One of the basic abilities of all living organisms is reproduction. There are two main options for the formation of new individuals. Experts also distinguish asexual.
Every living organism can create similar individuals. Many plants and lower animals use an asexual method of self-reproduction. To produce offspring, one parent is sufficient, which is capable of forming daughter organisms.
But this information is not enough to understand how sexual reproduction differs from asexual reproduction. These forms of reproduction are fundamentally different. Thus, sexual reproduction is possible only with the participation of two parent individuals. The sexual method is characterized by the formation of gametes. These are special reproductive cells with a haploid set of chromosomes.
The sexual method is considered more progressive compared to the asexual method. It is used by the vast majority of living beings to produce offspring. You can understand how sexual reproduction differs from asexual reproduction if you know the following.
The first form of reproduction requires the participation of two parent individuals. Each of them produces special sex cells - gametes. During the process of reproduction, they fuse and form a zygote. It is from it that a new organism is formed.
Gametes are not needed in the process. A new individual is formed from somatic cells. It is an exact copy of the parent organism. This method of reproduction makes it possible to quickly obtain offspring.
Self-reproduction of new organisms from has its advantages. Knowing them, it is easy to explain how sexual reproduction differs from asexual reproduction. It makes it possible to create a large number of individuals in a short time. In this case, the resulting offspring is no different from the parent individual. Daughter organisms are exact copies.
This method of reproduction is beneficial to those organisms that live in unchanging conditions. Genetic variation during asexual reproduction can only arise as a result of genetic mutations. In the process of such self-reproduction, cells divide, usually through mitosis.
Higher animals cannot reproduce their own kind asexually. The only exception is cloning them artificially.
There are several options for organisms to create their own kind without the participation of specialized germ cells. When figuring out how sexual reproduction differs from asexual reproduction, we should not forget that the latter method of reproducing offspring is divided into several types.
Separately, division, sporulation, vegetative propagation, including budding, and fragmentation are distinguished. With each of these methods, a new individual is formed from one or a group of somatic cells. Protozoa reproduce by division: amoeba, paramecium. This method is also used by certain bacteria.
All groups of green plants, fungi, some bacteria and protozoa reproduce by sporulation. Spores are formed in special structures - sporogony.
When clarifying the differences between sexual and asexual reproduction, do not forget that these methods differ significantly. After all, during self-reproduction without the participation of gametes, somatic cells begin to divide. For example, it is possible with the help of cuttings, tendrils, roots, rhizomes, tubers, bulbs, corms.
To obtain offspring using this method, two individuals of the same species are needed, which produce special germ cells. The appearance of offspring is possible when they merge and form zygotes. This is precisely what is worth remembering when telling how sexual reproduction differs from asexual reproduction.
Gametes contain a haploid (single) set of chromosomes. These cells are formed through the process of meiosis. It is with their help that genetic information is transmitted from both parents to daughter organisms. The process of fusion of gametes is called fertilization. As a result, the haploid nuclei unite and a zygote is formed. This is the basis for the intraspecific variability of organisms.
When clarifying the features of asexual and sexual reproduction, we must not forget that there are two types of gametes. They are produced by males and females. But in nature there are types of organisms that can simultaneously produce two types of germ cells. They are called hermaphrodites. Small crustaceans, snails, and some fish can reproduce this way.
You can understand how sexual reproduction differs from asexual reproduction if you know that the first method is characterized by the formation of special gametes, and in the second method, the somatic cells of the parent organism begin to divide.
It is important that for asexual reproduction one individual is enough, but for sexual reproduction two are needed. True, we should not forget about exceptions. These include hermaphroditism and parthenogenesis. Although the first indicated form of reproduction often involves gametes from different individuals, processes occur in the body that interfere with self-fertilization.
Also one of the types of sexual reproduction is parthenogenesis. With this method, female reproductive cells are able to develop into a new individual without the participation of male gametes. Both some animals and plants can produce offspring in this way.
Depending on the number of chromosomes in female germ cells, diploid and haploid parthenogenesis are distinguished. This reproductive mechanism allows you to regulate the number of offspring and their types. For example, a queen bee can lay eggs, which will produce either females (queens, workers) or males (drones). Reproduction - sexual and asexual - in classical versions does not have such capabilities.
Abstract: Asexual and sexual reproduction
Introduction
The ability to reproduce, that is, to produce a new generation of individuals of the same species, is one of the main characteristics of living organisms. During the process of reproduction, genetic material is transferred from the parent generation to the next generation, which ensures the reproduction of characteristics not only of a given species, but of specific parent individuals. For a species, the meaning of reproduction is to replace those of its representatives who die, which ensures the continuity of the existence of the species; in addition, under suitable conditions, reproduction makes it possible to increase the total number of the species.
Each new individual, before reaching the stage at which it is capable of reproduction, must go through a number of stages of growth and development. Some individuals die before reaching the reproductive stage (or sexual maturity) as a result of destruction by predators, diseases and various random events; therefore, the species can survive only on the condition that each generation produces more offspring than there were parent individuals who took part in reproduction. Population sizes fluctuate depending on the balance between reproduction and extinction of individuals. There are a number of different propagation strategies, each with distinct advantages and disadvantages; all of them will be described in this abstract.
And the purpose of my work is to consider some types of reproduction.
Asexual and sexual reproduction
There are two main types of reproduction - asexual and sexual. Asexual reproduction occurs without the formation of gametes and involves only one organism. Asexual reproduction usually produces identical offspring, and the only source of genetic variation is random mutations.
Genetic variability is beneficial to the species, since it supplies “raw materials” for natural selection, and therefore for evolution. The offspring that are most adapted to their environment will have an advantage in competition with other members of the same species and will have a greater chance of surviving and passing on their genes to the next generation. Thanks to this, species are able to change, i.e., the process of speciation is possible. Increased variation can be achieved by mixing the genes of two different individuals, a process called genetic recombination, which is an important feature of sexual reproduction; In a primitive form, genetic recombination is already found in some bacteria.
Asexual reproduction
In asexual reproduction, offspring come from one organism, without the fusion of gametes. Meiosis is not involved in the process of asexual reproduction (unless we talk about plant organisms with alternating generations), and the descendants are identical to the parent individual. Identical offspring descended from the same parent are called clones. Members of the same clone can be genetically different only if a random mutation occurs. Higher animals are not capable of asexual reproduction, but several successful attempts have recently been made to clone some species artificially; we will look at them later.
Division
Spore formation (sporulation)
A spore is a single-celled reproductive unit, usually microscopic in size, consisting of a small amount of cytoplasm and a nucleus. The formation of spores is observed in bacteria, protozoa, representatives of all groups of green plants and all groups of fungi. Spores can vary in type and function and are often formed in special structures.
Often, spores are formed in large quantities and have negligible weight, which makes them easier to spread by wind, as well as by animals, mainly insects. Due to their small size, the spore usually contains only minimal nutrient reserves; Because many spores do not reach a suitable location for germination, spore losses are very high. The main advantage of such spores is the ability to quickly reproduce and spread species, especially fungi.
Bacterial spores, strictly speaking, do not serve for reproduction, but to survive under unfavorable conditions, since each bacterium produces only one spore. Bacterial spores are among the most resistant: for example, they can often withstand treatment with strong disinfectants and boiling in water.
Budding
Budding is one of the forms of asexual reproduction, in which 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, completely identical to the parent. Budding occurs in different groups of organisms, especially in coelenterates such as Hydra (Fig. 1) and in single-celled fungi such as yeast. In the latter case, budding differs from fission (which is also observed in yeast) in that the two resulting parts have different sizes.
An unusual form of budding is described in the succulent plant bryophyllum, a xerophyte often grown as an ornamental houseplant: miniature plants equipped with small roots develop along the edges of its leaves (Fig. 2); these “buds” eventually fall off and begin to exist as independent plants.
Reproduction by fragments (fragmentation)
Fragmentation is the division of an individual into two or more parts, each of which grows and forms a new individual. Fragmentation occurs, for example, in filamentous algae such as Spirogyra. The spirogyra thread can break into two parts anywhere.
Fragmentation is also observed in some lower animals, which, unlike more highly organized forms, retain a significant ability to regenerate from relatively poorly differentiated cells. For example, the body of nemerteans (a group of primitive worms, mainly marine) is especially easily torn into many parts, each of which can give rise to a new individual as a result of regeneration. In this case, regeneration is a normal and regulated process; however, in some animals (for example, starfish), restoration from individual parts occurs only after accidental fragmentation. Animals capable of regeneration serve as objects for experimental study of this process; Often a free-living planarian worm is used. Such experiments help to understand the differentiation process.
Vegetative propagation
Vegetative propagation is a form of asexual propagation in which a relatively large, usually differentiated part is separated from the plant and develops into an independent plant. Essentially, vegetative propagation is similar to budding. Often, plants form structures specifically designed for this purpose: bulbs, corms, rhizomes, stolons and tubers. Some of these structures also serve to store nutrients, allowing the plant to survive periods of unfavorable conditions such as cold or drought. Storage organs allow the plant to survive the winter and produce flowers and fruits the following year (biennial plants) or survive for a number of years (perennial plants). These organs, called overwintering organs, include bulbs, corms, rhizomes and tubers.
Overwintering organs can also be stems, roots or entire shoots (buds), but in all cases the nutrients they contain are created mainly during the process of photosynthesis occurring in the leaves of the current year. The resulting nutrients are transferred to the storage organ and are then usually converted into some insoluble storage material, such as starch. When unfavorable conditions occur, the above-ground parts of the plant die, and the underground hibernating organ goes into a dormant state. At the beginning of the next growing season, nutrient reserves are mobilized with the help of enzymes: the buds awaken, and the processes of active growth and development begin in them due to the stored nutrients. If more than one bud sprouts, then we can assume that reproduction has occurred.
In some cases, special organs are formed that serve for vegetative propagation. These are the modified parts of the stem - potato tubers, onion bulbs, garlic bulbs, bulblets in the leaf axils of the bluegrass, shoots of the young, etc. Strawberries reproduce with “mustaches” (Fig. 3). Adventitious roots are formed at the nodes of the shoots, and shoots with leaves are formed from the axillary buds. Subsequently, the internodes die off, and the new plant loses its connection with the mother plant.
Plant propagation. One of the mandatory properties of living organisms is the reproduction of offspring (reproduction). Reproduction is associated with the subsequent dispersal of plants. According to V.I. Vernadsky, reproduction and settlement, that is, the spreading of life, is the most important biological factor on our planet. During reproduction, the number of individuals of a given species increases. The term "reproduction" reflects the qualitative side. The number of individuals as a result of reproduction can sometimes decrease (diatoms).
Reproduction as a property of living matter, i.e. the ability of one individual to give rise to its own kind existed even in the early stages of its development. The evolution of life paralleled the evolution of methods of reproduction.
Forms of plant reproduction can be divided into two types: asexual and sexual.
Actually asexual reproduction carried out using specialized cells - dispute. They are formed in the organs of asexual reproduction - sporangia as a result of mitotic division. During its germination, the spore reproduces a new individual, similar to the mother, with the exception of spores of seed plants, in which the spore has lost the function of reproduction and dispersal.
Asexual reproduction carried out without the participation of germ cells, with the help of spores that are formed in specialized organs - sporangia win zoosporangia. Inside the sporangium, reduction division occurs and single-celled spores, or zoospores (with flagella), spill out. Most of the lower plants reproduce by spores (algae), of the higher spore plants - bryophytes, lycophytes, horsetails, and ferns.
Reproduction of plants using vegetative organs (part of a shoot, leaf, root) or dividing unicellular algae in half, etc. called vegetative(Fig. 134). It is widely used in agriculture, especially when propagating varietal material, where it is necessary to preserve the maternal characteristics of the variety. Thus, many crops reproduce well with the help of lignified and green cuttings (sea buckthorn, lemongrass, actinidia, black currant, etc.), other fruit crops (apple, pear, cherry, apricot, etc.) - by grafting varietal cuttings into the crown of wild seedlings. Bulbous plants are propagated by bulbs (tulips, hyacinths, gladioli, etc.); Many perennial herbaceous plants are grown by rhizomes (lily of the valley, rosemary, perennial lupine, asparagus, etc.), root tubers (dahlias, Jerusalem artichoke, etc.). Some plants reproduce using shoots (Chokeberry,
sea buckthorn, common raspberry, etc.) or layering (garden strawberries, gooseberries, etc.).
Sexual reproduction carried out by special sex cells - gametes. Gametes are formed as a result of meiosis, they are male and female. As a result of their fusion appears zygote, from which a new organism subsequently develops. Plants differ in the types of gametes. In some unicellular organisms, the organism functions as a gamete during a certain period. Organisms of different sexes (gametes) fuse. This sexual process is called hologamia. If male and female gametes are morphologically similar and mobile, these are isogametes, and the sexual process is called isogamy(see Fig. 160, B, 2). If the female gamete is somewhat larger and less mobile than the male one, then these are heterogametes, and the sexual process is called heterogamy(Fig. 160, B, 3). More advanced in evolutionary terms oogamy(Fig. 160, B, 5), in which female gametes are quite large and immobile, and male gametes are small and mobile. The female gamete is called egg, and the gametangium, in which the egg is formed, in lower
plants (algae) is called oogonium, and for the higher ones - archegonia. Male gametes - spermatozoa- have flagella.
In most seed plants, male gametes have lost their flagella and are called sperm. The gametangia in which sperm are produced are called antheridia.
Most plants have all methods of reproduction, but many algae, higher spores and seed plants are characterized by alternating asexual and sexual types of reproduction. On the asexual generation in sporophyte, or diplobionte(2l), as a result of spore maturation and then reduction division, disputes (p), and in the sexual generation - gametophyte- women's and men's gametes (n), which when merged form zygote(2l). A sporophyte (2l) will grow from it again, i.e. the alternation of generations occurs with a change in nuclear phases.
Alternation of development phases. The alternation of developmental phases in different systematic groups of plants has been established. It was possible to find out a general pattern: the sporophyte develops better and becomes independent; gametophase, on the contrary, is increasingly reduced and completely loses its independence and depends on the sporophyte (gymnosperms and angiosperms). In the evolution of sexual reproduction, the reduction of the gametophyte had a progressive significance, which led to the formation of new rudiments of reproduction and distribution - seeds and fruits.
The most primitive development cycle is in mosses. Only among higher plants can one see a well-developed independent gametophyte (see Fig. 169).
In club mosses, horsetails, and ferns, the sporophyte predominates in life expectancy, and the gametophyte is represented by a thallus (thallus).
In the listed plants, the sexual process and gametophase serve to reproduce the sporophase, and the sporophase, although not for long, is still dependent on the gametophase.
Greater adaptability to the conditions of terrestrial existence is associated with the life cycle of gymnosperms and angiosperms. The specificity of the life cycle of gymnosperms is expressed in the structure of the ovule and its transformation into a seed. The megaspore of these plants has completely lost the function of the germ of reproduction and distribution. The male gametophyte (pollen), in the absence of an aquatic environment, acquires a new meaning: with the help of a pollen tube, it delivers gametes to the egg. Male gametes - sperm - are immobile. Thus, the change of generations of sporophyte and gametophyte in gymnosperms differs significantly from previous groups of plants, since the sexual generation - the male gametophyte (pollen grain) and the female gametophyte (primary endosperm) - is in a significantly reduced state contained in the tissues of the sporophyte and is completely dependent on it . And
The life cycle of angiosperms differs significantly from the life cycle of previous groups of plants. The female gametophyte of angiosperms is more reduced than the gametophyte of gymnosperms. This is the embryo sac. Archegonia are absent. Fertilization is double (one sperm fertilizes the egg, the other - the secondary nucleus of the embryo sac). The endosperm is trichuid.
Thus, in angiosperms, although there is a change of generations - sporophyte and gametophyte, the male and female gametophytes are reduced even more - to several cells located in the tissues of the sporophyte flower. Sporophytes are ordinary trees, shrubs and herbs that are well known to us (Fig. 135).
Introduction
The ability to reproduce, that is, to produce a new generation of individuals of the same species, is one of the main characteristics of living organisms. During the process of reproduction, genetic material is transferred from the parent generation to the next generation, which ensures the reproduction of characteristics not only of a given species, but of specific parent individuals. For a species, the meaning of reproduction is to replace those of its representatives who die, which ensures the continuity of the existence of the species; in addition, under suitable conditions reproduction allows you to increase the total number of the species.
Each new individual, before reaching the stage at which it is capable of reproduction, must go through a number of stages of growth and development. Some individuals die before reaching the reproductive stage (or sexual maturity) as a result of destruction by predators, diseases and various random events; therefore, the species can survive only on the condition that each generation produces more offspring than there were parent individuals who took part in reproduction. Population sizes fluctuate depending on the balance between reproduction and extinction of individuals. There are a number of different propagation strategies, each with distinct advantages and disadvantages; all of them will be described in this abstract.
And the purpose of my work is to consider some types of reproduction.
There are two main types of reproduction - asexual and sexual. Asexual reproduction occurs without the formation of gametes, and only one organism is involved. Asexual reproduction usually produces identical offspring, and the only source of genetic variation is random mutations.
Genetic variability is beneficial to the species, since it supplies “raw materials” for natural selection, and therefore for evolution. The offspring that are most adapted to their environment will have an advantage in competition with other members of the same species and will have a greater chance of surviving and passing on their genes to the next generation. Thanks to this, species are able to change, i.e., the process of speciation is possible. Increased variation can be achieved by mixing the genes of two different individuals, a process called genetic recombination, which is an important feature of sexual reproduction; In a primitive form, genetic recombination is already found in some bacteria.
In asexual reproduction, offspring come from one organism, without the fusion of gametes. Meiosis is not involved in the process of asexual reproduction (unless we talk about plant organisms with alternating generations), and the descendants are identical to the parent individual. Identical offspring descended from the same parent are called clones. Members of the same clone can be genetically different only if a random mutation occurs. Higher animals are not capable of asexual reproduction, but several successful attempts have recently been made to clone some species artificially; we will look at them later.
Reproduction is the reproduction by an organism of similar organisms. Thanks to him, continuity of life is ensured. There are two ways to form new organisms: asexual and sexual reproduction. Asexuality, in which only one organism participates, occurs through cell division in half, sporulation, budding, or vegetatively. It is characteristic mainly of primitive organisms. In asexual reproduction, the new organisms are a copy of the parent. Sexual reproduction occurs with the help of sex cells called gametes. It mainly involves two organisms, which contributes to the emergence of new individuals that differ from the parent ones. Many animals are characterized by alternating asexual and sexual reproduction.
Types of sexual reproduction
There are the following types of sexual reproduction:
Dioecious reproduction
Dioecious reproduction is characterized by the fusion of haploid gametes, which is called fertilization. Fertilization results in a diploid zygote containing genetic information from both parents. Dioecious reproduction is characterized by the presence of the sexual process.
Types of sexual process
There are three types of sexual process:
Hermaphroditism
Parthenogenesis
Some organisms are able to develop from an unfertilized cell. This sexual reproduction is called parthenogenesis. With its help, ants, bees, wasps, aphids and some plants reproduce. A type of parthenogenesis is pedogenesis. It is characterized by virgin reproduction of larvae. Some dipterans and beetles reproduce using pedogenesis. Parthenogenesis ensures a rapid increase in population size.
Plant propagation
Plants, like animals, can reproduce asexually and sexually. The difference is that sexual reproduction in angiosperms occurs through double fertilization. What is it? In double fertilization, discovered by S.G. Navashin, two sperm take part in the fertilization of the egg. One of them unites with the egg. This produces a diploid zygote. The second sperm fuses with the diploid central cell to form a triploid endosperm containing a supply of nutrients.
Biological meaning of sexual reproduction
Sexual reproduction makes organisms resistant to changing and unfavorable environmental conditions and increases their viability. This is facilitated by the diversity of offspring born as a result of the combination of heredity of two organisms.
