What forms of reproduction of organisms do you know. Forms of reproduction of organisms
Is the oldest?
2. Are all living beings capable of reproduction?
Reproduction is a universal property of living organisms, which consists in the ability produce similar individuals of their own species. Thanks to reproduction, there is an endless change of generations of each species. In the process of reproduction, unique combinations of genetic material can occur, resulting in the appearance of hereditary changes in the body. Thus, the genetic diversity of individuals within the same species arises and the foundations for the variability and further evolution of the species are laid.
Reproduction is a necessary condition for the existence of life on Earth.
Asexual reproduction.
The oldest form of reproduction on our planet is asexual reproduction. It consists in the division of a unicellular organism (or one or more cells of a multicellular organism) and the formation of daughter individuals. This form of reproduction is more common in prokaryotes, plants, fungi and protozoa, it is also observed in some animal species.
Types of asexual reproduction.
Consider the main types of asexual reproduction.
Reproduction by division.
In prokaryotes, before division, the only ring doubles, a partition appears between the two daughter chromosomes, and the cell divides in two.
Many unicellular algae (for example, chlamydomonas, green euglena) and protozoa (amoeba) divide by mitosis, forming two cells.
Reproduction by spores.
Spores are specialized haploid cells of fungi and plants (not to be confused with spores bacteria), serving for reproduction and resettlement. In fungi and lower plants, spores are formed by mitosis, in higher plants- as a result of meiosis.
In seed plants, spores have lost the function of settling, but are a necessary step cycle playback.
vegetative reproduction.
The methods of asexual reproduction presented above are united by the fact that in all these cases a new organism develops from a single cell of a unicellular or multicellular parent. However, very often during asexual reproduction of multicellular organisms, the offspring develops from a group of parental cells. This method of asexual reproduction is called vegetative. There are several types of vegetative propagation. The first of these is the reproduction of plants by parts of vegetative organs (part of the thallus, stem cutting, root cutting) or special modifications of shoots (rhizome, bulb, tuber).
Another type of vegetative propagation is fragmentation, a process based on regeneration.
So, for example, a fragment of the body of an earthworm gives rise to a whole individual. However, it should be borne in mind that fragmentation is rare under natural conditions, in particular, in polychaete worms, mold fungi, and some algae (spirogyra).
The third type of vegetative propagation is budding.
In this case, a group of cells of the parent individual begins to divide in concert, giving rise to a daughter individual, which develops for some time as part of the mother organism, and then separates from it (freshwater hydra) or forms colonies of many individuals (coral polyps).
Importance of asexual reproduction.
Asexual reproduction allows you to quickly increase the number of individuals of this species in favorable conditions. But with this method of reproduction, all descendants have a genotype identical to the parent. Consequently, with asexual reproduction, there is practically no increase in genetic diversity, which could be very useful if necessary to adapt to changed living conditions. For this reason, the vast majority of living organisms periodically or constantly reproduce sexually.
Asexual reproduction. vegetative reproduction.
1. What kind of reproduction is called asexual?
2. What types of asexual reproduction are distinguished?
3. What is the biological significance of asexual reproduction?
A special type of vegetative reproduction of organisms is polyembryony. In this case, the embryo (embryo) of higher animals shortly after formation is divided into several fragments, each of which independently develops into a full-fledged individual. Such division of embryos is found, for example, in armadillos. Polyembryony also includes the formation of identical twins in humans. In this case, the zygote resulting from the usual fertilization, breaking up, forms an embryo, which, for reasons not yet fully understood, is divided into several parts. Each of these parts goes through the path of a normal embryonic development, resulting in the birth of two or more practically identical babies, always of the same sex. The birth rate of identical twins does not exceed one in 250 normal births. But sometimes the separation of the emerging embryo is incomplete. In this case, organisms arise that have common parts of the body or internal organs. Such identical twins are usually called Siamese, in honor of Chang and Eng Bunker, who were born in Thailand (then Siam) (Fig. 50), Chang and Eng were connected in the chest area by a dense ligament about 9 cm thick. Even in those years they were probably , could have been surgically separated, but they did not agree to this. By marrying two American sisters, they became prosperous farmers. Their wives had a total of 22 children. Sometimes nature makes more serious mistakes. In France, a teenage girl suffering from anemia and curvature of the spine, during a medical examination, was unexpectedly found in the abdominal cavity of a baby fetus.
However, this embryo was not in the uterus, but was connected by blood vessels to the vessels of the abdominal cavity, since the embryo grew rapidly, it had to be removed surgically, otherwise its “mother” would have died. The embryo reached 30 cm in length. How could such a mistake of nature have arisen? Apparently, one of the cells in the girl's abdominal cavity began to split up in the same way as a zygote splits up after fertilization, and gave rise to a new human organism. However, the fetus was doomed from the start, and it would never have been able to turn into a full-fledged healthy child, as it developed in the wrong place, and was not supplied with the necessary hormones and nutrients. After the removal of the embryo, the girl quickly recovered and her internal organs, squeezed by the growing embryo, began to develop normally.
Kamensky A. A., Kriksunov E. V., Pasechnik V. V. Biology Grade 10
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reproduction- the property of living organisms to reproduce their own kind. There are two main breeding method- asexual and sexual.
Asexual reproduction is carried out with the participation of only one parent and occurs without the formation of gametes. The daughter generation in some species arises from one or a group of cells of the parent organism, in other species - in specialized organs. There are the following methods of asexual reproduction: fission, budding, fragmentation, polyembryony, spore formation, vegetative reproduction.
Division- a method of asexual reproduction, characteristic of unicellular organisms, in which the mother individual is divided into two or more daughter cells. We can distinguish: a) simple binary fission (prokaryotes), b) mitotic binary fission (protozoa, unicellular algae), c) multiple fission, or schizogony (malarial plasmodium, trypanosomes). During the division of paramecium (1), the micronucleus is divided by mitosis, the macronucleus by amitosis. During schizogony (2), the nucleus first divides repeatedly by mitosis, then each of the daughter nuclei is surrounded by cytoplasm, and several independent organisms are formed.
budding- a method of asexual reproduction, in which new individuals are formed in the form of outgrowths on the body of the parent individual (3). Daughter individuals can separate from the mother and move on to an independent lifestyle (hydra, yeast), they can remain attached to it, forming colonies in this case (coral polyps).
Fragmentation(4) - a method of asexual reproduction, in which new individuals are formed from fragments (parts) into which the parent individual breaks up (annelids, starfish, spirogyra, elodea). Fragmentation is based on the ability of organisms to regenerate.
Polyembryony- a method of asexual reproduction, in which new individuals are formed from fragments (parts) into which the embryo breaks up (monozygous twins).
Vegetative reproduction- a method of asexual reproduction, in which new individuals are formed either from parts of the vegetative body of the mother individual, or from special structures (rhizome, tuber, etc.) specially designed for this form of reproduction. Vegetative propagation is characteristic of many groups of plants, it is used in horticulture, horticulture, plant breeding (artificial vegetative propagation).
| Vegetative organ | Method of vegetative propagation | Examples |
|---|---|---|
| Root | root cuttings | Rosehip, raspberry, aspen, willow, dandelion |
| Root offspring | Cherry, plum, thistle, thistle, lilac | |
| Aerial parts of shoots | The division of the bushes | Phlox, daisy, primrose, rhubarb |
| stem cuttings | Grapes, currants, gooseberries | |
| layering | Gooseberries, grapes, bird cherry | |
| Underground parts of shoots | Rhizome | Asparagus, bamboo, iris, lily of the valley |
| Tuber | Potato, weekday, Jerusalem artichoke | |
| Bulb | Onion, garlic, tulip, hyacinth | |
| Corm | Gladiolus, crocus | |
| Sheet | leaf cuttings | Begonia, Gloxinia, Coleus |
sporulation(6) - reproduction through spores. controversy- specialized cells, in most species are formed in special organs - sporangia. In higher plants, spore formation is preceded by meiosis.
Cloning- a set of methods used by humans to obtain genetically identical copies of cells or individuals. Clone- a set of cells or individuals descended from a common ancestor through asexual reproduction. Cloning is based on mitosis (in bacteria, simple division).
sexual reproduction is carried out with the participation of two parent individuals (male and female), in which specialized cells are formed in special organs - gametes. The process of formation of gametes is called gametogenesis, the main stage of gametogenesis is meiosis. The daughter generation develops from zygotes- a cell formed as a result of the fusion of male and female gametes. The process of fusion of male and female gametes is called fertilization. An obligatory consequence of sexual reproduction is the recombination of genetic material in the daughter generation.
Depending on the structural features of gametes, the following can be distinguished forms of sexual reproduction: isogamy, heterogamy and ovogamy.
isogamy(1) - a form of sexual reproduction in which gametes (conditionally female and conditionally male) are mobile and have the same morphology and size.
Heterogamy(2) - a form of sexual reproduction in which female and male gametes are mobile, but female are larger than male and less mobile.
Ovogamy(3) - a form of sexual reproduction in which the female gametes are immobile and larger than the male gametes. In this case, the female gametes are called eggs, male gametes, if they have flagella, - spermatozoa if they don't have - sperm.
Ovogamy is characteristic of most animal and plant species. Isogamy and heterogamy are found in some primitive organisms (algae). In addition to the above, some algae and fungi have forms of reproduction in which germ cells are not formed: chologamy and conjugation. At chologamy unicellular haploid organisms merge with each other, which in this case act as gametes. The resulting diploid zygote then divides by meiosis to form four haploid organisms. At conjugations(4) the contents of individual haploid cells of the filamentous thalli are fused. Through specially formed channels, the contents of one cell flows into another, a diploid zygote is formed, which usually also divides by meiosis after a dormant period.
Go to lectures №13"Methods of division of eukaryotic cells: mitosis, meiosis, amitosis"
Go to lectures №15"Sexual reproduction in angiosperms"
The ability of living beings to reproduce their own kind is called reproduction. In this case, the genetic material is passed on to offspring, and parental traits to one degree or another will be inherent in the resulting daughter organisms.
Types of reproduction of offspring
Scientists distinguish two main forms of reproduction of organisms. It can be sexual or asexual. In the first case, 2 individuals are needed to reproduce the offspring, and in the second, only one is enough.
In asexual reproduction, a new organism arises from somatic cells. In nature, there are several ways to reproduce offspring without the participation of the genitals. These include vegetative reproduction, budding, fragmentation, sporulation, division, and cloning.
In sexual reproduction, new organisms appear as a result of the fusion of specialized germ cells called gametes, and the subsequent formation of a zygote. This method is more progressive than asexual.
Benefits Comparison
It is worth noting that both methods of reproduction of offspring have their advantages. For example, biologists highlight the following advantages of asexual reproduction:
- the ability to reproduce a significant number of individuals;
- offspring are similar to the parent organism in all respects.
This method of reproduction of new individuals makes it possible to quickly obtain numerous benefits for species that live in constant conditions. It is the rapid, numerous and accurate reproduction of copies of the mother's organism that is the meaning of asexual reproduction. This method of obtaining offspring is used by both plants and protozoa.
But sexual reproduction is characteristic of the predominant majority of living beings. It is able to guarantee the genetic diversity of the resulting offspring. This is what allows them to quickly adapt to changing living conditions. Indeed, during the formation of a new organism, a combination of the genes of the parents occurs.
Types of asexual reproduction of offspring
There are several ways to obtain daughter organisms without the participation of germ cells. All of them are studied by biology. Reproduction, in which the types of daughter organisms do not change in any way, can be carried out on the basis of the division of one or more cells.
In the first case, the following forms are distinguished:
- single or multiple (schizogony) cell division;
- spore formation;
- budding of unicellular organisms.
When dividing a group of cells, the classification is carried out as follows:
- fragmentation;
- budding of multicellular organisms (for example, hydra).
Each of these types of asexual reproduction has its own characteristics.
Forms of reproduction
The simplest option is the usual division. It is characteristic of many protozoa. Examples of asexual reproduction by binary fission: amoeba, ciliate shoe,
Spore formation is considered widespread. It is characteristic of almost all plants, fungi, some protozoa and prokaryotic organisms (for example, bacteria or blue-green algae).
But other examples of asexual reproduction of organisms can be cited. So, do not forget about fragmentation. In this process, the mother individual is divided into several parts. From each of them a new organism is formed. For example, the filamentous alga Spirogyra can be torn anywhere. From two parts in the future, two new organisms will turn out.
Plants are characterized by vegetative reproduction. According to the principle of the processes, it does not differ from budding or fragmentation. The plant can form special structures necessary for reproduction. Also, the appearance of a daughter organism is possible from a part of the mother's organism.
sexual reproduction
Most living beings reproduce their own similar organisms by mixing the genetic material of two individuals. To do this, two gametes merge, and as a result a diploid zygote is formed. In the process of development, a full-fledged new organism is obtained from it. Sexual forms of reproduction of organisms are characteristic of some flowering plants, most animals and, of course, humans.
Gametes are of two types - male and female. If the species is dioecious, then each of the cell types is produced respectively by male and female individuals. Some organisms are able to produce both types of gametes on their own. In this case, they are called hermaphrodites.
A variant of sexual reproduction is also possible, in which gametes do not participate. These are such types as conjugation, gametangiogamy, apogamy, hologamy.
breeding process
All organisms are made up of cells. Their growth and development are possible due to the fact that they are constantly reproduced. During life, some cells age and die. They are replaced by others. The only way to obtain new cells is to divide their precursors. This is a vital process for every living being. For example, in human body several million of these structural units are divided every second.
Biologists have described three methods for cell reproduction. Direct division is called amitosis, indirect - mitosis, reduction - meiosis. Regardless of the form of reproduction of organisms, these processes occur in each of them.
Amitosis and mitosis
The least common and poorly studied method of cell division is amitosis. In this process, the nucleus is separated by a constriction. At the same time, it is impossible to ensure a uniform distribution of genetic material. A cell that has divided by amitosis, in most cases, cannot continue to enter the normal cycle of mitosis. Therefore, it is considered doomed to death.
Mitosis is the universal way of reproduction of eukaryotic cells. In animal cells, it passes, as a rule, for an hour. The biological significance of reproduction cannot be underestimated, because it is thanks to it that the development and growth of all organisms is ensured.
Stages of mitosis
The sequence of all processes that occur during the formation of new cells is called the cell cycle. It consists of three stages: interphase, mitosis, cytokinesis. The duration of the cycle depends both on the types of cells and on external factors. Affects temperature, availability of nutrients, oxygen. For example, in the intestinal epithelium, such formation of new cells occurs every 8-10 minutes, in bacteria - every 20 minutes.
The process begins with interphase. At this time there are processes of intensive growth. Substances are produced that contribute to the growth of the cell and the performance of all its assigned functions. During interphase, DNA replication occurs.
All the necessary substances for the implementation of these processes are stored during the preliminary stage - interphase. Each stage of division consists of four periods: prophase, metaphase, anaphase and telophase. The same phases take place during mitosis, but each of the processes has its own characteristics.
The first meiosis is a cell division in which the number of chromosomes is reduced by 2 times. From one diploid formation, two haploid ones appear. At this time, the processes of DNA helicalization take place, a fission spindle is formed. In addition, conjugation is carried out in the prophase. The resulting pairs form a bivalent. In some of its places, the chromatids intersect. This process is called crossover.
The final stage is the so-called second meiosis. This is a division in which cells are formed with a haploid set of chromosomes consisting of one chromatid. As a result of the described processes, 4 cells emerge from one diploid formation (oogony or spermatogony).
The biological significance of meiosis is the formation of cells that provide sexual reproduction in animals or sporulation in higher animals. It is this method of reproduction that guarantees the maintenance of the genetic constancy of the species.
Features of sexual and asexual reproduction of organisms
Depending on how cells divide to produce offspring, they secrete different types this process. Separately, it should be noted that the survival of many organisms in changing conditions is due precisely to the fact that they can combine different methods of reproduction.
Of course, sexual and asexual reproduction of similar organisms differ significantly. A table of types of reproduction will help you understand what the fundamental difference is.
Key points | asexual way | sexual way |
Number of parents | ||
breeding process | There is no meiotic stage, gametes are not formed | Meiosis is a mandatory stage that prevents the duplication of chromosomes in future generations. As a result, haploid gametes are obtained, the nuclei of which fuse and form a diploid zygote. |
Received offspring | Daughter individuals are identical to the parent, genetic variability is possible only with random mutations | The offspring are different from the parents, there is genetic variability. It appears due to the recombination of genes. |
Organisms that have a characteristic mode of reproduction | lower animals, microorganisms | Most plants and animals |
It is clear that the sexual forms of reproduction of organisms are more perfect. But the asexual method guarantees the rapid reproduction of a large number of offspring. During sexual reproduction, the number of daughter organisms does not grow so intensively.
All known methods of reproduction of organisms in nature are reduced to two main forms: asexual and sexual.
asexual reproduction. In the asexual form, reproduction is carried out by the parent individual independently, without the exchange of hereditary information with other individuals. A daughter organism is formed by separating one or more somatic (corporeal) cells from the parent individual and their further reproduction through mitosis. The offspring inherits the traits of the parent, being genetically its exact copy. There are several types of asexual reproduction.
Simple division. Asexual reproduction is especially common in bacteria and blue-green algae. The only cell of these non-nuclear organisms is divided in half or at once into several parts. Each part is a complete functional organism.
Amoeba, ciliates, euglena and other protozoa reproduce by simple division. Separation occurs through mitosis, so the daughter organisms receive the same set of chromosomes from the parent.
budding. This type of reproduction is used by both unicellular and some multicellular organisms: yeast (lower fungi), ciliates, coral polyps.
budding in freshwater hydras, it occurs as follows. First, an outgrowth forms on the wall of the hydra, which gradually lengthens. At its end, tentacles and a mouth opening appear. A small hydra grows from the kidney, which separates and becomes an independent organism. In other creatures, the kidneys may remain on the body of the parent.
Fragmentation. A number of flat and annelids, echinoderms (starfish) can reproduce by dividing the body into several fragments, which are then completed to a complete organism. Fragmentation is based on the ability of many simple creatures to regenerate lost organs. So, if a ray is separated from a starfish, then a starfish will again develop from it. Hydra is able to recover from 1/200 of its body. Typically, reproduction by fragmentation occurs when damaged. Spontaneous fragmentation is carried out only by mold fungi and some marine annelids.
sporulation. The ancestor of a new organism can be a specialized cell of the parent creature - a spore. This method of reproduction is typical for plants and fungi. Multicellular algae, mosses, ferns, horsetails and club mosses reproduce by spores.
Spores are cells covered with a strong membrane that protects them from excessive moisture loss and is resistant to temperature and chemical influences. Spores of land plants are passively carried by wind, water, living beings. Once in favorable conditions, the spore opens the shell and proceeds to mitosis, forming a new organism. Algae and some fungi that live in water reproduce by zoospores equipped with flagella for active movement.
A single-celled animal, the malarial Plasmodium (the causative agent of malaria), reproduces through schizogony - multiple division. First, in his cell, by division, it is formed a large number of nuclei, then the cell breaks up into many subsidiaries.
vegetative reproduction. This type of asexual reproduction is widespread in plants. Unlike sporulation, vegetative reproduction is carried out not by special specialized cells, but by almost any part of the vegetative organs.
Perennial wild grasses propagate by rhizomes (thistle gives up to 1800 specimens/m2 of soil), strawberries - by mustaches, and grapes, currants and plums - by layering. Potatoes and dahlias use tubers for propagation - modified underground sections of the root. Tulips and onions reproduce by bulbs. In trees and shrubs, shoots - cuttings - take root with the formation of a new plant, and in begonias, leaves can play the role of cuttings. Raspberries, plums, cherries and roses are propagated by cuttings. On the roots and stumps of trees, shoots form, which then turn into independent plants.
sexual reproduction. Sexual reproduction, unlike asexual reproduction, involves a pair of individuals. Their sex cells (gametes) carry haploid sets of chromosomes. In the process of fertilization, gametes fuse and form a diploid fertilized egg (zygote), which gives rise to a new organism.
One of the homologous chromosomes of a somatic cell comes from the "mom", and the other from the "dad". As a result, parts of the genetic material of the parent individuals are combined, and new combinations of genes appear in the offspring. The diversity of genetic material allows the offspring to more successfully adapt to changing external conditions. Enrichment of hereditary information is the main advantage of sexual reproduction, its main biological significance.
Bisexual plants have a number of features that exclude self-fertilization. The stamens and pistils of bisexual flowers do not ripen at the same time, so it is cross-pollination of different individuals that occurs. Cannabis has separate male pistillate and female staminate flowers on different individuals.
The development of sex cells. The formation of germ cells (gametogenesis) occurs in the sex glands. The development of female gametes (eggs) occurs in the ovaries and lats. ovum egg + genesis origin). Men's<носит название овогенеза (гаметы (сперматозоиды) формируются в семенниках в процессе сперматогенеза. Половые железы практически всех существ имеют трубчатое строение. Гаметогенез происходит последовательно в трех зонах: размножения, роста и созревания. Соответственно выделяют и три периода развития гамет.
In the initial period of reproduction, germ cells have a diploid set of chromosomes and divide through mitosis. Male gametes reproduce especially intensively. In males, germ cells are formed almost all their lives. The formation of mammalian eggs occurs only in the embryonic period, then they remain in a state of rest.
Once in the growth zone, germ cells no longer divide, but only grow. Male gametes do not grow too much, and the eggs increase in size hundreds, thousands and millions of times (remember a chicken egg - an egg). The outer shells of the egg reliably protect the developing fetus, through them, especially through the shell of bird eggs, bacteria and viruses do not penetrate, and the air passes freely.
Spermatozoa are much smaller than eggs. In mammals, they are in the form of a long thread with a head, neck and flagellum. The head contains chromosomes, and on its front part there is a Golgi complex with enzymes that dissolve the egg cell membrane and ensure the penetration of the spermatozoon nucleus (the shell remains outside). Male gametes not only contribute genetic information, but also initiate the development of the egg. In the neck there is a centriole, which forms the flagellum of the spermatozoon, allowing it to move intensively. The energy source for the movements of the flagellum is the ATP molecules stored in the neck. To replenish ATP, mitochondria are located in the neck.
After the gametes grow to the size of adult germ cells, they enter the maturation zone.
The basis of gamete maturation is the specific process of dividing each germ cell into four new ones. The maturation of eggs and sperm cells proceeds in a basically similar way, differences appear only at the last stage for the following reason. A sufficiently large number of spermatozoa is necessary for successful fertilization. Therefore, all four formed male cells are functional and viable. The main task of the egg is not only fertilization, but also the successful maturation of the fetus. To this end, the process of division occurs unequally: the entire yolk goes into one egg, and it turns out to be the only viable one. The remaining three fully functional eggs do not receive nutrients during maturation and soon die. They are called directional, or polar bodies.
The period of maturation of gametes, accompanied by a specific division of each of them into four new ones, is called meiosis.
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