All animals and plants that we meet in everyday life are multicellular organisms. However, there is a microcosm where invisible creatures live for our eyes. 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: Typical Prokaryotic and Eukaryotic Cell Scheme
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 signs of a prokaryotic cell? First of all, it is the simplicity of the 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 the protrusion of the cytoplasmic membrane, which are called mesosomes. They are in most cases responsible for respiration or photosynthesis.
In prokaryotic cells, the surface apparatus is quite complicated, because it is represented by several layers. The first of them - the cytoplasmic membrane - plays a crucial role in the transport of substances between the cell and the environment. CPM is represented by a bilipid layer in which various proteins are anchored. Further, the prokaryotic cell is coated, 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 also has its limits.
The last layer of the surface apparatus may not always be present. It is a mucous membrane. Firstly, it helps the cell in the process of movement, reducing friction. Secondly, the mucous membrane contains the products of metabolism and secretion of these cells. These substances can be used for protective purposes or, conversely, to attack your victim. All prokaryotic organisms consist of one cell. These include bacteria in the first place.
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 does a living eukaryotic cell consist of? The following elements are distinguished in its structure:
- Nucleus.
- 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 organelles, cells are distinguished:
- Two-membrane structures (mitochondria and plastids).
- Single-membrane structures (lysosomes, Golgi apparatus, endoplasmic reticulum, vacuoles, peroxisomes, etc.).
- Non-membrane structures (ribosomes, cytoskeleton).
The eukaryotic membrane in structure resembles that of prokaryotes. However, it has a more complex organization. A eukaryotic cell consists of parts called compartments. Such an organization system greatly simplifies the course of all biochemical processes, because the cell is divided into various compartments.
Protists - Unicellular Eukaryotic Organisms
Among the whole variety of eukaryotic organisms, to which we belong, there are also creatures less noticeable to the human eye. They are called protists. They make up a separate kingdom in taxonomy. All protists are made up of a single cell, so the size does not exceed 250 microns. They are divided into several groups, among which sarcode, flagellates, and ciliates stand out.
Type Sarcode
These include amoeba, which consist of a single cell. These creatures live in soil, fresh or salt water. Their body does not have a constant shape, which allows them to form the so-called legs with which these protists capture their food.
Type Flagellates
Flagellates got their name due to the presence of a flagellum at the end of the body. It allows such cells to move quickly. This makes flagella excellent hunters. Among them, a large number of parasites of higher multicellular organisms are distinguished . The body of such creatures has a constant shape due to the sweaty cell membrane.
Type of Ciliates
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 evolved from ciliates. 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 whole body of the ciliates is covered with cilia. Metabolism 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 cells are connected to each other. They transmit information using synthesized signaling substances. They form tissues, organs and systems that differ functionally and morphologically from each other.
What does a human cell consist of? If we consider the cells of any body tissue, then they have all the signs of eukaryotes: the nucleus, organelles, cytoskeleton, the complexity of the organization of metabolism. However, among them, you can find exceptions that give the uniqueness of a particular fabric.
For example, red blood cells do not have a nucleus. This enables them 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 short dendrites and long axons are distinguished.