As you know, almost all organisms on our planet have a cellular structure. Basically, all cells have a similar structure. It is the smallest structural and functional unit of a living organism. Cells can have different functions and, consequently, variations in their structure. In many cases, they can act as independent organisms.
Plants, animals, fungi, bacteria have a cellular structure. However, there are some differences between their structural and functional units. And in this article we will consider the cellular structure. Grade 8 provides for the study of this topic. Therefore, the article will be of interest to schoolchildren, as well as to those who are simply interested in biology. This review will describe the cellular structure, cells of various organisms, similarities and differences between them.
History of the theory of cell structure
People didn't always know what organisms were made of. The fact that all tissues are formed from cells has become known relatively recently. science that studiesthis is biology. The cellular structure of the body was first described by scientists Matthias Schleiden and Theodor Schwann. It happened in 1838. Then the theory of cellular structure consisted of the following provisions:
- animals and plants of all kinds are formed from cells;
- they grow with the formation of new cells;
- cell is the smallest unit of life;
- an organism is a collection of cells.
Modern theory includes slightly different provisions, and there are a little more of them:
- cell can only come from mother cell;
- a multicellular organism does not consist of a simple collection of cells, but of those combined into tissues, organs and organ systems;
- cells of all organisms have a similar structure;
- cell is a complex system consisting of smaller functional units;
- cell is the smallest structural unit capable of acting as an independent organism.
Cell structure
Since almost all living organisms have a cellular structure, it is worth considering the general characteristics of the structure of this element. First, all cells are divided into prokaryotic and eukaryotic. In the latter, there is a nucleus that protects the hereditary information recorded on DNA. In prokaryotic cells, it is absent, and DNA floats freely. All eukaryotic cells are built according to the following scheme. They have a shell - a plasma membrane, around it is usuallyadditional protective formations are located. Everything below it, except for the nucleus, is the cytoplasm. It consists of hyaloplasm, organelles and inclusions. Hyaloplasm is the main transparent substance that serves as the internal environment of the cell and fills all its space. Organelles are permanent structures that perform certain functions, that is, they ensure the vital activity of the cell. Inclusions are non-permanent formations that also play a role, but do so temporarily.
Cell structure of living organisms
Now we will list the organelles that are the same for the cells of any living creature on the planet, except for bacteria. These are mitochondria, ribosomes, Golgi apparatus, endoplasmic reticulum, lysosomes, cytoskeleton. Bacteria are characterized by only one of these organelles - ribosomes. And now consider the structure and functions of each organelle separately.
Mitochondria
They provide intracellular respiration. Mitochondria play the role of a kind of "power plant", generating energy, which is necessary for the life of the cell, for the passage of certain chemical reactions in it.
They belong to two-membrane organoids, that is, they have two protective shells - external and internal. Under them is a matrix - an analogue of hyaloplasm in the cell. Cristae form between the outer and inner membranes. These are the folds that contain enzymes. These substances are needed in order to be able to carry outchemical reactions that release the energy needed by the cell.
Ribosome
They are responsible for protein metabolism, namely, for the synthesis of substances of this class. Ribosomes consist of two parts - subunits, large and small. This organelle has no membrane. Ribosome subunits unite only immediately before the process of protein synthesis, the rest of the time they are separated. Substances are produced here on the basis of information recorded on DNA. This information is delivered to the ribosomes with the help of tRNA, since it would be very impractical and dangerous to transport DNA here every time - the probability of damaging it would be too high.
Golgi Apparatus
This organoid consists of stacks of flat cisterns. The functions of this organoid are that it accumulates and modifies various substances, and also participates in the formation of lysosomes.
Endoplasmic reticulum
It is divided into smooth and rough. The first is built from flat tubes. It is responsible for the production of steroids and lipids in the cell. Rough is so called because on the walls of the membranes of which it consists, there are numerous ribosomes. It performs a transport function. Namely, it transfers proteins synthesized there from ribosomes to the Golgi apparatus.
Lysosomes
They are single-membrane organelles that contain the enzymes needed to carry out the chemical reactions that occur in the processintracellular metabolism. The largest number of lysosomes is observed in leukocytes - cells that perform an immune function. This is explained by the fact that they carry out phagocytosis and are forced to digest a foreign protein, which requires a large amount of enzymes.
Cytoskeleton
This is the last organelle that is common to fungi, animals and plants. One of its main functions is to maintain the shape of the cell. It is made up of microtubules and microfilaments. The former are hollow tubes made from the protein tubulin. Due to their presence in the cytoplasm, some organelles can move around the cell. In addition, cilia and flagella in unicellular organisms can also consist of microtubules. The second component of the cytoskeleton - microfilaments - consists of contractile proteins actin and myosin. In bacteria, this organelle is usually absent. But some of them are characterized by the presence of a cytoskeleton, however, a more primitive, not as complex structure as in fungi, plants and animals.
Plant cell organelles
The cellular structure of plants has some peculiarities. In addition to the organelles listed above, vacuoles and plastids are also present. The former are designed to accumulate substances in it, including unnecessary ones, since it is often impossible to remove them from the cell due to the presence of a dense wall around the membrane. The fluid that is inside the vacuole is called cell sap. In a young plant cell, there are initially several small vacuoles, which, as itaging merge into one big. There are three types of plastids: chromoplasts, leucoplasts, and chromoplasts. The former are characterized by the presence of red, yellow or orange pigment in them. Chromoplasts in most cases are needed to attract pollinating insects or animals that are involved in the distribution of fruits along with seeds with a bright color. It is thanks to these organelles that flowers and fruits have a variety of colors. Chromoplasts can form from chloroplasts, which can be observed in autumn, when the leaves turn yellow-red, and also during fruit ripening, when the green color gradually disappears completely. The next type of plastids - leukoplasts - are designed to store substances such as starch, some fats and proteins. Chloroplasts carry out the process of photosynthesis, thanks to which plants receive the necessary organic substances for themselves.
From six molecules of carbon dioxide and the same amount of water, a cell can get one molecule of glucose and six oxygen, which is released into the atmosphere. Chloroplasts are two-membrane organelles. Their matrix contains thylakoids grouped into grana. These structures contain chlorophyll, and here the photosynthesis reaction takes place. In addition, the chloroplast matrix also contains its own ribosomes, RNA, DNA, special enzymes, starch grains and lipid drops. The matrix of these organelles is also called the stroma.
Features of mushrooms
These organisms also have a cellular structure. In ancient times they were united in one kingdom withplants purely outwardly, but with the advent of more advanced science, it turned out that this could not be done.
Firstly, fungi, unlike plants, are not autotrophs, they are not capable of producing organic substances themselves, but only feed on ready-made ones. Secondly, the cell of the fungus is more similar to the animal, although it has some features of the plant. A fungal cell, like a plant, is surrounded by a dense wall, but it does not consist of cellulose, but of chitin. This substance is difficult to digest by the body of animals, which is why mushrooms are considered heavy food. In addition to the organelles described above, which are characteristic of all eukaryotes, there is also a vacuole here - this is another similarity between fungi and plants. But plastids are not observed in the structure of the fungal cell. Between the wall and the cytoplasmic membrane there is a lomasome, the functions of which are still not fully understood. The rest of the structure of the fungal cell resembles an animal. In addition to organelles, inclusions such as fat drops and glycogen also float in the cytoplasm.
Animal cells
They are characterized by all the organelles that were described at the beginning of the article. In addition, a glycocalyx is located on top of the plasma membrane - a membrane consisting of lipids, polysaccharides and glycoproteins. It is involved in the transport of substances between cells.
Core
Of course, in addition to common organelles, animal, plant, fungal cells have a nucleus. It is protected by two shells in which there are pores. The matrix is made up of karyoplasm(nuclear sap), in which chromosomes float with hereditary information recorded on them. There are also nucleoli, which are responsible for the formation of ribosomes and RNA synthesis.
Prokaryotes
These include bacteria. The cellular structure of bacteria is more primitive. They don't have a nucleus. The cytoplasm contains organelles such as ribosomes. Surrounding the plasma membrane is a murein cell wall. Most prokaryotes are equipped with organelles of movement - mainly flagella. An additional protective shell, a mucous capsule, can also be located around the cell wall. In addition to the basic DNA molecules, the cytoplasm of bacteria contains plasmids that contain information responsible for increasing the body's resistance to adverse conditions.
Are all organisms made up of cells?
Some believe that all living organisms have a cellular structure. But this is not true. There is such a kingdom of living organisms as viruses.
They are not made of cells. This organism is represented by a capsid - a protein shell. Inside it is DNA or RNA, on which a small amount of genetic information is recorded. Around the protein shell, a lipoprotein can also be located, which is called the supercapsid. Viruses can only reproduce inside foreign cells. In addition, they are capable of crystallization. As you can see, the statement that all living organisms have a cellular structure is incorrect.
Comparison chart
After weexamined the structure of various organisms, to summarize. So, the cellular structure, table:
| Animals | Plants | Mushrooms | Bacteria | |
| Core | Yes | Yes | Yes | No |
| Cell wall | No | Yes, made of cellulose | Eat, from chitin | Eat, from murein |
| Ribosome | Yes | Yes | Yes | Yes |
| Lysosomes | Yes | Yes | Yes | No |
| Mitochondria | Yes | Yes | Yes | No |
| Golgi Apparatus | Yes | Yes | Yes | No |
| Cytoskeleton | Yes | Yes | Yes | Yes |
| Endoplasmic reticulum | Yes | Yes | Yes | No |
| Cytoplasmic membrane | Yes | Yes | Yes | Yes |
| Additional shells | Glycocalyx | No | No | Mucoid Capsule |
That, perhaps, is all. We examined the cellular structure of all organisms that exist on the planet.
