The human body, like the body of all multicellular organisms, consists of cells. There are many billions of cells in the human body - this is its main structural and functional element.
Bones, muscles, skin - they are all built from cells. Cells actively respond to irritation, participate in metabolism, grow, multiply, and have the ability to regenerate and transmit hereditary information.
The cells of our body are very diverse. They can be flat, round, spindle-shaped, or have branches. The shape depends on the position of the cells in the body and the functions performed. The sizes of the cells are also different: from a few micrometers (small leukocyte) to 200 micrometers (ovum). Moreover, despite such diversity, most cells have a single structural plan: they consist of a nucleus and cytoplasm, which are externally covered with a cell membrane (shell).
Every cell except red blood cells has a nucleus. It carries hereditary information and regulates the formation of proteins. Hereditary information about all the characteristics of an organism is stored in deoxyribonucleic acid (DNA) molecules.
DNA is the main component of chromosomes. In humans, there are 46 chromosomes in each non-reproductive (somatic) cell, and 23 chromosomes in the germ cell. Chromosomes are clearly visible only during cell division. When a cell divides, hereditary information is transferred in equal quantities to daughter cells.
Outside, the nucleus is surrounded by a nuclear envelope, and inside it there is one or more nucleoli, in which ribosomes are formed - organelles that ensure the assembly of cell proteins.
The nucleus is immersed in the cytoplasm, consisting of hyaloplasm (from the Greek “hyalinos” - transparent) and the organelles and inclusions contained in it. Hyaloplasm forms the internal environment of the cell; it unites all parts of the cell with each other and ensures their interaction.
Cell organelles are permanent cellular structures that perform specific functions. Let's get to know some of them.
Endoplasmic reticulum resembles a complex labyrinth formed by many tiny tubules, vesicles, and sacs (cisterns). In some areas on its membranes there are ribosomes; such a network is called granular (granular). The endoplasmic reticulum is involved in the transport of substances in the cell. Proteins are formed in the granular endoplasmic reticulum, and animal starch (glycogen) and fats are formed in the smooth endoplasmic reticulum (without ribosomes).
The Golgi complex is a system of flat sacs (cisternae) and numerous vesicles. It takes part in the accumulation and transportation of substances that are formed in other organelles. Complex carbohydrates are also synthesized here.
Mitochondria are organelles whose main function is oxidation organic compounds accompanied by the release of energy. This energy goes into the synthesis of adenosine triphosphoric acid (ATP) molecules, which serves as a kind of universal cellular battery. The energy contained in LTF is then used by cells for various processes of their life: heat production, transmission of nerve impulses, muscle contractions and much more.
Lysosomes, small spherical structures, contain substances that destroy unnecessary, obsolete or damaged parts of the cell, and also participate in intracellular digestion.
On the outside, the cell is covered with a thin (about 0.002 µm) cell membrane, which separates the contents of the cell from environment. The main function of the membrane is protective, but it also perceives the influences of the cell’s external environment. The membrane is not solid, it is semi-permeable, some substances pass through it freely, i.e. it also performs a transport function. Communication with neighboring cells is also carried out through the membrane.
You see that the functions of organelles are complex and diverse. They play the same role for the cell as organs do for the whole organism.
The lifespan of the cells in our body varies. So, some skin cells live 7 days, red blood cells - up to 4 months, but bone cells - from 10 to 30 years.
A cell is a structural and functional unit of the human body, organelles are permanent cellular structures that perform specific functions.
Cell structure
Did you know that such a microscopic cell contains several thousand substances, which, in addition, also participate in various chemical processes.
If we take all 109 elements that are in Mendeleev’s periodic table, then most of them are found in cells.
Vital properties of cells:
Metabolism - Irritability - Movement
Cytology is a science that studies the structure and function of cells. The cell is the elementary structural and functional unit of living organisms. The cells of unicellular organisms have all the properties and functions of living systems.
The cells of multicellular organisms are differentiated by structure and function. Examples: amoeba, ciliates, euglena, malarial plasmodia- these are independent organisms that have all the above properties of life
Chemical composition cells
INORGANIC SUBSTANCES OF CELLS
Atomic composition: the cell contains about 70 elements periodic table Mendeleev's elements. 24 of them are present in all cell types. Elements such as O, C, >ї, H, β, P are called organogens, since they are part of any organisms. The elemental composition of the cell is divided into three main groups:
macroelements: O, C, K, N, v, K, Ca, Sh, R; microelements: Ee, C1, vts A1, Mn; ultramicroelements
you: gp, Si, Vg, E, I.
Molecular composition: the cell contains molecules of inorganic and organic compounds.
Water is one of the inorganic substances in cells. The water molecule has a nonlinear spatial structure and has polarity. Hydrogen bonds are formed between individual water molecules, which determine the physical and Chemical properties water.
It is the presence of hydrogen bonds that ensures the processes of thermoregulation in organisms, the transport of solutions along plant stems, and the structure of many organic compounds.
Physical properties of water
and High thermal conductivity of water ensures uniform distribution heat throughout the entire volume of fluid located in the cells, which protects the body from overheating.
■ High specific heat capacity. Breaking the hydrogen bonds that hold water molecules together requires the absorption of a large amount of energy. This property of water ensures the maintenance of thermal balance in the body.
■ High heat of vaporization. To evaporate water, quite a lot of energy is required. The boiling point of water is higher than that of many other substances. This property of water protects the body from overheating.
■ Water molecules are in constant motion, colliding with each other in the liquid phase.
■ Water can exist in three states - liquid, solid and gas.
■ Cohesion and surface tension. Hydrogen bonds determine the viscosity of water and the adhesion of its molecules with molecules of other substances (cohesion). Due to the adhesive forces of molecules, a film is created on the surface of water that has a characteristic such as surface tension.
and Density. When cooled, the movement of water molecules slows down. The number of hydrogen bonds between molecules becomes maximum. Water reaches its greatest density at 4 °C. When water freezes, it expands (needing space for hydrogen bonds to form) and its density decreases. That's why ice floats.
■ Ability to form colloidal structures. Water molecules form a shell around the insoluble molecules of some substances, preventing the formation of large particles. This state of these molecules is called dispersed (scattered). The smallest particles of substances, surrounded by water molecules, form colloidal solutions (cytoplasm, intercellular fluids).
Biological functions of water
Transport function
Water ensures the movement of substances in the cell and body, the absorption of substances and the removal of metabolic products. In nature, water carries waste products into soils and water bodies.
Metabolic function
■ Water is the medium for all biochemical reactions.
■ Water is an electron donor during photosynthesis.
■ Water is necessary for the hydrolysis of macromolecules to their monomers.
Water is involved in the formation of lubricating fluids and mucus, secretions and juices in the body.
The following body fluids help reduce friction: synovial (present in the joints of vertebrates), pleural (in the pleural cavity), pericardial (in the pericardial sac).
Mucus facilitates the movement of substances through the intestines and creates a moist environment on the mucous membranes respiratory tract and etc.
Secretions are saliva, tears, bile, sperm, etc. Inorganic ions
Inorganic ions of the cell include: cations K +, Ka +, Ca 2+, M£ 2+, N1^ and SG anions,
N0", n 2 ro;, nso;, nro 2"
The difference between the number of cations and anions on the surface and inside the cell ensures the occurrence of an action potential, which underlies nerve and muscle excitation
Phosphoric acid anions create phosphate buffer system, maintaining the pH of the intracellular environment of the body at a level of 6-9.
Carbonic acid and its anions create a bicarbonate buffer system and maintain the pH of the extracellular environment (blood plasma) at a level of 7-4.
Nitrogen compounds serve as a source of mineral nutrition, synthesis of proteins and nucleic acids. Phosphorus atoms are part of nucleic acids, phospholipids, as well as the bones of vertebrates and the chitinous cover of arthropods. Calcium ions - are part of the substance of bones; they are also necessary for muscle contraction and blood clotting.
EXAMPLES OF TASKS No. 3
1. Name the macro- and microelements of the cell.
2. What physical properties water determine its biological significance?
3. What is the difference between polar and non-polar solvents?
4. What is the role of salt cations and anions in the body? What is a buffer system?
5. Which of the properties of water is due to its polarity?
a) thermal conductivity; b) heat capacity; c) the ability to dissolve non-polar compounds; d) the ability to dissolve polar compounds.
6. Children develop rickets with a deficiency of:
a) manganese and iron; b) calcium and phosphorus; c) copper and zinc; d) sulfur and nitrogen.
7. The transmission of excitation along the nerve is explained:
a) the difference in the concentrations of sodium and potassium ions inside and outside the cell; b) breaking of hydrogen bonds between water molecules; c) polarity of water d) difference in concentrations of calcium and phosphorus inside the cell.
ORGANIC SUBSTANCES OF CELLS
Carbohydrates, lipids
The general formula of carbohydrates is C p (H 2 0) p.
Water-soluble carbohydrates
Water-soluble carbohydrates perform the following functions in the body: transport, protective, signaling, energy.
Monosaccharides. Glucose is the main source of energy for cellular respiration. Fructose is a component of flower nectar and fruit juices. Ribose and deoxyribose are structural elements of nucleotides, which are monomers of RNA and DNA.
Disaccharides. Sucrose (glucose + fructose) is the main product of photosynthesis transported in plants. Lactose (glucose + galactose) is a component of mammalian milk. Maltose (glucose + glucose) is a source of energy in germinating seeds.
Water-insoluble carbohydrates
Polymeric carbohydrates, starch, glycogen, cellulose, chitin, are insoluble in water.
Functions of polymer carbohydrates: structural, storage, energy, protective.
Starch - consists of branched spiral molecules that form storage substances in plant tissues.
Cellulose is a polymer formed by glucose residues consisting of several straight parallel chains connected by hydrogen bonds. This structure prevents the penetration of water and ensures the stability of the cellulose membranes of plant cells.
Chitin is the main structural element of the integument of arthropods and the cell walls of fungi.
Glycogen is a storage substance animal cell.
Lipids are esters fatty acids and glycerin. Insoluble in water, but soluble in non-polar solvents. Present in all cells. Lipids are made up of hydrogen, oxygen and carbon atoms.
Types of lipids: fats, waxes, phospholipids, sterols (steroids).
Functions of lipids
Storage - fats are stored in the tissues of vertebrate animals.
Energy - half of the energy consumed by the cells of vertebrates at rest is formed as a result of fat oxidation. Fats are also used as a source of water.
Protective - the subcutaneous fat layer protects the body from mechanical damage
Structural - phospholipids are part of cell membranes.
Thermal insulation - subcutaneous fat helps retain heat.
Electrical insulating - myelin secreted by Schwann cells insulates some neurons, which greatly speeds up the transmission of nerve impulses.
Nutritious - bile acids and vitamin B are formed from steroids.
Lubricating - waxes cover the skin, fur, feathers and protect them from water.
The leaves of many plants are covered with a waxy coating; wax is used in the construction of honeycombs.
Hormonal - adrenal hormone - cortisone and sex hormones are of lipid nature. Their molecules do not contain fatty acids.
EXAMPLES OF TASKS No. 4
1. Which of the following chemical compounds is not a biopolymer?
a) protein; b) glucose; c) deoxyribonucleic acid; d) cellulose.
2. Carbohydrates during photosynthesis are synthesized from:
a) 0 2 and H 2 0; b) C0 2 and H 2; c) C0 2 and H 2 0; d) C0 2 and H 2 C0 3.
3. In animal cells, storage carbohydrate is:
a) cellulose; b) starch; c) murein; d) glycogen.
4. Which of the following compounds is of lipid nature?
a) hemoglobin; b) insulin; c) testosterone; d) penicillin.
5. List the functions of lipids in the body.
6. In what organs of plants and animals are fats concentrated?
Proteins are biological heteropolymers whose monomers are amino acids. Polymers made up of amino acids are called polypeptides. Proteins are synthesized in living organisms and perform certain useful functions in them.
Rice. Protein structure:
1 - primary structure, 2 - secondary structure, 3 - tertiary structure, 4 - quaternary structure
All proteins are polypeptides, but not all polypeptides are proteins. Proteins can contain 20 different amino acids. The alternation of different amino acids in the polypeptide chain allows you to obtain great amount different proteins.
The sequence of amino acids in a protein molecule forms its primary structure (Fig. 1). She, in her
turn, depends on the sequence of nucleotides in the section of the DNA molecule (gene) encoding the given protein.
In the secondary structure, the protein molecule has the shape of a spiral (Fig. 2). Between the CO and IN groups of amino acid residues of adjacent turns of the helix, hydrogen bonds arise that hold the chain together. The protein molecule, which has a complex configuration in the form of a globule, acquires a tertiary structure (Fig. 3). The strength of this structure is ensured by hydrophobic, hydrogen, ionic and disulfide bonds.
Some proteins have a quaternary structure, formed by several polypeptide chains - tertiary structures (Fig. 4). The quaternary structure is also held together by weak non-covalent bonds - ionic, hydrogen, hydrophobic. However, the strength of these bonds is low, and the structure can be easily damaged. The disruption (denaturation) of quaternary, tertiary and secondary structures is reversible. The destruction of the primary structure is irreversible.
Functions of proteins
and Catalytic (enzymatic) - proteins accelerate breakdown nutrients in the digestive tract, carbon fixation during photosynthesis, participate in reactions matrix synthesis. Enzymes are specific proteins that have an active center - a region of the molecule that corresponds in geometric configuration to the molecules of the substrate. Each enzyme speeds up one and only one reaction (both forward and reverse). The rate of enzymatic reactions depends on the temperature of the medium, its pH level, as well as on the concentrations of the reacting substances and the concentration of the enzyme.
Enzyme Enzyme
Active
 |
Substrate Products
■ Transport - proteins provide active transport of ions across cell membranes, transport of oxygen and carbon dioxide (hemoglobin), transport of fatty acids (serum albumin).
■ Protective - antibodies provide immune protection body; fibrinogen and fibrin protect the body from blood loss.
■ Structural - proteins are part of cell membranes; the protein keratin forms hair and nails; proteins collagen and elastin - cartilage and tendons.
■ Contractile - provided by contractile proteins - actin and myosin.
■ Signal - protein molecules can receive signals and serve as their carriers in the body (hormones). It should be remembered that not all hormones are proteins.
EXAMPLES OF TASKS No. 5
1. Define the concept of “protein”.
2. List the main functions of proteins and explain how the structure of the protein determines the performance of these functions.
3. Give examples of different proteins.
4. How is a peptide bond formed?
5. Explain the features of the structural organization of a protein molecule.
6. What is denaturation?
Nucleic acids. Template synthesis reactions
The structure of the DNA molecule was established in 1953 by the American James Watson and the Englishman Francis Crick.
DNA is a linear polymer in the form of a double helix formed by a pair of antiparallel complementary chains. The monomers of DNA are nucleotides.
Each DNA nucleotide consists of a purine (A - adenine or G - guanine) or pyrimidine (T - thymine or C - cytosine) nitrogenous base, a five-carbon sugar - deoxyribose and a phosphate group.
The DNA molecule has the following parameters: the width of the helix is about 2 nm, the pitch, or complete turn of the helix, is 3.4 nm. One step contains 10 complementary base pairs. Nucleotides in a DNA molecule face each other with nitrogenous bases and are united in pairs in accordance with the rules of complementarity: thymine is located opposite adenine, and cytosine is located opposite guanine. The A - T pair is connected by two hydrogen bonds, and the G - C pair is connected by three.
The backbone of DNA chains is formed by sugar phosphate residues.
DNA replication is the process of self-duplication of a DNA molecule, carried out under the control of enzymes.
On each of the chains formed after the rupture of hydrogen bonds, a daughter DNA chain is synthesized with the participation of the enzyme DNA polymerase. The material for synthesis is free nucleotides present in the cytoplasm of cells.
The synthesis of daughter molecules on adjacent chains occurs at different rates. On one chain a new molecule is assembled continuously, on the other - with some lag and in fragments. After the process is completed, fragments of new DNA molecules are stitched together by the enzyme DNA ligase. So from one DNA molecule two DNA molecules arise, which are exact copies of each other and the mother molecule. This method of replication is called semi-conservative.
The biological meaning of replication lies in the accurate transfer of hereditary information from the mother molecule to the daughter molecules, which occurs during the division of somatic cells.
RNA is a linear polymer, usually consisting of a single chain of nucleotides. In RNA, the thymine nucleotide is replaced by uracil (U). Each RNA nucleotide contains a five-carbon sugar - ribose, one of four nitrogenous bases and a phosphoric acid residue.
Matrix, or information, RNA. Synthesized in the nucleus with the participation of the enzyme RNA polymerase. Complementary to the region of DNA where synthesis occurs. Makes up 5% of the cell's RNA. Ribosomal RNA is synthesized in the nucleolus and is part of ribosomes. Makes up 85% of the cell's RNA. Transport
RNA (more than 40 types). Transports amino acids to the site of protein synthesis. It has the shape of a clover leaf and consists of 70-90 nucleotides.
Template synthesis reactions
Template synthesis reactions include DNA replication, RNA synthesis from DNA (transcription), and protein synthesis from mRNA (translation), as well as synthesis of RNA or DNA from RNA viruses.
The mRNA molecule enters the cytoplasm onto ribosomes, where polypeptide chains are synthesized. The process of translating the information contained in the nucleotide sequence of mRNA into the amino acid sequence of a polypeptide is called translation.
A certain amino acid is delivered to the ribosomes by a certain type of tRNA from the cytoplasm. tRNA (anticodon) finds a complementary triplet to the mRNA (codon) and cleaves the delivered amino acid into the protein chain. The process of protein biosynthesis will be discussed in more detail below.
EXAMPLES OF TASKS Mb
1. Tell us about the structure of nucleic acids, comparing them in composition and functions performed in the body.
2. What is the sequence of matrix synthesis reactions?
3. Broadcast is in progress
a) transferring information from DNA to RNA; b) DNA replication; c) translation of RNA information into the sequence of amino acids in the protein; d) DNA repair.
4. In what case is the composition of a DNA nucleotide correctly indicated?
a) ribose, phosphoric acid residue, thymine;
b) phosphoric acid, uracil, deoxyribose; c) phosphoric acid residue, deoxyribose, adenine;
d) phosphoric acid residue, ribose, guanine.
The structure of living organisms has long interested scientists, but much cannot be seen with the naked eye. Therefore, biologists were able to study in detail the structure of living organisms only after the invention of magnifying devices.
History of the study of the cellular structure of organisms
Some small features external structure plants and animals can be viewed using a hand-held magnifying glass. However, study in detail internal structure living organisms is possible only with the help of a microscope (gr. micros - small and scope - considering).
The first microscope was created at the end of the 16th century. And in 1665, the English naturalist Robert Hooke used a more advanced microscope. With its help, he examined a thin section of a plant plug. The scientist discovered that the cork consists of tiny cells that fit tightly together. He called them cellula in Latin - cell. These were the first cells that man saw. This is how the new concept of cell entered science.
The microscope made it possible not only to learn more about plants and animals, but also to see the world of microscopic organisms. The Dutch naturalist Antonie van Leeuwenhoek (1675) was the first to observe creatures invisible to the human eye. He invented a microscope with 270x magnification.
20 years later, the cell theory was supplemented with an important provision: “every cell is from a cell,” that is, new cells are formed as a result of the division of the mother cell.
It has now been established that a cell is the smallest structural unit of a living organism. The cell has a very complex structure. All its parts are closely interconnected and work harmoniously. Included multicellular organism Cells of similar structure combine to form tissues.
THEORY
Structure and functions of cell organelles
| Organoid name | Structural features, functions |
| 1. Outer cytoplasmic membrane | Separates the contents of the cytoplasm from external environment; through the pores, ions and small molecules can penetrate into the cell with the help of enzymes; provides communication between cells in tissues; In addition to the cytoplasmic cell, a plant cell has a thick membrane consisting of cellulose - a cell wall, which animal cells do not have |
| 2. Cytoplasm | The liquid medium in which organelles and inclusions are suspended consists of liquid colloidal system, in which molecules of various substances are present |
| 3. Plastids (leukoplasts, chromoplasts, chloroplasts) | Characteristic only of plant cells, double-membrane organelles. Green plastids - chloroplasts containing chlorophyll in special formations - thylakoids (granas), in which photosynthesis occurs, are capable of self-renewal (have their own DNA) |
| 4. Endoplasmic reticulum | Located around the core, formed by membranes, branched network of cavities and channels: smooth EPS is involved in carbon and fat metabolism; rough provides protein synthesis using ribosomes |
| 5. Mitochondria | Double-membrane structure, the inner membrane has projections - cristae, on which there are many enzymes, providing the oxygen stage of energy metabolism(have their own DNA) |
| 6. Vacuoles | Obligatory organelles plant cell ; contain many organic substances and mineral salts in dissolved form; found in animal cells |
| 7. Ribosomes | Spherical particles consisting of two subunits are located freely in the cytoplasm or attached to the EPS membranes; carry out protein synthesis |
| 8. Cytoskeleton | A system of microtubules and bundles of protein fibers closely associated with the outer membrane and nuclear envelope |
| 9. Flagella and cilia | Organelles of movement have overall plan buildings. The movement of flagella and cilia is caused by the sliding of microtubules of each pair relative to each other |
QUESTIONS AND TASKS
- What is the function of carbohydrates in a cell?
1) catalytic 2) energetic 3) storage of hereditary information
4) participation in protein biosynthesis
- What function do DNA molecules perform in a cell?
1) construction 2) protective 3) carrier of hereditary information
4) energy absorption sunlight
- During the process of biosynthesis in the cell,
1) oxidation organic matter 2) supply of oxygen and removal of carbon dioxide
3) formation of more complex organic ingredients 4) breakdown of starch to glucose
- One of the provisions cell theory thing is
1) the cells of organisms are identical in structure and function
2) plant organisms consist of cells
3) animal organisms consist of cells
4) all the lower ones and higher organisms consist of cells
- Between concept ribosome and protein synthesis there is a certain connection. The same connection exists between the concept cell membrane and one of the ones below. Find this concept.
1) transport of substances 2) ATP synthesis 3) cell division 4) fat synthesis
- Internal environment cells are called
1) nucleus 2) vacuole 3) cytoplasm 4) endoplasmic reticulum
- In the nucleus of the cell are located
1) lysosomes 2) chromosomes 3) plastids 4) mitochondria
- What role does the nucleus play in a cell?
1) contains a supply of nutrients 2) communicates between organelles
3) promotes the entry of substances into the cell 4) ensures the similarity of the mother cell with its daughter cells
- Digestion of food particles and removal of dead cells occurs in the body with the help of
1) Golgi apparatus 2) lysosomes 3) ribosomes 4) endoplasmic reticulum
- What function do ribosomes perform in a cell?
1) synthesize carbohydrates 2) carry out protein synthesis
3) break down proteins into amino acids 4) participate in the accumulation of inorganic substances
- In mitochondria, unlike chloroplasts, there is
1) synthesis of carbohydrates 2) synthesis of enzymes 3) oxidation of minerals
4) oxidation of organic substances
- Mitochondria are absent in cells
1) cuckoo flax moss 2) city swallow 3) parrot fish 4) staphylococcus bacteria
- Chloroplasts are found in cells
1) freshwater hydra 2) mycelium of white mushroom 3) wood of alder stem 4) beet leaves
- The cells of autotrophic organisms differ from the cells of heterotrophs by the presence in them
1) plastids 2) membranes 3) vacuoles 4) chromosomes
- dense membrane, cytoplasm, nuclear substance, ribosomes, plasma membrane have cells
1) algae 2) bacteria 3) fungi 4) animals
- Endoplasmic reticulum in a cell
1) transports organic substances
2) restricts the cell from the environment or other cells
3) participates in the formation of energy
4) preserves hereditary information about the characteristics and properties of the cell
- Photosynthesis does not occur in fungal cells, because missing from them
1) chromosomes 2) ribosomes 3) mitochondria 4) plastids
- They do not have a cellular structure, they are active only in the cells of other organisms
1) bacteria 2) viruses 3) algae 4) protozoa
- In human and animal cells, they are used as an energy source.
1) hormones and vitamins 2) water and carbon dioxide
3) inorganic substances 4) proteins, fats and carbohydrates
- Which of the sequences of concepts reflects the organism as a single system
1) Molecules – cells – tissues – organs – organ systems – organism
2) Organ systems – organs – tissues – molecules – cells – organism
3) Organ – tissue – organism – cell – molecules – organ systems
4) Molecules – tissues – cells – organs – organ systems – organism
Famous English naturalist and traveler Charles Robin Darwin in his book “The Origin of Species” he convincingly proved that all life on Earth changes, more simple shapes life gives rise to more complex ones. The simplest living organisms, which appeared 2-3 billion years ago, are connected by a long chain of transformations with higher plants and animals living on Earth at the present time. On the long way historical development Numerous transformations and complications took place, the emergence of new, more and more advanced forms.
But all living organisms bear a trace of origin from the most distant ancestor. This trace is cellular structure.
Robert Hooke's first microscope
The study of cellular structure became possible only after inventions of the microscope in the 17th century. One of the first inventors of the microscope was an English naturalist and inventor Robert Hooke. When he constructed the original model of the microscope, a new, hitherto unseen world opened up before the scientist’s astonished gaze. With the help of his microscope, Hooke examined everything that came to hand.
Hooke's microscope was a very imperfect instrument. It gave a blurry, unclear image. The magnifying instruments of the 18th century were also imperfect. That is why, until the middle of the 19th century, the structure of the smallest particles discovered by Hooke continued to remain unclear to scientists.
Cell structure and life
If you look at the ripe juicy pulp of a watermelon, at the break of the pulp you can see tiny pink grains playing in the sun, like drops of dew. These are watermelon pulp cells. They have accumulated so much juice that they have reached a size at which the cell becomes visible without a microscope. Closer to the crust, the cells become smaller. Under a microscope, rectangular boxes called cells are visible in a thin slice of crust. Their walls - cell membranes - consist of a very strong substance - fiber. Under the protection of the shell are the main parts of the cell: a semi-liquid substance - protoplasm and spherical body - core. The watermelon pulp cell is one example of the structure of a plant cell. All plant organs - roots, stems, leaves, flowers, fruits - consist of countless cells.
The structure of an animal cell differs from a plant cell only in the absence of a separate cell membrane and cell sap. The main parts - protoplasm and nucleus - are found in both plant and animal cells. This allows us to talk about cellular structure both plants and animals.
How do cells reproduce?
The ability of cells to reproduce has great value for the body. Millions of cells continually die, having completed their vital task. Red blood cells only live for about three weeks. The integumentary cells of our body exist for no more than a month, then turning into dead horny scales. And if the supply of these cells were not replenished through constant reproduction, the body would be in danger of dying very quickly. But in the deep layers of the integumentary tissue of the skin, reproduction of young cover cells . Red blood cells are formed by the proliferation of young hematopoietic cells in bone marrow , where the development of blood elements occurs.
Cell proliferation occurs by dividing in two. This reveals the remarkable phenomenon of extremely accurate separation cell nucleus into two equal parts. Daughter cells are similar to each other and indistinguishable from the mother cell. When a cell of any type reproduces, it forms only cells similar to itself.
