In nature, there are two main methods of reproduction - sexual and asexual.
And, if with the first everything is somehow clear, then the types of asexual reproduction leave many perplexed. What is this?
Forms of asexual reproduction
Scientists classify asexual reproduction into the following categories: budding, fission, fragmentation, sporulation, vegetative reproduction. But, since not all types of living organisms living on Earth have been fully studied by scientists, it is possible that a new method of asexual reproduction will be discovered in the future.
Division is important primarily for unicellular organisms. Protozoa use the features of their bodies to bifurcate, followed by the emergence of life in each half. One individual eventually turns into two full-fledged organisms.
Fragmentation is somewhat similar to division: a creature is split into several simple parts that become new representatives of the species.
Budding is characteristic of primitive species. It involves the formation of a new individual from protrusions (they are called buds) on the body of the mother’s body. The budding creatures begin a full life cycle.
Palintomy is a process of randomly rapid division without going through the stages of growth and development.
Sporulation
Spores are reproductive, resting cells characterized by a negligibly low metabolic rate and the highest resistance.
Reproduction by spores involves the development of spores in vegetative cells under extremely favorable conditions. Mainly found in bacteria and plants.
Methods of vegetative propagation
Plant propagation by the development of individual parts is called vegetative.
There are several main types:
- Artificial. Achieved through anthropogenic influence on the process of reproduction of the species.
- Natural. Due to the natural course of the procreation procedure.
Such binary reproduction makes it possible to increase the likelihood of successful survival of kingdoms of organisms in an aggressive environment.
Biological role of asexual reproduction
Compared to sexual reproduction, asexual reproduction is characterized by the following advantages:
- takes less time, due to which the process of prolongation occurs faster;
- allows parent individuals to pass on the basic qualities of their organisms to the younger generation without changing the main genotype;
- due to its primitiveness, it facilitates the process of reproduction for lower forms of life.
Methods of asexual reproduction in the table
| Unicellular | Multicellular | Animals |
| Budding is the process of creating a younger individual from a growth on the body of the parent. Sporulation is reproduction by cellular spores. : This includes fission and fragmentation. |
Vegetative - mainly found in fungi and plants. Fragmentation is the splitting of the body into several parts, each of which grows into a full-fledged individual. Strogilation. Sporulation. Found in plants and fungi. Polyembryony. |
Vegetative is the only way of reproduction in animals using the asexual method. Budding is characteristic exclusively of sponges. The practical use of these methods is possible, but in practice it is usually not carried out. |
Comparison of sexual and asexual reproduction
Unlike sexual reproduction, asexual reproduction is more primitive, and therefore belongs to the lower ones.
It is also almost not inherent in animals; it practically does not occur in humans. In lower forms, this method predominates.
Also, sexual reproduction involves two individuals of the same species; asexual reproduction requires only one.
Somatic cells are involved in asexual prolongation of the genus; sexual prolongation is characterized by sexual ones.
Benefits of Asexual Reproduction
The main advantage of this is the rapid increase in the number of individuals to a specific species. This allows for guaranteed survival in a changing environment.
Another main advantage is the transfer of almost all parental qualities to children.
The lack of need for two participants in the biological process is also characteristic of asexual reproduction.
Features of asexual reproduction
These include:
- mitosis at the basis of asexual reproduction as the main difference from the sexual method;
- carrying out the process without the participation of germ cells;
- increase in the number of individuals in geometric progression.
Conclusion
Numerous studies have shown that asexual reproduction is characteristic of lower and unorganized forms of life.
However, it provides a stable influx of individuals to these species and occupies an important place in the field of biology.
In nature, there are two types of reproduction of organisms: asexual and sexual.
Asexual reproductionis 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 is based on mitosis. There are several forms of asexual reproduction.
Simple division or division in two, characteristic of unicellular organisms. From one cell, two daughter cells are formed through mitosis, each of which becomes a new organism.
Budding is a form of asexual reproduction in which a daughter organism is separated from the parent. This form is characteristic of yeast, hydra and some other animals.
In spore plants (algae, mosses, ferns), reproduction occurs with the help of dispute, special cells formed in the mother's body. Each spore, germinating, gives rise to a new organism.
Vegetative propagation- reproduction by individual organs, parts of organs or the body. It is based on the ability of organisms to restore missing parts of the body - regeneration. It is found in plants (reproduction by stems, leaves, shoots), and in lower invertebrate animals (coelenterates, flatworms and annelids).
Sexual reproduction– is the formation of a new organism with the participation of two parent individuals. The new organism carries hereditary information from both parents.
During sexual reproduction, the fusion of germ cells occurs - gametes male and female body. Sex cells are formed as a result of a special type of division. In this case, unlike the cells of an adult organism, which carry a diploid (double) set of chromosomes, the resulting gametes have a haploid (single) set. As a result of fertilization, the paired, diploid set of chromosomes is restored. One chromosome of the pair is paternal, and the other is maternal. Gametes are formed in the gonads or in specialized cells during the process of meiosis.
Meiosis- this is a cell division in which the chromosome set of the cell is halved (Fig. 56). This division is called reductionist.
Rice. 56. Phases of meiosis: A – first division; B – second division. 1, 2 – prophase I; 3 – metaphase I; 4 – anaphase I; 5 – telophase I; 6 – prophase II; 7 – metaphase II; 8 – anaphase II; 9 – telophase II
Meiosis is characterized by the same stages as mitosis, but the process consists of two successive divisions (meiosis I and meiosis II). As a result, not two, but four cells are formed. The biological meaning of meiosis is to ensure the constancy of the number of chromosomes in newly formed organisms during fertilization. Female reproductive cell - egg, always large, contains many nutrients, often immobile.
Male reproductive cells - sperm, small, often mobile, have flagella, they are produced in much greater numbers than eggs. In seed plants, male gametes are immobile and are called sperm.
Fertilization- the process of fusion of male and female reproductive cells, resulting in the formation zygote.
From the zygote an embryo develops, which gives rise to a new organism.
Fertilization can be external or internal. External fertilization characteristic of water inhabitants. Sex cells exit into the external environment and fuse outside the body (fish, amphibians, algae). Internal fertilization characteristic of terrestrial organisms. Fertilization occurs in the female genital organs. The embryo can develop both in the body of the mother’s body (mammals) and outside it - in the egg (birds, reptiles, insects).
The biological significance of fertilization is that during the fusion of gametes, the diploid set of chromosomes is restored, and the new organism carries hereditary information and characteristics of two parents. This increases the variety of characteristics of organisms and increases their vitality.
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 environmental conditions. 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. This is why sexual reproduction is superior to asexual reproduction, in which all offspring left behind will 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.
Is it the oldest?
2. Are all living things capable of reproduction?
Reproduction is a universal property of living organisms, consisting in the ability produce similar individuals of their own species. Thanks to reproduction, there is an endless change of generations of each species. During the process of reproduction, unique combinations of genetic material may arise, leading to the appearance of hereditary changes in the body. Thus, genetic diversity of individuals within one species arises and the foundations for 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 involves 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 occurs most often in prokaryote, plants, fungi and protozoa, it is also observed in some animal species.
Types of asexual reproduction.
Let's look at the main types of asexual reproduction.
Reproduction by division.
In prokaryotes, before division, the only ring doubles, a septum appears between the two daughter chromosomes, and the cell divides in two.
Many unicellular algae (for example, Chlamydomonas, Euglena green) 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 dispersal. In fungi and lower plants, spores are formed by mitosis, in higher plants - as a result of meiosis.
In seed plants, spores have lost their dispersal function, but are a necessary stage cycle playback
Vegetative propagation.
The methods of asexual reproduction presented above are united by the fact that in all these cases a new organism develops from one cell of a unicellular or multicellular parent. However, very often during asexual reproduction of multicellular organisms, offspring develop from a group of parent cells. This method of asexual reproduction is called vegetative. There are several types of vegetative propagation. The first of them is the propagation 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 taken into account that under natural conditions, fragmentation is rare, in particular in polychaete worms, molds, 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 maternal organism, and then separates from it (freshwater hydra) or forms colonies of many individuals (coral polyps).
The meaning of asexual reproduction.
Asexual reproduction allows a rapid increase in the number of individuals of a given species under 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 it is necessary to adapt to changed environmental conditions. For this reason, the vast majority of living organisms periodically or continuously reproduce sexually.
Asexual reproduction. Vegetative propagation.
1. What kind of reproduction is called asexual?
2. What types of asexual reproduction are there?
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, soon after formation, is divided into several fragments, each of which independently develops into a full-fledged individual. This division of embryos occurs, 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 that are not yet entirely clear, is divided into several parts. Each of these parts goes through the path of normal embryonic development, as a result of which two or more practically identical babies are born, 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 developing embryo is incomplete. In this case, organisms arise that have common body parts or internal organs. Such identical twins are usually called Siamese, in honor of Chang and Eng Banker, 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 be separated surgically, but they did not agree to this. Having married 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 who suffered from anemia and curvature of the spine was unexpectedly found to have a baby fetus in her abdominal cavity during a medical examination.
However, this embryo was not located in the uterus, but was connected by blood vessels to the vessels of the abdominal cavity, since the embryo grew quickly, 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 arise? Apparently, one of the cells in the girl’s abdominal cavity began to fragment in the same way as a zygote fragments after fertilization, and gave rise to a new human organism. However, the embryo was doomed from the beginning, and it would never have been able to turn into a full-fledged healthy child, since it developed in the wrong place and was not supplied with the necessary hormones and nutrients. After the embryo was removed, the girl quickly recovered and her internal organs, compressed by the growing embryo, began to develop normally.
Kamensky A. A., Kriksunov E. V., Pasechnik V. V. Biology 10th grade
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Reproduction is the ability of all organisms to reproduce their own kind, which ensures the continuity and acceptability of life. The main methods of reproduction are presented:
Asexual reproduction is based on cell division through mitosis, in which two equal daughter cells (two organisms) are created from each mother cell (organism). The biological role of asexual reproduction is the emergence of organisms identical to the parents in the content of hereditary material, as well as anatomical and physiological properties (biological copies).
The following are distinguished: methods of asexual reproduction: division, budding, fragmentation, polyembryony, sporulation, vegetative propagation.
Division- a method of asexual reproduction characteristic of unicellular organisms, in which the mother 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 the paramecium (1), the micronucleus is divided by mitosis, the macronucleus by amitosis. During schizogony (2), the nucleus is first divided 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), or they can remain attached to it, in this case forming colonies (coral polyps).
Fragmentation(4) - a method of asexual reproduction, in which new individuals are formed from fragments (parts) into which the maternal individual breaks up (anneli, 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 (monozygotic twins).
Vegetative propagation- 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.) specifically designed for this form of reproduction. Vegetative propagation is typical for many groups of plants and is used in gardening, vegetable gardening, and plant breeding (artificial vegetative propagation).
Sporulation(6) - reproduction through spores. Controversy- specialized cells, in most species they 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 collection of cells or individuals descended from a common ancestor through asexual reproduction. The basis for obtaining a clone is mitosis (in bacteria - simple division).
During sexual reproduction in prokaryotes, two cells exchange hereditary information as a result of the passage of a DNA molecule from one cell to another along a cytoplasmic bridge.
