1. Give definitions of concepts.
Interphase- the phase of preparation for mitotic division, when DNA duplication occurs.
Mitosis- this is a division, as a result of which there is a strictly identical distribution of exactly copied chromosomes between daughter cells, which ensures the formation of genetically identical cells.
Life cycle - the period of cell life from the moment of its appearance in the process of division to death or the end of subsequent division.

2. How does the growth of unicellular organisms differ from the growth of multicellular ones?
The growth of a unicellular organism is an increase in the size and complication of the structure of a single cell, and the growth of multicellular organisms is also an active division of cells - an increase in their number.

3. Why does an interphase necessarily exist in the life cycle of a cell?
In interphase, preparation for division and duplication of DNA occurs. If it did not occur, then with each cell division, the number of chromosomes would be halved, and pretty soon there would be no chromosomes left in the cell at all.

4. Fill in the "Phases of Mitosis" cluster.

5. Using figure 52 in § 3.4, complete the table.

6. Compose a syncwine for the term "mitosis".
Mitosis
Four-phase, uniform
Divides, distributes, splits
Provides genetic material to daughter cells
cell division.

7. Establish a correspondence between the phases of the mitotic cycle and the events taking place in them.
Phases
1. Anaphase
2. Metaphase
3. Interphase
4. Telophase
5. Prophase
Developments
A. The cell grows, organelles are formed, DNA doubles.
B. Chromatids separate and become independent chromosomes.
B. Spiralization of chromosomes begins, the nuclear envelope is destroyed.
D. Chromosomes are located in the equatorial plane of the cell. The spindle fibers attach to the centromeres.
D. The spindle of division disappears, nuclear membranes form, chromosomes unwind.

8. Why does the completion of mitosis - division of the cytoplasm occur differently in animal and plant cells?
Animal cells do not have a cell wall, their cell membrane bulges inward, and the cell divides by constriction.
In plant cells, the membrane is formed in the equatorial plane inside the cell and, spreading to the periphery, divides the cell in half.

9. Why does interphase take a much longer time in the mitotic cycle than division itself?
During interphase, the cell intensively prepares for mitosis, synthesis processes take place in it, DNA doubling, the cell grows, goes through its life cycle, not including the division itself.

10. Choose the correct answer.
Test 1
As a result of mitosis, one diploid cell produces:
4) 2 diploid cells.

Test 2
The division of the centromere and the divergence of chromatids to the poles of the cell occurs in:
3) anaphase;

Test 3
The life cycle is:
2) cell life from division to the end of the next division or death;

Test 4
Which term is misspelled?
4) telophase.

11. Explain the origin and general meaning of the word (term), based on the meaning of the roots that make it up.

12. Choose a term and explain how it contemporary meaning corresponds to the original meaning of its roots.
The chosen term is interphase.
Conformity. The term corresponds to, and means the period between the phases of mitosis, when preparation for division occurs.

13. Formulate and write down the main ideas of § 3.4.
The life cycle is the life of a cell from division to the end of the next division or death. Between divisions, the cell prepares for it during interphase. At this time, there is a synthesis of substances, duplication of DNA.
The cell divides by mitosis. It consists of 4 stages:
Prophase.
Metaphase.
Anaphase.
Telophase.
The purpose of mitosis: as a result of it, 2 daughter cells with an identical set of genes are formed from 1 mother cell. The amount of genetic material and chromosomes remains the same, ensuring the genetic stability of cells.

Textbook for grades 10-11

Section II. Reproduction and development of organisms
Chapter V. Reproduction of organisms

Every second on Earth, an astronomical number of living beings die from old age, diseases and predators, and only thanks to reproduction, this universal property of organisms, life on Earth does not stop.

It may seem that the processes of reproduction in living beings are very diverse, but all of them can be reduced to two forms: asexual and sexual. Some organisms have different forms of reproduction. For example, many plants can be propagated by cuttings, layering, tubers (asexual reproduction) and seeds (sexually).

During sexual reproduction, each organism develops from one cell, formed from the fusion of two germ cells - male and female.

The basis of reproduction and individual development of the body is the process of cell division.

§ 20. Cell division. Mitosis

The ability to divide is the most important property of cells. Without division, it is impossible to imagine an increase in the number of unicellular beings, the development of a complex multicellular organism from a single fertilized egg, the renewal of cells, tissues, and even organs lost during the life of the organism.

Cell division is carried out in stages. At each stage of division, certain processes occur. They lead to the doubling of the genetic material (DNA synthesis) and its distribution between daughter cells. The period of a cell's life from one division to the next is called the cell cycle.

Preparing for division. Eukaryotic organisms, consisting of cells with nuclei, begin preparing for division at a certain stage of the cell cycle, in interphase.

It is during the period of interphase in the cell that the process of protein biosynthesis occurs, the chromosomes double. Along the original chromosome from the chemical compounds present in the cell, its exact copy is synthesized, the DNA molecule is doubled. A doubled chromosome consists of two halves - chromatids. Each chromatid contains one DNA molecule.

Interphase in plant and animal cells lasts 10-20 hours on average. Then comes the process of cell division - mitosis.

During mitosis, the cell goes through a series of successive phases, as a result of which each daughter cell receives the same set of chromosomes as it was in the mother cell.

phases of mitosis. There are four phases of mitosis: prophase, metaphase, anaphase, and telophase. Figure 29 schematically shows the course of mitosis. In prophase, centrioles are clearly visible - formations located in the cell center and playing a role in the divergence of the daughter chromosomes of animals. (Recall that only some plants have centrioles in the cell center, which organizes the segregation of chromosomes.) We will consider mitosis on the example of an animal cell, since the presence of a centriole makes the process of chromosome segregation more visible. The centrioles double and diverge different poles cells. Microtubules extend from the centrioles, forming spindle fibers, which regulate the divergence of chromosomes to the poles of the dividing cell.

Rice. 29. Scheme of mitosis

At the end of prophase, the nuclear membrane disintegrates, the nucleolus gradually disappears, the chromosomes spiralize and as a result shorten and thicken, and they can already be observed under a light microscope. They are even better seen at the next stage of mitosis - metaphase.

In metaphase, chromosomes are located in the equatorial plane of the cell. It is clearly seen that each chromosome, consisting of two chromatids, has a constriction - a centromere. Chromosomes are attached to spindle fibers by their centromeres. After division of the centromere, each chromatid becomes an independent daughter chromosome.

Then comes the next stage of mitosis - anaphase, during which the daughter chromosomes (chromatids of one chromosome) diverge to different poles of the cell.

The next stage of cell division is telophase. It begins after the daughter chromosomes, consisting of one chromatid, have reached the poles of the cell. At this stage, the chromosomes despiralize again and acquire the same form as they had before the cell division began in the interphase (long thin filaments). A nuclear envelope arises around them, and a nucleolus is formed in the nucleus, in which ribosomes are synthesized. In the process of cytoplasm division, all organelles (mitochondria, Golgi complex, ribosomes, etc.) are more or less evenly distributed between daughter cells.

Thus, as a result of mitosis, two cells are obtained from one cell, each of which has a characteristic number and shape of chromosomes for a given type of organism, and, consequently, a constant amount of DNA.

The entire process of mitosis takes an average of 1-2 hours. Its duration is somewhat different for different types cells. It also depends on the conditions of the external environment (temperature, light regime and other indicators).

The biological significance of mitosis lies in the fact that it ensures the constancy of the number of chromosomes in all cells of the body. In the process of mitosis, the DNA of the chromosomes of the mother cell is distributed strictly equally between the two daughter cells that arise from it. As a result of mitosis, all daughter cells receive the same genetic information.

1. What changes in the cell precede division?
2. When is the spindle formed? What is its role?
3. Describe the phases of mitosis and briefly describe how this process occurs.
4. What is a chromatid? When does it become a chromosome?
5. What is a centromere? What role does it play in mitosis?
6. What is the biological significance of mitosis?

Recall from the course of botany, zoology, anatomy, physiology and human hygiene how reproduction occurs in the organic world.

Mitosis- this is a cell division in which the daughter cells are genetically identical to the parent and to each other. That is, during mitosis, chromosomes are doubled and distributed between daughter cells so that each receives one chromatid of each chromosomes.

There are several stages (phases) in mitosis. However, mitosis itself is preceded by a long interphase. Mitosis and interphase together make up cell cycle. In the process of interphase, the cell grows, organelles are formed in it, and synthesis processes are actively going on. In the synthetic period of interphase reduplicates, i.e., doubles, DNA.

After duplication of chromatids, they remain connected in the area centromeres, i.e., the chromosome consists of two chromatids.

In mitosis itself, four main stages are usually distinguished (sometimes more).

The first stage of mitosis is prophase. In this phase, the chromosomes spiral and acquire a compact twisted shape. Because of this, the processes of RNA synthesis become impossible. The nucleoli disappear, which means that ribosomes are also not formed, i.e., synthetic processes in the cell are suspended. Centrioles diverge to the poles (at different ends) of the cell, the division spindle begins to form. At the end of prophase, the nuclear envelope disintegrates.

prometaphase- This is a stage that is not always isolated separately. The processes occurring in it can be attributed to late prophase or early metaphase. In prometaphase, the chromosomes are in the cytoplasm, randomly moving around the cell until they are connected to the spindle thread in the region of the centromere.

The filament is a microtubule built from the protein tubulin. It grows by attaching new tubulin subunits. In this case, the chromosome moves away from the pole. From the side of the other pole, the spindle thread also joins it and also pushes it away from the pole.

Second stage of mitosis metaphase. All chromosomes are located in the equatorial region of the cell nearby. Attached to their centromeres are two filaments of the spindle. In mitosis, metaphase is the longest stage.

The third stage of mitosis is anaphase. In this phase, the chromatids of each chromosome are separated from each other and, due to the threads pulling them, the spindles of division move to different poles. Microtubules no longer grow, but disassemble. Anaphase is a relatively fast phase of mitosis. With the divergence of chromosomes, the organelles of the cell in approximately equal numbers also diverge closer to the poles.

Fourth stage of mitosis telophase- in many respects the reverse of prophase. Chromatids gather at the poles of the cell and unwind, i.e., despiralize. Nuclear membranes form around them. Nucleoli are formed and RNA synthesis begins. The spindle of division begins to collapse. Then the cytoplasm divides cytokinesis. In animal cells, this occurs due to the invagination of the membrane inward and the formation of a constriction. In plant cells, the membrane begins to form inside in the equatorial plane and goes to the periphery.

Mitosis. Table

Phase	Processes
Prophase	Spiralization of chromosomes. Disappearance of nucleoli. Disintegration of the nuclear envelope. Beginning of spindle formation.
prometaphase	Attachment of chromosomes to the spindle threads and their movement to the equatorial plane of the cell.
metaphase	Each chromosome is stabilized in the equatorial plane by two strands coming from different poles.
Anaphase	Rupture of the centromeres of chromosomes. Each chromatid becomes an independent chromosome. Sister chromatids move to different poles of the cell.
Telophase	Despiralization of chromosomes and resumption of synthetic processes in the cell. Formation of nucleoli and nuclear envelope. Destruction of the fission spindle. doubling of centrioles. Cytokinesis is the division of the cell body in two.

Interphase is the period between two cell divisions. In interphase, the nucleus is compact, has no pronounced structure, the nucleoli are clearly visible. The set of interphase chromosomes is chromatin. The composition of chromatin includes: DNA, proteins and RNA in a ratio of 1: 1.3: 0.2, as well as inorganic ions. The structure of chromatin is variable and depends on the state of the cell.

Chromosomes are not visible in the interphase; therefore, their study is carried out by electron microscopic and biochemical methods. Interphase includes three stages: presynthetic (G1), synthetic (S), and postsynthetic (G2). The symbol G is an abbreviation for the English. gap - interval; the symbol S is an abbreviation for English. synthesis - synthesis. Let's consider these stages in more detail.

Presynthetic stage (G1). Each chromosome is based on one double-stranded DNA molecule. The amount of DNA in a cell at the presynthetic stage is denoted by the symbol 2c (from the English content). The cell is actively growing and functioning normally.

Synthetic stage (S). Self-doubling, or DNA replication, occurs. At the same time, some parts of the chromosomes double earlier, while others double later, that is, DNA replication proceeds asynchronously. In parallel, there is a doubling of centrioles (if any).

Postsynthetic stage (G2). DNA replication is completed. Each chromosome contains two double DNA molecules, which are an exact copy of the original DNA molecule. The amount of DNA in a cell at the postsynthetic stage is denoted by the symbol 4c. The substances necessary for cell division are synthesized. At the end of the interphase, the synthesis processes stop.

Mitosis process

Prophase is the first phase of mitosis. Chromosomes spiralize and become visible under a light microscope in the form of thin filaments. Centrioles (if any) diverge towards the poles of the cell. At the end of prophase, the nucleoli disappear, the nuclear envelope breaks down, and the chromosomes emerge into the cytoplasm.

In prophase, the volume of the nucleus increases, and due to the spiralization of chromatin, chromosomes are formed. By the end of prophase, each chromosome is seen to consist of two chromatids. Gradually, the nucleoli and nuclear membrane dissolve, and the chromosomes are randomly located in the cytoplasm of the cell. The centrioles move towards the poles of the cell. An achromatin spindle is formed, some of the threads of which go from pole to pole, and some are attached to the centromeres of chromosomes. The content of genetic material in the cell remains unchanged (2n2хр).

Rice. 1. Scheme of mitosis in onion root cells

Rice. 2. Scheme of mitosis in onion root cells: 1 - interphase; 2,3 - prophase; 4 - metaphase; 5.6 - anaphase; 7.8 - telophase; 9 - formation of two cells

Rice. Fig. 3. Mitosis in the cells of the onion root tip: a - interphase; b - prophase; c - metaphase; g - anaphase; l, f - early and late telophases

Metaphase. The beginning of this phase is called prometaphase. In prometaphase, the chromosomes are arranged rather randomly in the cytoplasm. A mitotic apparatus is formed, which includes a division spindle and centrioles or other microtubule organization centers. In the presence of centrioles, the mitotic apparatus is called astral (in multicellular animals), and in their absence, anastral (in higher plants). The division spindle (achromatin spindle) is a system of tubulin microtubules in a dividing cell that ensures chromosome segregation. The division spindle consists of two types of filaments: polar (supporting) and chromosomal (pulling).

After the formation of the mitotic apparatus, the chromosomes begin to move into the equatorial plane of the cell; this movement of chromosomes is called metakinesis.

In metaphase, the chromosomes are maximally spiralized. The centromeres of chromosomes are located in the equatorial plane of the cell independently of each other. The polar threads of the spindle of division stretch from the poles of the cell to the chromosomes, and the chromosomal threads - from the centromeres (kinetochores) - to the poles. The set of chromosomes in the equatorial plane of the cell forms a metaphase plate.

Anaphase. Chromosomes are divided into chromatids. From this moment on, each chromatid becomes an independent single-chromatid chromosome, which is based on one DNA molecule. Single-chromatid chromosomes in anaphase groups diverge towards the poles of the cell. When chromosomes separate, chromosomal microtubules shorten and pole microtubules lengthen. In this case, the polar and chromosome threads slide along each other.

Telophase. The spindle of division is destroyed. Chromosomes at the poles of the cell are despiralized, nuclear envelopes are formed around them. Two nuclei are formed in the cell, genetically identical to the original nucleus. The content of DNA in the daughter nuclei becomes equal to 2c.

Cytokinesis. In cytokinesis, the separation of the cytoplasm and the formation of membranes of daughter cells occurs. In animals, cytokinesis occurs by cell ligation. In plants, cytokinesis occurs differently: vesicles form in the equatorial plane, which merge to form two parallel membranes.

This completes mitosis and the next interphase begins.