Mitosis and its stages. Meaning of mitosis. What is mitosis? Biological significance of the process
Secondary school No. 33 named after Kairat Ryskulbekov
Open lesson in biology
Topic: « Mitosis as the basis of asexual reproduction, its phases. The biological essence of mitosis.
9 "B" class
Teacher: Kalieva A.A.
Semey -2013 -2014 academic year.
Lesson number 16, 9 "B" class in biology.
The date: 24.10.2013
Topic: Mitosis as the basis of asexual reproduction, its phases. The biological essence of mitosis.
Target :
educational : to form in the lesson an idea of mitosis, as an indirect way of cell division; to study the phases of mitosis and its biological role; on the example of cell division, show the reflection of the law of dialectics, the negation of negation.
Educational : promote the development of analytical thinking and cognitive interest of students, develop memory, attention, observation; contribute to the formation of students' intellectual skills.
Educational : to cultivate a humane attitude towards nature; respect for other people's work; responsibility for the result of educational work, a sense of accuracy and conscientiousness.
Tasks:
Educational : to form the ability to distinguish mitosis from other methods of cell division; to distinguish the phases of mitosis according to the processes occurring in them; be able to reproduce them on paper; be able to apply the knowledge gained about mitosis to explain the significance of this process in the life of organisms.
Educational : develop the ability to analyze phenomena, make a comparative analysis of different phases of mitosis, draw logical conclusions; develop the skill of working with text tables; development of attentiveness when looking for errors.
Educational : strive to form a materialistic worldview; educate the ability to communicate with each other;,; educate cognitive independence and maintain interest in the subject.
Equipment : computer, interactive manual on the topic "Mitosis" table "Mitosis", a schematic representation of the different phases of mitosis, smiley pictures.
During the classes:
I . Organization of the beginning of the lesson.(1-2 min).
Preparing students for work in class: greeting; checking the readiness of students for the lesson, quickly including them in a business rhythm.
II . Checking homework(10-15 min).
To begin with, let's repeat a little, remember what we already know
Conversation on questions that need to be remembered for learning new material
What do you know about cell division? (division is a vital property of the cell);
What is a cell center? (organoid containing two centrioles, consisting of microtubules);
What is DNA? (keeper of hereditary information);
What is DNA Replication? (doubling of DNA molecules);
What are chromosomes? (organelles are carriers of hereditary information);
What is a diploid set of chromosomes? (double set, characteristic of somatic cells);
What is a haploid set of chromosomes? (single, characteristic of germ cells).
During the conversation, work is carried out to correct knowledge.
So, you have successfully coped with the questions, and we are moving on to the study of new material.
Today we will get acquainted with the process of cell division - mitosis, find out what the life cycle of a cell is.
Guys, what do you think, what qualities should be inherent in a modern person so that he can succeed? (industriousness, responsibility, purposefulness, professionalism). You are right, we will need all these qualities in today's lesson.
As an epigraph to our lesson, I would like to take the words of a German poetG.E. Lessing
« Argue, err, make mistakes, but, for God's sake, think, and although crooked, but yourself » . (Slide #1)
The topic of our lesson : Mitosis as the basis of asexual reproduction, its phases. The biological essence of mitosis. ( slide number 2). (20 minutes)
Lesson Objectives:
To get acquainted with the features of mitosis and its biological role in nature.
To reveal the features of the course of each phase of mitosis.
Consider the mechanisms that ensure the genetic identity of daughter cells.(slide number 3)
III . Explanation of new material . (Slide number 4)
One of the methods of asexual reproduction that we have studied is fission. In biology, processes obey the laws of philosophy. We have already met with the law of struggle and the unity of opposites when we studied catabolism and anabolism. And there is another law - the law of negation of negation. The seedling denies the seed, and the new cell denies the old. Division is an increase in the number of cells. (I open a slide with dividing cells), the basis of reproduction and development. From one old large decrepit cell, as a result of division, two young young cells are obtained, which begin to grow, increase in size, perform their functions and, finally, begin to divide - their life cycle ends. Therefore, the life cycle of a cell or, in other words, the cell cycle is
THE CELL CYCLE IS A SEQUENCE OF EVENTS THAT OCCUR BETWEEN THE FORMATION OF A CELL AND ITS NEXT DIVISION OR DEATH. (Slide number 5)
There are 3 stages of the cell cycle:slide number 6)
1. INTERPHASE
2.MITOSIS (KARYOKINESIS)
3.CYTOKINESIS (CYTOPLASMA DIVISION)
The cell cycle begins with interphase. This is the biggest phase. It has 3 important steps.
1. INTERPHASE - it is directly the life of the cell, during which the cell performs its inherent functions, for which it was born, carries out cellular metabolism, biosynthesis, carries out the processes of transcription and translation, forms mitochondria, chloroplasts, and other cell organelles. (I'm attaching a diagram).
2. At the end of interphase, the cell begins to prepare for division. In this case, doubling (replication) of DNA occurs, shortening of DNA strands due to their spiralization. After all, a strand of DNA is approx. 2 meters and it fits so compactly that the chromosomes are already clearly visible in a light microscope. (I'm attaching a diagram)
Now let's remember how many chromosomes does a human cell contain? 46. Therefore, one cell contains 46 chromosomes, and after dividing, how many chromosomes will the daughter cells contain?
23 23
It is logical, but if each cell is further divided in half, then there will be a fractional number, and so on.
So, on the top of the head, one number of chromosomes, and on the heels another? Do you agree? Not? And how then to get out of the situation? How to get the same number of chromosomes throughout the body without violating the laws of mathematics? (children express their guesses)
It remains only to recognize such a division scheme - not very logical, but correct.
46 46
Then the question arises? But how can this happen? (Students give their guesses)
This is so because mitosis is special - indirect cell division.
MITOSIS is such a division of the cell nucleus, in which the formed daughter cells have identical sets of chromosomes to the mother. Mitosis is the division of somatic cells (body cells).(Slide number 7)
Mitosis was first discovered as a method of somatic cell division in 1879. Boveri and Fleming.
The process includes 4 phases.
I suggest that you write such a table in your notebook.
Let's schematically depict the essence of the process. I draw on the board, and you look carefully, and draw in notebooks with me. You write down the name of the phase in the first column in the table andfeatures of thisin the second.
(Slide number 8)
1. Prophase. In the first phase of mitosis, the nuclear membrane collapses, the nucleolus disappears, and the centrioles diverge along the poles of the cell. Between them, the threads of the division spindle are stretched. Each chromosome consists of two chromatids connected by a constriction called a centromere. The prophase is over.(Slide number 9).
2. Metaphase . Chromosomes are attached to the spindle fibers with their constrictions and line up along the equator of the cell.(Slide number 10).
3. Anaphase. The shortest. The spindle fibers stretch the chromatids in different directions.(Slide number 11).
4. Telophase. The phase is reverse to prophase. The separated chromatids become chromosomes and begin to unwind. The nuclear membrane, the nucleolus, is formed.(Slide number 12).
The process of mitosis ends. Cytokinesis begins - the division of the cytoplasm and organelles. The duration of mitosis is 1.5 - 2 hours. In animals, a constriction is formed between the cells, and in plants, a median septum. 2 daughter cells are obtained.
Now compare the picture of telophase and interphase: compare the number of chromosomes and answer the question. What process led to this? (Doubling of chromosomes in interphase).(Slide number 13).
I show the general scheme of mitosis on the monitor.
The biological meaning of mitosis is that all cells of one organism have the same set of chromosomes.
The zygote formed as a result of fertilization begins to divide by mitosis into equivalent cells, giving rise to a new organism, all cells of which, despite their diversity, have the same, equivalent set of chromosomes. Thanks to mitosis, the body grows, regenerates organs, and also determines the similarity of offspring with parents from generation to generation.
(2 minutes).
(Video: Human liver cell division process)
(Slide number 14).
During mitosis, there is a strict
exactly the same distribution
copied chromosomes between daughter cells, which ensures the formation of genetically identical identical cells.(Slide number 15).
Guys lesson. ends, let's repeat what we learned with youand we conclude:
(Slide number 16).
Mitosis Meaning:
As a result of mitosis, two daughter cells arise, containing the same number of chromosomes as there were in the nucleus of the mother cell.
Thanks to mitosis, the processes of regeneration and replacement of dying cells are carried out.(Slide number 17). (2 minutes)
IV .Securing. (test) (5 min).
1. Mark the wrong answer.
Vaccinations are used for plant propagation, as:
a) it is a faster way than growing from seeds;
b) while maintaining the desired set of features;
c) the resulting plants combine the characteristics of both parents.
2. What is the cellular or life cycle of a cell?
a) the life of the cell during its division;
b) the life of a cell from division to the next division or to death;
c) cell life during interphase.
3. Mitosis is the main way of division:
a) germ cells;
b) somatic cells;
c) a + b.
4. In the prophase of mitosis, the following occurs:
a) doubling the DNA content;
b) synthesis of enzymes necessary for cell division;
c) spiralization of chromosomes.
5. In the anaphase of mitosis, a divergence occurs:
a) daughter chromosomes;
b) homologous chromosomes;
c) non-homologous chromosomes;
d) cell organelles.
6. In which of the phases of mitosis does the thickening (spiralization) of chromosomes occur, the nucleolus disappears, the nuclear membrane disintegrates, the centrioles diverge to the poles and the division spindle is formed?
a) anaphase;
b) telophase;
c) prophase;
d) metaphase.
7. Chromosomes are located in the same plane in the center of the cell (at the equator). To each of them in the region of the centromere, spindle threads are attached on both sides. This is typical for the phase of mitosis:
a) prophase;
b) metaphases;
c) anaphases;
d) telophase.
8. Replication occurs in
a) prophase;
b) metaphase;
c) interphase;
d) telophase.
9. The division of centromeres and the divergence of chromatids to the poles of the cell occurs in: a) prophase;
b) metaphase;
c) anaphase;
d) telophase.
10. The biological significance of mitosis lies in: a) strictly the same distribution between the daughter cells of the material of the cytoplasm and nucleus
b) increase in the number of cells
c) a + b
Answers to the test: 1– in; 2– b; 3–b; 4– in; 5– a; 6– in; 7– b; 8–c; 9–c; 10th century
Criteria for evaluation : 100%–85% – 5, 84–75% – 4, 74–50% – 3, 49% –2.
Grading students for a lesson
Now write downhomework: item 16 , fill in the table in the notebook to the end, correlating the processes of the phases with their drawings(Slide number 18) (1 -2 min).
The biological significance of mitosis is very high. It is even difficult for the uninitiated to imagine what role the process of simple cell division in the body plays in life. The ability of cells to divide is their most important function, fundamental. Without this, it is impossible to continue life on Earth, increase the populations of unicellular organisms, it is impossible to develop and continue the existence of a large multicellular organism, it is also impossible to reproduce sexually and develop a new life from a fertilized egg.
The biological significance of mitosis would be much less if cell division were not the essence of most of the biological processes occurring on our planet. This process takes place in several stages. Each of them includes several actions inside the cell. The result of this is the obligatory multiplication of the genetic basis of one cell in two by duplicating DNA, so that subsequently the mother cell will give birth to two daughter cells.
The whole life of a cell can be concluded in the period from the formation of a daughter cell to its subsequent division in two. This period is called the "cell cycle" in biology.
The very first phase of mitosis is the actual preparation for cell division. The period in which cells endowed with nuclei perform direct preparation for division is called interphase. All the most important things take place in it, namely, the duplication of the DNA chain and other structures, as well as the synthesis of a large amount of protein. Thus, the chromosomes of the cell become doubled, and each half of such a double chromosome is called a "chromatid".
After interphase, the process of division itself begins directly - mitosis. It also goes through several steps. As a result, all doubled parts are stretched symmetrically over the cell, so that after the formation of the central partition, the same number of formed components remains in each new cell.
The phases of mitosis and meiosis are similar, but in the latter (during the division of germ cells) there are two divisions, and as a result, not two, but four “daughter” cells are obtained. Also, before the second division, there is no doubling of chromosomes, so their set in daughter cells remains half.
1. Prophase. In this phase, the centrioles of the cell are very clearly visible. They are present only in the cell of animals and humans. Plants do not have centrioles.
2. Prometaphase. At this point, prophase ends and metaphase begins.
3. Metaphase. At this point, the chromosomes lie on the "equator" of the cell.
4. Anaphase. Chromosomes move to different poles.
5. Telophase. One "mother" cell divides by forming a central septum into two "daughter" cells. This is the end of cell division or mitosis.
The most important biological significance of mitosis is the absolutely identical division of duplicated chromosomes into 2 identical parts and their placement in two "daughter" cells. Different types of cells and cells of different organisms have varying times for the duration of division - mitosis, but on average it takes about an hour and a half. There are many factors influencing this very fragile process. Any changing environmental conditions, for example, ambient temperature, light phase mode, pressure in the environment and inside the body and cell, as well as many other factors, can significantly affect both the duration and quality of the cell division process. Also, the duration of the entire mitosis and its individual steps can be directly dependent on the type of tissue in whose cells it occurs.
The biological significance of mitosis with each new discovery in the field of cytology becomes more valuable, because life on the planet is impossible without this process.
Questions of self-control. The biological significance of mitosis
Task number 1
Topic 14. Sexual reproduction.
Questions of self-control
The biological significance of mitosis.
TELOPHASE
ANAPHASE
METAPHASE.
Chromosomes acquire an ordered arrangement, moving towards the equator. Having reached the equator, the chromosomes are located in the same plane, and at this moment one of the spindle threads is attached to the centromeres of each chromosome.
In metaphase, it is clearly seen that the chromosomes consist of two chromatids connected only in the centromere region.
The chromatids of each chromosome begin to diverge towards the poles of the cell: one chromatid goes to one pole, the other to the opposite. The movement of chromosomes is carried out due to the spindle threads, which contract and stretch the daughter chromosomes from the equator to the opposite poles of the cell. When moving, the energy of ATP is used.
At this moment, there are two diploid sets of chromosomes in the cell.
Chromosome cells approaching the poles begin to unwind and again take the form of long threads intertwining with each other, which is characteristic of a non-dividing nucleus. In the daughter nuclei, the nuclear membrane is again formed, the nucleolus is formed, and the structure of the nucleus characteristic of the interphase is completely restored. During telophase, cytoplasmic division also occurs, as a result of which two daughter cells separate from each other. These cells are completely similar in structure to the parent, but differ from it in smaller sizes.
As a result of mitosis, each daughter cell receives exactly the same chromosomes as the mother cell had. The number of chromosomes in both daughter cells is equal to the number of chromosomes in the mother cell.
Consequently, the biological significance of mitosis lies in the strictly uniform distribution of chromosomes between the nuclei of two daughter cells. This means that mitosis provides a subtle transfer of all hereditary information to each of the daughter nuclei.
If there is a violation of the normal course of mitosis and in the daughter cell there are fewer or more chromosomes than in the mother cell, then this will either lead to death or to significant changes in the life of the cell - to the occurrence of mutations.
1. What forms of reproduction are characteristic of living organisms?
2. What kind of reproduction is called asexual?
4. What forms of asexual reproduction are characteristic of organisms?
5. Which form of asexual reproduction is the youngest?
6.What is mitosis?
7. What cells divide by mitosis?
8. What set of chromosomes do cells contain at the end of interphase?
9. In which of the phases of mitosis are the chromosomes located in the plane of the equator?
10. In what phase of mitosis do chromatids diverge to the poles of the cell?
11. At what stage of the cell is the division spindle formed?
12. What is the biological significance of mitosis?
1. Read the study material below.
2. Analyze tables from the application
3. Answer the self-control questions.
sexual reproduction- change of generations and development of organisms on the basis of specialized sex cells.
However, in invertebrates, sperm and eggs are often formed in the body of one organism. This phenomenon - bisexuality - is called hermaphroditism.
There are cases when a new organism does not necessarily appear as a result of the fusion of germ cells. In some species of animals and plants, development is observed from an unfertilized egg (bees, wasps, aphids, some crustaceans (daphnia)). Such reproduction is called virgin or parthenogenetic.
Sexual reproduction. A new organism is formed as a result of the fusion of germ cells-gametes (n). A zygote (2n) is formed with a unique set of chromosomes. Sexual reproduction is characteristic of most living organisms. Advantages : each individual has a unique genotype, which allows, as a result of natural selection, to adapt to various environmental conditions.
The following features are characteristic: two individuals usually take part in reproduction - male and female; more often carried out with the help of specialized cells - gametes; reduction in the number of chromosomes and recombination of genetic material in gametes occurs as a result of meiosis; offspring (with the exception of identical twins) are genetically distinct from each other and from parental individuals.
Spermatogenesis, oogenesis (oogenesis).
Gametogenesis is the process of development of sex cells - gametes. The precursors of gametes (gametocytes) are diploid. The process of formation of spermatozoa is called spermatogenesis, and the formation of eggs is called oogenesis (ovogenesis). In the sex glands, three different areas, or zones, are distinguished: breeding area, growth zone, ripening zone. Spermatogenesis and oogenesis include three identical phases: reproduction, growth, maturation (division). In spermatogenesis, there is another phase - formation.
breeding phase: Diploid cells divide repeatedly by mitosis. The number of cells in the gonads grows, they are called oogonia and spermatogonia. Set of chromosomes 2n.
In the growth phase their growth occurs, the resulting cells are called oocytes of the 1st order and spermatocytes of the 1st order.
In the ripening phase meiosis occurs, as a result of the first meiotic division, gametocytes of the 2nd order are formed (a set of chromosomes n2c), which enter the second meiotic division, and cells with a haploid set of chromosomes (nc) are formed. Oogenesis at this stage almost ends, and spermatogenesis includes another phase of formation during which spermatozoa are formed.
In contrast to the formation of spermatozoa, which occurs only after reaching puberty (in particular, in vertebrates), the process of formation of eggs begins even in the embryo. The reproduction period is fully carried out at the embryonic stage of development and ends by the time of birth (in mammals and humans). During the growth period, oocytes increase in size due to the accumulation of nutrients (proteins, fats, carbohydrates) and pigments - a yolk is formed. Then the oocytes of the 1st order enter the period of maturation. The first meiotic division produces two daughter cells. One of them, relatively small, called the first polar body, is not functional, and the other, larger one (2nd order oocyte), undergoes further transformations.
The second division of meiosis is carried out up to the stage of metaphase II and will continue only after the second-order oocyte interacts with the spermatozoon and fertilization occurs. Thus, strictly speaking, not an ovum comes out of the ovary, but an oocyte of the 2nd order. After fertilization, it divides, resulting in an egg (or egg) and a second polar body. However, traditionally, for convenience, an oocyte is called an oocyte of the 2nd order, ready to interact with a spermatozoon. Thus, as a result of oogenesis, one normal egg and three polar bodies are formed.
Gametes. These are germ cells, at the fusion of which a zygote is formed, giving rise to a new organism. They are highly specialized cells involved in the implementation of processes associated with sexual reproduction. Gametes have a number of features that distinguish them from somatic cells.: the chromosome set of somatic cells is diploid (2n2c), and the gametes are haploid (nc); gametes do not divide; gametes, especially eggs, larger than somatic cells; the egg contains a lot of nutrients, the sperm contains little (practically absent); gametes have an altered nuclear-cytoplasmic ratio compared to somatic cells (in the egg, the nucleus occupies a much larger volume than the cytoplasm, in the sperm, on the contrary, and the nucleus has the same dimensions as in the egg). An active role in fertilization belongs to the spermatozoon. Therefore, it is small and mobile (in animals). The egg not only brings its own set of chromosomes to the zygote, but also ensures the development of the embryo in the early stages. Therefore, it is large in size and, as a rule, contains a large supply of nutrients.
Organization of animal eggs. The size of the eggs varies widely - from several tens of micrometers to several centimeters (a human egg is about 100 microns, an ostrich egg, which has a length of about 155 mm with a shell, is also an egg). The egg has a number of membranes located on top of the plasma membrane, and reserve nutrients. In mammals, the eggs have a shiny shell, on top of which there is a radiant crown - a layer of follicular cells.
The amount of nutrients accumulated in the egg cell depends on the conditions in which the embryo develops. So, if the development of the egg occurs outside the mother's body and leads to the formation of large animals, then the yolk can be more than 95% of the volume of the egg. A mammalian egg contains less than 5% yolk. In connection with the accumulation of nutrients, polarity appears in the eggs. Opposite poles are called vegetative and animal. Polarization is manifested in the fact that the location of the nucleus in the cell changes (it shifts towards the animal pole), as well as in the distribution of cytoplasmic inclusions (in many eggs, the amount of yolk increases from the animal to the vegetative pole).
organization of spermatozoa. The length of a human spermatozoon is 50–60 microns. The functions of the spermatozoon determine its structure. The head is the largest part of the spermatozoon, formed by the nucleus, which is surrounded by a thin layer of cytoplasm. At the anterior end of the head is an acrosome - a part of the cytoplasm with a modified Golgi apparatus. It produces an enzyme that helps dissolve the membranes of the egg. At the point of transition of the head to the middle part, an interception is formed - the neck of the spermatozoon, in which two centrioles are located. Behind the neck is the middle part of the spermatozoon, which contains mitochondria, and the tail, which has a structure typical of all eukaryotic flagella and is an organelle of spermatozoon movement. The energy for movement is supplied by ATP hydrolysis, which occurs in the mitochondria of the middle part of the spermatozoon.
Fertilization. The set of processes leading to the fusion of male and female gametes, the unification of their nuclei and the formation of a zygote, which gives rise to a new organism, is called fertilization.
There are external fertilization, in which the meeting of spermatozoa and eggs occurs in the external environment, and internal fertilization, in which the meeting of spermatozoa and eggs occurs in the genital tract of the female.
Most often, the spermatozoon is completely drawn into the egg, sometimes the flagellum remains outside and is discarded. From the moment the sperm enters the egg, the gametes cease to exist, as they form a single cell - the zygote. Depending on the number of sperm that enter the egg during fertilization, there are: monospermy - fertilization, in which only one sperm enters the egg (the most common fertilization), and polyspermy - fertilization, in which several sperm enter the egg. But even in this case, the nucleus of only one of the spermatozoa merges with the nucleus of the egg, and the remaining nuclei are destroyed.
Meiosis
First meiotic division.
1. Prophase I.
Chromosomes spiralize. It can be distinguished that each chromosome consists of two chromatids connected to each other at the centromere.
Homologous chromosomes closely approach each other, connect along their entire length and twist - this process is called conjugation. Next, there is an exchange of identical, or homologous regions (gene exchange) - crossing over.
After conjugation, the chromosomes separate.
2. Metaphase I.
Chromosomes are attached to the spindle fibers by their centromeres and are located in the equatorial plane.
3. Anaphase I.
To the poles of the cell go to the halves of each chromosome, including each chromosome, including one chromatid, as in mitosis, and whole chromosomes, each of which consists of 2 chromatids. Consequently, only one of each pair of homologous chromosomes enters the daughter cell.
The number of chromosomes is halved, the chromosome set becomes haploid.
4. Telophase I.
For a long time, the nuclear envelope is formed. Since the individual chromosomes of the haploid daughter cells continue to be duplicated, DNA duplication does not occur during interphase between the first and second divisions of meiosis. Cells are formed as a result of the 1st division of maturation, differing in the composition of paternal and maternal chromosomes and, consequently, in the set of genes.
For example, all human cells, including primary germ cells, contain 46 chromosomes. Of these, 23 are from the father and 23 from the mother. After the 1st meiotic division, only 23 chromosomes enter spermatocytes and oocytes - one chromosome from each pair of homologous chromosomes. However, due to the random segregation of paternal and maternal chromosomes in anaphase I, the resulting cells receive a wide variety of combinations of parental chromosomes. For example, in one of them there may be 3 paternal and 20 maternal chromosomes, in another 10 paternal and 12 maternal, in the third 20 paternal and 3 maternal, etc. The number of possible combinations is very large.
Consequently, meiosis – basis of combinative genotypic variability.
Second meiotic division.
It proceeds, in general, in the same way as ordinary mitotic division, with the only difference being that the dividing cell is haploid.
Prophase II
Chromosomes spiralize, a spindle of division is formed.
Metaphase II
Chromosomes are located in the equatorial plane of the cell, spindle fibers are attached to centomeres.
Anaphase II.
Chromatids diverge towards the poles of the cell.
Thermal phase II.
That. four haploid cells with a chromosome set were formed from the initial primary germ cell.
The essence of the maturation period is that in germ cells the number of chromosomes is halved.
The biological meaning of the 2nd meiotic division is that the amount of DNA is brought into line with the chromosome set.
In the males all four haploid cells are formed as a result of meiosis, later converted into gametes - spermatozoa.
In the females due to uneven meiosis, only one cell produces a viable egg. Three other cells are much smaller, they turn into the so-called directional or reduction cells, which soon die. The biological meaning of this is the need to preserve in one cell all the reserve nutrients that will be needed for the development of the future embryo.
1. What kind of reproduction is called sexual?
2. What are the advantages of sexual reproduction over asexual reproduction?
3. What are the main stages in the formation of eggs and sperm?
4. Name the distinctive features of meiosis and mitosis.
5. What process is called conjugation?
6. What process is called crossing over?
7. What is the biological meaning of meiosis?
Topic 15. Individual development of organisms: the embryonic period
What is the biological significance of mitosis
Svetlana syshchenko
genetic stability. As a result of mitosis, two nuclei are obtained, each containing the same number of chromosomes as there were in the parent nucleus. These chromosomes are descended from parental chromosomes by exact DNA replication, so their genes contain exactly the same hereditary information. Daughter cells are genetically identical to the parent cell, so mitosis cannot make any changes to the genetic information. Therefore, cell populations (clones) derived from parental cells have genetic stability.
Growth. As a result of mitosis, the number of cells in the body increases (a process known as hyperplasia), which is one of the main mechanisms of growth.
Asexual reproduction, regeneration and replacement of cells. Many animal and plant species reproduce asexually by mitotic cell division alone. In addition, mitosis provides for the regeneration of lost parts (for example, legs in crustaceans) and cell replacement, which occurs to one degree or another in all multicellular organisms.
Angelina
MITOSIS is the main form of cell division, the essence of which is the uniform distribution of chromosomes between daughter cells; cell division is asexual (somatic cells), two daughter cells are formed with a set of chromosomes 2n
Write what is the essence of mitosis. What is its biological significance?
Help with homework! Please!
The most important component of the cell cycle is the mitotic (proliferative) cycle. It is a complex of interrelated and coordinated phenomena during cell division, as well as before and after it. The 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 of performance by the cell of its functions and periods of rest. At this time, the further cell fate is uncertain: the cell may begin to divide (enter mitosis) or begin to prepare to perform specific functions.
The biological knowledge of mitosis is that it ensures the hereditary transmission of traits and properties in a number of generations of cells during the development of a multicellular organism. Due to the exact and uniform distribution of chromosomes during mitosis, all cells of a single organism are genetically the same.
Mitotic cell division underlies all forms of asexual reproduction in both unicellular and multicellular organisms. Mitosis causes the most important phenomena of life: growth, development and restoration of tissues and organs and asexual reproduction of organisms.
http://xn--90aeobapscbe.xn--p1ai/Educational-materials/Cell-Division/41-Mitosis-its-phases-biological-importance
Irina
What is the essence of mitosis? what is its biological significance?
Metosis is the main form of cell division, the essence of which is the uniform distribution of chromosomes between daughter cells. The biological significance of metosis. Metosis underlies the growth and vegetative reproduction of all organisms that have an enukriot nucleus. It ensures the constancy of the number of chromosomes in all cells of the body.
Cell cycle. Mitosis
One of the most important properties of life is the self-reproduction of biological systems, which is based on cell division: “Not only the phenomena of heredity, but also the very continuity of life depend on cell division” (E. Wilson). The universal way of dividing eukaryotic cells is indirect division, or mitosis (from the ancient Greek "mitos" - a thread). The biological significance of mitosis lies in the preservation of the volume and quality of hereditary information.
A Brief History of the Discovery of Mitosis
For the first time, cell division (crushing of frog eggs) was observed by the French scientists Prevost and Dumas (1824). This process was described in more detail by the Italian embryologist M. Rusconi (1826). The process of nuclear fission during the crushing of eggs in sea urchins was described by K. Baer (1845). The first description of cell division in algae was made by B. Dumortier (1832). Separate phases of mitosis were observed by the German botanist W. Hofmeister (1849; cells of the filament of tradescantia), Russian botanists E. Russov (1872; mother cells of spores of ferns, horsetails, lilies) and I.D. Chistyakov (1874; spores of horsetail and club moss), German zoologist A. Schneider (1873; crushing eggs of flatworms), Polish botanist E. Strasburger (1875; spirogyra, club moss, onion).
To designate the processes of movement of the constituent parts of the nucleus, the German histologist W. Schleichner proposed the term karyokinesis (1879), and the German histologist W. Flemming introduced the term mitosis (1878). In the 1880s The general morphology of chromosomes was described in the works of Hofmeister, but only in 1888 did the German histologist W. Waldeyer introduce the term chromosome. The leading role of chromosomes in the storage, reproduction and transmission of hereditary information was proved only in the twentieth century.
biological significance
The process of mitosis ensures a strictly uniform distribution of chromosomes between two daughter nuclei, so that in a multicellular organism all cells have exactly the same (in number and character) sets of chromosomes. Chromosomes contain genetic information encoded in DNA, and therefore a regular, ordered mitotic process also ensures the complete transfer of all information to each of the daughter nuclei; as a result, each cell has all the genetic information necessary for the development of all the characteristics of the organism. In this regard, it becomes clear why one cell taken from a fully differentiated adult plant can, under suitable conditions, develop into a whole plant. We have described mitosis in a diploid cell, but this process proceeds in a similar way in haploid cells, for example, in cells of the gametophyte generation of plants.
Those. The biological significance of mitosis lies in the fact that mitosis ensures the hereditary transmission of traits and properties in a number of cell generations during the development of a multicellular organism. Due to the exact and uniform distribution of chromosomes during mitosis, all cells of a single organism are genetically the same.
Mitotic cell division underlies all forms of asexual reproduction in both unicellular and multicellular organisms. Mitosis causes the most important phenomena of vital activity: growth, development and restoration of tissues and organs and asexual reproduction of organisms.
Mitosis - indirect cell division, karyokinesis, [~ 1] the most common method of reproduction of eukaryotic cells. The biological significance of mitosis lies in the strictly identical distribution of chromosomes between daughter nuclei, which ensures the formation of genetically identical daughter cells and preserves continuity in a number of cell generations.
Mitosis consists of four phases: prophase, metaphase, anaphase, telophase.
in prophase the volume of the nucleus increases, the chromosomes become visible due to spiralization, two centrioles diverge towards the poles of the cell. As a result of the spiralization of chromosomes, it becomes impossible to read genetic information from DNA
and RNA synthesis stops. Threads of the achromatin spindle are stretched between the poles: an apparatus is formed that ensures the divergence of chromosomes to the poles of the cell. At the end of prophase, the nuclear membrane breaks up into separate fragments, the edges of which close. Small vesicles are formed, similar to the endoplasmic reticulum.
During prophase, the spiralization of chromosomes continues, which thicken and shorten. After the disintegration of the nuclear membrane, the chromosomes lie freely and randomly in the cytoplasm.
In metaphase spiralization of chromosomes reaches a maximum, and shortened chromosomes rush to the equator of the cell, located at an equal distance from the poles. It can be seen that the chromosomes consist of two chromatids connected only at the centromere. The centromeric regions of chromosomes are located in the same plane. The mitotic spindle is already fully formed by this time. Part of the threads of the spindle goes from pole to pole - these are continuous threads. Other threads - chromosomal - connect the poles to the centromeres of the chromosomes.
in anaphase centromeres are separated, and from that moment sister chromatids become independent daughter chromosomes. The mechanism of movement of daughter chromosomes to the poles of the cell is provided by the following processes. First, by sliding of the chromosome thread of the spindle, to which the chromosome is attached. Secondly, by splitting off fragments of the chromosome thread by enzymes in the region of the cell center (or centromeric region), as a result of which the thread is shortened and brings the chromosome closer to the pole. Thus, in the anaphase, the chromatids of the doubled chromosomes still in the interphase exactly diverge towards the poles of the cell. At this point, the cell contains two diploid sets of chromosomes. Mitosis ends with telophase. Chromosomes gathered at the poles despiralize and become barely visible. The nuclear envelope is formed from the membrane structures of the cytoplasm. In animal cells, the cytoplasm is divided due to the constriction of the cell body into two smaller ones, each of which contains one diploid set of chromosomes. In plant cells, the cytoplasmic membrane arises in the middle of the cell and extends to the periphery, dividing the cell in half. After the formation of a transverse cytoplasmic membrane, a cellulose wall appears in plant cells. Starting from a fertilized egg - a zygote - all daughter cells formed as a result of mitosis contain the same set of chromosomes and the same genes, ensuring the continuity of the genotype in a series of cell generations. Thus, the biological meaning of mitosis as a method of cell division lies in the precise distribution of genetic material between daughter cells. As a result of mitosis, both daughter cells receive a diploid set of chromosomes. The biological significance of mitosis. The constancy of the structure and the correct functioning of the organs and tissues of a multicellular organism would be impossible without the preservation of the same set of genetic material in countless cell generations. Mitosis provides important manifestations of vital activity: embryonic development, growth, restoration of organs and tissues after damage, maintenance of the structural integrity of tissues with constant loss of cells in the course of their functioning (replacement of dead erythrocytes, skin cells, intestinal epithelium, etc.). In protozoa, mitosis ensures asexual reproduction.
Meiosis and its stages.
MEIOSIS is a cell division in which there is a reduction in the number of chromosomes and their recombination in daughter cells compared to the mother. Meiosis is the basis of sexual reproduction, in which the offspring are not identical to the parents. Its most important evolutionary role is a barrier to unviable combinations of chromosomes and genes. Meiosis proceeds in two stages, the first of which is called reduction (during this particular stage, the number of chromosomes in daughter cells is halved), and the second is equational (as a result of it, chromosomes are evenly distributed among daughter cells, it is similar to mitosis). With a decrease in the number of chromosomes as a result of meiosis, a transition from the diploid phase to the haploid phase occurs in the life cycle.
Due to the fact that in the prophase of the first, reduction, stage, pairwise fusion (conjugation) of homologous chromosomes occurs, the correct course of meiosis is possible only in diploid cells or in even polyploid (tetra-, hexaploid, etc. cells). Meiosis can also occur in odd polyploids (tri-, pentaploid, etc. cells), but in them, due to the inability to ensure pairwise fusion of chromosomes in prophase I, chromosome divergence occurs with disturbances that threaten the viability of the cell or the developing from it a multicellular haploid organism.
Phases of meiosis
Meiosis consists of 2 consecutive divisions with a short interphase between them.
Prophase I - the prophase of the first division is very complex and consists of 5 stages:
o Leptothena or leptonema - packing of chromosomes, condensation of DNA with the formation of chromosomes in the form of thin threads (chromosomes shorten).
o Zygotene or zygonem - conjugation occurs - the connection of homologous chromosomes with the formation of structures consisting of two connected chromosomes, called tetrads or bivalents and their further compaction.
o Pachytene or pachinema - (the longest stage) crossing over (crossover), exchange of sections between homologous chromosomes; homologous chromosomes remain connected to each other.
o Diploten or diplonema - partial decondensation of chromosomes occurs, while part of the genome can work, transcription processes (RNA formation), translation (protein synthesis) occur; homologous chromosomes remain connected to each other. In some animals, chromosomes in oocytes at this stage of prophase of meiosis acquire the characteristic shape of lampbrush chromosomes.
o Diakinesis - DNA condenses as much as possible again, synthetic processes stop, the nuclear envelope dissolves; centrioles diverge towards the poles; homologous chromosomes remain connected to each other.
By the end of Prophase I, centrioles migrate to the poles of the cell, spindle fibers are formed, and the nuclear membrane and nucleoli are destroyed.
Metaphase I - bivalent chromosomes line up along the equator of the cell.
Anaphase I - microtubules contract, bivalents divide and chromosomes diverge towards the poles. It is important to note that, due to the conjugation of chromosomes in the zygotene, whole chromosomes consisting of two chromatids each diverge towards the poles, and not individual chromatids, as in mitosis.
Telophase I - chromosomes despiralize and the nuclear envelope appears.
The second division of meiosis follows immediately after the first, without a pronounced interphase: there is no S-period, since no DNA replication occurs before the second division.
Prophase II - condensation of chromosomes occurs, the cell center divides and the products of its division diverge to the poles of the nucleus, the nuclear envelope is destroyed, a fission spindle is formed.
Metaphase II - univalent chromosomes (consisting of two chromatids each) are located on the "equator" (at an equal distance from the "poles" of the nucleus) in the same plane, forming the so-called metaphase plate.
Anaphase II - univalents divide and chromatids diverge towards the poles.
Telophase II - chromosomes despiralize and the nuclear membrane appears.
As a result, four haploid cells are formed from one diploid cell. In those cases where meiosis is associated with gametogenesis (for example, in multicellular animals), the first and second divisions of meiosis are sharply uneven during the development of eggs. As a result, one haploid egg and two so-called reduction bodies are formed.
Mitosis. Its essence, phases, biological significance. Amitosis.
Mitosis(from Greek mitos - thread), or karyokinesis (Greek karyon - core, kinesis - movement), or indirect division. This is the process during which the condensation of chromosomes and the uniform distribution of daughter chromosomes between daughter cells occurs. Mitosis has five phases: prophase, prometaphase, metaphase, anaphase, and telophase. AT prophase Chromosomes condense (twist), become visible and arranged in a ball. Centrioles divide into two and begin to move towards the cell poles. Between the centrioles, filaments consisting of the protein tubulin appear. The mitotic spindle is formed. AT prometaphase the nuclear membrane breaks up into small fragments, and the chromosomes immersed in the cytoplasm begin to move towards the equator of the cell. In metaphase Chromosomes are established on the equator of the spindle and become maximally compacted. Each chromosome consists of two chromatids connected to each other by centromeres, and the ends of the chromatids diverge, and the chromosomes take on an X-shape. in anaphase daughter chromosomes (former sister chromatids) diverge to opposite poles. The assumption that this is provided by the contraction of the spindle threads has not been confirmed.
Many researchers support the sliding filament hypothesis, according to which neighboring spindle microtubules, interacting with each other and with contractile proteins, pull chromosomes towards the poles. in telophase daughter chromosomes reach the poles, despiralize, a nuclear envelope is formed, and the interphase structure of the nuclei is restored. Then comes the division of the cytoplasm - cytokinesis. In animal cells, this process manifests itself in the constriction of the cytoplasm due to the retraction of the plasmolemma between the two daughter nuclei, and in plant cells, small ER vesicles, merging, form a cell membrane from the inside of the cytoplasm. Cellulosic cell wall is formed due to the secret accumulated in dictyosomes.
The duration of each of the phases of mitosis is different - from several minutes to hundreds of hours, which depends on both external and internal factors and tissue type.
Violation of cytotomy leads to the formation of multinucleated cells. If the reproduction of centrioles is impaired, multipolar mitoses may occur.
AMITOSIS
This is a direct division of the cell nucleus, preserving the interphase structure. In this case, the chromosomes are not detected, there is no formation of a division spindle and their uniform distribution. The nucleus is divided by constriction into relatively equal parts. The cytoplasm can divide by constriction, and then two daughter cells are formed, but it may not divide, and then binuclear or multinuclear cells are formed.
Amitosis as a method of cell division can occur in differentiated tissues, such as skeletal muscles, skin cells, as well as in pathological changes in tissues. However, it is never found in cells that need to retain full genetic information.
11. Meiosis. Stages, biological significance.
Meiosis(Greek meiosis - reduction) - a method of division of diploid cells with the formation of four daughter haploid cells from one parent diploid cell. Meiosis consists of two successive nuclear divisions and a short interphase between them. The first division consists of prophase I, metaphase I, anaphase I, and telophase I.
In prophase I paired chromosomes, each of which consists of two chromatids, approach each other (this process is called conjugation of homologous chromosomes), cross over (crossing over), forming bridges (chiasmata), then exchange sites. Crossing over occurs when genes are recombined. After crossing over, the chromosomes separate.
In metaphase I paired chromosomes are located along the equator of the cell; Spindle threads are attached to each of the chromosomes.
In anaphase I two-chromatid chromosomes diverge to the poles of the cell; at the same time, the number of chromosomes at each pole becomes half that in the mother cell.
Then comes telophase I- two cells are formed with a haploid number of two-chromatid chromosomes; Therefore, the first division of meiosis is called reduction.
Telophase I is followed by a short interphase(in some cases, telophase I and interphase are absent). In the interphase between two divisions of meiosis, doubling of chromosomes does not occur, because. each chromosome already consists of two chromatids.
The second division of meiosis differs from mitosis only in that cells with a haploid set of chromosomes go through it; in the second division, prophase II is sometimes absent.
In metaphase II bichromatid chromosomes are located along the equator; the process goes on in two daughter cells at once.
In anaphase II already single-chromatid chromosomes depart to the poles.
In telophase II in four daughter cells, nuclei and partitions (in plant cells) or constrictions (in animal cells) are formed. As a result of the second division of meiosis, four cells are formed with a haploid set of chromosomes (1n1c); the second division is called equational (equalizing) (Fig. 18). These are gametes in animals and humans or spores in plants.
The significance of meiosis lies in the fact that a haploid set of chromosomes and conditions for hereditary variability are created due to crossing over and probabilistic divergence of chromosomes.
12.Gametogenesis: ovo - and spermatogenesis.
Gametogenesis- the process of formation of eggs and sperm.
spermatogenesis- from Greek. sperma, genus n. spermatos - seed and ... genesis), the formation of differentiated male germ cells - spermatozoa; in humans and animals - in the testes, in lower plants - in the antheridia.
In most higher plants, spermatozoa are formed in the pollen tube, often called spermatozoa. Spermatogenesis begins simultaneously with the activity of the testicle under the influence of sex hormones during the puberty of a teenager and then proceeds continuously (in most men almost until the end of life), has a clear rhythm and uniform intensity. Spermatogonia containing a double set of chromosomes divide by mitosis, leading to the emergence of subsequent cells - spermatocytes of the 1st order. Further, as a result of two successive divisions (meiotic divisions), spermatocytes of the 2nd order are formed, and then spermatids (cells of spermatogenesis immediately preceding the spermatozoon). With these divisions, a decrease (reduction) in the number of chromosomes by half occurs. Spermatids do not divide, enter the final period of spermatogenesis (the period of sperm formation) and, after a long phase of differentiation, turn into spermatozoa. This happens by gradual elongation of the cell, changes, elongation of its shape, as a result of which the cell nucleus of the spermatid forms the head of the spermatozoon, and the membrane and cytoplasm form the neck and tail. In the last phase of development, the spermatozoa heads closely adjoin the Sertoli cells, receiving nutrition from them until full maturation. After that, the spermatozoa, already mature, enter the lumen of the testicular tubule and further into the epididymis, where they accumulate and are excreted from the body during ejaculation.
Ovogenesis- the process of development of female germ cells of gametes, ending with the formation of eggs. A woman only has one egg during her menstrual cycle. The process of oogenesis has a fundamental similarity with spermatogenesis and also goes through a series of stages: reproduction, growth and maturation. Oocytes are formed in the ovary, developing from immature germ cells - ovogonia containing a diploid number of chromosomes. Owogonia, like spermatogonia, undergo successive mitotic
divisions, which are completed by the time of the birth of the fetus. Then a period of growth of oogonia begins, when they are called oocytes of the first order. They are surrounded by a single layer of cells - the granulosa membrane - and form the so-called primordial follicles. The female fetus on the eve of birth contains about 2 million of these follicles, but only about 450 of them reach the stage II oocytes and exit the ovary during ovulation. The maturation of the oocyte is accompanied by two successive divisions, leading to
halving the number of chromosomes in a cell. As a result of the first division of meiosis, a large oocyte of the second order and the first polar body are formed, and after the second division, a mature one, capable of fertilization and further
development of an egg with a haploid set of chromosomes and a second polar body. Polar bodies are small cells that do not play a role in oogenesis and are eventually destroyed.
13.Chromosomes. Their chemical composition, supramolecular organization (levels of DNA packaging).
