Peerless reproduction. Types and forms of asexual reproduction. Biological role of asexual reproduction

Living organisms occur with the participation of only one cell without the formation gametes. In this case, new organisms are formed in some species in special organs, and in others - from one or more cells of the mother’s body. The following types of asexual reproduction are distinguished: vegetative propagation, sporulation, polyembryony, fragmentation, budding and fission.

Vegetative propagation is a type of asexual reproduction in which the reproduction of cells of a new organism occurs from special structures of the mother’s body (tubers, rhizomes, etc.) or from part of the vegetative body of the mother. This type of reproduction is often found among plants.

Vegetative propagation in examples.

Type of vegetative organ	Method of vegetative propagation	Examples in the plant world
	Leaf cuttings	Coleus, gloxinia, begonia
Corm	Tuberous	Crocus, gladiolus
	Root suckers	Cherry, sow thistle, plum, lilac, thistle
	Root cuttings	Raspberry, aspen, willow, rosehip, dandelion
Underground parts of shoots	Bulb	Tulip, onion, garlic, hyacinth
		Jerusalem artichoke, potatoes, weekday
	Rhizome	Bamboo, iris, asparagus, lily of the valley
Aboveground parts of shoots	Stem cuttings	Currants, grapes, gooseberries
	Dividing bushes	Daisy, rhubarb, primrose, phlox
		Grapes, bird cherry, gooseberry

Sporulation- This is reproduction using spores. Spores are cells that usually form in sporangia - specialized organs. In higher organisms, before the formation of pores, meiosis.

Polyembryony(schizogony) is a type of asexual reproduction in which a new generation develops from the parts into which the embryo breaks up (monozygotic twins).

Fragmentation is a type of asexual reproduction in which daughter organisms are formed from parts into which the mother organism breaks down. Elodea, spirogyra, starfish, and annelids reproduce in this way.

Budding is a type of asexual reproduction in which daughter organisms are formed as shoots on the mother organism. During budding, a new organism can separate from the parent and live separately (for example, hydra), or it can remain attached to the parent organism. The latter type of budding is common in coral colonies.

Division is the simplest method of asexual reproduction in which the mother organism is divided into two or more daughter organisms. This method is typical for many single-celled organisms.

The essence of the reproduction process. Reproduction- This is the property of living organisms to reproduce their own kind. During reproduction, hereditary information is transferred from parental forms to offspring, which ensures the reproduction of characteristics not only of a given species, but also of specific parental individuals. Consequently, reproduction maintains the long-term existence of the species, while maintaining continuity between parents and their offspring over many generations.

There are two types of reproduction: asexual and sexual.

Asexual reproduction is the reproduction of organisms without the participation of germ cells. Only one parent individual participates in asexual reproduction, which in most cases leads to the appearance of monotonous offspring that inherit all the characteristics of the parent. There are several methods of asexual reproduction: cell division, budding, fragmentation, vegetative propagation, sporulation, etc.

Bacteria and many single-celled protists (amoebas, euglena, ciliates etc.) reproduce cell division. The resulting daughter cells grow, reaching the size of the mother's body, and divide again.

At budding a new organism is formed on the body of the parent individual in the form of a small outgrowth - a bud, which grows and then separates, turning into an independent organism (Fig. 77). Budding is characteristic of sponges, coelenterates, some worms If in this case the daughter individuals are not separated from the mother (for example, in corals), then a colony is formed.

Many mushrooms can reproduce by fragments (sections) of hyphae, and lichens And multicellular algae- fragments of thalli. This method of reproduction is called fragmentation. The reproduction of organisms by fragmentation is based on regeneration - the ability to restore lost or damaged body parts. Fragmentation is also observed in sponges, coelenterates, flat and some annelids.

Vegetative propagation- this is the formation of new individuals from vegetative organs. Vegetative propagation, like fragmentation, is based on the phenomenon of regeneration. This method of reproduction is widespread in the plant world, but reaches its greatest diversity in flowering plants(Fig. 78).

In nature, during vegetative propagation, new individuals can be formed from the roots, on which adventitious buds are formed (root shoots cherry, rosehip, lilac), from shoots (stem layerings currants, gooseberries) or parts thereof (for example, from cuttings brittle willow, leaves Kalanchoe). In this case, an apical or lateral bud must be present on the shoot fragment, or additional buds must form under the influence of external conditions (for example, injury).

Vegetative propagation can also be carried out using modified shoots: tubers ( potatoes, Jerusalem artichoke), bulbs (onion, garlic, tulip, narcissus), rhizomes (wheatgrass, lily of the valley, nettle), mustache (strawberries, creeping buttercup).

In some plants (aspens, willows, plums, cherries, raspberries etc.) vegetative reproduction may even prevail over sexual reproduction. An example of a plant that actively reproduces vegetatively is Elodea canadensis- a dioecious plant that lives in fresh water bodies. Only female specimens of this plant were brought to Europe from North America. Despite this, Elodea began to reproduce very quickly vegetatively, developing new bodies of water year after year.

In plant growing practice, artificial vegetative propagation of plants is widely used. Thus, many cultivated plants can be propagated by stems ( currants, grapes) and leafy (Usambara violet, begonia) cuttings, layering ( gooseberry) and in other ways. In gardening, vegetative propagation using grafting is common. This method allows you to quickly propagate valuable plants and ensure their accelerated development while fully maintaining varietal qualities. The grafted cultivated plant (scion) can obtain such valuable properties of the rootstock (the plant on which the graft is made), such as frost resistance, disease resistance, undemanding to soil fertility, etc.

Asexual reproduction by cell division, budding, fragmentation and vegetative organs is carried out by somatic cells. Along with this, many protists, fungi and plants are characterized by sporulation, in which specialized cells are formed - disputes. They consist of a nucleus and cytoplasm with a minimal amount of nutrients. Spores are formed by mitosis or meiosis in ordinary somatic cells of the mother's body or in specialized organs - sporangia. Under favorable conditions, the spores germinate and give rise to a new organism. The main advantage of this method of reproduction is the possibility of producing a large number of descendants and rapid dispersal.

With any form of asexual reproduction, the number of individuals of a given species increases. The advantage of asexual reproduction lies in its simplicity and efficiency - there is no need to find a partner, almost any individual can leave offspring, etc.

1. What words in the sentences are missing and replaced with letters (a-c)?

The reproduction by living organisms of their own kind is called (a).

There are two types of reproduction: (b) and (c).

2. What is the biological significance of the reproduction of organisms?

3. In what ways can asexual reproduction occur in bacteria, protists, fungi, plants and animals? What forms of asexual reproduction are based on the phenomenon of regeneration?

4. What methods of vegetative propagation are widely used in agriculture? Why? Give examples.

5. What are the features of asexual reproduction of plants and animals?

6. When propagating plants from lignified cuttings, it is recommended to make an incision in the lower part of the cutting for faster rooting. What layer of tissue do you think should be drilled down to? What type of roots form on cuttings?

7. In horsetails, the outer shell of each spore forms two ribbons, which unwind in dry air and unite the spores with each other. Thanks to this, horsetail spores spread in groups. In other plants, such as the shield fern, the spores disperse singly. What is the reason for the presence of ribbons in horsetail spores and why do shield spores not have such devices?

Chapter 1. Chemical components of living organisms

§ 1. Content of chemical elements in the body. Macro- and microelements
§ 2. Chemical compounds in living organisms. Inorganic substances

Chapter 2. Cell - structural and functional unit of living organisms

§ 10. History of the discovery of the cell. Creation of cell theory
§ 15. Endoplasmic reticulum. Golgi complex. Lysosomes

Chapter 3. Metabolism and energy conversion in the body

§ 24. General characteristics of metabolism and energy conversion

Chapter 4. Structural organization and regulation of functions in living organisms

Chapter 5. Reproduction and individual development of organisms

4. Forms of reproduction of organisms

The succession of generations of organisms in nature is carried out through reproduction. Reproduction- This is the ability of an organism to reproduce its own kind. In nature, there are two types of reproduction: asexual and sexual.

Types of asexual reproduction

Asexual reproduction- the formation of a new organism from one cell or group of cells of the original maternal organism. In this case, only one parent individual participates in reproduction, which passes on its hereditary information to its daughter individuals. Asexual reproduction produces identical offspring. The only source of variability is random hereditary changes that can arise during the process of individual development.

Asexual reproduction is based on mitosis. There are several types of asexual reproduction.

Asexual reproduction in bacteria is interesting (Fig. 7).

Rice. 7. Asexual reproduction of bacteria: A - general reproduction scheme; B - cell division diagram

The circular DNA molecule attaches to the cell membrane and replicates. A transverse partition begins to form in the cell on the side where DNA molecules attach. The transverse septum then bifurcates, moving the anchored DNA to different parts of the cell. Ribosomes are evenly distributed between the two daughter cells, and a constriction is formed that divides the cell into two daughter cells.

Budding - This is a form of asexual reproduction in which a small outgrowth (bud) is separated from the parent individual and a daughter organism is formed. A new organism develops from a group of cells of the original organism. This type of asexual reproduction is characteristic of coelenterates (hydra) and some other animals and plants. Single-celled fungi - yeasts - also reproduce by budding. In contrast to simple division, during budding the mother cell is divided into unequal parts, budding a constantly smaller daughter cell (Fig. 8, B).

Rice. 8. Types of asexual reproduction: A - simple division in two of green euglena (longitudinal); B - budding of yeast and hydra; B - sporulation of mosses; G - vegetative propagation by begonia leaves

Reproduction by spores (sporulation) is typical for spore-bearing plants (algae, mosses, ferns). Reproduction occurs with the help of special cells - spores formed in the mother's body (Fig. 8, B). A spore is a small cell consisting of a nucleus and a small amount of cytoplasm. They are formed in large quantities in the original maternal organism. Each spore, germinating, gives rise to a new organism. Since they are microscopically small, they are easily transported by wind, water or other organisms, which facilitates the spread of these plants. Fungi, such as penicillum and cap mushrooms, also reproduce by spores.

Vegetative propagation- reproduction by individual organs, parts of organs or the body. Vegetative propagation most often occurs in plants that can reproduce by roots, shoots and parts of shoots (stems, leaves), modified shoots. Methods of vegetative propagation of plants are very diverse. This is propagation by bulbs (tulip), underground stolons - tubers (potatoes), rhizomes (wheatgrass), root cones (dahlia), layering (currants), root suckers (raspberries), leaves (begonia, violet), aboveground stolons - tendrils (strawberries ) etc. (Fig. 8, D).

Fragmentation- this is the division of an individual into two or more parts, each of which can give rise to a new organism. This method is based on regeneration- the ability of organisms to restore missing parts of the body. It is characteristic of lower invertebrate animals (coelenterates, flatworms, starfish, etc.). The animal's body, divided into separate parts, completes the missing fragments. For example, under unfavorable conditions, the planarian flatworm breaks up into separate parts, each of which, when favorable conditions occur, can give rise to a new organism.

Fragmentation also occurs in plants; for example, multicellular algae can reproduce in parts of the thallus.

Cloning. An artificial reproduction method that appeared relatively recently, in the early 60s. XX century It is based on obtaining a new organism from one cell of the original one. Since the cell nucleus contains the entire set of chromosomes, and therefore genes, under certain conditions it can be forced to divide, which will lead to the formation of a new organism. The formation of a clone is based on mitosis. To clone plants, the cells of the educational tissue are separated and grown on special nutrient media. A plant cell, dividing successively, gives rise to a whole organism. This method is currently widely used to obtain valuable plant varieties.

There is experience in animal cloning. It was first introduced by the English biologist D. Gurdon and gave positive results in experiments with the South American toad. Tadpole intestinal cells were used as a nuclear donor. The nuclei of the recipient eggs were destroyed by ultraviolet rays and the intestinal epithelial nuclei were transplanted into these cells. As a result of the experiment, it was possible to obtain several cloned toad individuals, completely identical to each other. In 1995, English scientists managed to obtain a clone of sheep that were similar to the original maternal individual. However, the lambs died at an early age, before reaching nine months.

In 1997, Dolly the sheep was obtained by cloning. To do this, the nuclei of mammary gland cells from a sheep of one breed (nucleus donor) were taken and transplanted into eggs with previously destroyed nuclei from a sheep of another breed (recipient). The cloned sheep was no different from the nuclear donor, but very different from the recipient.

The use of the cloning method will make it possible not only to preserve economically valuable animals, but also to reproduce them without limit. Currently, work is underway on human cloning, which causes heated debate not only among scientists, but also among various groups of the population. However, using this method, it is intended to reproduce only individual organs and tissues for subsequent transplantation into the donor’s body, and not to create individual individuals. This method will solve the problem of incompatibility of tissues of different organisms.

Features of sexual reproduction

Sexual reproduction - This is the formation of a new organism with the participation of two parent individuals. The new organism carries hereditary information from two parents, and the resulting offspring differ genetically from each other and from their parents. This process is characteristic of all groups of organisms; in its simplest form, it occurs even in prokaryotes.

During sexual reproduction, special cells are formed in the body sex cells - gametes male and female types that are capable of merging. Male gametes - spermatozoa, or sperm(if they are motionless). Female gamete - egg. Gametes are different from all other cells in the body, which are called somatic(from lat. soma - body). They always have haploid set of chromosomes (n).

As a result of the fusion of two gametes, the diploid set of chromosomes is restored again. In this case, half of all chromosomes are paternal, and the other half are maternal. For example, a person has 46 chromosomes, of which 23 are received from the mother and 23 from the father.

Sexual reproduction has a number of advantages. As a result of this process, a change in hereditary information occurs, and new individuals combine the characteristics of two parents. This leads to the emergence of new combinations of traits and genes. Sexual reproduction makes the organism more competitive and adapted to changing environmental conditions, as it increases the chances of survival. In the process of evolution, sexual reproduction turned out to be more preferable and progressive.

Questions for self-control

1. What types of reproduction occur in organisms? How are they different from each other?

2. What type of cell division underlies asexual reproduction?

3. Compare reproduction by spores and vegetative reproduction in plants. What are their similarities and differences?

4. What advantage does spore reproduction provide to the body?

5. Describe the features of each type of asexual reproduction.

6. What are the features of sexual reproduction? What advantages does this type of reproduction provide?

7. What cells are called gametes? What makes them special?

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4.1. Types of reproduction In the process of the evolution of living organisms, there was also an evolution of methods of reproduction, the diversity of which is observed in living species. All reproduction options can be divided into two fundamentally different types - asexual and

Playback(or self-reproduction) - the formation by a living organism of a new, genetically similar organism.

Reproduction- an increase in the number of individuals of a given species, due to their reproduction and ensuring continuity and continuity of life in a number of generations.

Continuity means that when individuals reproduce, all genetic information contained in the parent generation is transferred to the daughter generation.

Continuity of life means an unlimitedly long existence of species and populations of organisms, conditioned by a change of generations.

Life cycle- a set of stages and phases of development of an organism from the moment of formation of the zygote until the onset of maturity, characterized by the ability to give rise to the next generation.

Types of life cycles: simple and complex.

Simple life cycle is completely carried out during the life of one individual and is characterized by the preservation of the general structural plan of the organism.

Complex life cycle can be expressed in the alternation of sexual and asexual generations (in plants) or in the phenomenon of metamorphosis (in some animals).

Types of reproduction: asexual and sexual.

Asexual reproduction

Asexual reproduction- type of reproduction in which reproduction involves one parent , and its descendants develop from one not sexual (somatic) cell or group of such cells of the parent organism. Daughter organisms produced by asexual reproduction are called clones.

❖ Features of asexual reproduction:
■ daughter organisms have a genotype identical to the genotype
parent organism (they are called clones)’,
■ produces a large number of offspring;
■ complicates evolution, as it provides material for stabilizing natural selection.

Clone- genetically homogeneous offspring of one individual, resulting from asexual reproduction (clones are also called cells formed as a result of the mitotic division of one cell)

Forms of asexual reproduction of unicellular organisms:
■ cell division in two(found in bacteria and protozoa - amoebas, ciliates, euglena, etc.);
■ budding- cell division into unequal parts ; a smaller cell buds from a larger one (found in yeast and some bacteria);
■ multiple fission(schizogony) - repeated division of the nucleus of the original cell, after which this cell breaks up into the corresponding number of mononuclear daughter cells (found in protozoa and some algae);
■ sporulation(sporogony) - reproduction by the formation of spores (found in algae, bacteria, protozoa - sporozoans).

Spore- single-celled embryo, i.e. a cell that, when exposed to favorable conditions, can develop into a new organism. The spore is always covered with a dense shell that protects its internal contents from unfavorable external conditions.

❖ Forms of asexual reproduction in multicellular organisms:
■ sporulation(observed in mosses, horsetails, ferns);
■ budding- reproduction by the formation and subsequent separation of buds (in hydras, sponges); in some species of organisms (coral polyps) the buds do not separate (colonies are formed);
■ strobilation(found in some coelenterates): division of the upper part of the polyp by transverse constrictions into daughter individuals (strobili), which are separated from the parent;
■ vegetative- reproduction by body parts (mycelium in mushrooms, thallus in algae and lichens);
■ vegetative organs— daughter organisms grow from a stem (currant), rhizome (wheatgrass), tuber (potato), bulb (onion), etc.; characteristic of flowering plants;
■ fragmentation- reproduction from individual fragments of the parent organism (found in some flat and annelids).

Bud- a group of cells that forms a protrusion on the body of the parent organism, from which the daughter organism develops.

Sexual reproduction

Sexual reproduction- type of reproduction in which reproduction involves two parents ; a new organism develops from zygotes, formed as a result of the fusion of male and female reproductive cells - gametes.

Features of sexual reproduction:
■ it is distinguished by the presence of the sexual process;
■ ensures the exchange of hereditary information between individuals of the same species;
■ creates conditions for the emergence of hereditary variability;
■ provides more diverse offspring;
■ increases the ability of organisms to adapt to constantly changing environmental conditions;
■ creates conditions for natural selection and evolution;
■ produces a small number of offspring;
■ characteristic of all eukaryotes,
■ predominates in animals and higher plants.

Sexual process- a set of events that ensure the exchange of hereditary information between individuals of the same species and create conditions for the emergence of hereditary variability.

❖ The main forms of the sexual process:
■ conjugation,
■ copulation (gametogamy).

Transformation and transduction are also observed in bacteria.

Conjugation(characteristic of ciliates, some bacteria, algae and fungi) - the process of fertilization by exchange of migrating nuclei , which move from the cell of one individual to the cell of another along the cytoplasmic bridge formed between them.

During conjugation, the number of individuals does not increase; their reproduction occurs asexually (by division in two).

Copulation(or gametogamy ) is the process of fusion of two sex-different cells (gametes) to form a zygote. In this case, two gamete nuclei form one zygote nucleus.

■ Copulation is also called: the sexual process in animals that have copulatory organs, and the union during sexual reproduction of two individuals that do not have genital organs (for example, earthworms).

❖ Forms of sexual reproduction:
■ without fertilization;
■ with fertilization.

❖ Organs of sexual reproduction:
■ in lower plants and many fungi - gametangia;
■ in higher spore plants - antheridia(male organs) and archegonia(female organs);
■ in seed plants - pollen grains(male organs) and embryo sacs(female organs);
■ in animals - gonads (gonads): testes (in males), ovaries (in females);
■ absent in sponges and coelenterates; gametes arise from various somatic cells.

Fertilization- the process of fusion of male and female reproductive cells (gametes). As a result of fertilization, a zygote is formed.

Zygote - fertilized diploid (2n1хр) egg , carrying the hereditary inclinations of both parents, i.e. a cell formed by the fusion of gametes of different sexes. A new daughter organism develops from the zygote; sometimes (in some algae and fungi) the zygote becomes covered with a dense shell and turns into a zygospore.

Ovum - women's germ cell (usually has a spherical shape, is much larger than somatic cells, immobile, contains many nutrients in the form of yolk grains and protein).

Sperm — men's germ cell (a small, very mobile cell that moves with the help of one or more flagella; found in male animals, some fungi and many plants, the sexual reproduction of which is ensured by the presence of an aquatic environment). Consists of a head, neck and tail. The head contains a nucleus with a haploid set of chromosomes (lnlxp), the neck contains mitochondria that produce energy for movement, and a centriole that provides vibrations of the flagellum.

Spermin- without flagella men's germ cells angiosperms and gymnosperms; delivered to the egg using a pollen tube.

❖ Gametogenesis- the process of formation and development of germ cells.

■ Spermatogenesis is the process of formation of male germ cells (male gametes); occurs in the testes.

■ Oogenesis - the process of formation of eggs (female gametes); occurs in the ovaries.

❖ Stages of gametogenesis:

■reproduction: mitotic division primary reproductive diploid cells (spermatogonia in males and oogonia in females) tissue of the seminiferous tubules of the testes (in males) or ovaries (in females); in female mammals this stage is realized during the embryonic development of the organism, in males - from the moment of puberty of the individual;

■ height(at the interphase of the cell cycle): an increase in the size of spermatogonia and oogonia due to an increase in the amount of cytoplasm in them; DNA replication and formation of the second chromatid; formation of first order spermatocytes from spermatogonia (in males) and from oogonia (in females) - oocytes of the first order (2n2хр);

■ maturation - meiotic division:

- the result of the first meiotic division: in males - the formation of two second-order spermatocytes (1n2хр) from one first-order spermatocyte, in females - the formation of one second-order oocyte (1n2хр) and a secondary (reduction) body from one first-order oocyte;

- result of the second meiotic division: males have education four haploid monochromatid spermatid ( lnlxp), in females— one haploid single-chromatid egg (lnlxp) and three secondary bodies; secondary bodies subsequently die;

■ formation: spermatids do not divide; from each of them a sperm is formed (this stage is absent in female gametes).

❖Parthenogenesis (or virgin reproduction) - development of an organism from an unfertilized egg.

Types of parthenogenesis(depending on the set of chromosomes in the egg):
■ haploid (bees, ants, etc.):
■ diploid (lower crustaceans, some lizards, etc.).

Fertilization

Fertilization (see above) is preceded by insemination. Insemination is the process that ensures the meeting of sperm and eggs.

Types of insemination: external (characteristic of aquatic inhabitants; sperm and eggs are released into the water, where they merge) and internal (occurring with the help of copulatory organs; characteristic of land dwellers).

In mammals and humans, eggs acquire the ability to fertilize as a result of ovulation.

Ovulation- exit of mature cells in mammals into the body cavity. The frequency of ovulation is regulated by the nervous system and hormones of the endocrine system.

❖ Fertilization phases:
■ penetration of the sperm into the egg (in this case, a fertilization membrane is formed in the egg, which prevents the penetration of other sperm into the egg);
■ nuclear fusion and restoration of the diploid set of chromosomes;
■ activation of zygote development (formation of a division spindle, inducing the zygote to divide).

The concept of ontogenesis

Ontogenesis is a set of processes of individual development of an organism from the moment of formation of the zygote (fertilization of the egg) until the end of the individual’s life.

❖ Periods of ontogenesis:
■ embryonic- from the moment of formation of the zygote until the germination of seeds (in plants) or the birth of a young individual (in animals);
■ postembryonic- from seed germination (in plants) or birth (in animals) to the death of the organism.

Asexual reproduction

Asexual reproduction, or agamogenesis - a form of reproduction in which an organism reproduces itself independently, without any participation of another individual. It should be distinguished asexual reproduction from same-sex reproduction(parthenogenesis), which is a special form of sexual reproduction.

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