Mitosis and meiosis to help you pass the Unified State Exam. A brief description of the stages and pattern of cell division through meiosis. A message on the topic of mitosis and meiosis.
Life cycle- this is the time of existence of a cell from the moment of its formation by dividing the mother cell until its own division or natural death. In the cells of a complex organism (for example, a human), the cell life cycle may be different. Highly specialized cells (erythrocytes, nerve cells, striated muscle cells) do not reproduce. Their life cycle consists of birth, performance of intended functions, death (heterocatalytic interphase).
The most important component of the cell cycle is mitotic (proliferative) cycle. It is a complex of interrelated and coordinated phenomena during cell division, as well as before and after it. Mitotic cycle is a set of processes occurring in a cell from one division to the next and ending with the formation of two cells of the next generation. In addition, the concept of the life cycle also includes the period during which the cell performs its functions and periods of rest. At this time, the further cell fate is uncertain: the cell may begin to divide (enters mitosis) or begin to prepare to perform specific functions.
Mitosis is the main type of division of somatic eukaryotic cells. The division process includes several successive phases and is a cycle. Its duration varies and ranges from 10 to 50 hours in most cells. In human body cells, the duration of mitosis itself is 1–1.5 hours, the G2 period of interphase is 2–3 hours, and the S period of interphase is 6–10 hours .
Mitosis.
The mitotic cycle consists of four consecutive periods: presynthetic (or postmitotic) G1, synthetic S, postsynthetic (or premitotic) G2, components interphase (preparatory period), and mitosis itself (Fig. 1).
Interphase stages:
1) presynthetic (G1). Occurs immediately after cell division. DNA synthesis has not yet occurred. The cell is actively growing in size, storing substances necessary for division: proteins (histones, structural proteins, enzymes), RNA, ATP molecules. Division of mitochondria and chloroplasts (i.e., structures capable of self-reproduction) occurs. The organizational features of the interphase cell are restored after the previous division;
2) synthetic (S). Genetic material is duplicated through DNA replication. It occurs in a semi-conservative manner, when the double helix of the DNA molecule diverges into two chains and a complementary chain is synthesized on each of them.
The result is two identical DNA double helices, each consisting of one new and one old DNA strand. The amount of hereditary material doubles. In addition, the synthesis of RNA and proteins continues. Also, a small part of mitochondrial DNA undergoes replication (the main part of it is replicated in the G2 period);
3) postsynthetic (G2). DNA is no longer synthesized, but the defects made during its synthesis in the S period are corrected (repair). Energy and nutrients are also accumulated, and the synthesis of RNA and proteins (mainly nuclear) continues.
After this, mitosis proper occurs, which consists of four phases.
Phases of mitosis.
Mitosis consists of four successive phases - prophase, metaphase, anaphase and telophase.
Mitosis phases:
1) prophase. The centrioles of the cell center divide and move to opposite poles of the cell. A fission spindle is formed from microtubules, which connects the centrioles of different poles. At the beginning of prophase, the nucleus and nucleoli are still visible in the cell; by the end of this phase, the nuclear envelope is divided into separate fragments (the nuclear membrane is dismantled), and the nucleoli disintegrate. Chromosomes begin to condense: they curl, thicken, and become visible under a light microscope. In the cytoplasm, the number of rough ER structures decreases, the number of polysomes sharply decreases;
2) metaphase. The formation of the fission spindle ends.
Condensed chromosomes line up along the equator of the cell, forming a metaphase plate. Spindle microtubules are attached to centromeres, or kinetochores (primary constrictions), of each chromosome. After this, each chromosome is longitudinally split into two chromatids (daughter chromosomes), which are connected only at the centromere;
3) anaphase. The connection between the daughter chromosomes is destroyed, and they begin to move to the opposite poles of the cell at a speed of 0.2–5 μm/min. At the end of anaphase, each pole has a diploid set of chromosomes. Chromosomes begin to decondense and unwind, becoming thinner and longer;
4) telophase. Chromosomes are completely despiralized, the structure of the nucleoli and interphase nucleus is restored, and the nuclear membrane is “mounted.” The fission spindle is destroyed. Cytokinesis (cytoplasm division) occurs. In animal cells, this process begins with the formation of a constriction in the equatorial plane, which becomes deeper and deeper and eventually completely divides the mother cell into two daughter cells.
The duration of each phase depends on the type of tissue, the physiological state of the body, exposure to external factors (light, temperature, chemicals), etc.
Rice. 1. Cell cycle (mitosis).
Meiosis.
During the formation of gametes, i.e. germ cells - sperm and eggs - cell division occurs, called meiosis (Fig. 2). The original cell has a diploid set of chromosomes, which then double. But, if during mitosis the chromatids in each chromosome simply separate, then during meiosis a chromosome (consisting of two chromatids) is closely intertwined in its parts with another chromosome homologous to it (also consisting of two chromatids), and crossing over - exchange of homologous regions of chromosomes. Then new chromosomes with mixed “mother’s” and “father’s” genes diverge and cells with a diploid set of chromosomes are formed, but the composition of these chromosomes is already different from the original one; recombination . The first meiotic division is completed, and the second meiotic division occurs without DNA synthesis, so during this division the amount of DNA is halved. From initial cells with a diploid set of chromosomes, gametes with a haploid set arise. From one diploid cell four haploid cells are formed. The phases of cell division that follow interphase are called prophase, metaphase, anaphase, telophase, and after division again interphase.
In meiosis, the phases are also called, but it is indicated which division of meiosis it belongs to. Crossing over - the exchange of parts between homologous chromosomes - occurs in prophase of the first division of meiosis (prophase I), which includes the following stages: leptotene, zygotene, pachytene, diplotene, diakinesis (Fig. 3). The processes occurring in the cell are described in detail in the textbook ed. V.N. Yarygina, and they should be known.
Rice. 2. The main stages of mitotic and meiotic division.
Rice. 3. Stages of prophase I of meiosis.
Table
Types of cell division
Tests:
1. In humans, a mature plasma cell has lost the ability to reproduce and began to secrete antibodies - immunoglobulins. What stage of the life cycle is it at?
B. S-period.
D. Differentiation.
D. Prometaphase.
2. Studying the woman’s oocytes under a microscope, the scientist saw in them that the conjugating chromosomes were intertwined and crossover occurred between them. Indicate the prophase stage of the first meiotic division.
A. Pahinema
B. Zygonema
V. Leptonema
G. Diplonema
D. Diakinesis
3. In a large family there are four sons and three daughters, phenotypically different from one another in many ways. This is explained by the fact that during the process of gametogenesis, the parents got different combinations of chromosomes into each of the gametes. Name the stage of meiosis in which this occurred:
A. Anaphase of meiosis II
B. Anaphase of meiosis I
B. Metaphase of meiosis II
D. Prophase of meiosis II
D. Prophase of meiosis I
4. During the post-synthetic period of the mitotic cycle, the synthesis of proteins - tubulins - was disrupted. What consequences can this lead to?
A. Violation of spindle formation
B. Impaired cytokinesis
B. Violation of chromosome spiralization
D. Impaired DNA repair
D. Reducing the duration of mitosis
5. At one stage of the cell cycle, identical chromosomes reach the cell poles, despiral, and a nuclear membrane and nucleolus are formed around them. What phase of mitosis is the cell in?
A. Telophase
B. Prophase
B. Prometaphase
G. Metaphase
D. Anaphase
6. It is known that the cell cycle includes several successive transformations in the cell. At one of the stages, processes occur that prepare DNA synthesis. During what period of a cell's life does this occur?
A. Presynthetic
B. Synthetic
B. Mitosis itself
G. Premitotic
D. Postsynthetic
7. Maximum spiralized chromosomes were formed in the cell. They are located along the equator of the somatic cell. Which phase of mitosis does this correspond to:
A. Metaphase
B. Telophase
V. Profase
G. Anaphase
D. Prometaphase
8. During the life cycle of a cell and during the process of mitosis, a natural change in the amount of hereditary material occurs. At what stage does the amount of DNA double?
A. Interphase
B. Prophase
B. Metaphase
G. Anaphase
D. Telophase
9. In the presynthetic period of the mitotic cycle, DNA synthesis does not occur, because there are as many DNA molecules as there are chromosomes. How many DNA molecules does a human somatic cell have in the presynthetic period?
A. 46 DNA molecules
B. 92 DNA molecules
B. 23 DNA molecules
D. 69 DNA molecules
D. 48 DNA molecules
10. In anaphase of mitosis, single-chromatid chromosomes diverge to the poles. How many chromosomes does a human cell have in anaphase of mitosis?
A. 92 chromosomes
B. 46 chromosomes
B. 23 chromosomes
D. 69 chromosomes
D. 96 chromosomes
Knowledge control tasks:
Task 1. When studying proliferative activity using 3 H-thymidine, it turned out that within 24 hours, 80 cells entered the phase of DNA synthesis, but the total number of mitoses per day was only 21. How to explain these differences?
Task 2. With significant cell losses, the constancy of tissue composition is maintained by resting cells. At what phases do they enter the mitotic cycle?
Task 3. The alkaloid colchicine blocks the synthesis of the protein tubulin. What cellular structures can this drug affect? How will this affect the course of mitotic division?
Problem 4. In some cases, tumor growth is associated with the transition of a certain cell population to reproduction through amitosis. How will the cells of such a population differ from a normal one in which typical mitosis occurs?
Task 5. In humans, during crossing over, the action of a mutagenic factor led to the appearance of a chemical bond between homologous X chromosomes, preventing their subsequent divergence. What chromosome set will the resulting cells (gametes) receive?
Task 6. It is known that the mechanism of the second division of meiosis is similar to that in mitosis. What differences will there be in the morphological picture of the metaphase of the second meiotic division and the metaphase of mitosis in cells of the same organism?
6.Materials for review with the teacher and control of its assimilation:
6.1. Analysis with the teacher of key issues to master the topic of the lesson.
6.2. Demonstration of techniques by teacher practical techniques on the topic.
6.3. Material for control mastering the material:
Questions for discussion with the teacher:
1. Organization of the cell in time. Changes in cells and their structures during the mitotic cycle (interphase and mitosis).
2. Cell cycle, peridization and possible directions.
3. Methods of cell division: amitosis, mitosis, meiosis. Amitosis and its mechanisms.
4. Endomitosis, polyteny.
5. Mitotic cycle, its periodization. Mitosis, characteristics of phases. Mitotic activity of tissues. Mitosis disorders.
6. Meiosis, characteristics of phases. Biological significance.
7. Molecular mechanisms of cell proliferation.
8. Cell death
9. Life of cells outside the body. Cell cloning.
Practical part
1. Study the types of cell division. Enter into the protocol the table “Types of cell division”
2. Examine karyokinesis in onion root cells on microscopic slides and sketch it.
3. Using the educational table, study the scheme of meiotic cell division. Draw it in an album.
4. Solve situational problems.
WORK IN THE LABORATORY
8.Literature:
Main:
1. Biology: In 2 books. Book 1: Textbook. for medical specialists universities /ed. V.N.Yarygina. 6th ed. -M.: Higher School, 2004.- P.55-61
2. Biology/A.A.Slyusarev, S.V.Zhukova.- K.: Vishcha school. Head publishing house, 1992.- P.41-45
3. Biology. Guide to practical exercises for students of dental faculties, ed. acad. RANS prof. V.V. Markina. Ed. M. "GEOTAR-Media" 2010
Additional:
10. Medical biology: Pidruchnik /edited by V.P.Pishak, Yu.I.Bazhori.-Vinnytsia: New book, 2004.- P.26-28, 104-107, 118-125
11. Alberts G., Gray D., Lewis J. et al. Molecular biology of the cell. M.: Mir, 1986. – In 3 volumes, 2nd ed. T.1.- pp. 176-177
12. Logical structure graph.
13. Lecture notes.
OBJECTIVE (general): It is necessary to pay attention to general issues of cytology and molecular biology.
The lesson is conducted with the aim of consolidating previously studied material.
Students who have not missed lectures or practical classes and have completed and signed protocols by the teacher are allowed to attend the colloquium.
The final assessment consists of:
1. 40 test tasks (0 - 1 points) – max 40 points.
2. 2 problems (0-5-15 points for each problem) - max 30 points.
3. Theoretical question (0-5-10 points) - max 10 points.
__________________________________max 80 points.
ASSESSMENT CRITERIA:
SCORE - EXCELLENT
BALLA - GOOD
Related information.
Accompanied by a halving of the number of chromosomes. It consists of two sequential divisions that have the same phases as mitosis. However, as shown in table “Comparison of mitosis and meiosis”, the duration of individual phases and the processes occurring in them differ significantly from the processes occurring during mitosis.
These differences are mainly as follows.
In meiosis prophase I longer lasting. What happens in it conjugation(connection of homologous chromosomes) and exchange of genetic information. In anaphase I centromeres, holding chromatids together, don't share, and one of the homologmeiosis of mitosis and egg chromosomes goes to the poles. Interphase before the second division very short, in it DNA is not synthesized. Cells ( halites), formed as a result of two meiotic divisions, contain a haploid (single) set of chromosomes. Diploidy is restored by the fusion of two cells - maternal and paternal. The fertilized egg is called zygote.
Mitosis and its phases
Mitosis, or indirect division, most widely distributed in nature. Mitosis underlies the division of all non-reproductive cells (epithelial, muscle, nerve, bone, etc.). Mitosis consists of four consecutive phases (see table below). Thanks to mitosis uniform distribution of the genetic information of the parent cell between the daughter cells is ensured. The period of cell life between two mitoses is called interphase. It is ten times longer than mitosis. A number of very important processes take place in it prior to cell division: ATP and protein molecules are synthesized, each chromosome doubles, forming two sister chromatids, held together by a common centromere, the number of main organelles of the cytoplasm increases.
In prophase spiral and as a result chromosomes thicken, consisting of two sister chromatids held together by a centromere. By the end of prophase the nuclear membrane and nucleoli disappear and the chromosomes are dispersed throughout the cell, the centrioles move to the poles and form spindle. In metaphase, further spiralization of chromosomes occurs. During this phase they are most clearly visible. Their centromeres are located along the equator. The spindle threads are attached to them.
In anaphase Centromeres divide, sister chromatids separate from each other and, due to the contraction of spindle filaments, move to opposite poles of the cell.
In telophase The cytoplasm divides, chromosomes unwind, and nucleoli and nuclear membranes are formed again. In animal cells the cytoplasm is laced, in plant- a septum is formed in the center of the mother cell. So from one original cell (mother) two new daughter cells are formed.
Table - Comparison of mitosis and meiosis
| Phase | Mitosis | Meiosis | |
| 1 division | 2 division | ||
| Interphase |
Chromosome set 2n. There is an intensive synthesis of proteins, ATP and other organic substances. The chromosomes double, each consisting of two sister chromatids held together by a common centromere. |
Set of chromosomes 2n The same processes are observed as in mitosis, but longer, especially during the formation of eggs. | The set of chromosomes is haploid (n). There is no synthesis of organic substances. |
| Prophase | It is short-lived, spiralization of chromosomes occurs, the nuclear membrane and nucleolus disappear, and a fission spindle is formed. | Longer lasting. At the beginning of the phase, the same processes occur as in mitosis. In addition, chromosome conjugation occurs, in which homologous chromosomes come together along their entire length and become twisted. In this case, an exchange of genetic information can occur (crossing of chromosomes) - crossing over. The chromosomes then separate. | Short; the same processes as in mitosis, but with n chromosomes. |
| Metaphase | Further spiralization of chromosomes occurs, their centromeres are located along the equator. | Processes similar to those in mitosis occur. | |
| Anaphase | The centromeres holding sister chromatids together divide, each of them becomes a new chromosome and moves to opposite poles. | Centromeres do not divide. One of the homologous chromosomes, consisting of two chromatids held together by a common centromere, departs to opposite poles. | The same thing happens as in mitosis, but with n chromosomes. |
| Telophase | The cytoplasm divides, two daughter cells are formed, each with a diploid set of chromosomes. The spindle disappears and nucleoli form. | Does not last long. Homologous chromosomes end up in different cells with a haploid set of chromosomes. Cytoplasm does not always divide. | The cytoplasm divides. After two meiotic divisions, 4 cells with a haploid set of chromosomes are formed. |
Comparison table between mitosis and meiosis.
In the last two years, more and more questions have begun to appear in the test versions of the Unified State Exam in biology on methods of reproduction of organisms, methods of cell division, differences between different stages of mitosis and meiosis, sets of chromosomes (n) and DNA content (c) in different stages of cell life.
I agree with the authors of the assignments. To thoroughly understand the essence of the processes of mitosis and meiosis, you need to not only understand how they differ from each other, but also know how the set of chromosomes changes ( n), and, most importantly, their quality ( With), at various stages of these processes.
We remember, of course, that mitosis and meiosis are different methods of division kernels cells rather than the division of the cells themselves (cytokinesis).
We also remember that thanks to mitosis, diploid (2n) somatic cells multiply and asexual reproduction is ensured, and meiosis ensures the formation of haploid (n) germ cells (gametes) in animals or haploid (n) spores in plants.
For ease of perception of information
In the figure below, mitosis and meiosis are depicted together. As we can see, this diagram does not include, nor does it contain a complete description of what happens in cells during mitosis or meiosis. The purpose of this article and this figure is to draw your attention only to those changes that occur with the chromosomes themselves at different stages of mitosis and meiosis. This is precisely what the emphasis is placed on in the new USE test tasks.
In order not to overload the figures, the diploid karyotype in cell nuclei is represented by only two pairs homologous chromosomes (i.e. n = 2). The first pair are larger chromosomes ( red And orange). The second pair are smaller ones ( blue And green). If we were to specifically depict, for example, a human karyotype (n = 23), we would have to draw 46 chromosomes.
So what was the set of chromosomes and their quality before the start of division in the interphase cell during the period G1? Of course he was 2n2c. We do not see cells with such a set of chromosomes in this figure. Since after S During the interphase period (after DNA replication), the number of chromosomes, although remains the same (2n), but since each chromosome now consists of two sister chromatids, the cell karyotype formula will be written like this : 2n4c. And these are the cells with such double chromosomes, ready to begin mitosis or meiosis, that are shown in the figure.
This drawing allows us to answer the following test questions:
— How does prophase of mitosis differ from prophase I of meiosis? In prophase I of meiosis, chromosomes are not freely distributed throughout the entire volume of the former cell nucleus (the nuclear membrane dissolves in prophase), as in prophase of mitosis, but homologues unite and conjugate (intertwine) with each other. This can lead to crossover : exchange of some identical regions of sister chromatids among homologues.
— How does metaphase of mitosis differ from metaphase I of meiosis? In metaphase I of meiosis, cells are not lined up along the equator bichromatid chromosomes as in metaphase of mitosis, in bivalents(two homologues together) or tetrads(tetra - four, according to the number of sister chromatids involved in conjugation).
— How does anaphase of mitosis differ from anaphase I of meiosis? During anaphase of mitosis, the spindle filaments move the cells towards the poles sister chromatids(which at this time should already be called single chromatid chromosomes). Please note that at this time, since two single-chromatid chromosomes were formed from each bichromatid chromosome, and two new nuclei have not yet been formed, the chromosomal formula of such cells will be 4n4c. In anaphase I of meiosis, dichromatid homologues are pulled apart by spindle filaments towards the cell poles. By the way, in the figure at anaphase I we see that one of the sister chromatids of the orange chromosome has sections from the red chromatid (and, accordingly, vice versa), and one of the sister chromatids of the green chromosome has sections from the blue chromatid (and, accordingly, vice versa). Therefore, we can assert that during prophase I of meiosis, not only conjugation, but also crossing over occurred between homologous chromosomes.
— How does telophase of mitosis differ from telophase I of meiosis? During the telophase of mitosis, the two newly formed nuclei (there are not two cells yet, they are formed as a result of cytokinesis) will contain diploid set of single chromatid chromosomes - 2n2c. In telophase I of meiosis, the two resulting nuclei will contain haploid set of bichromatid chromosomes - 1n2c. Thus, we see that meiosis I has already provided reduction division (the number of chromosomes has halved).
— What ensures meiosis II? Meiosis II is called equational(equalizing) division, as a result of which the four resulting cells will contain a haploid set of normal single-chromatid chromosomes - 1n1c.
— How does prophase I differ from prophase II? In prophase II, cell nuclei do not contain homologous chromosomes, as in prophase I, so homologues do not combine.
— How does metaphase of mitosis differ from metaphase II of meiosis? A very “insidious” question, since from any textbook you will remember that meiosis II generally proceeds as mitosis. But, pay attention, during the metaphase of mitosis, the cells line up along the equator dichromatid chromosomes and each chromosome has its homologue. In metaphase II of meiosis, they also line up along the equator dichromatid chromosomes, but no homologous ones . In a color drawing, as in this article above, this is clearly visible, but in the exam the drawings are black and white. This black and white drawing of one of the test tasks depicts metaphase of mitosis, since there are homologous chromosomes (large black and large white are one pair; small black and small white are the other pair).
— There may be a similar question regarding anaphase of mitosis and anaphase II of meiosis .
— How does telophase I of meiosis differ from telophase II? Although the set of chromosomes in both cases is haploid, during telophase I the chromosomes are bichromatid, and during telophase II they are single-chromatid.
When I wrote such an article on this blog, I never thought that the content of tests would change so much in three years. Obviously, due to the difficulties of creating more and more new tests, based on the school curriculum in biology, the authors no longer have the opportunity to “dig in breadth” (everything has long been “dug up”) and they are forced to “dig deep”.
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The development and growth of living organisms is impossible without the process of cell division. In nature, there are several types and methods of division. In this article we will briefly and clearly talk about mitosis and meiosis, explain the main significance of these processes, and introduce how they differ and how they are similar.
Mitosis
The process of indirect division, or mitosis, is most often found in nature. It is the basis for the division of all existing non-reproductive cells, namely muscle, nerve, epithelial and others.
Mitosis consists of four phases: prophase, metaphase, anaphase and telophase. The main role of this process is the uniform distribution of the genetic code from the parent cell to the two daughter cells. At the same time, the cells of the new generation are one to one similar to the maternal ones.
Rice. 1. Scheme of mitosis
The time between division processes is called interphase . Most often, interphase is much longer than mitosis. This period is characterized by:
- synthesis of protein and ATP molecules in the cell;
- chromosome duplication and formation of two sister chromatids;
- increase in the number of organelles in the cytoplasm.
Meiosis
The division of germ cells is called meiosis, it is accompanied by a halving of the number of chromosomes. The peculiarity of this process is that it takes place in two stages, which continuously follow each other.
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The interphase between the two stages of meiotic division is so short that it is practically unnoticeable.
Rice. 2. Meiosis scheme
The biological significance of meiosis is the formation of pure gametes that contain a haploid, in other words a single, set of chromosomes. Diploidy is restored after fertilization, that is, the fusion of the maternal and paternal cells. As a result of the fusion of two gametes, a zygote with a full set of chromosomes is formed.
The decrease in the number of chromosomes during meiosis is very important, since otherwise the number of chromosomes would increase with each division. Thanks to reduction division, a constant number of chromosomes is maintained.
Comparative characteristics
The difference between mitosis and meiosis is the duration of the phases and the processes occurring in them. Below we offer you a table “Mitosis and Meiosis”, which shows the main differences between the two methods of division. The phases of meiosis are the same as those of mitosis. You can learn more about the similarities and differences between the two processes in the comparative description.
|
Phases |
Mitosis |
Meiosis |
|
|
First division |
Second division |
||
|
Interphase |
The set of chromosomes of the mother cell is diploid. Protein, ATP and organic substances are synthesized. The chromosomes double and two chromatids are formed, connected by a centromere. |
Diploid set of chromosomes. The same actions occur as during mitosis. The difference is the duration, especially during the formation of eggs. |
Haploid set of chromosomes. There is no synthesis. |
|
Short phase. The nuclear membranes and nucleolus dissolve, and the spindle is formed. |
Takes longer than mitosis. The nuclear envelope and nucleolus also disappear, and a fission spindle is formed. In addition, the process of conjugation (bringing together and merging homologous chromosomes) is observed. In this case, crossing over occurs - the exchange of genetic information in some areas. Then the chromosomes separate. |
The duration is a short phase. The processes are the same as in mitosis, only with haploid chromosomes. |
|
|
Metaphase |
Spiralization and arrangement of chromosomes in the equatorial part of the spindle are observed. |
Similar to mitosis |
The same as in mitosis, only with a haploid set. |
|
Centromeres are divided into two independent chromosomes, which diverge to different poles. |
Centromere division does not occur. One chromosome, consisting of two chromatids, extends to the poles. |
Similar to mitosis, only with a haploid set. |
|
|
Telophase |
The cytoplasm is divided into two identical daughter cells with a diploid set, and nuclear membranes with nucleoli are formed. The spindle disappears. |
The duration of the phase is short. Homologous chromosomes are located in different cells with a haploid set. Cytoplasm does not divide in all cases. |
The cytoplasm divides. Four haploid cells are formed. |
Rice. 3. Comparative diagram of mitosis and meiosis
What have we learned?
In nature, cell division differs depending on their purpose. For example, non-reproductive cells divide by mitosis, and sex cells - by meiosis. These processes have similar division patterns at some stages. The main difference is the presence of the number of chromosomes in the formed new generation of cells. So, during mitosis, the newly formed generation has a diploid set, and during meiosis, a haploid set of chromosomes. The timing of the fission phases also differs. Both methods of division play a huge role in the life of organisms. Without mitosis, not a single renewal of old cells, reproduction of tissues and organs takes place. Meiosis helps maintain a constant number of chromosomes in the newly formed organism during reproduction.
Test on the topic
Evaluation of the report
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The purpose of the lesson: repetition of material about methods of cell reproduction.
Tasks
Educational: to form and consolidate knowledge about two types of cell division, about the importance of cell division for unicellular and multicellular organisms, about the processes occurring in the various phases of mitosis and meiosis, about the differences between meiosis and mitosis.
Developmental: development of skills to work in a group, characterize objects and phenomena, compare them, substantiate conclusions, apply knowledge, evaluate yourself and your knowledge; development of interest in the subject.
Educational: fostering respectful attitudes towards each other.
Equipment: sheets of Whatman paper and paper, felt-tip pens, glue, tape, scissors, files with tasks, instruction card for each team.
Preparing for the lesson
1. At the previous lesson, students should be familiarized with the principles and rules of conducting a workshop lesson.
2. Since the topic “Cell Division” was studied in the 9th grade and the students forgot a lot, as homework they had to repeat the material on the topic: “Cell Division”.
Dividing the class into teams
Students are asked to choose one of the following questions and write it down on a piece of paper. (Most likely, the student will choose a question for which he knows or assumes he knows the answer.)
What is the biological meaning of meiosis?
How is mitosis different from meiosis?
What is the biological meaning of mitosis?
From a piece of paper with a written question you need to fold a paper airplane. Standing in a circle, students launch their airplanes (all at the same time at the teacher’s command) and, picking up the airplane that fell nearby, repeat this operation 2 times. Having opened the airplanes, students are divided into three teams - on the same questions.
Each team receives a file containing material for work: a list of terms, definitions, diagrams, historical information.
Instruction card
Select from the list of terms (Appendix 2) those that are relevant to the topic “Cell division. Mitosis. Meiosis". The selected command words are read aloud.
Select definitions (Appendix 3) that correspond to the selected terms from the previous assignment. Be careful, some definitions have been replaced! To complete this task correctly, you need to find and ask the other team for your definition. Terms cannot be changed!
Select the appropriate pictures for the processes occurring in a cell during mitosis or meiosis (Appendix 4).
Paste words, definitions and pictures in a logical sequence onto a piece of Whatman paper. Prepare a short story about this biological process.
(Teams display their work on a stand. Team members talk about the processes depicted on whatman paper.)
Answer the question written on your “airplane” sheet. Write the answer in your notebook. (When completing this task, you can use the original source. Each team reads its answer to the question out loud.)
Reflection
Option 1(if there is a lot of time left until the end of the lesson).
Give two or three arguments in support of the fact that the topic “Cell division. Mitosis and meiosis" must be studied in a high school general biology course.
Option 2(if there is not enough time).
Are you satisfied with the lesson, your work in the lesson? Think, evaluate your emotional state. Write down the answer on a piece of paper and stick it on the stand when you leave.
Homework
Answer the following questions.
What factors cause disruption of mitosis and meiosis?
What consequences can this lead to?
Appendix 1. Historical background
Flemming Walter (1843–1905), German histologist. Professor at universities in Prague (from 1873) and Kiel (1876–1901). His main works were on the histology of mollusks, tissue regeneration, the study of connective and adipose tissue, the structure of follicles, spinal ganglion cells, etc. His studies of the fine structure of cells became especially famous. Using the methods of fixation (Flemming's liquid) and staining he developed, he studied the structure of protoplasm, nucleus, centrosomes and, in particular detail, the process of cell division (direct and indirect). These studies were of great importance for the development of cytology; his methods of fixation and staining became widespread in laboratory practice.
Strasburger Edward (1844–1912), German botanist, Pole by origin, member of the Polish Academy of Sciences in Krakow (1888). Studied in Warsaw, Bonn and Jena. He was an associate professor at the Warsaw (1867–1869), a professor at the Jena (1869–1880) and Bonn (1880–1911) universities. Main works in the field of cytology, anatomy and embryology of plants. Studied mitosis. He described meiosis in higher plants and explained the biological significance of the reduction in the number of chromosomes. He studied the process of fertilization, the phenomena of parthenogenesis and apogamy. The scientist’s work was of great importance for the preparation of the chromosomal theory of heredity and the development of ideas about the genetic unity of higher plants. Improved the methodology of cytological studies. Co-author of the republished course of botany (Textbook of Botany, 1894; 30th edition - 1971), translated into a number of languages, including Russian.
Chistyakov Ivan Dorofeevich (1843–1877), Russian botanist. He graduated from Moscow University (1868) and was retained there, from 1871 he became a professor and head of the Botanical Garden. Founder of the Moscow school of embryologists and plant cytologists. One of the first to observe and describe mitosis in plants (1874).
Appendix 2. Terms
(The underlined words are the students' correct choices.)
File No. 1 (blue)
Mitosis, prophase, metaphase, anaphase, telophase, amitosis, cell cycle, photosynthesis.
File No. 2 (green)
Meiosis, 1st division, prophase 1, metaphase 1, anaphase 1, telophase 1, crossing over, assimilation, dissimilation.
File No. 3 (red)
Meiosis, 2nd division, prophase 2, metaphase 2, anaphase 2, telophase 2, interphase, polymers.
Appendix 3. Definitions
File No. 1 (blue)
Mitosis is a method of dividing eukaryotic cells in which each of the two newly emerging cells receives the same genetic material as in the original cell.
Prophase– chromosomes spiral and become clearly visible in a light microscope, the nucleolus disappears, two centrioles diverge to the poles of the cell, microtubules extending from them form a spindle, the nuclear envelope disintegrates.
Anaphase
Telophase– a nuclear membrane is formed around the chromosomes collected at the poles, the chromosomes despiral (from compact they turn into thin and long, indistinguishable in a light microscope). Nucleoli are formed. This stage ends with cytokinesis (division of the cytoplasm) and the formation of two diploid cells.
Amitosis– direct division of nuclei by constriction does not always end with cytokinesis; as a result, multinucleated cells usually appear. After amitosis, cells are not able to begin mitotic division. This process is characteristic of dying cells.
Cell cycle– the period of cell life from division to division, the main part of the cell’s life.
Interphase– period between divisions (lat. inter- between). The cell grows rapidly, the number of structures and substances in the cell increases, the number of chromosomes doubles.
(Definition interphase in this file onlyno, but the definition metaphases absent.)
File No. 2 (green)
Meiosis(Greek meiosis
1st division- first division of meiosis.
Prophase 1– chromosomes begin to condense and become visible under a light microscope. Then homologous chromosomes begin to move closer to each other - to conjugate. A pair of conjugating chromosomes is called a bivalent (each bivalent is formed by 4 chromatids). DNA replication ends. The phase ends with the disappearance of the nuclear membrane and nucleolus.
Metaphase 1– bivalents line up in the equatorial plane of the cell. The spindle filaments are attached to the centromeres.
Anaphase 1– the bivalent breaks up into two chromosomes, which go to different poles of the cell.
Telophase 1– chromosomes decondense (from compact they turn into thin and long ones, indistinguishable in a light microscope). A nuclear envelope is formed around the chromosomes collected at the poles. Nucleoli are formed. This stage ends with cytokinesis (division of the cytoplasm) and the formation of two diploid cells.
Metaphase
(Definition metaphases in this file onlyno, but the definition crossing over absent.)
File No. 3 (red)
Meiosis(Greek meiosis– reduction) is a method of dividing eukaryotic cells, in which a reduction (decrease) in the number of chromosomes occurs, i.e. From a diploid (containing a double set of chromosomes) cells, haploid (containing a single set of chromosomes) cells are formed.
2nd division- second division of meiosis.
Prophase 2– chromosomes spiral and become clearly visible in a light microscope, the nucleolus disappears, two centrioles diverge to the poles of the cell, microtubules extending from them form a spindle.
Metaphase 2– all chromosomes line up in the equatorial plane of the cell; at this stage they can be clearly distinguished and counted in the cell.
Anaphase 2- the stage during which sister chromatids, which have become independent chromosomes, diverge to opposite poles of the cell.
Telophase 2– a nuclear membrane is formed around the chromosomes collected at the poles. Chromosomes despiral (from compact they turn into thin and long ones, indistinguishable under a light microscope). Nucleoli are formed. This stage ends with cytokinesis (division of the cytoplasm) and the formation of four haploid cells.
Crossing over(English) сrossing-over– precross) – exchange of identical sections of homologous chromosomes.
(Definition crossing over in this file onlyno, but the definition interphase absent.)
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