Therefore, they can only be seen under a microscope. What features can be distinguished in unicellular organisms?
Cell structure: diagram 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 characteristics in structure, physiology, biochemistry. What are the characteristics of a prokaryotic cell? First of all, it is the simplicity of organization. This type of cell lacks a nucleus, and the genetic information is contained in DNA. And in this form, it "floats" in the cytoplasm. Also a characteristic feature is that such cells lack any organelles. Their functions replace protrusionscytoplasmic membrane, which are called mesosomes. They are in most cases responsible for respiration or photosynthesis.
In prokaryotic cells, the surface apparatus is rather complicated, since it is represented by several layers. The first of them - the cytoplasmic membrane - plays a decisive 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, which 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 surface apparatus may not always be present. It is a mucous membrane. First, it helps the cell move by reducing friction. Secondly, the mucous membrane contains the products of metabolism and secretion of these cells. These substances can be used for defensive purposes or, conversely, to attack their victim. All prokaryotic organisms consist of a single cell. These include primarily bacteria.
Features of eukaryotes
Eukaryotic cells are distinguished by their complexity of organization. They have a large number of formations and structures, and numerous biochemical processes require the presence of many specific enzymes and formations. What is a living eukaryotic cell made of? The following elements stand out in its structure:
- Core.
- Organelles and cytoplasm.
- Membrane and cytoskeleton.
The nucleus is the central structure of any eukaryotic cell, which stores hereditary information. It contains chromosomes and nucleoli. They are responsible for the transfer and implementation of genetic information. Among the cell organelles, there are:
- Two-membrane structures (mitochondria and plastids).
- Single-membrane structures (lysosomes, Golgi apparatus, endoplasmic reticulum, vacuoles, peroxisomes, etc.).
- Non-membrane structures (ribosomes, cytoskeleton).
The structure of the eukaryotic membrane resembles that of prokaryotes. However, it has a more complex organization. A eukaryotic cell is made up of parts called compartments. Such an organization system greatly simplifies the flow of all biochemical processes, since the cell is divided into various compartments.
Protists are single-celled eukaryotic organisms
Among the variety of eukaryotic organisms, to which we also belong, there are creatures that are less noticeable to the human eye. They are called protists. They constitute a separate realm in taxonomy. All protists consist of one cell; therefore, their size does not exceed 250 microns. They are divided into several groups, among which are sarcodes, flagellates, ciliates.
Type Sarcode
These include amoeba, which consist of a single cell. These creatures live in soil, fresh or s alt water. Their body does not have a permanent shape, whichallows them to form the so-called legs with which these protists capture their food.
Type Flagellates
Flagellates got their name from the presence of a flagellum at the end of the body. It enables such cells to move quickly. This makes flagellates excellent hunters. Among them, a large number of parasites of higher multicellular organisms are distinguished. The body of such creatures has a permanent shape due to the sweaty cell membrane.
Ciliates Type
Ciliates consist of one 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 descended from ciliates. These creatures have a dense cell wall. They have two nuclei in the cytoplasm: a generative one, which controls reproduction, and a vegetative one, which is responsible for vital processes. The entire body of ciliates is covered with cilia. Metabolic products are removed through a special hole - powder.
Human cells: variety of shapes and structural features
Our body is a multicellular formation in which cells are connected to each other. They transmit information using synthesized signal substances. They form tissues, organs and systems that differ from each other functionally and morphologically.
What does a human cell consist of? If we consider cellsany tissue of the body, they have all the signs of eukaryotes: the nucleus, organelles, cytoskeleton, the complexity of the organization of metabolism. However, even among them you can find exceptions that make this or that fabric unique.
For example, red blood cells do not have a nucleus. This gives them the ability to bind more oxygen or carbon dioxide. An egg 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 are short dendrites and long axons.
