Senior one must be the focus.

College entrance examination biology review required 1 chapter 1 to chapter 6.

Walk into the cell

1 Cell is the basic unit of organism structure and function.

2. The structural levels of life system are biosphere, ecosystem, community, population, individual, system, organ, tissue and cell.

Prokaryotic cells: divided into cell membrane, cytoplasm and pseudonucleus (non-eukaryote)

Eukaryotic cells: divided into cell membrane, cytoplasm, nucleus, etc.

Scientists divide cells into prokaryotic cells and eukaryotic cells according to whether they have nuclei or not.

Prokaryotic cell eukaryotic cell

The cell wall is smaller (1- 10 micron) and larger (10- 100 micron).

There is no nucleus in the nuclear structure, and the substances constituting the nucleus are concentrated in the pseudonucleus, and the nuclear membrane and nucleolus have formed the nucleus, while the substances constituting the nucleus are concentrated in the pseudonucleus, including the nuclear membrane and nucleolus.

Organelle ribosome various organelles

Chromosomes have no chromosomes.

Prokaryotes (bacteria, actinomycetes, cyanobacteria) Eukaryotes (plants, animals, fungi)

Chapter two. Molecules that make up cells

Part one: Elements and compounds in cells.

I. Chemical elements that make up an organism

Although the chemical elements that make up organisms are roughly the same, their contents are different. According to the different contents of chemical elements in organisms, they can be divided into macroelements and microelements. Among them, a large number of elements are C H O N P S K Ca Mg；; Trace elements include iron, manganese, zinc, copper, boron, molybdenum and so on.

Second, the important role of chemical elements that make up organisms.

Among a large number of elements, C H O N is the basic element of cells, among which carbon is the most basic element; Although the content of trace elements in organisms is very small, it is indispensable to maintain normal life activities.

Third, the unity and difference between the biological world and the abiotic world.

The chemical elements that make up an organism can be found in nature, and none of them is unique to the biological world. This fact shows that the biological world and the non-biological world have unity; The content of chemical elements that make up an organism is very different in biological and inorganic nature. This fact shows that there is a difference between living and non-living worlds.

Four. Compound P 17 constitutes a cell.

inorganic compound

: glucose, deoxyribose, glycogen, etc.

: lecithin, sex hormones, cholesterol, etc. ;

: insulin, antibody, hemoglobin, etc. ;

Organic compounds:,.

Part II: protein.

The basic unit of protein is amino acid, and there are about 20 kinds of amino acids that make up protein in organisms, all of which conform to the general structural formula. Amino acid molecules are bound to each other through peptide bonds. A compound formed by condensation of two amino acid molecules is called dipeptide, and a compound formed by condensation of multiple amino acid molecules is called polypeptide, which usually has a chain structure and is called peptide chain. A protein molecule may contain one or several peptide chains, which form a complex (specific) spatial structure by winding and folding. The molecular structure of protein is characterized by diversity. The reasons are: there are hundreds of amino acids that make up protein, the amino acid sequences are ever-changing, the folding methods of polypeptide chains are different, and the spatial structure of polypeptide chains is different. Due to the diversity of structure, protein also has the characteristics of functional diversity. Its functions mainly include: (1) structural proteins, such as muscle, carrier protein and hemoglobin; (2) information transmission, such as insulin; (3) Immune function, such as antibody; (4) Most enzymes are protein, such as pepsin; (5) Cell recognition, such as glycoprotein on cell membrane. In a word, all life activities are inseparable from protein, and protein is the main undertaker of life activities.

Section III: Nucleic Acid

Nucleic acid is the carrier of genetic information and the genetic material of all living things, which plays an extremely important role in the genetic variation of living things and the biosynthesis of protein. Nucleic acids include deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) The basic unit is nucleotide, which consists of one molecule of nitrogenous bases, one molecule of pentose and one molecule of phosphoric acid. Nucleic acid consists of five bases, two pentoses and eight nucleotides.

Deoxyribonucleic acid, abbreviated as DNA, mainly exists in the nucleus, and mitochondria and chloroplasts in the cytoplasm are also its carriers.

RNA, abbreviated as RNA, mainly exists in cytoplasm. For organisms with cell structure, the genetic material is DNA；; Viruses without cell structure, some genetic materials are DNA such as phage; Some genetic materials are RNA, such as tobacco mosaic virus.

Section 4: Sugar and Lipids in Cells

Sugar is composed of three elements, C, H and O, and sugar is the main energy substance of cells.

Sugar can be divided into monosaccharide, disaccharide and polysaccharide. Monosaccharides are non-hydrolyzable sugars, including glucose, fructose, galactose, ribose and deoxyribose, in which glucose is an important energy substance of cells, while ribose and deoxyribose are generally not energy substances, but components of nucleic acids; Among disaccharides, sucrose and maltose are plant sugars, while lactose and glycogen are animal sugars. Glycogen in polysaccharide is animal sugar, starch and cellulose are plant sugars, and glycogen and starch are important energy storage substances in cells.

Lipids are mainly composed of three chemical elements, C·H·O, and some also contain P (such as phospholipids). Lipids include fats, phospholipids and sterols. Fat is an energy storage substance in organisms. In addition, fat has the functions of heat preservation, buffering and decompression; Phospholipids are important components of membrane materials including cell membranes. Sterols mainly include cholesterol, sex hormones, vitamin D and so on. These substances play an important regulatory role in maintaining the normal life activities of organisms.

Polysaccharide, protein, nucleic acid, etc. They are all biological macromolecules, and their basic units are monosaccharide (glucose), amino acid and nucleotide respectively. These basic units are called monomers, and these biomacromolecules are called monomer multimers. Each monomer has a carbon chain consisting of several connected carbon atoms as its basic skeleton, and many monomers are connected to form polymers.

Section 5: Inorganic substances in cells

Water is the most abundant compound in living cells. The content of water in different kinds of organisms is different; The content of water is different in different tissues and organs.

There are two forms of water in cells: free water and bound water. Combined with other substances, bound water is an important part of cell structure, accounting for about 4.5%. Free water exists in free form and is a good solvent for cells. It can also directly participate in biochemical reactions and transport nutrients and wastes. In a word, all life activities of various creatures are inseparable from water.

Most inorganic salts in cells exist in ionic state, although the content is small, but they have many important functions: some inorganic salts are important components of some complex compounds in cells, such as iron, hemoglobin, magnesium, etc., and are essential components of chlorophyll molecules; Many inorganic ions play an important role in maintaining the life activities of cells and organisms. For example, if the calcium content in the blood is too low, convulsions will occur. Inorganic salts are also important for maintaining the acid-base balance of cells.

Identification of organic substances in cells

The reducing sugar (glucose, fructose) in sugar can react with Fehling reagent to form brick red precipitate;

Fat can be dyed orange by Sudan red ⅳ; Protein reacts with biuret reagent to produce purple reaction. In the detection of reducing sugar, solution A and solution B of Linfei reagent should be mixed evenly and heated in water bath before use. When detecting protein, we should first add 1ml biuret reagent A solution to the tissue sample solution, and then add 4 drops of biuret reagent B solution without heating.

Methyl green can make DNA appear green, and Pyrolone red can make RNA appear red, so dyeing cells with these two dyes can show the distribution of DNA and RNA in cells. In this experiment, the role of hydrochloric acid is to change the permeability of membrane and accelerate the entry of pigment into cells. Taking human oral epithelial cells as experimental materials, the experimental steps are making slices, hydrolyzing, smearing, dyeing and observing.

Chapter III Basic Structure of Cells

Except for a few organisms such as viruses, all living things are made up of cells. Cell is the basic unit of organism structure and function.

The chemical components of the virus are DNA and protein or RNA and protein.

I. Structure and function of eukaryotic cells

(1) Cell Wall Plant cells have a cell wall outside the cell membrane, which is mainly composed of cellulose and pectin, and can be removed by cellulase and pectinase. Cell wall plays a supporting and protecting role.

(2) Cell membrane

The chemical analysis of cell membrane shows that cell membrane is mainly composed of lipid (phospholipid) molecules and protein molecules, of which lipid is the most, accounting for about 50%; Besides, there is a small amount of sugar. Among the lipids that make up the cell membrane, phospholipids are the most abundant. The function of cell membrane is to isolate cells from the external environment, control substances to enter and leave cells, and exchange information between cells.

(3) Cytoplasm

In the cell membrane, the part outside the nuclear membrane is called cytoplasm. The cytoplasm of living cells is in a state of continuous flow, and the cytoplasm mainly includes cytoplasmic matrix and organelles.

1, cytoplasmic matrix

Cytoplasmic matrix contains water, inorganic salts, lipids, sugars, amino acids, nucleotides and various enzymes, which carry out various chemical reactions in cytoplasm.

2, organelles

(1) mitochondria

Mitochondria widely exist in the cytoplasm matrix, which is the main place for aerobic respiration and is called "power workshop".

Mitochondria are oval under light microscope and composed of double-layer membranes under electron microscope. The outer membrane separates it from the surrounding cytoplasmic matrix, and some parts of the inner membrane fold inward to form ridges, which increases the membrane area in mitochondria. There are many enzymes related to aerobic respiration and a small amount of DNA in mitochondria.

(2) Chloroplast

Chloroplast is a unique organelle of plants, mesophylls and cells. Chloroplast is a kind of organelle in photosynthetic cells of green plants, which is called "food workshop" and "energy conversion station". Under the electron microscope, we can see that there is a double-layer membrane outside the chloroplast, and there are several to dozens of grana stacked by saccular structures, and the grana are filled with matrix. These cystic structures are called thylakoids, which contain chlorophyll.

(3) endoplasmic reticulum

Endoplasmic reticulum is a network structure composed of single membranes, which greatly increases the membrane area in cells. ER is related to the synthesis and processing of intracellular protein, and it is also the "workshop" of lipid synthesis.

(4) Ribosomes

Ribosomes in cells are granular bodies, some of which are attached to endoplasmic reticulum and some of which are free in cytoplasm. Ribosome is the place where protein is synthesized in cells, and it is called "the machine for producing protein".

(5) Golgi apparatus

Golgi can't synthesize protein by itself, but protein can process, classify and package it. Golgi apparatus is related to the formation of cell wall during plant cell division.

(6) vacuole

Mature plant cells all have vacuoles. Vacuoles contain cellular fluid, including sugars, inorganic salts, pigments, protein and other substances. It can regulate the environment in which cells live, and keep the cells in a certain shape and expand.

(7) centrosome

There are centrosomes in animal cells and lower plant cells, and each centrosome consists of two centrioles arranged vertically to each other and their surrounding substances. The centrosome of animal cells is related to mitosis.

(8) lysosomes

Lysosome is an organelle with a single membrane structure, which contains a variety of hydrolases and can decompose a variety of substances.

(4) the nucleus

Each eukaryotic cell usually has only one nucleus, while some cells have more than two nuclei, such as humans.

Muscle cells, some cells have no nucleus, such as mammalian red blood cells.

1, structure

The observation of eukaryotic cells in mitotic interphase after fixation and staining under electron microscope shows that the main nuclear structure is as follows.

Nuclear membrane, nucleolus, chromatin

The nuclear membrane is composed of a double-layer membrane with nuclear pores, which are the channels for material exchange and information exchange between the nucleus and cytoplasm.

In different kinds of organisms, the forms and quantities of nucleoli are different, and they disappear and reappear periodically during cell division. Nucleoli are related to the synthesis of some RNA and the formation of ribosomes.

Chromatin is mainly composed of DNA and protein, which can be dyed dark by basic dyes. During the interval of cell mitosis, chromatin is filamentary and interwoven into a network; During mitosis, chromatin is spiral, shorter and thicker, and becomes cylindrical or rod-shaped chromosomes. So chromatin and chromosome are two forms of the same substance in cells at different times.

2. Function

The nucleus is the main place of genetic material and the control center of cells, so the nucleus is the most important part of cells. Storage, replication, metabolism, heredity

(5) Cell biofilm system.

Among the above cell structures and organelles, there are mitochondria and chloroplasts with double membranes, and endoplasmic reticulum, Golgi apparatus, lysosomes and vacuoles with single membrane. They are all made of biofilm. These organelle membranes, cell membranes, nuclear membranes and other structures together constitute the biofilm system of cells.

Cell biofilm system plays an extremely important role in cell life activities.

First of all, cell membrane not only makes cells have a relatively stable internal environment, but also plays a decisive role in the process of material transportation, energy conversion and information transmission between cells and the environment.

Second, many important chemical reactions of cells are carried out on biofilm.

The wide membrane area in cells provides a large number of attachment sites for enzymes, which creates favorable conditions for the smooth progress of various chemical reactions.

Thirdly, the biofilm in the cell divides the cell into small compartments, so that various chemical reactions can be carried out simultaneously in the cell without interfering with each other, ensuring the efficient and orderly life activities of the cell.

Chapter IV Material Input and Output of Cells

1, three pictures of "Water in and out of mammalian red blood cells" (see textbook P60).

Can hemoglobin and other organic substances in normal living red blood cells penetrate the cell membrane and reach the outside of the membrane? cannot

According to the phenomenon, what is the cell membrane of red blood cells equivalent to? A: Semipermeable membrane

When the concentration of external solution is low, will red blood cells absorb water and burst? A: No.

How much water does red blood cells absorb or lose depends on what? Answer: the difference between the relative contents of water in the solution on both sides.

2. For plant cells, water must pass through protoplasm to enter and leave the cell. Protoplast layer is equivalent to semi-permeable membrane, and plant cell membrane and vacuole membrane are biofilm. (P6 1) They have basically the same chemical composition and structure as the cell membrane of red blood cells. The above example is very similar to the water loss and water absorption of red blood cells.

3. Separation and repair of cytoplasmic wall of purple onion scale leaves.

The size of central vacuole, the position of protoplasm layer and the size of cells.

30% sucrose solution becomes smaller (cell loses water), and the protoplast layer becomes smaller when it leaves the cell wall.

The clear water gradually recovered to its original size (cells absorbed water), and the protoplasm layer recovered to its original position, basically unchanged.

4. In the process of establishing biofilm model, the progress of experimental technology has played a key role in promoting. For example, the birth of electron microscope made people finally see the existence of film; Freeze etching technology and scanning electron microscope technology make people realize that the inside and outside of the film are asymmetric; The fusion experiment of fluorescent labeled mouse cells and human cells proved the fluidity of the membrane. Without the support of these technologies, human understanding cannot develop.

5. Elaborate the basic content of fluid mosaic model P68.

6, the way of material in and out of the battery

Mode of transportation: Does the direction of transportation require the carrier? Example: Does it consume energy?

Free diffusion from high concentration to low concentration No No P70 Write a few examples.

Actively convert low concentration into high concentration Yes Yes Yes Yes

Does it help to diffuse high concentration to low concentration?

The significance of active transportation is to ensure that living cells actively absorb nutrients and discharge metabolic wastes and harmful substances according to the needs of life activities.

Chapter V Energy Supply and Utilization of Batteries

1. sumner, an American scientist, confirmed by experiments that enzyme is a kind of protein with catalytic effect. Scientists Cech and Altman found that a few RNA also had biocatalysis. In a word, enzyme is a catalytic organic substance produced by living cells. Most enzymes such as pepsin and salivary amylase are protein, and a few are RNA. It can't be said that all protein and RNA are enzymes, only protein or RNA with catalytic effect is called an enzyme. The enzyme is characterized by high efficiency and specificity P79.

2. Conduct relevant experiments and explorations, learn to control independent variables, observe and detect the changes of dependent variables, set up control groups, and repeat experiments.

3. The Chinese name of ATP is adenosine triphosphate, and the structural abbreviation is A-P ~ P ~ P. Almost all the energy of life activities comes directly from the hydrolysis of ATP, and the energy needed for ATP synthesis comes from the respiration of animals and the photosynthesis and respiration of plants. ATP can be synthesized in mitochondria or chloroplasts of organelles, and also in cytoplasm matrix. The ATP content in cells is very low, and the transformation is rapid. I am familiar with the picture on page 89.

4. Living cells that make up an organism are constantly transforming ATP and ADP, and at the same time, accompanied by

With the release and storage of energy. Therefore, ATP is compared to the "common currency" circulating in cells.

5. The essence of respiration is to oxidize and decompose organic matter and release energy, and oxygen is not necessarily needed.

Divided into aerobic breathing and anaerobic breathing, 93 pages. ,

6. The reaction formula of aerobic respiration is:

The first stage is carried out in cytoplasm matrix, with sugar as raw material and products of pyruvate, hydrogen and ATP. The second stage is carried out in mitochondria, with pyruvate and water as raw materials and products of CO2, ATP and hydrogen. The third stage is carried out in mitochondria, with hydrogen and oxygen as raw materials and water and ATP as products; The products of the first and second stages are hydrogen and ATP, and the products of the third stage are * * *. 1mol glucose aerobic respiration produces 2870 KJ, of which1161kj (38 molatp) can be used for life activities, 1709 KJ can be dissipated by thermal energy, and the available energy produced by anaerobic respiration is 61.08.

7. Write two anaerobic respiratory reaction formulas.

C6H 12O6 2C2H5OH (alcohol) +2CO2+ energy

Energy of C6H 12O62C3H3O3+

The site of anaerobic respiration is the cytoplasmic matrix, which is divided into two stages. In the first stage, glucose is decomposed into pyruvate, and in the second stage, pyruvate is decomposed into CO2 and alcohol or C3H3O3 (lactic acid). Familiar with the chart on page 95.

8, the discovery of photosynthesis

Times innovation fa

Modern people's innovative experimental design thought and phenomenon experimental conclusion

177 1 year price

Terry lights candles and green plants in a closed glass cover. This phenomenon is _ _ _ _ _ _ _ _.

Rats and green plants are in a closed glass cover, and the phenomenon is _ _ _ _ _ _ _ _ _ _ _ _.

1864, saxophone left the green leaves in the dark for several hours, with the purpose of _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Jean 1880

German sponges are dark and have no air.

Irradiation of chloroplasts by extremely thin beams → phenomenon _ _ _ _ _ _ _ _

Aerobic bacteria microscope observation of complete exposure → phenomenon _ _ _ _ _ _ _ _ _ _ _ _

20th century

Rubin in the 1930s

And Carmen's experimental method is _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.

H2 18O, CO2→ phenomenon _ _ _ _ _ _ _ _ phenomenon

H2O, C 18O2→ phenomenon _ _ _ _ _ _ _ _ _ _ _ _

9. Chloroplast pigments absorb visible light, mainly red-orange light and blue-violet light (chlorophyll a and chlorophyll b mainly absorb blue-violet light and red-orange light, while carotene and lutein mainly absorb blue-violet light). The place of light reaction is on chloroplast thylakoid membrane (because all pigments and all photoreactive enzymes are in the thylakoid structure). The raw materials are water, ADP and Pi, the power is light energy, and the products are oxygen, hydrogen and ATP. The dark reaction site is chloroplast matrix, the raw material is CO2, the power is the energy released by ATP hydrolysis, and the products are organic matter (CH2O) and C5. Photoreaction provides reducing agents hydrogen and ATP (energy) for dark reaction. Before CO2 is reduced, it needs to be fixed, part of C3 compounds are reduced to organic compounds, and the other part becomes pentacarbon compounds. The total reaction formula of photosynthesis is CO2+H2O (CH2O)+O2. The most basic material and energy metabolism in nature is photosynthesis. Oxygen produced by photosynthesis comes from H2O, and O in organic matter comes from CO2. Significance of photosynthesis: 1. Make organic matter, fix solar energy, and provide material and energy needs for other living things; 2. Making oxygen, maintaining the balance between O2 and CO2, and enabling aerobic organisms to develop; 3. The O3 layer is formed, which makes the living things evolve from aquatic to terrestrial. Familiar with page 103.

10, one of the important conditions to improve crop yield is to improve the utilization rate of light energy. Methods to improve the utilization rate of crop light energy are as follows:

1) Prolonging photosynthesis time 2) Increasing photosynthesis area.

3) control of light intensity 4) supply of essential mineral elements 5) supply of 5)CO2.

When the carbon dioxide content is very low, green plants can't produce organic matter. With the increase of CO2 content, photosynthesis is gradually enhanced. When the CO2 content increases to a certain extent, the intensity of photosynthesis will no longer increase with the increase of CO2 content.

Please compare photosynthesis and respiration by yourself.

Chapter VI Life Course of Cells

Cell proliferation Cell proliferation is an important life feature of living things. Cells proliferate through division, single-celled organisms can produce offspring through division, while multicellular organisms can divide and differentiate from a fertilized egg and eventually develop into multicellular individuals. In the process of proliferation, the copied genetic material can be distributed to two daughter cells, indicating that cell proliferation is the basis of organism growth, development, reproduction and inheritance.

Eukaryotic cells have mitosis, amitosis and meiosis.

I. Mitosis

The mitosis of somatic cells has a cell cycle, which refers to the continuous division process from the beginning of one division to the completion of the next division, including interphase and mitosis.

1, division interval

The most important feature of interphase is the replication of DNA molecules and the synthesis of protein, and the cells grow moderately at the same time. For cell division, it is the stage of preparing for the interval in the whole cycle.

2. Split period

(1) prophase

The most obvious change is the spiral winding of chromatin filaments, which becomes shorter and thicker into chromosomes. At this time, each chromosome contains two chromatids connected by centromeres, which are called sister chromatids. At the same time, nucleoli disintegrated, nuclear contact disappeared, and spindle filament formed spindle.

(2) medium term

Chromosomes are clearly visible, and the centromere of each chromosome is arranged on a plane in the center of the cell, so the morphology of chromosomes is relatively stable and the number is relatively clear, which is convenient for observation.

(3) Late stage

Each centromere is divided into two parts, and the sister chromatids are separated to form two sub-chromosomes, which move to the two poles of the cell under the traction of spindle filaments.

(4) Late stage

After the chromosomes reach the poles, they gradually turn into filamentary chromatin, at the same time, the spindle disappears, nucleoli and nuclear model reappear, chromatin is surrounded to form two new daughter cells, and then the cells split into two.

(5) Comparison of mitosis between animal and plant cells.

Animals and plants

Spindle is composed of two poles and centrosome of cells.

Cells are divided into two ways.

meaning

Second, amitosis

Mitosis is relatively simple. Generally, the nucleus is elongated, depressed inward from the middle of the nucleus, divided into two nuclei, and then the whole cell is divided into two cells from the middle. There are no spindle filaments and chromosomes in this process, so it is named amitosis, such as red blood cell division in frogs.

Second, cell differentiation, canceration and aging.

I. Cell differentiation

Cell differentiation refers to the process of stability differences in morphology, structure and physiological functions of offspring produced by the proliferation of one or a class of cells during individual development. It is a permanent change, which occurs in the whole life of an organism, but reaches its maximum in the embryonic period. After cell differentiation, various cells and tissues will be formed in organisms, and this difference in stability is irreversible.

However, scientific research confirms that highly differentiated plant cells still have the ability to develop into complete plants, that is, to maintain totipotency. Cell totipotency refers to the characteristic that the cells of an organism have the potential to make the offspring cells form a complete individual. Every cell of an organism contains all the genetic information unique to the species and all the genetic materials necessary for the development of a complete individual. Theoretically, every living cell of an organism should be omnipotent. In all kinds of biological cells, fertilized eggs have the highest totipotency.

Generally, cells in organisms do not show totipotency, but differentiate into different cells and tissues, which is the result of selective expression of genes under specific time and space conditions.

Second, the canceration of cells.

In the process of individual development, most cells can differentiate normally. However, some cells can't differentiate normally under the action of carcinogens, but become malignant proliferative cells that are not controlled by organisms and continue to divide. This kind of cell is cancer cell, and the generation of this kind of cell is related to the generation of cell.

Directly related.

Compared with normal cells, cancer cells have the following characteristics: P 126.

( 1) ;

(2) ;

(3) 。

Due to the decrease of glycoprotein and other substances on the cell membrane, the adhesion between cells decreases, which leads to the easy dispersion and metastasis of cancer cells in organisms.

At present, there are three main types of carcinogens: the first type of physical carcinogens, such as radiation carcinogens; The second category is chemical carcinogens, such as arsenic, benzene and coal tar. The other is viral carcinogen, and the virus that causes cancer is called carcinogenic virus. In addition, scientists have confirmed that cancer cells are caused by the activation of proto-oncogenes into oncogenes.

Third, cell aging.

Most cells in organisms will experience undifferentiation, division, differentiation and death. Therefore, cell aging and death is a normal life phenomenon. The main characteristics of aging cells are as follows:

(1) The decrease of intracellular water content leads to cell atrophy, smaller volume and slower cell metabolic rate.

(2) In aging cells, the activity of enzymes is decreased. For example, human hair turns white because tyrosinase activity decreases when melanocytes age; (3) Pigments in cells will accumulate with the aging of cells, which will affect the normal physiological functions of cells such as material exchange and information transmission, and eventually lead to cell death; (4) The permeability of cell membrane changes, and the transport capacity of substances decreases. Apoptosis and cell necrosis P 123~ 124