Biology worksheet asexual reproduction. Abstract: Forms of asexual reproduction. Asexual reproduction in multicellular organisms

Reproduction - the ability of organisms to reproduce their own kind.

In nature, there are two types of reproduction: asexual and sexual.

I. Asexual reproduction - reproduction of organisms that occurs without the formation of gametes with the participation of only one parent organism.

Identical offspring descended from the same parent are called clone.

Members of the same clone can be genetically different only if a random mutation occurs.

Asexual reproduction is based on mitotic division .

Types of asexual reproduction:

Types of asexual reproduction	Characteristics	Examples of organisms
1. Simple (binary)	From one cell, two daughter cells are formed through mitosis, each of which becomes a new organism identical to the mother.	Bacteria, many protozoa (amoeba), all unicellular algae (chlorella)
2. Multiple division (schizogony)	The cell nucleus undergoes multiple divisions, after which the cell itself divides into many daughter cells. The stage at which multiple division occurs is called schizont, and the process itself is called schizogony.	Sporozoans (a group of protozoa to which the causative agent of malaria, Plasmodium falciparum, belongs); some algae
3. Sporulation (spore formation)	A spore is a single-celled reproductive unit of microscopic size, consisting of a nucleus and a small amount of cytoplasm. Spores can be formed by mitosis or meiosis. There are also sexual spores (Chlamydomonas zoospores), they perform the functions of gametes.	Algae, mosses, ferns, horsetails, mosses; mushrooms
4. Budding	A new individual is formed in the form of an outgrowth (bud) on the body of the parent individual, and then separates from it, turning into an independent organism.	Coelenterate, unicellular fungi (yeasts)
5. Fragmentation	The division of an individual into two or more parts, each of which grows and gives rise to a new organism. This method is based on the ability of organisms to regenerate (restore missing body parts).	Planarian flatworm (under unfavorable conditions); nemerteans (sea worms); filamentous algae (spirogyra)
6. Vegetative propagation	Reproduction by individual organs, parts of organs or body. Often plants form structures specifically designed for this: s bulbs(short stem, fleshy leaves); s corms(swollen underground stem, no fleshy leaves); s rhizome(underground stem growing horizontally); s stolon(a creeping horizontal stem spreading along the surface of the soil; s mustache (lash)– varieties of stolons that grow rapidly in length; s tuber(underground storage shoot); s root tubers (cones) – swollen adventitious roots; s fleshy tap roots; s leaves.	tulip, daffodil, onion; saffron, gladiolus; iris, wheatgrass, aster, mint; blackberries, gooseberries, black and red currants; strawberries, creeping buttercup; potato; dahlias;
7. Cloning	Growing an individual genetically identical to a given organism by transplanting the nucleus from a somatic cell into an egg from which the nucleus has previously been removed.	Higher plants and some animals.

Asexual reproduction evolutionarily arose before sexual , is a very effective process.

The meaning of asexual reproduction:

Advantages of asexual reproduction:

Disadvantages of asexual reproduction:

1. Only one parent required . Sexual reproduction involves two individuals, and this involves spending time and energy searching for a partner or, in immobile organisms (plants), special mechanisms, such as pollination, during which many gametes die. 2. Genetically identical offspring . If the species is well adapted to living conditions, this is an advantage, since successful combinations of genes are preserved. 3. Settlement and distribution of the species . Microscopic and light spores are carried by wind over long distances, fast growth rhizomes, etc. 4. Reproduction speed . Under favorable conditions, the number of the species increases rapidly

1. Lack of genetic variability among descendants. 2. If reproduction involves the production of spores, then many of them fail to find a suitable place for germination, so the energy and materials spent on their creation are wasted. 3. If a species spreads into one area, overpopulation and depletion may occur nutrients.

II. Sexual reproduction - the process of obtaining offspring as a result of the fusion of genetic material from the haploid nuclei of two gametes.

Gametes - sex haploid cells.

Sperm - male gametes.

Ovules - female gametes.

Fertilization - process of gamete fusion.

Zygote - the result of the fusion of gametes (fertilized egg), the first diploid cell of the future organism.

Species that have separate male and female individuals are called dioecious (most animals and humans).

Species in which the same individual is capable of producing both male and female gametes are called bisexual (bisexual) or hermaphroditic (protozoa, coelenterates, flatworms, oligochaetes (earthworms), crustaceans, molluscs such as snails, some fish and lizards, most flowering plants).

Parthenogenesis (virgin reproduction) - one of the modifications of sexual reproduction in which the female gamete develops into a new individual without fertilization by the male gamete. Thus, parthenogenesis is sexual, but unisexual reproduction. Parthenogenesis occurs in both the animal and plant kingdoms.

Distinguish :

s facultative parthenogenesis, in which eggs can develop both after fertilization and without it (bees, ants, rotifers - females develop from fertilized eggs, and males from unfertilized eggs);

s obligate parthenogenesis (obligatory), in which eggs are capable only of parthenogenetic reproduction (Caucasian rock lizard).

In many species, parthenogenesis is cyclical, for example, in aphids, daphnia, rotifers, summer time Only females exist, and in the fall parthenogenesis gives way to reproduction with fertilization.

The basis of sexual reproduction is the process of formation of germ cells - gametogenesis .

Gametogenesis – the process of formation and development of germ cells.

Spermatogenesis – the process of formation of male reproductive cells – sperm.

Oogenesis (oogenesis) – the process of formation of female reproductive cells – eggs.

In the process of formation of germ cells, a number of stages are distinguished:

gametogenesis	Type and phase of division	Spermatogenesis (in the testes)	Oogenesis (in the ovaries)
Reproduction		Primary germ cells divide by mitosis; diploid cells with single chromatid chromosomes are formed (2 n 2 c ) – gametocytes I order (spermatocytes and oocytes)
	Interphase	Gametocytes of the first order increase in size. DNA synthesis occurs and the second chromatid is completed; diploid cells with bichromatid chromosomes are formed (2 n 4 c )
Maturation		spermatocytes I order share with education spermatocytes II order ( n 2 c ) . As a result of the second division, four haploid cells are formed spermatids – cells with single chromatid chromosomes ( nc ) .	During the first (reduction) division oocytes I order share with education oocytes II order ( n 2 c ) and directional corpuscle ( n 2 c ). During the second division, an egg is formed from a second-order oocyte ( nc ) and guide body ( nc ) ; from the first directional body - two new ones. As a result of meiosis, an egg and three directional (reduction) bodies are formed. All cells are haploid with single chromatid chromosomes. Reduction bodies soon die
Formation		Acquisition of a certain shape and size by cells, corresponding to their specific function
Formation of sperm: the Golgi apparatus is located at the anterior edge of the head, transforming into acrosome (releases enzymes that dissolve the egg membrane); mitochondria are compactly packed around the emerging flagellum, forming a neck.	Increasing the amount of yolk. In many animals - the formation of additional membranes (protecting the egg and developing embryo from adverse effects)

Fertilization – the process of fusion of a sperm with an egg and the formation of a fertilized egg – zygotes .

Zygote – the initial single-cell stage of development of a new organism.

III. Ontogenesis – individual development of an organism – the period of life of an individual from the moment of formation of the zygote until the death of the organism. During the process of ontogenesis, hereditary information received from parents is realized.

Ontogenesis includes two periods:

Embryonic period - from the formation of the zygote to birth or exit from the egg membranes. Postembryonic period - from birth to death of the organism.

The embryonic period includes three main stages:

Splitting up – formation of a single-layer multicellular embryo as a result of mitotic division of the zygote.

At the stage of two germ layers, development ends in sponges and coelenterates. In other animals, the third germ layer is formed - mesoderm – from the endoderm and is located between the ectoderm and endoderm.

During gastrulation, cell differentiation begins organogenesis :

from ectoderm :

s nervous system;

s components of the organs of vision, hearing, smell;

s skin epithelium and its derivatives (milk, sweat and sebaceous glands, hair, feathers, nails, tooth enamel);

s anterior and posterior sections digestive system(epithelium of the oral cavity and rectum);

s external gills;

s thyroid gland;

from endoderm:

s epithelium of the digestive, respiratory and genitourinary systems;

s digestive glands (liver, pancreas);

from mesoderm:

s cartilage and bone skeleton;

s muscle tissue (striated skeletal and smooth muscle internal organs);

s circulatory system and blood;

s excretory system;

s gonads;

s all connective tissue;

s adrenal glands.

U different types In animals, the same germ layers give rise to the same organs and tissues. So they homologous . Homology – proof of the unity of origin of the animal world.

The postembryonic period is of two types:

Direct postembryonic development– occurs without transformation, when the born organism resembles an adult individual and differs only in size, underdevelopment of a number of organs and body proportions (birds, mammals, reptiles, some insects, crustaceans, etc.) Indirect postembryonic development– proceeds with metamorphosis, i.e. with transformation into an adult. The larva is adapted to active feeding, movement, growth and development, but cannot reproduce (exception: the axolotl - the larva of the amphibian ambystoma - with a lack of thyroid hormone, does not turn into an adult, but is able to reproduce at this stage). The biological meaning of metamorphosis is that larvae and adults feed on different foods and are adapted to different conditions, which eliminates competition between them and promotes the survival of the young.

The postembryonic period ends with aging and death.

Reproduction is the ability of all living beings to leave offspring with a similar structure and life processes. There are 2 main methods of reproduction - asexual and sexual.

Asexual reproduction

In asexual division, where only one individual is involved, the reproduction process occurs without the formation of gametes. Offspring are formed by budding from the mother’s body or being deposited in special organs.

The following types of asexual reproduction exist:

Division- predominantly found in simple organisms, in which the original mother cell divides into two parts, forming an identical daughter generation.

The following subspecies are distinguished:

• Division in two is characteristic of prenuclear species;
• mitotic division - found in protozoa;
• multiple fission is a typical phenomenon for Plasmodium falciparum.

Budding- characterized by the formation of daughter organisms in the form of protrusions on the mother’s body. After maturation, they separate from the parent’s body and further develop independently. If the daughter forms do not bud and maintain contact with the mother organism, colonies are formed (representatives of the cnidarian type).

Fragmentation- a process in which mature individuals develop from individual parts of the body of an adult (protostomes, chirophyte algae, water plague). Fragmentation is possible due to the regenerative abilities of the body.

Polyembryony- new individuals are formed when the embryo divides into several parts (identical twins).

Vegetative reproduction - the birth of new individuals comes from individual organs of the mother's body. The formation of a young plant is possible from the root system, branches or leaves (rarely).

The root serves as the basis for the formation of adventitious buds, from which above-ground shoots develop. Newly formed shoots are attached to the soil with the help of additional roots. After the death of the mother root, the sprouted plants begin independent life.

Vegetative propagation contributes to the rapid spread of viburnum, thistle, and fireweed. Plants from the legume family or the genus Loosestrife reproduce using surface shoots that spread along the ground and additional roots sprout in places where the soil and shoot nodes come into contact. This is how the plant begins to develop independently.

Sporulation- characteristic of some protozoa and plants that can form spores. Spore cells, entering a humid environment, develop and reach maturity. The formation of spore cells occurs in sporangia - special organs of angiosperms. In fungi and algae, spores are formed from all cells of the body.

Cloning- one of the types of asexual reproduction used by scientists to copy the original genetic material. This is how identical copies are obtained from maternal individuals.

The role of asexual reproduction

Organisms that reproduce asexually adapt well to gradually changing conditions environment. Their offspring are always multiple, quickly mature and begin to divide, which contributes to the growth of the population. Well-known species with asexual reproduction: hydra, amoeba, yeast fungi.

All cells of our body are constantly renewed, this is possible thanks to asexual reproduction. Somatic cells divide during the process of mitosis.

Given the rapid rates of maturation and division, plants and animals that divide asexually are often used by plant breeders.

Sexual reproduction

Sexual reproduction occurs through the interaction of a pair of opposite-sex individuals. They have a reproductive system where sex cells - gametes - are formed. Females are characterized by the formation of eggs, and males - sperm.

The formation of germ cells is called gametogenesis, the main point of their formation is meiosis. During the fusion of gametes, fertilization and the birth of a new life occur. The formed zygote will not be an exact version of the parents, because the process of meiosis involves rearrangement of genetic information.

Using the example of hydra

The gametes of different representatives differ from each other, therefore the following forms of sexual reproduction are distinguished: homogamy, anisogamy and oogamy.

Homogamy- the division of gametes into male and female is conventional, because the germ cells of organisms of different sexes have an identical structure and shape.

Anisogamy- germ cells of both sexes can move. Eggs are larger than sperm, but they are almost immobile.

Oogamy- female gametes cannot move independently and are much larger than male ones.

Oogamy is the most common, characteristic of many representatives of the animal and plant world. Homogamy and anisogamy are inherent in the simplest species (photoautotrophic unicellular organisms).

Certain types of algae and fungi can reproduce without forming gametes; these forms of division are called: hologamy and conjugation.

In progress hologamy single-celled individuals with a single set of chromatids merge with each other, thereby taking on the role of germ cells. The newly formed zygote then divides meiotically, forming 4 haploid individuals.

Division by conjugation characteristic of fungi, in which fusion occurs between the haploid cells of the thallus filaments. After the exchange of information, diploid germ cells are formed.

The role of sexual reproduction

Sexual reproduction is an important natural phenomenon that provides a high level of variability and makes it possible to survive in dramatically changing conditions. That is why sexual reproduction superior to asexual, in which all remaining offspring inherit an exact copy of the parents' genome.

During sexual division, the genetic code is rearranged, which is manifested by a variety of characteristics in the descendants. The emergence of new characteristics and adaptation mechanisms is the basis for evolutionary processes. Therefore, sexual reproduction occupies a central position in nature.

Reproduction is the property of organisms to leave offspring.

Forms of asexual reproduction, definition, essence, biological significance.

Two forms of reproduction: sexual and asexual.

Sexual reproduction is a change of generations and the development of organisms based on the fusion of specialized germ cells and the formation of a zygote.

With asexual reproduction, a new individual appears from unspecialized cells: somatic, asexual; bodies.

Asexual reproduction, or agamogenesis, is a form of reproduction in which an organism reproduces itself independently, without any participation of another individual.

Reproduction by division

Division is primarily characteristic of unicellular organisms. As a rule, it is carried out by simply dividing the cell in two. In some protozoa, for example, foraminifera, division occurs into a larger number of cells. In all cases, the resulting cells are completely identical to the original one. The extreme simplicity of this method of reproduction, associated with the relative simplicity of the organization of single-celled organisms, allows reproduction very quickly. Thus, under favorable conditions, the number of bacteria can double every 30-60 minutes. An organism that reproduces asexually is capable of endlessly reproducing itself until a spontaneous change in the genetic material occurs - a mutation. If this mutation is favorable, it will be preserved in the offspring of the mutated cell, which will represent a new cell clone. Same-sex reproduction involves one parent organism, which is capable of forming many organisms identical to it.

Reproduction by spores

Asexual reproduction of bacteria is often preceded by the formation of spores. Bacterial spores are resting cells with reduced metabolism, surrounded by a multilayered membrane, resistant to desiccation and other unfavorable conditions that cause the death of ordinary cells. Sporulation serves both to survive such conditions and to spread bacteria: once in a suitable environment, the spore germinates, turning into a vegetative dividing cell.
Asexual reproduction with the help of unicellular spores is also characteristic of various fungi and algae. Spores in many cases are formed by mitosis of mitospores, and sometimes especially in fungi in huge quantities; upon germination, they reproduce the mother's organism. Some fungi, such as the harmful plant pest Phytophthora, form motile spores equipped with flagella, called zoospores or wanderers. After floating in droplets of moisture for some time, such a wanderer “calms down”, loses its flagella, becomes covered with a dense shell and then, under favorable conditions, germinates.

Vegetative propagation

Another option for asexual reproduction is carried out by separating from the body a part of it, consisting of a larger or smaller number of cells. From them the adult organism develops. An example is budding in sponges and coelenterates or propagation of plants by shoots, cuttings, bulbs or tubers. This form of asexual reproduction is usually called vegetative reproduction. It is fundamentally similar to the regeneration process. Vegetative propagation plays an important role in plant growing practices. So, it may happen that a sown plant, for example an apple tree, has some successful combination of characteristics. In the seeds of a given plant, this successful combination will almost certainly be disrupted, since seeds are formed as a result of sexual reproduction, and this is associated with gene recombination. Therefore, when growing apple trees, vegetative propagation is usually used - by layering, cuttings or grafting buds onto other trees.

Budding

Some species of unicellular organisms are characterized by a form of asexual reproduction called budding. In this case, mitotic division of the nucleus occurs. One of the resulting nuclei moves into the emerging local protrusion of the mother cell, and then this fragment buds off. The daughter cell is significantly smaller than the mother cell, and it takes some time for it to grow and complete the missing structures, after which it takes on the appearance characteristic of a mature organism. Budding is a type of vegetative propagation. Many lower fungi, such as yeast and even multicellular animals, such as freshwater hydra, reproduce by budding. When yeast budding, a thickening forms on the cell, which gradually turns into a full-fledged daughter yeast cell. On the hydra’s body, several cells begin to divide, and gradually a small hydra grows on the mother individual, which forms a mouth with tentacles and an intestinal cavity connected to the intestinal cavity of the “mother.”

Fragmentation body division

Some organisms can reproduce by dividing the body into several parts, and from each part a full-fledged organism grows, similar in all respects to the parent individual (flatworms, annelids, and echinoderms).

Sexual reproduction is a process in most eukaryotes associated with the development of new organisms from germ cells.

The formation of germ cells, as a rule, is associated with the passage of meiosis at some stage of the life cycle of the organism. In most cases, sexual reproduction is accompanied by the fusion of germ cells, or gametes, and a double set of chromosomes, relative to gametes, is restored. Depending on the systematic position of eukaryotic organisms, sexual reproduction has its own characteristics, but as a rule, it allows the genetic material from two parent organisms to be combined and produces offspring with a combination of properties not found in the parental forms.

The effectiveness of combining genetic material in descendants obtained as a result of sexual reproduction is facilitated by:
chance meeting of two gametes

random arrangement and divergence to division poles of homologous chromosomes during meiosis

crossing over between chromatids.

This form of sexual reproduction, known as parthenogenesis, does not involve the fusion of gametes. But since the organism develops from the germ cell of the oocyte, parthenogenesis is still considered sexual reproduction.
In many groups of eukaryotes, the secondary disappearance of sexual reproduction has occurred, or it occurs very rarely. In particular, the department of deuteromycetes includes a large group of phylogenetic ascomycetes and basidiomycetes that have lost the sexual process. Until 1888, it was assumed that among terrestrial higher plants, sexual reproduction was completely lost in sugarcane. The loss of sexual reproduction has not been described in any group of metazoans. However, many species of lower crustaceans are known - daphnia, some types of worms, capable of reproducing parthenogenetically under favorable conditions for tens and hundreds of generations. For example, some species of rotifers reproduce only parthenogenetically for millions of years, even forming new species!
In a number of polypliodic organisms with an odd number of sets of chromosomes, sexual reproduction plays a small role in maintaining genetic variability in the population due to the formation of unbalanced sets of chromosomes in gametes and descendants.
The ability to combine genetic material during sexual reproduction has great importance for the selection of model and economically important organisms.

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 individual development 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.

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 dispersal 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 by 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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