Distinguish a plant cell from an animal cell. Plant and animal cell
Plant and animal cells have common organelles, such as the nucleus, endoplasmic reticulum, ribosomes, mitochondria, and Golgi apparatus. However, a plant cell has significant differences from an animal cell.
A plant cell, like an animal cell, is surrounded by a cytoplasmic membrane, but besides it it is limited by a thick cell wall consisting of cellulose, which animal cells do not have.
Vacuoles accumulating cell sap exist in both plant and animal cells, but in animal cells they are weakly expressed.
The predominance of synthetic processes over energy release processes is one of the most characteristic features of plant metabolism. The primary synthesis of carbohydrates from inorganic substances occurs in plastids. Thus, in animal cells, unlike plant cells, the following plastids are absent: chloroplasts (responsible for the photosynthesis reaction), leucoplasts (responsible for the accumulation of starch) and chromoplasts (give color to the fruits and flowers of plants)
Conclusions website
- A plant cell has a strong and thick cell wall made of cellulose.
- In a plant cell, a network of vacuoles is developed, in an animal cell it is poorly developed
- A plant cell contains special organelles - plastids (namely, chloroplasts, leucoplasts and chromoplasts), but an animal cell does not contain them.
All living organisms, with the exception of viruses, are composed of cells. However, viruses cannot be called fully independent living organisms. They need cells to reproduce, meaning they infect other organisms. Thus, we can say that life can only be fully realized in cells.
Cells of different living organisms have a common structural plan; many processes occur in the same way. However, there are some key differences between the cells of organisms belonging to different kingdoms. For example, bacterial cells do not have nuclei. Animal and plant cells have nuclei. But they have other differences.
Plant cells, unlike animal cells, have three distinct features. These are the presence of a cell wall, plastids and a central vacuole.
Both plant cells and animal cells are surrounded by a cell membrane. It limits the contents of the cell from the external environment, allows some substances to pass through and does not allow others to pass through. At the same time, plants on the outside of the membrane also have cell wall, or cell membrane. It is quite rigid and gives the plant cell its shape. Thanks to cell walls, plants do not need a skeleton. Without them, the plants would probably “spread” across the ground. And even grass can stand upright. In order for substances to penetrate through the cell membrane, it has pores. Also, through these pores, cells contact each other, forming cytoplasmic bridges. The cell wall is made of cellulose.
Only plant cells have plastids. Plastids include chloroplasts, chromoplasts and leucoplasts. The most important ones are chloroplasts. The process of photosynthesis occurs in them, in which organic substances are synthesized from inorganic substances. Animals cannot synthesize organic substances from inorganic ones. They receive ready-made organic substances with food, if necessary, break them down into simpler ones and synthesize their own organic substances. Although plants can photosynthesize, the vast majority of their organic matter also comes from other organic matter. However, the ancestor of everything organic in them is organic matter, which is obtained in chloroplasts from inorganic substances. This substance is glucose.
Large central vacuole characteristic only of plant cells. Animal cells also have vacuoles. However, as the cell grows, they do not merge into one large vacuole, which pushes the rest of the cell contents towards the membrane. This is exactly what happens in plants. The vacuole contains cell sap, which contains mainly storage substances. A large vacuole creates internal pressure on the cell membrane. Thus, along with the cell membrane, it maintains the shape of the cell.
The reserve nutrient of the carbohydrate type in plant cells is starch, and in animal cells it is glycogen. Starch and glycogen are very similar in structure.
Animal cells also have “their own” organelles, which higher plants do not have. These are centrioles. They are involved in the process of cell division.
The remaining organelles in plant and animal cells are similar in structure and function. These are mitochondria, Golgi complex, nucleus, endoplasmic reticulum, ribosomes and some others.
There are 3 kingdoms - plants, animals and fungi.
1. Differences in nutrition
Plants are autotrophs, i.e. They make organic substances for themselves from inorganic substances (carbon dioxide and water) through the process of photosynthesis.
Animals and fungi are heterotrophs, i.e. finished organic substances are obtained from food.
2. Growth or movement
Animals are able to move and grow only before reproduction begins.
Plants and mushrooms do not move, but they grow unlimitedly throughout their lives.
3. Differences in the structure and functioning of the cell*
1) Plastids (chloroplasts, leucoplasts, chromoplasts) are found only in plants.
2) Only plants have a large central vacuole. It occupies most of the adult cell. The shell of this vacuole is called tonoplast, and the contents are cell sap.**
3) Centrioles (cell center) are found only in animals.***
4) There is no cell wall (dense membrane) in animals; in plants it is made of cellulose (fiber), and in fungi it is made of chitin.
5) The storage carbohydrate in plants is starch, and in animals and fungi it is glycogen.
*WHAT IS IT REALLY like? (real biology is very slow, but it is moving forward in the Unified State Examination, so you should be up to date)
**Vacuoles, including large ones, are found not only in plants, but also in fungi. But only animals have lysosomes.
***All plants have centroles except gymnosperms and flowering plants.
PLANTS
1. What features, unlike animal and fungal cells, does a plant cell have?
1) forms a cellulose cell wall
2) includes ribosomes
3) has the ability to divide repeatedly
4) accumulates nutrients
5) contains leukoplasts
6) does not have centrioles
Answer
2. Choose three correct answers out of six and write down the numbers under which they are indicated. The plant cell of higher plants has
1) plastids
2) centrioles
3) autotrophic type of nutrition
4) carbohydrate - glycogen
5) decorated core
6) cell wall made of chitin
Answer
PLANTS - ANIMALS
1. Establish a correspondence between the characteristics and the kingdom of organisms: 1) plants, 2) animals
A) Synthesize organic substances from inorganic ones
B) They have unlimited growth
B) Absorb substances in the form of solid particles
D) The storage nutrient is glycogen.
D) The reserve nutrient is starch.
E) Most organisms do not have cell center centrioles in their cells.
Answer
2. Establish a correspondence between the characteristics of organisms and the kingdoms for which they are characteristic: 1) plants, 2) animals. Write numbers 1 and 2 in the correct order.
A) heterotrophic type of nutrition
B) the presence of chitin in the exoskeleton
B) the presence of educational tissue
D) regulation of life activity only with the help of chemicals
D) formation of urea during metabolism
E) the presence of a rigid cell wall made of polysaccharides
Answer
3. Establish a correspondence between the characteristic of an organism and the kingdom for which this characteristic is characteristic: 1) Plants, 2) Animals. Write numbers 1 and 2 in the order corresponding to the letters.
A) cell wall
B) autotrophs
B) larval stage
D) consumers
D) connective tissue
E) tropisms
Answer
4. Establish a correspondence between organelles and cells: 1) plant, 2) animal. Write numbers 1 and 2 in the order corresponding to the letters.
A) cell wall
B) glycocalyx
B) centrioles
D) plastids
D) starch granules
E) glycogen granules
Answer
5. Establish a correspondence between the characteristics of the vital functions of organisms and the kingdoms for which they are characteristic: 1) Plants, 2) Animals. Write numbers 1 and 2 in the order corresponding to the letters.
A) heterotrophic nutrition in most representatives
B) maturation of gametes by meiosis
B) primary synthesis of organic substances from inorganic substances
D) transport of substances through conductive tissue
D) neurohumoral regulation of vital processes
E) reproduction by spores and vegetative organs
Answer
FORMING 6:
A) the ability to phagocytose
B) the presence of a large storage vacuole
PLANTS ANIMALS DIFFERENCES
1. Choose three options. The cells of a flowering plant differ from the cells of an animal body in the presence
1) fiber casings
2) chloroplasts
3) decorated core
4) vacuoles with cell sap
5) mitochondria
6) endoplasmic reticulum
Answer
2. Choose three correct answers out of six and write down the numbers under which they are indicated. The cells of plant organisms, unlike animals, contain
1) chloroplasts
2) mitochondria
3) nucleus and nucleolus
4) vacuoles with cell sap
5) cell wall made of cellulose
6) ribosomes
Answer
3. Select three elements that distinguish a plant cell from an animal cell.
1) absence of mitochondria
2) the presence of leukocytes
3) absence of glycocalyx
3) presence of thylakoids
5) the presence of cell sap
6) absence of a plasma membrane
Answer
PLANTS - MUSHROOMS
1. Establish a correspondence between the characteristics of organisms and the kingdom to which it belongs: 1) Fungi, 2) Plants. Write numbers 1 and 2 in the correct order.
A) the cell wall contains chitin
B) autotrophic nutrition type
C) form organic substances from inorganic ones
D) starch is a reserve nutrient
D) in natural systems they are decomposers
E) the body consists of mycelium
Answer
2. Establish a correspondence between the structural feature of the cell and the kingdom for which it is characteristic: 1) Fungi, 2) Plants. Write numbers 1 and 2 in the correct order.
A) the presence of plastids
B) absence of chloroplasts
B) reserve substance – starch
D) the presence of vacuoles with cell sap
D) the cell wall contains fiber
E) the cell wall contains chitin
Answer
3. Establish a correspondence between the characteristics of the cell and its type: 1) fungal, 2) plant. Write numbers 1 and 2 in the correct order.
A) reserve carbohydrate – starch
B) chitin gives strength to the cell wall
B) there are no centrioles
D) there are no plastids
D) autotrophic nutrition
E) there is no large vacuole
Answer
4. Establish a correspondence between the characteristics of cells and their type: 1) plant, 2) fungal. Write numbers 1 and 2 in the order corresponding to the letters.
A) phototrophic nutrition
B) heterotrophic nutrition
B) the presence of a cellulose shell
D) storage substance - glycogen
D) the presence of a large storage vacuole
E) the absence of a cell center in most centrioles
Answer
5. Establish a correspondence between the characteristics of cells and the kingdoms of organisms to which these cells belong: 1) Plants, 2) Fungi. Write numbers 1 and 2 in the order corresponding to the letters.
A) cell wall made of chitin
B) the presence of large vacuoles with cell sap
C) absence of centrioles of the cell center in most representatives
D) storage carbohydrate glycogen
D) heterotrophic mode of nutrition
E) the presence of various plastids
Answer
PLANT MUSHROOMS SIMILARITIES
Choose three options. Plants, like mushrooms,
2) have limited growth
3) absorb nutrients from the body surface
4) feed on ready-made organic substances
5) contain chitin in cell membranes
6) have a cellular structure
Answer
ANIMALS EXCEPT
1. All of the characteristics listed below, except two, are used to describe the structure of most animal cells. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) centrioles of the cell center
2) cell membrane made of chitin
3) semi-autonomous organelles
4) plastids
5) glycocalyx
Answer
2. All of the concepts listed below, except two, can be used to characterize the somatic cell of a vertebrate animal. Identify two concepts that “fall out” from the general list and write down the numbers under which they are indicated.
1) glycogen
2) mitosis
3) haploid set
4) cell wall
5) sex chromosomes
Answer
ANIMAL MUSHROOMS
1. Establish a correspondence between the characteristics and kingdoms of organisms: 1) Animals, 2) Fungi. Write numbers 1 and 2 in the order corresponding to the letters.
A) cell walls contain chitin
B) the presence of mycelium consisting of filaments-hyphae
B) the presence of a glycocalyx on cell membranes
D) growth throughout life
D) ability to move independently
Answer
2. Establish a correspondence between the characteristics of organisms and the kingdoms for which they are characteristic: 1) Fungi, 2) Animals. Write numbers 1 and 2 in the order corresponding to the letters.
A) rigid cell wall
B) active movement in space
C) absorption of nutrients by the body surface by all representatives of the kingdom
D) unlimited growth for all representatives
D) external and internal fertilization
E) the presence of tissues and organs
Answer
ANIMAL MUSHROOMS SIMILARITY
Choose three options. The similarity between fungal and animal cells is that they have
1) a shell of chitin-like substance
2) glycogen as a storage carbohydrate
3) decorated core
4) vacuoles with cell sap
5) mitochondria
6) plastids
Answer
MUSHROOMS
1. Choose three options. Signs characteristic of mushrooms
1) the presence of chitin in the cell wall
2) storage of glycogen in cells
3) absorption of food by phagocytosis
4) ability for chemosynthesis
5) heterotrophic nutrition
6) limited growth
Answer
2. Choose three correct answers out of six and write down the numbers under which they are indicated. The following characteristics are characteristic of mushrooms:
1) are prenuclear organisms
2) act as decomposers in the ecosystem
3) have root hairs
4) have limited growth
5) by type of nutrition - heterotrophs
6) contain chitin in cell membranes
Answer
3. Choose three correct answers out of six and write down the numbers under which they are indicated in the answer. From the listed characteristics, select those that fungal cells have.
1) the hereditary apparatus is located in the nucleotide
2) the cell wall contains chitin
3) eukaryotic cell
4) storage substance – glycogen
5) there is no cell membrane
6) type of nutrition – autotrophic
Answer
MUSHROOMS EXCEPT
1. All but two of the terms listed below are used to describe a fungal cell. Identify two terms that “drop out” from the general list and write down the numbers under which they are indicated in the table.
1) core
2) chemosynthesis
3) cell wall
4) autotrophic nutrition
5) glycogen
Answer
2. All of the characteristics listed below, except two, are used to describe the structure of a fungal cell. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) presence of a designed core
2) the presence of a cellulose shell
3) ability for phagocytosis
4) the presence of membrane organelles
5) the presence of glycogen as a reserve substance
Answer
MUSHROOMS PLANT DIFFERENCES
1. Choose three correct answers out of six and write down the numbers under which they are indicated. Fungi, unlike plants,
1) belong to nuclear organisms (eukaryotes)
2) grow throughout life
3) feed on ready-made organic substances
4) contain chitin in cell membranes
5) play the role of decomposers in the ecosystem
6) synthesize organic substances from inorganic ones
Answer
2. Select three characteristics that distinguish mushrooms from plants.
1) chemical composition of the cell wall
2) unlimited growth
3) immobility
4) way of eating
5) reproduction by spores
6) presence of fruiting bodies
Answer
MUSHROOMS ANIMALS SIMILARITY
1. Choose three options. Mushrooms, like animals,
1) grow throughout life
2) do not contain ribosomes in cells
3) have a cellular structure
4) do not contain mitochondria in cells
5) contain chitin in organisms
6) are heterotrophic organisms
Answer
2. Choose three correct answers out of six and write down the numbers under which they are indicated. Mushrooms, like animals,
2) have a vegetative body consisting of mycelium
3) lead an active lifestyle
4) have unlimited growth
5) store carbohydrates in the form of glycogen
6) form urea during metabolism
Answer
MUSHROOMS ANIMALS DIFFERENCES
Choose three correct answers out of six and write down the numbers under which they are indicated. By what characteristics can mushrooms be distinguished from animals?
1) feed on ready-made organic substances
2) have a cellular structure
3) grow throughout life
4) have a body consisting of filaments-hyphae
5) absorb nutrients from the surface of the body
6) have limited growth
Answer
1. The characteristics listed below, except two, are used to describe the characteristics of the cells shown in the figure. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated.
1) have a formed core
2) are heterotrophic
3) capable of photosynthesis
4) contain a central vacuole with cell sap
5) accumulate glycogen
Answer
2. All of the characteristics listed below, except two, are used to describe the cell shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) the shape of the cell is maintained by turgor
2) storage substance - starch
3) the cell does not have centrioles
4) the cell does not have a cell wall
5) all proteins are synthesized in chloroplasts
Answer
3. The terms listed below, except two, are used to characterize the cell shown in the figure. Identify two terms that “drop out” from the general list and write down the numbers under which they are indicated.
1) starch
2) mitosis
3) meiosis
4) phagocytosis
5) chitin
Answer
4. All but two of the terms listed below are used to describe the cell shown in the figure. Identify two terms that “drop out” from the general list and write down the numbers under which they are indicated
1) photosynthesis
2) cell wall
3) chitin
4) nucleoid
5) core
Answer
5. All of the signs listed below, except two, are used to describe the cell shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) mitosis
2) phagocytosis
3) starch
4) chitin
5) meiosis
Answer
6. All of the signs listed below, except two, are used to describe the cell shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) the presence of chloroplasts
2) presence of glycocalyx
3) ability to photosynthesize
4) ability to phagocytose
5) ability for protein biosynthesis
Answer
7. All of the characteristics listed below, except two, can be used to describe the cell shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) has a nucleus in which DNA molecules are located
2) the area where DNA is located in the cytoplasm is called a nucleoid
3) DNA molecules are circular
4) DNA molecules are associated with proteins
5) various membrane organelles are located in the cytoplasm
Answer
1. All the signs listed below, except two, are used to describe the cell shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) cells are always single
2) eat osmotrophically
3) protein is synthesized by ribosomes
4) contain a cellulose wall
5) DNA is in the nucleus
Answer
2. All of the signs listed below, except two, can be used to describe the cell shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) there is a cell membrane
2) the cell wall consists of chitin
3) the hereditary apparatus is contained in a ring chromosome
4) storage substance - glycogen
5) the cell is capable of photosynthesis
Answer
1. All the signs listed below, except two, are used to describe the cell shown in the figure. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated.
1) has a glycocalyx
2) has a cell wall
3) feeds autotrophically
4) contains a cell center
5) divides by mitosis
Answer
2. All of the characteristics listed below, except two, are used to describe the cell shown in the figure. Identify two characteristics that “drop out” from the general list, write down the numbers under which they are indicated.
1) the presence of a nucleolus with chromatin
2) the presence of a cellulose cell membrane
3) presence of mitochondria
4) prokaryotic cell
5) ability for phagocytosis
Answer
3. All of the signs listed below, except two, are used to describe the cell shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) the presence of chloroplasts
2) the presence of a developed network of vacuoles
3) presence of glycocalyx
4) presence of a cell center
5) ability for intracellular digestion
Answer
4. All of the concepts listed below, except two, are used to characterize the cell shown in the figure. Identify two concepts that “fall out” from the general list and write down the numbers under which they are indicated.
1) mitochondria
2) nucleoid
3) eukaryotes
4) chloroplasts
5) microtubules
Answer
In what form do cells of various organisms store glucose? Identify two true statements from the general list and write down the numbers under which they are indicated.
1) Plants store glucose in the form of glycogen
2) Animals store glucose in the form of sucrose
3) Plants store glucose in the form of starch
4) Fungi and plants store glucose in the form of cellulose
5) Fungi and animals store glucose in the form of glycogen
Answer
Analyze the text “Difference between a plant cell and an animal cell.” Fill in the blank text cells using the terms in the list. For each cell indicated by a letter, select the corresponding term from the list provided. A plant cell, unlike an animal cell, has ___(A), which in old cells ___(B) and displaces the cell nucleus from the center to its shell. Cell sap may contain ___ (B), which give it a blue, purple, crimson color, etc. The shell of a plant cell mainly consists of ___ (D).
1) chloroplast
2) vacuole
3) pigment
4) mitochondria
5) merge
6) disintegrate
7) cellulose
8) glucose
Answer
Establish a correspondence between the characteristics of the cell and its type: 1) bacterial, 2) fungal, 3) plant. Write the numbers 1, 2 and 3 in the correct order.
A) absence of membrane organelles
B) storage substance – starch
B) the ability to chemosynthesize
D) the presence of a nucleoid
D) the presence of chitin in the cell wall
Answer
1) chloroplasts
2) central vacuole
3) endoplasmic reticulum
4) mitochondria
5) Golgi apparatus
Answer
All but two of the following organelles are present in all types of eukaryotic cells. Identify two characteristics that “drop out” from the general list, and write down the numbers under which they are indicated in your answer.
1) plasma membrane
2) endoplasmic reticulum
3) flagella
4) mitochondria
5) chloroplasts
Answer
Look at the picture depicting this cell and determine (A) the type of this cell, (B) its type of nutrition, (C) the organelle indicated in the picture by number 1. For each letter, select the corresponding term from the list provided.
1) bacterial
2) mitochondria
3) autotrophic
4) vegetable
5) construction
6) heterotrophic
7) animal
8) core
Answer
Match the characteristics and kingdoms of the organisms shown in the figure. Write the numbers 1 and 2 in the sequence corresponding to the letters.
A) characterized by an autotrophic type of nutrition
B) have a variety of tissues and organs
C) most representatives have centrioles of the cell center in their cells
D) reserve nutrient - glycogen
D) many representatives have a fruiting body
E) are producers in ecosystems
Answer
Establish a correspondence between the characters and cells of different kingdoms. Write numbers 1 and 2 in the order corresponding to the letters.
A) have a shell made of chitin
B) maintain shape with the help of turgor
B) have a developed cytoskeleton
D) cells are always deprived of their own mobility
D) does not contain vacuoles with cell sap
E) contain lysosomes
Answer
Establish a correspondence between the characteristics and organisms: 1) yeast, 2) amoeba. Write numbers 1 and 2 in the order corresponding to the letters.
A) cells are not capable of movement
B) capture food by phagocytosis
C) are able to exist in anaerobic conditions
D) cells are covered with a shell of chitin
D) lysosomes are present in the cell
E) has a contractile vacuole
Answer
© D.V. Pozdnyakov, 2009-2019
According to their structure, the cells of all living organisms can be divided into two large sections: non-nuclear and nuclear organisms.
In order to compare the structure of plant and animal cells, it should be said that both of these structures belong to the superkingdom of eukaryotes, which means they contain a membrane membrane, a morphologically shaped nucleus and organelles for various purposes.
In contact with
| Vegetable | Animal | |
| Nutrition method | Autotrophic | Heterotrophic |
| Cell wall | It is located outside and is represented by a cellulose shell. Does not change its shape | Called glycocalyx, it is a thin layer of cells of protein and carbohydrate nature. The structure can change its shape. |
| Cell center | No. Can only be found in lower plants | Eat |
| Division | A partition is formed between the daughter structures | A constriction is formed between the daughter structures |
| Storage carbohydrate | Starch | Glycogen |
| Plastids | Chloroplasts, chromoplasts, leucoplasts; differ from each other depending on color | No |
| Vacuoles | Large cavities that are filled with cell sap. Contain a large amount of nutrients. Provide turgor pressure. There are relatively few of them in the cell. | Numerous small digestive, some contractile. The structure is different with plant vacuoles. |
Features of the structure of a plant cell:
Features of the structure of an animal cell:
Brief comparison of plant and animal cells
What follows from this
- The fundamental similarity in the structural features and molecular composition of plant and animal cells indicates the relationship and unity of their origin, most likely from unicellular aquatic organisms.
- Both species contain many elements of the Periodic Table, which mainly exist in the form of complex compounds of inorganic and organic nature.
- However, what is different is that in the process of evolution these two types of cells have moved far away from each other, because They have completely different methods of protection from various adverse influences of the external environment and also have different methods of nutrition from each other.
- A plant cell is mainly distinguished from an animal cell by its strong shell, consisting of cellulose; special organelles - chloroplasts with chlorophyll molecules in their composition, with the help of which we carry out photosynthesis; and well-developed vacuoles with a supply of nutrients.
Cell structure
Cell shapes are very diverse. In unicellular organisms, each cell is a separate organism. Its shape and structural features are associated with the environmental conditions in which this single-celled organism lives, with its way of life.
Differences in cell structure
The body of every multicellular animal and plant is composed of cells that differ in appearance, which is associated with their functions. Thus, in animals one can immediately distinguish a nerve cell from a muscle or epithelial cell (epithelium is the integumentary tissue). In plants, many cells of the leaf, stem, etc. are not the same.
Cell sizes are just as variable. The smallest of them (some bacteria) do not exceed 0.5 microns. The size of the cells of multicellular organisms ranges from several micrometers (the diameter of human leukocytes is 3-4 microns, the diameter of erythrocytes is 8 microns) to enormous sizes (the processes of one human nerve cell are more than 1 m). In most plant and animal cells, their diameter ranges from 10 to 100 microns.
Despite the diversity of structure, shapes and sizes, all living cells of any organism are similar in many features of their internal structure. A cell is a complex, integral physiological system in which all basic life processes take place: metabolism and energy, irritability, growth and self-reproduction.
Main components in the structure of a cell
The main common components of a cell are the outer membrane, cytoplasm and nucleus. A cell can live and function normally only in the presence of all these components, which closely interact with each other and with the environment.
The structure of the outer membrane. It is a thin (about 7.5 nm thick) three-layer cell membrane, visible only in an electron microscope. The two outer layers of the membrane consist of proteins, and the middle one is formed by fat-like substances. The membrane has very small pores, thanks to which it easily allows some substances to pass through and retains others. The membrane takes part in phagocytosis (the cell captures solid particles) and pinocytosis (the cell captures droplets of liquid with substances dissolved in it). Thus, the membrane maintains the integrity of the cell and regulates the flow of substances from the environment into the cell and from the cell into its environment.
On its inner surface, the membrane forms invaginations and branches that penetrate deeply into the cell. Through them, the outer membrane is connected to the shell of the nucleus. On the other hand, the membranes of neighboring cells, forming mutually adjacent invaginations and folds, very closely and reliably connect cells into multicellular tissues.
Cytoplasm is a complex colloidal system. Its structure: transparent semi-liquid solution and structural formations. The structural formations of the cytoplasm common to all cells are: mitochondria, endoplasmic reticulum, Golgi complex and ribosomes. All of them, together with the nucleus, represent the centers of certain biochemical processes, which together make up the metabolism and energy in the cell. These processes are extremely diverse and occur simultaneously in a microscopically small volume of the cell. This is related to the general feature of the internal structure of all structural elements of the cell: despite their small size, they have a large surface on which biological catalysts (enzymes) are located and various biochemical reactions are carried out.
Mitochondria are the energy centers of the cell. These are very small bodies, but clearly visible in a light microscope (length 0.2-7.0 µm). They are found in the cytoplasm and vary significantly in shape and number in different cells. The liquid contents of mitochondria are enclosed in two three-layer membranes, each of which has the same structure as the outer membrane of the cell. The inner membrane of the mitochondrion forms numerous invaginations and incomplete septa within the body of the mitochondrion. These invaginations are called cristae. Thanks to them, with a small volume, a sharp increase in the surface area is achieved on which biochemical reactions take place, and among them, first of all, the reactions of accumulation and release of energy through the enzymatic conversion of adenosine diphosphoric acid into adenosine triphosphoric acid and vice versa.
The endoplasmic reticulum is a multiply branched invagination of the outer membrane of the cell. The membranes of the endoplasmic reticulum are usually arranged in pairs, and tubules are formed between them, which can expand into larger cavities filled with biosynthesis products. Around the nucleus, the membranes that make up the endoplasmic reticulum directly pass into the outer membrane of the nucleus. Thus, the endoplasmic reticulum connects all parts of the cell together. In a light microscope, when examining the structure of a cell, the endoplasmic reticulum is not visible.
In the structure of the cell, a rough and smooth endoplasmic reticulum is distinguished. The rough endoplasmic reticulum is densely surrounded by ribosomes, where protein synthesis occurs. The smooth endoplasmic reticulum is devoid of ribosomes and synthesizes fats and carbohydrates. The tubules of the endoplasmic reticulum carry out intracellular exchange of substances synthesized in various parts of the cell, as well as exchange between cells. At the same time, the endoplasmic reticulum, as a denser structural formation, serves as the skeleton of the cell, giving its shape a certain stability.
Ribosomes are found both in the cytoplasm of the cell and in its nucleus. These are tiny grains with a diameter of about 15-20 nm, which makes them invisible in a light microscope. In the cytoplasm, the bulk of ribosomes are concentrated on the surface of the tubules of the rough endoplasmic reticulum. The function of ribosomes lies in the most important process for the life of the cell and the organism as a whole - the synthesis of proteins.
The Golgi complex was first found only in animal cells. However, recently similar structures have been discovered in plant cells. The structure of the Golgi complex is close to the structural formations of the endoplasmic reticulum: these are tubules of various shapes, cavities and vesicles formed by three-layer membranes. In addition, the Golgi complex includes rather large vacuoles. Some synthesis products accumulate in them, primarily enzymes and hormones. During certain periods of a cell’s life, these reserved substances can be removed from a given cell through the endoplasmic reticulum and are involved in the metabolic processes of the body as a whole.
The cellular center is a formation that has so far been described only in the cells of animals and lower plants. It consists of two centrioles, the structure of each of which is a cylinder up to 1 micron in size. Centrioles play an important role in mitotic cell division. In addition to the described permanent structural formations, certain inclusions periodically appear in the cytoplasm of various cells. These are droplets of fat, starch grains, protein crystals of a special shape (aleurone grains), etc. Such inclusions are found in large quantities in the cells of storage tissues. However, in the cells of other tissues such inclusions can exist as a temporary reserve of nutrients.
The nucleus, like the cytoplasm with the outer membrane, is an essential component of the vast majority of cells. Only in some bacteria, when examining the structure of their cells, it was not possible to identify a structurally formed nucleus, but in their cells all the chemical substances inherent in the nuclei of other organisms were found. There are no nuclei in some specialized cells that have lost the ability to divide (red blood cells of mammals, sieve tubes of plant phloem). On the other hand, there are multinucleated cells. The nucleus plays a very important role in the synthesis of enzyme proteins, in the transmission of hereditary information from generation to generation, and in the processes of individual development of the body.
The nucleus of a non-dividing cell has a nuclear envelope. It consists of two three-layer membranes. The outer membrane is connected through the endoplasmic reticulum to the cell membrane. Through this entire system, there is a constant exchange of substances between the cytoplasm, the nucleus and the environment surrounding the cell. In addition, there are pores in the nuclear shell, through which the nucleus is also connected to the cytoplasm. Inside, the nucleus is filled with nuclear juice, which contains clumps of chromatin, a nucleolus and ribosomes. Chromatin is made up of protein and DNA. This is the material substrate that, before cell division, is formed into chromosomes, visible in a light microscope.
Chromosomes are constant in number and shape, identical for all organisms of a given species. The functions of the nucleus listed above are primarily associated with chromosomes, or more precisely, with the DNA that is part of them.
One or more nucleoli are present in the nucleus of a nondividing cell and are clearly visible in a light microscope. At the moment of cell division it disappears. Recently, the enormous role of the nucleolus has been elucidated: ribosomes are formed in it, which then enter the cytoplasm from the nucleus and carry out protein synthesis there.
All of the above applies equally to animal cells and plant cells. Due to the specificity of metabolism, growth and development of plants and animals, in the structure of the cells of both there are additional structural features that distinguish plant cells from animal cells.
Animal cells, in addition to the listed components, have special formations in the structure of the cell - lysosomes. These are ultramicroscopic vesicles in the cytoplasm filled with liquid digestive enzymes. Lysosomes carry out the function of breaking down food substances into simpler chemical substances. There are some indications that lysosomes are also found in plant cells.
The most characteristic structural elements of plant cells (except for those common ones that are inherent in all cells) are plastids. They exist in three forms: green chloroplasts, red-orange-yellow chromoplasts, and colorless leucoplasts. Under certain conditions, leukoplasts can turn into chloroplasts (greening of potato tubers), and chloroplasts, in turn, can become chromoplasts (autumn yellowing of leaves).
Chloroplasts are a “factory” for the primary synthesis of organic substances from inorganic ones using solar energy. These are small bodies of quite varied shapes, always green in color due to the presence of chlorophyll. The structure of chloroplasts in a cell: they have an internal structure that ensures maximum development of free surfaces. These surfaces are created by numerous thin plates, clusters of which are located inside the chloroplast.
On the surface, the chloroplast, like other structural elements of the cytoplasm, is covered with a double membrane. Each of them, in turn, is three-layered, like the outer membrane of the cell.
Chromoplasts are close in nature to chloroplasts, but contain yellow, orange and other pigments close to chlorophyll, which determine the color of fruits and flowers in plants.
Unlike animals, plants grow throughout their lives. This occurs both by increasing the number of cells through division and by increasing the size of the cells themselves. In this case, most of the cell body structure is occupied by vacuoles. Vacuoles are dilated lumens of tubules in the endoplasmic reticulum, filled with cell sap.
The structure of the shell of plant cells, in addition to the outer membrane, additionally consists of fiber (cellulose), which forms a thick cellulose wall at the periphery of the outer membrane. In specialized cells, these walls often acquire specific structural complications.