The purpose of the lesson: deepen knowledge about the features and methods of asexual reproduction of organisms in nature.
Tasks:
educational: characterize reproduction as one of the stages of individual development of organisms; expand and deepen knowledge about asexual reproduction (methods of asexual reproduction and its practical significance in nature and human activity);
developing: continue to develop the skills and abilities of independent work with the textbook, highlight the main points and formulate conclusions;
educational: to form a scientific and practical worldview among students to apply this knowledge in practice.
New knowledge: mitosis, sporulation, budding, vegetative propagation.
Core Knowledge: Viruses
Form of delivery: lesson
Methods of conducting: explanatory and illustrative, reproductive, problematic.
Lesson type: lesson on learning new knowledge.
Equipment: drawings, tables, Internet.
During the classes
I. Organizational moment
II. Updating students’ sensory experience and basic knowledge
Guys, we have an unusual lesson today. Before starting the lesson, let's answer some questions:
What are the main properties of living things? Metabolism, respiration, nutrition, reproduction.
Yes, through reproduction, organisms increase in number and spread throughout planet Earth.
Remember what is called reproduction and what forms of reproduction do you know? Reproduction is the reproduction of one's own kind.
That's right, reproduction is one of the fundamental properties of living things. Which is based on cell division and growth.
Forms of reproduction, as you noted, are asexual and sexual.
Remember the definition of asexual and sexual reproduction. Reproduction in which only one parent is involved is called asexual reproduction. Sexual reproduction involves two parents.
Asexual reproduction.
Sexual reproduction.
Why does asexual reproduction ensure the constancy of the chromosome set over generations? We will get an answer to this question after studying a new topic.
III. Motivation for educational activities of schoolchildren
Guys, please look at the pictures. What do they show? ? Plant reproductive organs.
Right! What type of reproduction are these organs typical for? (Asexual reproduction)
Well done! As you probably already understood, the topic of our lesson today is “Asexual reproduction.
Asexual reproduction is a method of reproduction of organisms in which one or more somatic cells of the maternal organism give rise to new individuals. Asexual reproduction arose very early in evolution. It is based on cell division through mitosis. Thanks to mitosis, the constancy of the number of chromosomes is maintained in cell generations, i.e. daughter cells receive the same genetic information contained in the nucleus of the mother cell.
In nature, there are unicellular and multicellular organisms. Many of them reproduce asexually. (Bacteria, slipper ciliates, hydra, mushrooms, fern)
Think about how these organisms reproduce? Bacteria - by cell division, fungi and ferns - by spores, hydra - by budding and sexually, plants - by vegetative and sexually.
Right. Thus, asexual reproduction has many ways: cell division, sporulation, budding and vegetative reproduction.
Let us consider in more detail the process of asexual reproduction in various organisms.
Working with the textbook text and table, you need to give examples of organisms and write them in the table
Table 1
Methods of asexual reproduction
| Reproduction method | Features of reproduction | Examples of organisms |
| 1. Cell division into two | The body of the original (parental) cell is divided by mitosis into two parts, each of which gives rise to new full-fledged cells | Single-celled organisms, bacteria, amoeba |
| 2. Multiple cell division | The body of the original cell divides mitotically into several parts, each of which becomes a new cell. | Unicellular organisms malarial plasmodium, chlorella, chlamydomonas |
| 3. Budding | A tubercle containing a nucleus is first formed on the mother cell. The bud grows, reaches the size of the mother bud, and separates. | Yeast, hydra, sucking ciliates |
| 4. Sporulation | A spore is a special cell covered with a dense shell that protects from external influences. | Mushrooms, mosses, ferns, mosses, multicellular algae |
| 5. Vegetative propagation: | An increase in the number of individuals of a given species occurs by separating the viable parts of the vegetative body of the plant organism | Plants |
| a) in plants | Formation of buds, stem and root tubers, bulbs, rhizomes, leaves, stems | Lilies, nightshades, gooseberries, currants, strawberries |
| b) in animals | Ordered and unordered division | Coelenterates (hydra, polyps), starfish, flatworms and annelids |
First, the table is filled out together, then students move on to fill it out independently using the textbook material. The third column is filled in by students.
After studying and filling out the table, what conclusion did you come to?
Conclusion.
There are many and varied methods of asexual reproduction.
Asexual reproduction is widespread in nature.
How does vegetative propagation differ from sporulation, cell division, and budding? Vegetative propagation is reproduction by parts of a multicellular organism. For example, plants reproduce by roots and shoots.
These methods of asexual reproduction begin life from one cell, and vegetative reproduction begins from cells of body parts of a multicellular organism.
IV. Generalization and systematization of concepts studied in class and previously acquired knowledge
Continue listing methods of vegetative propagation as independent work.
table 2
Vegetative propagation of plants
Answers: 1 - brood buds, 2 - cuttings, 3 - leaf, 4 - tuber, 5 - bulb, 6 - rhizome, 7 - tendrils, 8 - layerings.
The meaning of asexual reproduction:
Fast and energetically beneficial reproduction;
Does not depend on the environment, the presence of a partner or pollinating insects;
Completely preserves a set of genes and traits, which is useful in unchanging environmental conditions;
Widely used in plant growing.
V. Summing up the lesson
Why, with all the variety of methods of vegetative reproduction, do new organisms exactly repeat the genotype of the maternal organism?
What cytological process results in asexual reproduction not being accompanied by an increase in genetic diversity?
Conclusion of the lesson.
1. With asexual reproduction, new individuals are formed from one or more cells of the mother’s body through mitotic divisions. That. their cells receive the same hereditary information that was contained in the cells of the mother's body.
2. Consequently, new organisms that arose asexually are genetically exact copies of the maternal one.
VI. Homework
Your homework is to create a crossword puzzle on the topic “Asexual reproduction.”
References.
- Biology. 10th grade: lesson plans based on the textbook by V.B. Zakharov, S.G. Mamontov, S.I. Sonina / author. T.I.Chaika. - Volgograd: Teacher, 2006. -205 p.
- General biology: Textbook for grades 10-11. school with depth studied biology / A.O. Ruvinsky, L.V. Vysotskaya, M.S. Glagolev, etc.; Ed. A.O.Ruvinsky. -M.: Education, 1993. -544 p.: ill.
- Biology textbook for 10-11 grades. general education textbook institutions /V.B.Zakharov, S.G.Mamontov, N.I.Sonin. 5th ed., stereotype. – M.: Bustard, 2002.
Life on Earth has existed for several billion years thanks to the ability of organisms to reproduce - to reproduce similar offspring.
Reproduction methods
There are two methods of reproduction: asexual and sexual. Asexual reproduction involves one individual. In this case, the daughter organism bears all the characteristics of the mother organism. Asexual reproduction occurs through spores or vegetative organs. A spore is a special cell that separates from the mother’s body and germinates under favorable conditions, forming a new organism. One plant can produce millions of spores. During vegetative propagation, a new organism develops from cells or parts of vegetative organs.
Sexual reproduction differs from asexual reproduction in that a new organism is formed as a result of the fusion of two sex cells. The fusion of germ cells is called fertilization. As a result of fertilization, a new organism develops that bears the characteristics of both parents.
Bacteria reproduction
Bacteria reproduce by dividing cells into two. A bacterial cell contains one chromosome in the form of a ring. It doubles before division. Each daughter cell receives one chromosome and serves as a copy of the mother cell. Bacteria have a very high reproduction rate. This explains the fact that once pathogenic bacteria enter the human body, they can lead to the development of a dangerous disease in just a few hours. When there is a lack of nutrients, bacterial growth stops.
In many bacteria, spores are formed as a result of compaction of the internal contents and cell membrane. They are resistant to adverse conditions and can exist for many years. Spores serve to preserve individuals, and not for reproduction, as in plants.
Reproduction of unicellular algae
Single-celled algae reproduce asexually and sexually.
Asexual reproduction of Euglena greena begins with the elongation of the nucleus, which later divides into two parts diverging from each other. Then a septum is formed in the cytoplasm, dividing the mother cell into two independent organisms.
The green algae Chlorella reproduces by spores. In a chlorella cell, the nucleus divides several times. Around each new nucleus, a section of cytoplasm is separated and a shell is formed. Thus, several spores are formed inside the mother cell. The wall of the mother cell breaks and the spores come out. New organisms are formed.
Reproduction of unicellular fungi
Unicellular yeast fungi reproduce vegetatively - by budding. The nucleus of the mother cell divides, after which one nucleus remains in the original cell, and the other, along with part of the cytoplasm, passes into the daughter cell. The latter grows to the size of the mother. The “isthmus” between the cells becomes narrow, a septum is formed, and the daughter cell is separated from the mother cell.
Reproduction of single-celled animals
Single-celled animals most often reproduce asexually. In the common amoeba, before dividing, the mother cell stops feeding and elongates. The core is lengthened, then laced in half. At the same time, a constriction forms in the cell, which divides it into two approximately equal parts. Under favorable conditions, the amoeba divides once a day.
Under unfavorable conditions, the body of the amoeba becomes round, and a dense shell forms on its surface. The amoeba turns into a cyst state, thanks to which it can tolerate lack of moisture and low temperatures. When exposed to favorable conditions, the amoeba emerges from the cyst and begins to multiply again.
Natural vegetative propagation of plants and fungi
Vegetative reproduction of multicellular algae occurs by separating part of the algae's body.
In higher plants there are several methods of vegetative propagation. One of them is the formation of root suckers. Thus, raspberries and rose hips form buds on the roots, from which young shoots grow. They grow faster than shoots developing from seeds, as they use an already developed root system.
Vegetative propagation is possible using modified shoots - bulbs, tubers and rhizomes. Numerous baby bulbs are formed in tulips and lilies. Potatoes reproduce by tubers, and wheatgrass weed by rhizomes. Strawberries reproduce with the help of tendrils (creeping above-ground shoots). Fungi can reproduce by separating one or more cells, giving rise to a new organism.
In nature, vegetative propagation allows plants to survive and disperse in conditions where sexual reproduction by seeds is difficult.
Artificial vegetative propagation of plants
When propagating cultivated plants, humans use natural and some artificial methods of vegetative propagation. The following methods are widely used: layering, cuttings, grafting. Layerings are shoots specially removed from the plant and pressed to the ground for rooting. A cutting is a part of a shoot with stems, roots or leaves. A new plant grows from a cutting. This way you can propagate currants, willow, and various indoor plants.
Currently, cell cultures are used for vegetative propagation of plants. With this method of propagation, a whole plant is obtained from several cells, which allows you to quickly propagate valuable varieties.
Reproduction of fungi and plants using spores
When propagated by spores, special organs are formed on the parent organism. Numerous unicellular spores develop in them.
In fungi, such organs are formed on hyphae or hyphal outgrowths. In higher plants, spores develop in special formations that have different shapes, and in mosses, for example, this is a capsule.
An important property of all organisms is reproduction, which ensures the maintenance of life.
Reproduction carried out without the participation of reproductive cells is called asexual reproduction.
Asexual reproduction
Asexual reproduction is characterized by the fact that the daughter cells are completely identical to the parent cells in terms of the content of hereditary information, morphological, anatomical and physiological characteristics. Asexual reproduction is carried out with the help of individual (asexual) cells (various methods of division, sporulation), from which daughter cells are formed or multicellular organisms develop.
Vegetative propagation is ensured by the separation of multicellular sections from the mother multicellular organism (root, leaf, shoot, cuttings, layering, as well as modified underground shoots - tubers, bulbs, rhizomes in plants and body parts, “buds” in animals).
The biological significance of asexual and vegetative reproduction is that in a short period the number of species can be significantly increased.
Sexual reproduction
Sexual reproduction is characterized by the exchange of genetic information between females and males through special haploid sex cells - gametes.
Gametogenesis is the process of formation of gametes.
Sexual reproduction exists in almost all plants and animals. Mature highly specialized germ cells - gametes: female - eggs, male - sperm - when fused, they form a zygote, from which a new daughter organism develops. Upon reaching sexual maturity, the new organism in turn produces gametes that give rise to subsequent offspring. This is how the continuity of generations is carried out.
Gametes are formed from diploid cells through a special type of cell division - meiosis.
The process of meiosis consists of two successive divisions - meiosis and meiosis.
| Phases | Processes |
|---|---|
| First meiotic division | |
| Pairing of homologous chromosomes (one of them is maternal, the other is paternal). Formation of the division apparatus. Chromosome set n | |
|
Arrangement of homologous chromosomes along the equator, n chromosomes |
|
Separation of pairs of chromosomes (consisting of two chromatids) and their movement to the poles |
|
Formation of daughter cells Set of chromosomes n |
|
| Second meiotic division | |
|
Daughter cells arising in telophase I undergo mitotic division |
|
|
Centromeres divide, the chromatids of the chromosomes of both daughter cells move towards the poles. Chromosome set n |
|
|
Formation of four haploid nuclei or cells (spore formation in mosses and ferns) |
The main feature of meiosis is the reduction in the number of chromosomes by 2 times.
Comparing mitosis and meiosis, we can note the following similarities and differences:
| Similarities and differences | Mitosis | Meiosis |
|---|---|---|
| Similarities |
|
|
| Difference |
One division |
Two alternating divisions |
| In metaphase, double chromosomes line up along the equator |
Pairs of homologous chromosomes line up along the equator |
|
| No chromosome conjugation | Homologous chromosomes conjugate | |
| Between divisions, DNA molecules (chromosomes) are doubled | Between the 1st and 2nd division there is no interphase and duplication of the DNA molecule (chromosomes) | |
| Two daughter cells are formed | 4 cells with a haploid set of chromosomes are formed | |
During the formation of germ cells in animals, a decrease in the number of chromosomes occurs at the last stage of oogenesis and spermatogenesis (the formation of female and male germ cells).
By merging, the gametes form a zygote (fertilized egg), which carries the makings of both parents, due to which the hereditary variability of the descendants sharply increases. This is the advantage of sexual reproduction over asexual reproduction.
Types of reproduction
A type of sexual reproduction is parthenogenesis (from the Latin “parthenos” - virgin + gr. “genesis” - birth), in which the development of a new organism occurs from an unfertilized egg (in bees). Conjugation - two individuals come together and exchange hereditary material (ciliates).
Copulation is the fusion of two cells of equal size into one (colonial flagella, etc.)
In higher plants, meiosis occurs not during the formation of gametes, but at an earlier stage of development - during the formation of spores (in angiosperms - during the formation of pollen and the embryo sac).
For angiosperms, the process of double fertilization, discovered by S. G. Navashin in 1898, is typical.
The peculiarity of fertilization in flowering plants, in contrast to animals, is that it involves not one, but two spermatozoa, which is why it is called double fertilization. Its essence lies in the fact that one sperm fuses with the egg, and the second with the central diploid cell, from which the endosperm further develops.
In nature, reproduction with alternating sexual and asexual generations is widespread in plants and some animals (coelenterates). This type of reproduction is described in detail in the first part of the manual.
Reproduction in which one or more cells are separated from part of the mother's body is called asexual. In this case, one parent is sufficient for the appearance of offspring.
Types of asexual reproduction
In nature, there are several options for how living organisms can reproduce their own kind. Methods of asexual reproduction are quite diverse. All of them consist in the fact that cells begin to divide and reproduce daughter individuals. In single-celled protozoa, the entire body is divided into two parts. In multicellular organisms, reproduction begins with the division of one or more cells at the same time.
Plants, fungi and some animal species are characterized by asexual reproduction. Reproduction methods can be as follows: division, sporulation. Separately, the forms of the appearance of offspring are noted, in which they are formed from a group of cells of the maternal individual. They are called vegetative propagation. Separately, budding and fragmentation are distinguished. These are common methods of asexual reproduction. The table makes it possible to understand how they differ.
Reproduction method | Peculiarities | Types of organisms |
The cell splits into 2 parts, forming 2 new individuals | Bacteria, protozoa |
|
Sporulation | Spores are formed in special parts of the body (sporgania) | Some plants, fungi, some protozoa |
Vegetative | A daughter organism is formed from several cells of the parent | Annelids, coelenterates, plants |
Features of simple reproduction
In all organisms that are capable of producing offspring by division, the ring chromosome is first doubled. The core is divided into two parts. From one parent cell two daughter cells are formed. Each contains identical genetic material. A constriction appears between the two formed daughter cells, along which the parent individual is divided into two cells. This is the simplest asexual reproduction.
Reproduction methods may be different. But green euglena, chlamydomonas, amoeba, and ciliates use division. The resulting offspring are no different from the parent individuals. He has exactly the same set of chromosomes. This method of reproduction allows you to obtain a large number of identical organisms in a short time.
Sporulation
Some fungi and plants reproduce using special haploid cells. They are called spores. In many fungi, these cells are formed during the process of mitosis. And in higher plant organisms their formation is preceded by meiosis. A peculiarity of this process is that the spores of such plants contain a haploid set of chromosomes. They are able to give rise to a new generation, which is different from the maternal one. It can reproduce sexually. At the same time, we should not forget about their unique feature. The methods of sexual and asexual reproduction in such plants alternate.
In most fungi and plants, the spores formed are cells that are protected by special membranes. They can persist for some time in unfavorable conditions. When they change, the shells open, and the cell begins to actively divide into a new organism.
Vegetative self-reproduction
Most higher plants use other methods of asexual reproduction. The table allows you to understand what types of vegetative reproduction exist.
Vegetative propagation method | Peculiarities |
Separation of roots, cuttings, bulbs, tendrils, tubers, rhizomes | For reproduction, a well-formed part of the mother’s body is necessary, from which the daughter will begin to develop. |
Fragmentation | The parent individual is divided into several parts, from each a separate independent organism develops |
Budding | A bud is formed on the parent body, from which a new full-fledged organism is formed |
During vegetative propagation, plants can form special structures. For example, potatoes and dahlias produce tubers. This is what root or stem thickenings are called. The swollen base of the stem from which the offspring is formed is called a corm.
Plants such as aster and valerian reproduce by rhizomes. Also called horizontally growing underground stems from which buds and leaves emerge.
Produces offspring with the help of a mustache. They grow quite quickly, new leaves and buds appear from them. All these methods of asexual reproduction of organisms are called vegetative. These also include reproduction using cuttings of stems, roots, and parts of thalli.
Fragmentation
This type of reproduction is characterized by the fact that when the maternal organism is divided into several parts, a new individual is formed from each of them. Some annelids and flatworms, echinoderms (starfish) use such asexual reproduction. Methods of reproduction by fragmentation are based on the fact that some organisms can recover through regeneration.
For example, if a ray is torn from a starfish, a new individual will form from it. The same thing will happen with an earthworm divided into several parts. Hydra, by the way, can be restored from 1/200 of the part separated from its body. Typically, such reproduction is observed during damage. Spontaneous fragmentation is observed in molds and some marine worms.
Budding
Asexual reproduction methods make it possible to reproduce exact copies of parent organisms. In some cases, daughter individuals are formed from special cells - buds. This method of self-reproduction is characteristic of some fungi, animals (sponges, protozoa, coelenterates, a number of worms, pterobranchs, tunicates), and hepatic mosses.
For coelenterates, for example, such asexual reproduction is typical. Their methods of reproduction are quite interesting. A growth appears on the mother’s body and increases in size. As soon as it reaches the size of an adult, it separates.
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