Cytoplasm is perhaps the most important part of any cellular structure, representing a kind of “connective tissue” between all the components of the cell.
The functions and properties of the cytoplasm are diverse; its role in ensuring the life of the cell can hardly be overestimated.
This article describes most of the processes occurring in the smallest living structure at the macro level, where the main role is played by the gel-like mass that fills the internal volume of the cell and gives it its appearance and shape.
Cytoplasm is a viscous (jelly-like) transparent substance that fills each cell and is bounded by the cell membrane. It consists of water, salts, proteins and other organic molecules.
All organelles of eukaryotes, such as the nucleus, endoplasmic reticulum and mitochondria, are located in the cytoplasm. The part of it that is not contained in organelles is called cytosol. Although it may seem that the cytoplasm has neither shape nor structure, it is actually a highly organized substance, which is provided by the so-called cytoskeleton (protein structure). The cytoplasm was discovered in 1835 by Robert Brown and other scientists.
Chemical composition
Mainly the cytoplasm is the substance that fills the cell. This substance is viscous, gel-like, consists of 80% water and is usually clear and colorless.
Cytoplasm is the substance of life, also called molecular soup, in which cellular organelles are suspended and connected to each other by a bilayer lipid membrane. The cytoskeleton, located in the cytoplasm, gives it its shape. The process of cytoplasmic flow ensures the movement of useful substances between organelles and the removal of waste products. This substance contains many salts and is a good conductor of electricity.
As was said, substance consists of 70−90% water and is colorless. Most cellular processes occur in it, for example, glycosis, metabolism, cell division processes. The outer transparent glassy layer is called ectoplasm or cell cortex, the inner part of the substance is called endoplasm. In plant cells, the process of cytoplasmic flow takes place, which is the flow of cytoplasm around the vacuole.
Main characteristics
The following properties of the cytoplasm should be listed:
Structure and components
In prokaryotes (such as bacteria), which do not have a membrane-bound nucleus, the cytoplasm represents the entire contents of the cell within the plasma membrane. In eukaryotes (for example, plant and animal cells), the cytoplasm is formed by three distinct components: the cytosol, organelles, and various particles and granules called cytoplasmic inclusions.
Cytosol, organelles, inclusions
The cytosol is a semi-liquid component located external to the nucleus and internal to the plasma membrane. The cytosol makes up approximately 70% of the cell volume and consists of water, cytoskeletal fibers, salts, and organic and inorganic molecules dissolved in water. Also contains proteins and soluble structures such as ribosomes and proteasomes. The inner part of the cytosol, the most fluid and granular, is called the endoplasm.
The network of fibers and high concentrations of dissolved macromolecules, such as proteins, lead to the formation of macromolecular aggregates, which strongly influence the transfer of substances between the components of the cytoplasm.
Organoid means "small organ" that is associated with a membrane. Organelles are located inside the cell and perform specific functions necessary to maintain the life of this smallest building block of life. Organelles are small cellular structures that perform specialized functions. The following examples can be given:
- mitochondria;
- ribosomes;
- core;
- lysosomes;
- chloroplasts (in plants);
- endoplasmic reticulum;
- Golgi apparatus.
Inside the cell there is also a cytoskeleton - a network of fibers that help it maintain its shape.
Cytoplasmic inclusions are particles that are temporarily suspended in a jelly-like substance and consist of macromolecules and granules. Three types of such inclusions can be found: secretory, nutritious, and pigmented. Examples of secretory inclusions include proteins, enzymes and acids. Glycogen (the storage molecule for glucose) and lipids are prime examples of nutrient inclusions, and melanin found in skin cells is an example of pigment inclusions.
Cytoplasmic inclusions, being small particles suspended in the cytosol, represent a diverse range of inclusions present in different types of cells. These can be either crystals of calcium oxalate or silicon dioxide in plants, or granules of starch and glycogen. A wide range of inclusions are lipids that have a spherical shape, are present in both prokaryotes and eukaryotes, and serve for the accumulation of fats and fatty acids. For example, such inclusions occupy most of the volume of adiposites - specialized storage cells.
Functions of the cytoplasm in the cell
The most important functions can be presented in the following table:
- ensuring the shape of the cell;
- habitat of organelles;
- transport of substances;
- supply of nutrients.
Cytoplasm serves to support organelles and cellular molecules. Many cellular processes occur in the cytoplasm. Some of these processes include protein synthesis, the first stage of cellular respiration, which is called glycolysis, processes of mitosis and meiosis. In addition, the cytoplasm helps hormones move throughout the cell, and waste products are also removed through it.
Most of the different actions and events take place in this gelatin-like liquid, which contains enzymes that promote the decomposition of waste products, and many metabolic processes also take place here. Cytoplasm provides the cell with shape, filling it, and helps maintain the organelles in their places. Without it, the cell would appear "deflated" and various substances could not easily move from one organelle to another.
Transport of substances
The liquid substance of the cell contents is very important for maintaining its vital activity, since allows for easy exchange of nutrients between organelles. This exchange is due to the process of cytoplasmic flow, which is the flow of cytosol (the most mobile and fluid part of the cytoplasm) transporting nutrients, genetic information and other substances from one organelle to another.
Some of the processes that occur in the cytosol also include metabolite transfer. The organelle can produce amino acid, fatty acid and other substances, which move through the cytosol to the organelle that needs these substances.
Cytoplasmic flows lead to the cell itself can move. Some of the smallest life structures are equipped with cilia (small hair-like structures on the outside of the cell that allow the cell to move through space). For other cells, for example, amoeba, the only way to move is the movement of fluid in the cytosol.
Nutrient supply
In addition to the transport of various materials, the liquid space between organelles acts as a kind of storage chamber for these materials until the moment when they are actually needed by one or another organelle. Proteins, oxygen, and various building blocks are suspended inside the cytosol. In addition to useful substances, the cytoplasm also contains metabolic products that wait their turn until the removal process removes them from the cell.
Plasma membrane
The cell, or plasma, membrane is a formation that prevents the flow of cytoplasm from the cell. This membrane is composed of phospholipids that form a lipid bilayer, which is semi-permeable: only certain molecules can penetrate this layer. Proteins, lipids, and other molecules can cross the cell membrane through the process of endocytosis, which produces a vesicle containing these substances.
A vesicle containing fluid and molecules breaks away from the membrane, forming an endosome. The latter moves inside the cell to its recipients. Waste products are eliminated through the process of exocytosis. In this process, vesicles formed in the Golgi apparatus connect to a membrane, which pushes their contents into the environment. The membrane also provides the cell with shape and serves as a supporting platform for the cytoskeleton and cell wall (in plants).
Plant and animal cells
The similarity of the internal contents of plant and animal cells indicates their similar origin. Cytoplasm provides mechanical support to the internal structures of the cell, which are suspended in it.
Cytoplasm maintains the shape and consistency of the cell and also contains many chemicals that are key to maintaining life processes and metabolism.
Metabolic reactions such as glycosis and protein synthesis occur in the jelly-like contents. In plant cells, unlike animal cells, there is a movement of cytoplasm around the vacuole, which is known as cytoplasmic flow.
The cytoplasm of animal cells is a substance similar to a gel dissolved in water; it fills the entire volume of the cell and contains proteins and other important molecules necessary for life. The gel-like mass contains proteins, hydrocarbons, salts, sugars, amino acids and nucleotides, all cellular organelles and the cytoskeleton.
Cytoplasm is called the internal environment of the body because it is constantly moving and moves all cellular components. The cytoplasm constantly undergoes metabolic processes and contains all organic and non-organic substances.
Structure
Cytoplasm consists of a permanent liquid part - hyaloplasm and elements that change - organelles and inclusions.
Organelles of the cytoplasm are divided into membrane and non-membrane, the latter in turn can be double-membrane and single-membrane.
- Non-membrane organelles: ribosomes, vacuoles, centrosome, flagella.
- Double membrane organelles: mitochondria, plastids, nucleus.
- Single-membrane organelles: Golgi apparatus, lysosomes, vacuoles, endoplasmic reticulum.
Also, the components of the cytoplasm include cellular inclusions, presented in the form of lipid droplets or glycogen granules.
The main features of the cytoplasm:
- Colorless;
- elastic;
- mucous-viscous;
- structured;
- movable.
The liquid part of the cytoplasm differs in its chemical composition in cells of different specializations. The main substance is water from 70% to 90%; it also contains proteins, carbohydrates, phospholipids, trace elements, and salts.
The acid-base balance is maintained at 7.1–8.5pH (slightly alkaline).
Cytoplasm, when studied at high magnification of a microscope, is not a homogeneous medium. There are two parts - one is located on the periphery in the area of the plasmalemma (ectoplasm), the other is near the core (endoplasm).
Ectoplasm serves as a link with the environment, intercellular fluid and neighboring cells. Endoplasm- This is the location of all organelles.
The structure of the cytoplasm contains special elements - microtubules and microfilaments.
Microtubules– non-membrane organelles necessary for the movement of organelles within the cell and the formation of the cytoskeleton. The globular protein tubulin is the main building block for microtubules. One tubulin molecule does not exceed 5 nm in diameter. In this case, the molecules are able to combine with each other, together forming a chain. 13 such chains form a microtubule with a diameter of 25 nm.
Tubulin molecules are in constant motion to form microtubules; if the cell is exposed to unfavorable factors, the process is disrupted. Microtubules are shortened or completely denatured. These elements of the cytoplasm are very important in the life of plant and bacterial cells, as they take part in the structure of their membranes.
Microfilaments- These are submicroscopic non-membrane organelles that form the cytoskeleton. They are also part of the contractile apparatus of the cell. Microfilaments consist of two types of proteins - actin and myosin. Actin fibers are thin up to 5 nm in diameter, and myosin fibers are thick – up to 25 nm. Microfilaments are mainly concentrated in the ectoplasm. There are also specific filaments that are characteristic of a particular cell type.
Microtubules and microfilaments together form the cell cytoskeleton, which ensures the interconnection of all organelles and intracellular metabolism.
High molecular weight biopolymers are also isolated in the cytoplasm. They are combined into membrane complexes that permeate the entire internal space of the cell, determine the location of organelles, and delimit the cytoplasm from the cell wall.
The structural features of the cytoplasm lie in the ability to change its internal environment. It can exist in two states: semi-liquid ( sol) and viscous ( gel). So, depending on the influence of external factors (temperature, radiation, chemical solutions), the cytoplasm passes from one state to another.
Functions
- Fills the intracellular space;
- connects all structural elements of the cell with each other;
- transports synthesized substances between organelles and outside the cell;
- establishes the location of organelles;
- is a medium for physical and chemical reactions;
- responsible for cell turgor, the constancy of the internal environment of the cell.
The functions of the cytoplasm in a cell also depend on the type of cell itself: plant, animal, eukaryotic or prokaryotic. But in all living cells, an important physiological phenomenon occurs in the cytoplasm - glycolysis. The process of glucose oxidation, which occurs under aerobic conditions and ends with the release of energy.
Movement of the cytoplasm
The cytoplasm is in constant motion; this characteristic is of great importance in the life of the cell. Thanks to movement, metabolic processes inside the cell and the distribution of synthesized elements between organelles are possible.
Biologists observed the movement of cytoplasm in large cells, while monitoring the movement of vacuoles. Microfilaments and microtubules, which are activated in the presence of ATP molecules, are responsible for the movement of the cytoplasm.
The movement of the cytoplasm shows how active the cells are and how capable they are of survival. This process is dependent on external influences, so the slightest changes in environmental factors stop or accelerate it.
The role of the cytoplasm in protein biosynthesis. Protein biosynthesis is carried out with the participation of ribosomes, which are located directly in the cytoplasm or on the granular ER. Also, through nuclear pores, mRNA enters the cytoplasm, which carries information copied from DNA. The exoplasm contains the necessary amino acids for protein synthesis and enzymes that catalyze these reactions.
Summary table of the structure and functions of the cytoplasm
| Structural elements | Structure | Functions |
|---|---|---|
| Ectoplasm | Dense layer of cytoplasm | Provides connection with the external environment |
| Endoplasm | More fluid layer of cytoplasm | Location of cell organelles |
| Microtubules | Constructed from a globular protein - tubulin with a diameter of 5 nm, which is capable of polymerization | Responsible for intracellular transport |
| Microfilaments | Composed of actin and myosin fibers | Form the cytoskeleton, maintain connections between all organelles |
Scientists position the animal cell as the main part of the body of a representative of the animal kingdom - both unicellular and multicellular.
They are eukaryotic, with a true nucleus and specialized structures - organelles that perform differentiated functions.
Plants, fungi and protists have eukaryotic cells; bacteria and archaea have simpler prokaryotic cells.
The structure of an animal cell differs from a plant cell. An animal cell does not have walls or chloroplasts (organelles that perform).
Drawing of an animal cell with captions
A cell consists of many specialized organelles that perform various functions.
Most often, it contains most, sometimes all, existing types of organelles.
Basic organelles and organelles of an animal cell
Organelles and organelles are the “organs” responsible for the functioning of a microorganism.
Core
The nucleus is the source of deoxyribonucleic acid (DNA), the genetic material. DNA is the source of the creation of proteins that control the state of the body. In the nucleus, strands of DNA wrap tightly around highly specialized proteins (histones) to form chromosomes.
The nucleus selects genes to control the activity and functioning of the tissue unit. Depending on the type of cell, it contains a different set of genes. DNA is found in the nucleoid region of the nucleus where ribosomes are formed. The nucleus is surrounded by a nuclear membrane (karyolemma), a double lipid bilayer that separates it from the other components.
The nucleus regulates cell growth and division. When chromosomes are formed in the nucleus, they are duplicated during the process of reproduction, forming two daughter units. Organelles called centrosomes help organize DNA during division. The core is usually represented in the singular.
Ribosomes
Ribosomes are the site of protein synthesis. They are found in all tissue units, in plants and animals. In the nucleus, the DNA sequence that codes for a specific protein is copied into a free messenger RNA (mRNA) strand.
The mRNA strand travels to the ribosome via messenger RNA (tRNA), and its sequence is used to determine the arrangement of amino acids in the chain that makes up the protein. In animal tissue, ribosomes are located freely in the cytoplasm or attached to the membranes of the endoplasmic reticulum.
Endoplasmic reticulum
The endoplasmic reticulum (ER) is a network of membranous sacs (cisternae) extending from the outer nuclear membrane. It modifies and transports proteins created by ribosomes.
There are two types of endoplasmic reticulum:
- granular;
- agranular.
The granular ER contains attached ribosomes. The agranular ER is free of attached ribosomes and is involved in the creation of lipids and steroid hormones and the removal of toxic substances.
Vesicles
Vesicles are small spheres of lipid bilayer that are part of the outer membrane. They are used to transport molecules throughout the cell from one organelle to another and participate in metabolism.
Specialized vesicles called lysosomes contain enzymes that digest large molecules (carbohydrates, lipids and proteins) into smaller ones to facilitate their use by the tissue.
Golgi apparatus
The Golgi apparatus (Golgi complex, Golgi body) also consists of cisterns that are not interconnected (unlike the endoplasmic reticulum).
The Golgi apparatus receives proteins, sorts them, and packages them into vesicles.
Mitochondria
The process of cellular respiration occurs in mitochondria. Sugars and fats are broken down and energy is released in the form of adenosine triphosphate (ATP). ATP controls all cellular processes, mitochondria produce ATP cells. Mitochondria are sometimes called "generators".
Cell cytoplasm
Cytoplasm is the fluid environment of the cell. It can function even without a core, however, for a short time.
Cytosol
Cytosol is called cellular fluid. The cytosol and all the organelles within it, excluding the nucleus, are collectively called the cytoplasm. The cytosol is primarily composed of water and also contains ions (potassium, proteins, and small molecules).
Cytoskeleton
The cytoskeleton is a network of filaments and tubes distributed throughout the cytoplasm.
It performs the following functions:
- gives shape;
- provides strength;
- stabilizes tissue;
- secures organelles in certain places;
- plays an important role in signal transmission.
There are three types of cytoskeletal filaments: microfilaments, microtubules and intermediate filaments. Microfilaments are the smallest elements of the cytoskeleton, and microtubules are the largest.
Cell membrane
The cell membrane completely surrounds the animal cell, which does not have a cell wall, unlike plants. The cell membrane is a double layer consisting of phospholipids.
Phospholipids are molecules containing phosphates attached to glycerol and fatty acid radicals. They spontaneously form double membranes in water due to their simultaneously hydrophilic and hydrophobic properties.
The cell membrane is selectively permeable—it is capable of allowing certain molecules to pass through. Oxygen and carbon dioxide pass easily, while large or charged molecules must pass through a special channel in the membrane to maintain homeostasis.
Lysosomes
Lysosomes are organelles that degrade substances. The lysosome contains about 40 digestive enzymes. It is interesting that the cellular organism itself is protected from degradation in the event of a breakthrough of lysosomal enzymes into the cytoplasm; mitochondria that have completed their functions are subject to decomposition. After cleavage, residual bodies are formed, primary lysosomes turn into secondary ones.
Centriole
Centrioles are dense bodies located near the nucleus. The number of centrioles varies, most often there are two. The centrioles are connected by an endoplasmic bridge.
What does an animal cell look like under a microscope?
Under a standard optical microscope, the main components are visible. Due to the fact that they are connected into a constantly changing organism that is in motion, it can be difficult to identify individual organelles.
The following parts are not in doubt:
- core;
- cytoplasm;
- cell membrane.
A higher resolution microscope, a carefully prepared specimen, and some practice will help you study the cell in more detail.
Centriole functions
The exact functions of the centriole remain unknown. There is a widespread hypothesis that centrioles are involved in the division process, forming the division spindle and determining its direction, but there is no certainty in the scientific world.
The structure of a human cell - drawing with captions
A unit of human cell tissue has a complex structure. The figure shows the main structures.
Each component has its own purpose; only in a conglomerate do they ensure the functioning of an important part of a living organism.
Signs of a living cell
A living cell is similar in its characteristics to a living being as a whole. It breathes, eats, develops, divides, and various processes occur in its structure. It is clear that the fading of natural processes for the body means death.
Distinctive features of plant and animal cells in the table
Plant and animal cells have both similarities and differences, which are briefly described in the table:
| Sign | Vegetable | Animal |
| Getting food | Autotrophic. Photosynthesizes nutrients |
Heterotrophic. Does not produce organic matter. |
| Power storage | In vacuole | In the cytoplasm |
| Storage carbohydrate | starch | glycogen |
| Reproductive system | Formation of a septum in the maternal unit | Formation of constriction in the maternal unit |
| Cell center and centrioles | In lower plants | All types |
| Cell wall | Dense, retains its shape | Flexible, allows change |
The main components are similar for both plant and animal particles.
Conclusion
An animal cell is a complex functioning organism with distinctive features, functions, and a purpose for existence. All organelles and organoids contribute to the life process of this microorganism.
Some components have been studied by scientists, while the functions and features of others have yet to be discovered.
The science that studies the structure and function of cells is called cytology.
Cell- an elementary structural and functional unit of living things.
Cells, despite their small size, are very complex. The internal semi-liquid contents of the cell are called cytoplasm.
Cytoplasm is the internal environment of the cell, where various processes take place and cell components - organelles (organelles) are located.
Cell nucleus
The cell nucleus is the most important part of the cell.
The nucleus is separated from the cytoplasm by a shell consisting of two membranes. The nuclear membrane has numerous pores so that various substances can enter the nucleus from the cytoplasm and vice versa.
The internal contents of the kernel are called karyoplasma or nuclear juice. Located in the nuclear juice chromatin And nucleolus.
Chromatin is a strand of DNA. If the cell begins to divide, then the chromatin threads are tightly wound into a spiral around special proteins, like threads on a spool. Such dense formations are clearly visible under a microscope and are called chromosomes.
Core contains genetic information and controls the life of the cell.
Nucleolus is a dense round body inside the core. Typically, there are from one to seven nucleoli in the cell nucleus. They are clearly visible between cell divisions, and during division they are destroyed.
The function of the nucleoli is the synthesis of RNA and proteins, from which special organelles are formed - ribosomes.
Ribosomes participate in protein biosynthesis. In the cytoplasm, ribosomes are most often located on rough endoplasmic reticulum. Less commonly, they are freely suspended in the cytoplasm of the cell.
Endoplasmic reticulum (ER) participates in the synthesis of cell proteins and transport of substances within the cell.
A significant part of the substances synthesized by the cell (proteins, fats, carbohydrates) is not consumed immediately, but through the EPS channels enters for storage in special cavities laid in peculiar stacks, “cisterns”, and delimited from the cytoplasm by a membrane. These cavities are called Golgi apparatus (complex). Most often, the cisterns of the Golgi apparatus are located close to the cell nucleus.
Golgi apparatus takes part in the transformation of cell proteins and synthesizes lysosomes- digestive organelles of the cell.
Lysosomes They are digestive enzymes, “packed” into membrane vesicles, budded and distributed throughout the cytoplasm.
The Golgi complex also accumulates substances that the cell synthesizes for the needs of the whole organism and which are removed from the cell to the outside.
Mitochondria- energy organelles of cells. They convert nutrients into energy (ATP) and participate in cell respiration.
Mitochondria are covered with two membranes: the outer membrane is smooth, and the inner one has numerous folds and projections - cristae.
Plasma membrane
For a cell to be a single system, it is necessary that all its parts (cytoplasm, nucleus, organelles) are held together. For this purpose, in the process of evolution, it developed plasma membrane, which, surrounding each cell, separates it from the external environment. The outer membrane protects the internal contents of the cell - the cytoplasm and nucleus - from damage, maintains a constant shape of the cell, ensures communication between cells, selectively allows necessary substances into the cell and removes metabolic products from the cell.
The structure of the membrane is the same in all cells. The basis of the membrane is a double layer of lipid molecules, in which numerous protein molecules are located. Some proteins are located on the surface of the lipid layer, others penetrate both layers of lipids through and through.
Special proteins form the finest channels through which potassium, sodium, calcium ions and some other ions of small diameter can pass into or out of the cell. However, larger particles (nutrient molecules - proteins, carbohydrates, lipids) cannot pass through membrane channels and enter the cell using phagocytosis or pinocytosis:
- At the point where the food particle touches the outer membrane of the cell, an invagination is formed, and the particle enters the cell, surrounded by a membrane. This process is called phagocytosis (plant cells are covered with a dense layer of fiber (cell membrane) on top of the outer cell membrane and cannot capture substances by phagocytosis).
- Pinocytosis differs from phagocytosis only in that in this case the invagination of the outer membrane captures not solid particles, but droplets of liquid with substances dissolved in it. This is one of the main mechanisms for the penetration of substances into the cell.
The cells of animals and plants, both multicellular and unicellular, are in principle similar in structure. Differences in the details of cell structure are associated with their functional specialization.
The main elements of all cells are the nucleus and cytoplasm. The nucleus has a complex structure that changes at different phases of cell division, or cycle. The nucleus of a nondividing cell occupies approximately 10–20% of its total volume. It consists of karyoplasm (nucleoplasm), one or more nucleoli (nucleoli) and a nuclear membrane. Karyoplasm is a nuclear sap, or karyolymph, in which there are strands of chromatin that form chromosomes.
Basic properties of the cell:
- metabolism
- sensitivity
- reproductive capacity
The cell lives in the internal environment of the body - blood, lymph and tissue fluid. The main processes in the cell are oxidation and glycolysis - the breakdown of carbohydrates without oxygen. Cell permeability is selective. It is determined by the reaction to high or low salt concentrations, phago- and pinocytosis. Secretion is the formation and release by cells of mucus-like substances (mucin and mucoids), which protect against damage and participate in the formation of intercellular substance.
Types of cell movements:
- amoeboid (pseudopods) – leukocytes and macrophages.
- sliding – fibroblasts
- flagellar type – spermatozoa (cilia and flagella)
Cell division:
- indirect (mitosis, karyokinesis, meiosis)
- direct (amitosis)
During mitosis, the nuclear substance is distributed evenly between daughter cells, because Nuclear chromatin is concentrated in chromosomes, which split into two chromatids that separate into daughter cells.
Structures of a living cell
Chromosomes
Mandatory elements of the nucleus are chromosomes, which have a specific chemical and morphological structure. They take an active part in the metabolism in the cell and are directly related to the hereditary transmission of properties from one generation to another. It should, however, be borne in mind that although heredity is ensured by the entire cell as a single system, nuclear structures, namely chromosomes, occupy a special place in this. Chromosomes, unlike cell organelles, are unique structures characterized by constant qualitative and quantitative composition. They cannot replace each other. An imbalance in the chromosomal complement of a cell ultimately leads to its death.
Cytoplasm
The cytoplasm of the cell exhibits a very complex structure. The introduction of thin sectioning techniques and electron microscopy made it possible to see the fine structure of the underlying cytoplasm. It has been established that the latter consists of parallel complex structures in the form of plates and tubules, on the surface of which there are tiny granules with a diameter of 100–120 Å. These formations are called the endoplasmic complex. This complex includes various differentiated organelles: mitochondria, ribosomes, Golgi apparatus, in the cells of lower animals and plants - centrosome, in animals - lysosomes, in plants - plastids. In addition, the cytoplasm reveals a number of inclusions that take part in the cell’s metabolism: starch, fat droplets, urea crystals, etc.
Membrane
The cell is surrounded by a plasma membrane (from the Latin “membrane” - skin, film). Its functions are very diverse, but the main one is protective: it protects the internal contents of the cell from the influences of the external environment. Thanks to various outgrowths and folds on the surface of the membrane, the cells are firmly connected to each other. The membrane is permeated with special proteins through which certain substances needed by the cell or to be removed from it can move. Thus, metabolism occurs through the membrane. Moreover, what is very important, substances are passed through the membrane selectively, due to which the required set of substances is maintained in the cell.
In plants, the plasma membrane is covered on the outside with a dense membrane consisting of cellulose (fiber). The shell performs protective and supporting functions. It serves as the outer frame of the cell, giving it a certain shape and size, preventing excessive swelling.
Core
Located in the center of the cell and separated by a two-layer membrane. It has a spherical or elongated shape. The shell - karyolemma - has pores necessary for the exchange of substances between the nucleus and the cytoplasm. The contents of the nucleus are liquid - karyoplasm, which contains dense bodies - nucleoli. They secrete granules - ribosomes. The bulk of the nucleus is nuclear proteins - nucleoproteins, in the nucleoli - ribonucleoproteins, and in the karyoplasm - deoxyribonucleoproteins. The cell is covered with a cell membrane, which consists of protein and lipid molecules that have a mosaic structure. The membrane ensures the exchange of substances between the cell and the intercellular fluid.
EPS
This is a system of tubules and cavities, on the walls of which there are ribosomes that provide protein synthesis. Ribosomes can be freely located in the cytoplasm. There are two types of EPS - rough and smooth: on the rough EPS (or granular) there are many ribosomes that carry out protein synthesis. Ribosomes give membranes their rough appearance. Smooth ER membranes do not carry ribosomes on their surface; they contain enzymes for the synthesis and breakdown of carbohydrates and lipids. Smooth EPS looks like a system of thin tubes and tanks.
Ribosomes
Small bodies with a diameter of 15–20 mm. They synthesize protein molecules and assemble them from amino acids.
Mitochondria
These are double-membrane organelles, the inner membrane of which has projections - cristae. The contents of the cavities are matrix. Mitochondria contain a large number of lipoproteins and enzymes. These are the energy stations of the cell.
Plastids (characteristic only of plant cells!)
Their content in the cell is the main feature of the plant organism. There are three main types of plastids: leucoplasts, chromoplasts and chloroplasts. They have different colors. Colorless leucoplasts are found in the cytoplasm of cells of uncolored parts of plants: stems, roots, tubers. For example, there are many of them in potato tubers, in which starch grains accumulate. Chromoplasts are found in the cytoplasm of flowers, fruits, stems, and leaves. Chromoplasts provide yellow, red, and orange colors to plants. Green chloroplasts are found in the cells of leaves, stems and other parts of the plant, as well as in a variety of algae. Chloroplasts are 4-6 microns in size and often have an oval shape. In higher plants, one cell contains several dozen chloroplasts.
Green chloroplasts are able to transform into chromoplasts - that’s why the leaves turn yellow in the fall, and green tomatoes turn red when ripe. Leucoplasts can transform into chloroplasts (greening of potato tubers in the light). Thus, chloroplasts, chromoplasts and leucoplasts are capable of mutual transition.
The main function of chloroplasts is photosynthesis, i.e. In chloroplasts, in the light, organic substances are synthesized from inorganic ones due to the conversion of solar energy into the energy of ATP molecules. The chloroplasts of higher plants are 5-10 microns in size and resemble a biconvex lens in shape. Each chloroplast is surrounded by a double membrane that is selectively permeable. The outside is a smooth membrane, and the inside has a folded structure. The main structural unit of the chloroplast is the thylakoid, a flat double-membrane sac that plays a leading role in the process of photosynthesis. The thylakoid membrane contains proteins similar to mitochondrial proteins that participate in the electron transport chain. The thylakoids are arranged in stacks resembling stacks of coins (10 to 150) called grana. Grana has a complex structure: chlorophyll is located in the center, surrounded by a layer of protein; then there is a layer of lipoids, again protein and chlorophyll.
Golgi complex
This is a system of cavities delimited from the cytoplasm by a membrane and can have different shapes. The accumulation of proteins, fats and carbohydrates in them. Carrying out the synthesis of fats and carbohydrates on membranes. Forms lysosomes.
The main structural element of the Golgi apparatus is the membrane, which forms packets of flattened cisterns, large and small vesicles. The cisterns of the Golgi apparatus are connected to the channels of the endoplasmic reticulum. Proteins, polysaccharides, and fats produced on the membranes of the endoplasmic reticulum are transferred to the Golgi apparatus, accumulate inside its structures and are “packaged” in the form of a substance, ready either for release or for use in the cell itself during its life. Lysosomes are formed in the Golgi apparatus. In addition, it is involved in the growth of the cytoplasmic membrane, for example during cell division.
Lysosomes
Bodies delimited from the cytoplasm by a single membrane. The enzymes they contain accelerate the breakdown of complex molecules into simple ones: proteins into amino acids, complex carbohydrates into simple ones, lipids into glycerol and fatty acids, and also destroy dead parts of the cell and entire cells. Lysosomes contain more than 30 types of enzymes (protein substances that increase the rate of chemical reactions tens and hundreds of thousands of times) capable of breaking down proteins, nucleic acids, polysaccharides, fats and other substances. The breakdown of substances with the help of enzymes is called lysis, hence the name of the organelle. Lysosomes are formed either from the structures of the Golgi complex or from the endoplasmic reticulum. One of the main functions of lysosomes is participation in the intracellular digestion of nutrients. In addition, lysosomes can destroy the structures of the cell itself when it dies, during embryonic development, and in a number of other cases.
Vacuoles
They are cavities in the cytoplasm filled with cell sap, a place of accumulation of reserve nutrients and harmful substances; they regulate the water content in the cell.
Cell center
It consists of two small bodies - centrioles and centrosphere - a compacted section of the cytoplasm. Plays an important role in cell division
Cell movement organoids
- Flagella and cilia, which are cell outgrowths and have the same structure in animals and plants
- Myofibrils are thin filaments more than 1 cm long with a diameter of 1 micron, located in bundles along the muscle fiber
- Pseudopodia (perform the function of movement; due to them, muscle contraction occurs)
Similarities between plant and animal cells
The characteristics that are similar between plant and animal cells include the following:
- Similar structure of the structure system, i.e. presence of nucleus and cytoplasm.
- The metabolic process of substances and energy is similar in principle.
- Both animal and plant cells have a membrane structure.
- The chemical composition of the cells is very similar.
- Plant and animal cells undergo a similar process of cell division.
- Plant cells and animal cells have the same principle of transmitting the code of heredity.
Significant differences between plant and animal cells
In addition to the general features of the structure and vital activity of plant and animal cells, there are also special distinctive features of each of them.
Thus, we can say that plant and animal cells are similar to each other in the content of some important elements and some vital processes, and also have significant differences in structure and metabolic processes.