Remark 1

All known unicellular and many cellular organisms divided into two groups - prokaryotes and eukaryotes.

Animal cells, cells of most plant and fungal species are characterized by an interphase nucleus and organelles typical of all cells. These organisms are called nuclear, or eukaryotes.

Another, smaller group of organisms, and probably more ancient in origin, is called prokaryotes (pre-nuclear). These are bacteria and blue-green algae (cyanobacteria) that lack a true nucleus and many cytoplasmic organelles.

Prokaryotic cells

Prokaryotic cells have a relatively simple structure. A prokaryotic cell does not have a true nucleus, nucleolus, or chromosomes. Instead of cell nucleus there is an equivalent - nucleoid(nucleus-like formation), devoid of a shell and consisting of a single circular DNA molecule associated with a very small amount of protein. This cluster nucleic acids and proteins lying in the cytoplasm, and not separated from it by a membrane.

Remark 2

It is this feature that is decisive in the division of cells into prokaryotic (pre-nuclear) and eukaryotic (nuclear).

Prokaryotic cells have no internal membranes other than the dents in the plasmalemma. This means that they lack organelles such as mitochondria, endoplasmic reticulum, chloroplasts, lysosomes and the Golgi complex, which are surrounded by a membrane and are present in eukaryotic cells. There are also no vacuoles. Of the organelles, there are only smaller ribosomes than those of eukaryotic cells.

Prokaryotic cells are covered with a dense cell wall and often with a mucous capsule.

The cell wall contains murein. Its molecule consists of parallel polysaccharide chains cross-linked with each other by short chains of peptides.

The plasma membrane can sag into the cytoplasm, forming mesosomes. Redox enzymes are located on the membranes of mesosomes, and in photosynthetic prokaryotes they also have the corresponding pigments (bacteriochlorophyll in bacteria, chlorophyll a and phycobilins in cyanobacteria). Due to this, such membranes are able to perform the functions of mitochondria, chloroplasts, and other organelles. Asexual reproduction of prokaryotes is carried out by simple cell division in half.

eukaryotic cells

All eukaryotic cells are divided into compartments - reaction spaces - by numerous membranes. In these compartments, various chemical reactions occur independently of each other simultaneously.

In the cell, the main functions are distributed between the nucleus and various organelles - mitochondria, ribosomes, the Golgi complex, etc. The nucleus, plastids and mitochondria are separated from the cytoplasm by a two-membrane membrane. The cell nucleus contains the genetic material. Plant chloroplasts mainly perform the function of capturing solar energy and converting it into the chemical energy of carbohydrates during photosynthesis, while mitochondria produce energy by breaking down carbohydrates, fats, proteins and other organic compounds.

The membrane systems of the cytoplasm of eukaryotic cells include the endoplasmic reticulum and the Golgi complex, which are necessary for the implementation life processes cells. Lysosomes, peroxisomes and vacuoles also perform specific functions.

Only chromosomes, ribosomes, microtubules and microfilaments of non-membrane origin.

Eukaryotic cells divide by mitosis.

One of the important classifications in cell biology is their division into prokaryotes and eukaryotes.

Speaking about the evolution of microbiology, it is worth noting the significant contribution of the scientist Pasteur, who was its founder. It was thanks to this man that the fields of immunology and biotechnology began to develop.

He gave a basic definition of the main concepts related to the cell, substantiated the principles and operation of the mechanism on the relevance of the role of microorganisms in all spheres of life of organisms. His work was continued by Koch.

Let's try to figure out which organisms belong to each of these two main classes of cells. What is the structure of cells and how do they differ? What is the classification of each of these types.

How are they useful for humans and the biosphere, and what is their significance in general? The reader will find answers to all these questions below.

What are prokaryotes and eukaryotes

It is known that all living organisms by their nature are divided into cellular and non-cellular (viruses). Moreover, the former are also divided into 2 categories: prokaryotes (the pre-nuclear kingdom) and eukaryotes (the nuclear kingdom).

Prokaryotes include:

For eukaryotes:

• mushrooms;
• plants;
• animals.

How are they different? Consider below.

Signs of a eukaryotic cell

It is believed that nuclear cellular organisms appeared about 1.5 billion years ago. Although in the past, scientists poorly understood the essence of phenomena at the cellular level, but in their writings they often began to appear approximate drawings of this unit of the body.

Signatures in each state one distinctive feature of cells of this type - the presence of a nucleus covered with a double layer of membrane.

It is in the nucleus that the main genetic material of these organisms is stored. In addition, it has several nucleoli with most of the volume of all types of RNA.

Also in such a cell there are other formations - organelles that are located in its cytoplasm. These include:

• mitochondria - resemble proteins in their structure, also contain DNA;
• lysosomes - are vesicles that help the overall metabolism of this cell;
• chloroplasts.

These compounds are also separated by membranes, the main role of which is the connection of the various elements of the organism unit with the external environment. In order for all the elements of the composition to function well, for a complete "skeleton" in this cell there are filaments and microtubules.

The process of respiration is more common among living organisms formed by these cells.

The structure of prokaryotic cells

Unlike the previous superkingdom, protozoa lack a nucleus in the cell.

In it, instead of the nucleus, there is one chromosome in the cytoplasm, which transmits the genetic material.

They reproduce simply by cell division. Very little in cell fluid various kinds structures. They are also covered with a membrane. They contain ribosomes.

Consider the main representatives of this super-kingdom.

Bacteria and cyanobacteria

The former are single-celled microorganisms. With the help of flagella, they are very mobile.

They live in all areas of life. From the external environment, they are protected by murein and a special shell.

The second type is represented by the simplest cells with small ribosomes and one hereditary chromosome.

Seaweed

They live mainly in aquatic environment and on the ground. They have autotrophic nutrition. Their buoyancy is determined by vacuoles. In addition, for them, as for representatives of the plant kingdom, photosynthesis is characteristic.

Examples are represented by green algae. They also reproduce by simple division. At very adverse conditions spores can be used for movement.

Similarities and differences between prokaryotes and eukaryotes

The comparative table "Characteristics of the super-kingdoms" shows signs by which it is easy to identify the main differences.

Conclusion

So, without representatives of these two kingdoms it is impossible to imagine life on earth. What is their role in nature? It's simple: protozoa are organisms without which almost all biochemical processes in a biosystem are impossible. In addition, many are involved in the process of photosynthesis, serve as a source of nutrition and respiration for plants.

Eukaryotes are not only food for others, but also the main regulatory force of the population. different types, i.e., one of the mechanisms of natural selection.

Prokaryotic cells differ in very small sizes (from 0.5 to 5 microns) and the simplest structure (Fig. 36). They have immobile cytoplasm, plasma membrane and cell wall. The cytoplasm contains few small ribosomes and various inclusions in the form of lipid granules and other substances. The genetic material (DNA) is not separated by membranes from the cytoplasm, there are no well-formed chromosomes, and a single circular DNA molecule is conventionally called a “chromosome”.

eukaryotic cells are very complex units of wildlife and are characterized by a large structural and functional diversity (Fig. 37). In this case, the shape of cells often depends on the functions they perform in a multicellular organism. However, the general plan of the structure of all eukaryotic cells has a fundamental similarity. In eukaryotic cells, there is a well-formed nucleus, delimited from the cytoplasm by a sheath of two membranes; chromosomes of long twisted strands of DNA; a complete set of various organelles.

The difference between prokaryotes and eukaryotes especially well seen when comparing their main features (table).

This is the oldest group that appeared about 3.5 billion years ago; besides, these are the smallest organisms possessing cell structure. The properties of prokaryotes are summarized in Table. 2.2. As a rule, prokaryotes are represented by single cells, although blue-green algae (cyanobacteria, Cyanobacteria) can form chains of cells called threads.

Some bacteria adhere to each other, forming characteristic clusters resembling bunches of grapes (Fig. 2.10), but the combined cells remain completely independent of each other. An individual bacterial cell can only be seen using , which is why they are called microorganisms. Science that studies bacteria bacteriology- constitutes an important branch.

Bacteria vary in size: their length ranges from 0.1 to 10 microns, and the average diameter is 1 micron. Thus, in bacterial cell there is enough space to fit 200 molecules of medium-sized globular proteins (5 nm in diameter) across it. Since such molecules are capable of diffusing at a distance of about 60 microns per second, these organisms do not need any special transport mechanisms.

Bacteria can be found everywhere: in soil and dust, in water and in the air, inside and on the surface and. Some bacteria live in hot springs with temperatures of 78°C or higher. Others are able to survive under very low temperatures and even survive certain periods of freezing in the ice. Bacteria are also found in deep crevices on the ocean floor at very high pressure and temperature 360°C. They start unique food chains in these areas of the ocean.

The number of bacteria is unimaginably large; found that one gram of fertile soil contains 2.5 billion bacteria; in 1 cm 3 of fresh milk, their content can exceed 3 billion. Together with fungi, bacteria are of vital importance for all other organisms, since, destroying organic substances as a result of their vital activity, they ensure the circulation of biogenic elements in nature. In addition, they are becoming increasingly important in human life, and not only because some of them are the causative agents of various diseases, but also because, due to the diversity of their biological chemical reactions they can be used in many biotechnological processes. This issue is discussed in more detail in Chap. 12.

Two types of cells are known in modern and fossil organisms: prokaryotic and eukaryotic. They differ so sharply in structural features that this served to distinguish two superkingdoms of the living world - prokaryotes, i.e. prenuclear, and eukaryotes, i.e. true nuclear organisms. Intermediate forms between these largest living taxa are still unknown.

The main features and differences between prokaryotic and eukaryotic cells (table):

The main difference between prokaryotic and eukaryotic cells is that their DNA is not organized into chromosomes and is not surrounded by a nuclear envelope. Eukaryotic cells are much more complex. Their protein-bound DNA is organized into chromosomes, which are located in a special formation, in fact the largest organelle of the cell - the nucleus. In addition, the extranuclear active content of such a cell is divided into separate compartments using the endoplasmic reticulum formed by the elementary membrane. Eukaryotic cells are usually larger than prokaryotic ones. Their sizes vary from 10 to 100 microns, while the sizes of prokaryotic cells (various bacteria, cyanobacteria - blue-green algae and some other organisms), as a rule, do not exceed 10 microns, often being 2-3 microns. In a eukaryotic cell, gene carriers - chromosomes - are located in a morphologically formed nucleus, delimited from the rest of the cell by a membrane. In exceptionally thin, transparent preparations, living chromosomes can be seen with a light microscope. More often they are studied on fixed and stained preparations.

Chromosomes are made up of DNA, which is complexed with histone proteins rich in the amino acids arginine and lysine. Histones make up a significant part of the mass of chromosomes.

A eukaryotic cell has a variety of permanent intracellular structures - organelles (organelles) that are absent in a prokaryotic cell.

Prokaryotic cells can divide into equal parts by constriction or bud, i.e. form a daughter cell smaller than the mother cell, but never divide by mitosis. Cells eukaryotic organisms, in contrast, divide by mitosis (excluding some very archaic groups). In this case, the chromosomes "split" longitudinally (more precisely, each DNA strand reproduces its own similarity around itself), and their "halves" - chromatids (full copies of the DNA strand) diverge in groups towards the opposite poles of the cell. Each of the cells that are then formed receives the same set of chromosomes.

The ribosomes of a prokaryotic cell differ sharply from the ribosomes of eukaryotes in size. A number of processes inherent in the cytoplasm of many eukaryotic cells, - phagocytosis, pinocytosis and cyclosis (rotational movement of the cytoplasm) - not found in prokaryotes. The prokaryotic cell does not require vitamin C, but eukaryotic ones cannot do without it.

Mobile forms of prokaryotic and eukaryotic cells differ significantly. Prokaryotes have motor adaptations in the form of flagella or cilia, consisting of flagellin protein. The motor adaptations of mobile eukaryotic cells are called undulipodia, which are fixed in the cell with the help of special bodies of kinetosomes. Electron microscopy revealed the structural similarity of all undulipodia of eukaryotic organisms and their sharp differences from prokaryotic flagella.

1. The structure of a eukaryotic cell.

The cells that make up the tissues of animals and plants vary considerably in shape, size and internal structure. However, all of them show similarities in the main features of the processes of vital activity, metabolism, in irritability, growth, development, and the ability to change.
Cells of all types contain two main components, closely related to each other - the cytoplasm and the nucleus. The nucleus is separated from the cytoplasm by a porous membrane and contains nuclear sap, chromatin, and the nucleolus. Semi-liquid cytoplasm fills the entire cell and is penetrated by numerous tubules. Outside, it is covered with a cytoplasmic membrane. It has specialized organelle structures, permanently present in the cell, and temporary formations - inclusions. Membrane organelles : outer cyto plasma membrane(HCM), endoplasmic reticulum (ER), Golgi apparatus, lysosomes, mitochondria and plastids. The basis of the structure of all membrane organelles is the biological membrane. All membranes have a fundamentally unified structural plan and consist of a double layer of phospholipids, in which protein molecules are immersed from different sides and at different depths. The membranes of organelles differ from each other only in the sets of proteins included in them.

cytoplasmic membrane. In all plant cells, multicellular animals, protozoa and bacteria, the cell membrane is three-layered: the outer and inner layers consist of protein molecules, the middle one consists of lipid molecules. It limits the cytoplasm from the external environment, surrounds all organelles of the cell and is a universal biological structure. In some cells outer shell formed by several membranes that are tightly adjacent to each other. In such cases cell wall becomes dense and elastic and allows you to keep the shape of the cell, as, for example, in euglena and ciliates shoes. Most plant cells, in addition to the membrane, also have a thick cellulose membrane on the outside - cell wall. It is clearly visible in a conventional light microscope and performs a supporting function due to a rigid outer layer that gives the cells a clear shape.
On the surface of cells, the membrane forms elongated outgrowths - microvilli, folds, protrusions and protrusions, which greatly increases the suction or excretory surface. With the help of membrane outgrowths, cells are connected to each other in the tissues and organs of multicellular organisms; various enzymes involved in metabolism are located on the folds of the membranes. Separating the cell from environment, the membrane regulates the direction of diffusion of substances and simultaneously carries out their active transfer into the cell (accumulation) or out (excretion). Due to these properties of the membrane, the concentration of potassium, calcium, magnesium, phosphorus ions in the cytoplasm is higher, and the concentration of sodium and chlorine is lower than in the environment. Through the pores of the outer membrane from the external environment, ions, water and small molecules of other substances penetrate into the cell. Penetration into the cell of relatively large solid particles is carried out by phagocytosis(from the Greek "fago" - I devour, "drink" - a cell). Wherein outer membrane bends inside the cell at the point of contact with the particle, dragging the particle deep into the cytoplasm, where it undergoes enzymatic degradation. Drops of liquid substances enter the cell in a similar way; their absorption is called pinocytosis(from the Greek "pino" - I drink, "cytos" - a cell). The outer cell membrane also performs other important biological functions.
Cytoplasm 85% consists of water, 10% of proteins, the rest is lipids, carbohydrates, nucleic acids and mineral compounds; all these substances form a colloidal solution similar in consistency to glycerin. colloidal substance cell, depending on its physiological state and the nature of the impact of the external environment, has the properties of both liquid and elastic, more dense body. The cytoplasm is permeated with channels various shapes and quantities, which are called endoplasmic reticulum. Their walls are membranes that are in close contact with all the organelles of the cell and together with them form a single functional and structural system for the exchange of substances and energy and the movement of substances inside the cell.

In the walls of the tubules are the smallest grains - granules, called ribosomes. Such a network of tubules is called granular. Ribosomes can be located on the surface of the tubules separately or form complexes of five to seven or more ribosomes, called polysomes. Other tubules do not contain granules, they make up a smooth endoplasmic reticulum. Enzymes involved in the synthesis of fats and carbohydrates are located on the walls.

The inner cavity of the tubules is filled with waste products of the cell. Intracellular tubules, forming a complex branching system, regulate the movement and concentration of substances, separate various molecules of organic substances and their stages of synthesis. On the inner and outer surfaces of membranes rich in enzymes, proteins, fats and carbohydrates are synthesized, which are either used in metabolism, or accumulate in the cytoplasm as inclusions, or are excreted.

Ribosomes found in all types of cells - from bacteria to cells of multicellular organisms. These are round bodies, consisting of ribonucleic acid (RNA) and proteins in almost equal proportions. Their composition certainly includes magnesium, the presence of which maintains the structure of ribosomes. Ribosomes can be associated with the membranes of the endoplasmic reticulum, from the outside cell membrane or lie freely in the cytoplasm. They carry out protein synthesis. Ribosomes, in addition to the cytoplasm, are found in the nucleus of the cell. They are produced in the nucleolus and then enter the cytoplasm.

Golgi complex in plant cells it looks like individual bodies surrounded by membranes. In animal cells, this organoid is represented by cisterns, tubules and vesicles. The membrane tubes of the Golgi complex from the tubules of the endoplasmic reticulum receive the secretion products of the cell, where they are chemically rearranged, compacted, and then transferred to the cytoplasm and either used by the cell itself or removed from it. In the tanks of the Golgi complex, polysaccharides are synthesized and combined with proteins, resulting in the formation of glycoproteins.

Mitochondria- small rod-shaped bodies, bounded by two membranes. Numerous folds, called cristae, extend from the inner membrane of the mitochondria; various enzymes are located on their walls, with the help of which the synthesis of a high-energy substance, adenosine triphosphoric acid (ATP), is carried out. depending on cell activity and external influences Mitochondria can move, change their size and shape. Ribosomes, phospholipids, RNA and DNA are found in mitochondria. The presence of DNA in mitochondria is associated with the ability of these organelles to reproduce by constriction formation or budding during cell division, as well as the synthesis of some mitochondrial proteins.

Lysosomes- small oval formations limited by the membrane and scattered throughout the cytoplasm. Found in all cells of animals and plants. They arise in the extensions of the endoplasmic reticulum and in the Golgi complex, are filled with hydrolytic enzymes, and then separate and enter the cytoplasm. Under normal conditions, lysosomes digest particles that enter the cell by phagocytosis and organelles of dying cells. Lysosome products are excreted through the lysosome membrane into the cytoplasm, where they are incorporated into new molecules. When the lysosome membrane is ruptured, enzymes enter the cytoplasm and digest its contents, causing cell death.
plastids is found only in plant cells and is found in most green plants. Organic substances are synthesized and accumulated in plastids. There are three types of plastids: chloroplasts, chromoplasts and leukoplasts.

Chloroplasts - green plastids containing the green pigment chlorophyll. They are found in leaves, young stems, unripe fruits. Chloroplasts are surrounded by a double membrane. In higher plants inner part The chloroplast is filled with a semi-liquid substance, in which the plates are laid parallel to each other. Paired membranes of plates, merging, form stacks containing chlorophyll. In each stack of chloroplasts of higher plants, layers of protein molecules and lipid molecules alternate, and chlorophyll molecules are located between them. This layered structure provides maximum free surfaces and facilitates the capture and transfer of energy during photosynthesis.
Chromoplasts - plastids, which contain plant pigments (red or brown, yellow, orange). They are concentrated in the cytoplasm of cells of flowers, stems, fruits, leaves of plants and give them the appropriate color. Chromoplasts are formed from leukoplasts or chloroplasts as a result of the accumulation of pigments. carotenoids.

Leucoplasts—colorless plastids located in the unpainted parts of plants: in stems, roots, bulbs, etc. Starch grains accumulate in the leukoplasts of some cells, oils and proteins accumulate in the leukoplasts of other cells.

All plastids arise from their predecessors - proplastids. They revealed DNA that controls the reproduction of these organelles.

cell center, or centrosome, plays important role during cell division and consists of two centrioles . It is found in all cells of animals and plants, except for flowering, lower fungi and some protozoa. Centrioles in dividing cells take part in the formation of the division spindle and are located at its poles. In a dividing cell, the cell center divides first, at the same time an achromatin spindle is formed, orienting the chromosomes when they diverge towards the poles. One centriole leaves each daughter cell.
Many plant and animal cells have special purpose organelles: cilia, performing the function of movement (ciliates, cells respiratory tract), flagella(the simplest unicellular, male germ cells in animals and plants, etc.).

Inclusions - temporary elements that arise in a cell at a certain stage of its life as a result of a synthetic function. They are either used or removed from the cell. Inclusions are also reserve nutrients: in plant cells, starch, fat droplets, proteins, essential oils, many organic acids, salts of organic and inorganic acids; in animal cells - glycogen (in liver cells and muscles), fat drops (in subcutaneous tissue); Some inclusions accumulate in cells as waste - in the form of crystals, pigments, etc.

Vacuoles - these are cavities bounded by a membrane; are well expressed in plant cells and are present in protozoa. Occur in different areas extensions of the endoplasmic reticulum. And gradually separate from it. Vacuoles maintain turgor pressure, they contain cell or vacuolar juice, the molecules of which determine its osmotic concentration. It is believed that the initial products of synthesis - soluble carbohydrates, proteins, pectins, etc. - accumulate in the cisterns of the endoplasmic reticulum. These accumulations represent the beginnings of future vacuoles.
cytoskeleton . One of distinctive features eukaryotic cell is the development in its cytoplasm of skeletal formations in the form of microtubules and bundles of protein fibers. The elements of the cytoskeleton are closely connected with the outer cytoplasmic membrane and the nuclear membrane, forming complex interlacings in the cytoplasm. The supporting elements of the cytoplasm determine the shape of the cell, ensure the movement of intracellular structures and the movement of the entire cell.

Core cell plays a major role in its life, with its removal, the cell ceases its functions and dies. Most animal cells have one nucleus, but there are also multinucleated cells (human liver and muscles, fungi, ciliates, green algae). Mammalian erythrocytes develop from progenitor cells containing a nucleus, but mature erythrocytes lose it and do not live long.
The nucleus is surrounded by a double membrane penetrated by pores, through which it is closely connected with the channels of the endoplasmic reticulum and the cytoplasm. Inside the nucleus is chromatin- spiralized sections of chromosomes. During cell division, they turn into rod-shaped structures that are clearly visible under a light microscope. Chromosomes are a complex set of proteins and DNA called nucleoprotein.

The functions of the nucleus consist in the regulation of all vital functions of the cell, which it carries out with the help of DNA and RNA-material carriers of hereditary information. In preparation for cell division, DNA is doubled, during mitosis, chromosomes separate and are transferred to daughter cells, ensuring the continuity of hereditary information in each type of organism.

Karyoplasm - the liquid phase of the nucleus, in which the products of the vital activity of nuclear structures are in dissolved form.

nucleolus- isolated, densest part of the nucleus.

The nucleolus consists of complex proteins and RNA, free or bound phosphates of potassium, magnesium, calcium, iron, zinc, and ribosomes. The nucleolus disappears before the start of cell division and re-forms in the last phase of division.

Thus, the cell has a fine and very complex organization. An extensive network of cytoplasmic membranes and the membrane principle of the structure of organelles make it possible to distinguish between many chemical reactions simultaneously occurring in the cell. Each of the intracellular formations has its own structure and specific function, but only with their interaction is the harmonious life of the cell possible. Based on this interaction, substances from the environment enter the cell, and waste products are removed from it into external environment This is how metabolism works. Perfection structural organization The cell could only arise as a result of a long biological evolution, during which the functions it performed gradually became more complex.
The simplest unicellular forms are both a cell and an organism with all its vital manifestations. AT multicellular organisms cells form homogeneous groups - tissues. In turn, tissues form organs, systems, and their functions are determined by the overall vital activity of the whole organism.

2. Prokaryotic cell.

Prokaryotes include bacteria and blue-green algae (cyanoea). The hereditary apparatus of prokaryotes is represented by one circular DNA molecule that does not form bonds with proteins and contains one copy of each gene - haploid organisms. In the cytoplasm there is a large number of small ribosomes; there are no or weakly expressed internal membranes. The enzymes of plastic metabolism are located diffusely. The Golgi apparatus is represented by individual vesicles. Enzyme systems of energy metabolism are ordered on the inner surface of the outer cytoplasmic membrane. Outside, the cell is surrounded by a thick cell wall. Many prokaryotes are capable of sporulation under adverse conditions of existence; at the same time, a small area of ​​the cytoplasm containing DNA is released, and is surrounded by a thick multilayer capsule. The metabolic processes inside the spores practically stop. Getting into favorable conditions, the spore is converted into an active cellular form. Reproduction of prokaryotes occurs by simple fission in two.

The average size of prokaryotic cells is 5 µm. They do not have any internal membranes other than invaginations of the plasma membrane. The layers are missing. Instead of the cell nucleus, there is its equivalent (nucleoid), devoid of a shell and consisting of a single DNA molecule. In addition, bacteria can contain DNA in the form of tiny plasmids similar to eukaryotic extranuclear DNA.
AT prokaryotic cells capable of photosynthesis (blue-green algae, green and purple bacteria) there are variously structured large invaginations of the membrane - thylakoids, which in their function correspond to eukaryotic plastids. The same thylakoids or, in colorless cells, smaller invaginations of the membrane (and sometimes even the plasma membrane itself) functionally replace mitochondria. Other, complexly differentiated invaginations of the membrane are called mesosomes; their function is not clear.
Only some prokaryotic cell organelles are homologous to the corresponding eukaryotic organelles. Prokaryotes are characterized by the presence of a murein sac - a mechanically strong element of the cell wall

Comparative characteristics of cells of plants, animals, bacteria, fungi

When comparing bacteria with eukaryotes, the only similarity can be distinguished - the presence of a cell wall, but the similarities and differences of eukaryotic organisms deserve closer attention. You should start comparing with the components that are characteristic of plants, animals, and fungi. These are the nucleus, mitochondria, the Golgi apparatus (complex), the endoplasmic reticulum (or endoplasmic reticulum) and lysosomes. They are characteristic of all organisms, have a similar structure and perform the same functions. Now let's focus on the differences. A plant cell, unlike an animal cell, has a cell wall made of cellulose. In addition, there are organelles characteristic plant cells- plastids and vacuoles. The presence of these components is due to the need for plants to maintain their shape, in the absence of a skeleton. There are differences in the characteristics of growth. In plants, it occurs mainly due to an increase in the size of vacuoles and cell elongation, while in animals there is an increase in the volume of the cytoplasm, and the vacuole is completely absent. Plastids (chloroplasts, leukoplasts, chromoplasts) are predominantly characteristic of plants, since their main task is to provide an autotrophic way of nutrition. Animals, as opposed to plants, have digestive vacuoles that provide a heterotrophic mode of nutrition. Mushrooms occupy a special position and their cells are characterized by signs characteristic of both plants and animals. Like animal fungi, a heterotrophic type of nutrition is inherent, a cell membrane containing chitin, and glycogen is the main storage substance. At the same time, they, like plants, are characterized by unlimited growth, inability to move, and nutrition by absorption.