Forms of reproduction of organisms. Table of species of reproduction

The ability of living beings to reproduce themselves is called multiplication. In this case, the genetic material is transferred to the offspring, and the parental attributes will be inherent in one or another degree to the newly emerged 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, reproduction of the offspring requires 2 individuals, and in the second, only one is needed.

With asexual reproduction, a new organism appears from somatic cells. In nature, there are several ways to reproduce without the participation of genitals. These include vegetative reproduction, budding, fragmentation, sporulation, division, cloning.

During sexual reproduction, new organisms appear as a result of the fusion of specialized sex cells called gametes, and the subsequent formation of a zygote. This method is more progressive than asexual.

Comparison of advantages

It should be noted that both ways of reproduction of offspring have their own merits. For example, biologists distinguish the following advantages of asexual reproduction:

• The ability to reproduce a significant number of individuals;
• Offspring is similar to the parental organism by all signs.

This way of reproducing new individuals makes it possible to quickly obtain a large number of offspring. This is beneficial for species that live in permanent 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 producing offspring is used by both plants and protozoans.

But sexual reproduction is characteristic of the predominant majority of living things. It is capable of guaranteeing the genetic diversity of the obtained offspring. This is what allows them to quickly adapt to the changing conditions of life. After all, during the formation of a new organism, a combination of parents' genes occurs.

Types of asexual reproduction of offspring

There are several ways to get daughter organisms without the participation of sex cells. All of them are studied by biology. Reproduction, the types of child organisms in which there is no change at all, can be accomplished by dividing one or more cells.

In the first case, the following forms are distinguished:

• Single or multiple (schizogony) cell division;
• Spore formation;
• Budding unicellular.

When dividing a group of cells, the classification is carried out as follows:

• fragmentation;
• Budding of multicellular organisms (eg 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 of the simplest. Examples of asexual reproduction by binary fission: amoeba, infusoria-shoe, euglena green.

Spore formation is widely believed. It is characteristic of almost all plants, fungi, some protozoa and prokaryotic organisms (for example, bacteria or blue-green algae).

In a number of unicellular and multicellular organisms , a form of reproduction such as budding occurs. This is as follows: a mound appears on the maternal body, which increases in size. Then there are the rudiments of all organs. When the process is completed, a spin-off occurs. This method of reproduction uses coelenterates (hydra), unicellular (yeast, some types of infusoria).

But there are other examples of asexual reproduction of organisms. So, do not forget about the fragmentation. In this process, the parent is divided into several parts. From each of them a new organism is formed. For example, filamentous alga spirogyra can be ripped anywhere. Of the two parts in the future will be two new organisms.

The plants are characterized by vegetative reproduction. According to the principle of processes, it does not differ from budding or fragmentation. A plant can form special structures necessary for reproduction. Also, the appearance of a child organism is possible with a part of the mother organism.

Sexual reproduction

Most living creatures reproduce similar organisms by mixing the genetic material of the two individuals. For this, the 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 peculiar to some flowering plants, to most animals and, of course, to humans.

Gametes are of two kinds - male and female. If the species is dioecious, then each type of cell is produced by male and female individuals, respectively. Some organisms are able to produce both types of gametes independently. In this case, they are called hermaphrodites.

A variant of sexual reproduction in which gametes do not participate is also possible. These are such species as conjugation, gametangiogamy, apogamy, nogamy.

The process of reproduction

All organisms are made up of cells. Their growth, development is possible due to the fact that they are constantly reproduced. In the process of life, some of the cells grow old and die. They are replaced by others. The only way to get new cells is to divide their precursors. This is a vital process for every living being. For example, in the human body, several million of these structural units are divided every second.

Biologists have described three ways of multiplying cells. Direct division is called amitosis, indirect - mitosis, reduction - meiosis. Regardless of the form of reproduction of organisms, in each of these processes occur.

Amytosis and mitosis

The least common and poorly studied method of cell division is amitosis. In this process, the core is separated by a constriction. At the same time, it is impossible to ensure an even distribution of genetic material. The cell, divided by amitosis, in most cases can not continue to enter the usual cycle of mitosis. Therefore, it is considered doomed to perish.

The universal way of reproduction of eukaryotic cells is mitosis. In animal cells it passes, as a rule, for an hour. Do not underestimate the biological significance of reproduction, because it is thanks to him that the development and growth of all organisms is ensured.

Stages of mitosis

The sequence of all the 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 on both cell types and external factors. The temperature, availability of nutrients, oxygen influences. 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. The substances that promote the growth of the cell and the fulfillment of all its functions are developed. During interphase, DNA replication takes place.

Directly during the phase of mitosis , the nucleus divides. Chromatides during this process are separated from each other and redistributed among the formed daughter cells in the form of chromosomes.

The process, during which it separates between new cytoplasmic structures, is called cytokinesis.

During mitosis, cells are formed in which the hereditary information is completely identical to the mother's body. During this process, the number of chromosomes doubles.

Meiosis

With this method of cell division, the number of chromosomes is halved. Thus, sexual reproduction of animals and sporogenesis in plants is ensured. During meiosis, two consecutive divisions are observed, and they are preceded by a single reduplication of DNA.

All the necessary substances for these processes are stored during the preliminary stage - the interphase. Each stage of division consists of four periods: prophase, metaphase, anaphase and telophase. The same phases also occur with mitosis, but each of the processes has its own peculiarities.

The first meiosis is cell division, in which the number of chromosomes decreases by a factor of 2. From one diploid formation two haploid appear. At this time, the processes of spiralization of DNA occur, the spindle of division is formed. In addition, prophase conjugates homologous chromosomes. The resulting pairs form a bivalent. In some places, the chromatids cross. This process is called a crossing-over.

The final stage is the so-called second meiosis. This division, in which cells with a haploid set of chromosomes, consisting of a single chromatid, are formed. As a result of the described processes, 4 cells emerge from one diploid formation (oogonia or spermatogonia).

Biological meaning of meiosis is the formation of cells that ensure sexual reproduction of animals or sporulation in higher animals. It is this way of reproduction that guarantees the maintenance of genetic permanence of species.

Features of sexual and asexual reproduction of organisms

Depending on how the cells are divided into progeny, different types of this process are distinguished. Separately, it should be noted that the survival of many organisms in a changing environment is due precisely to the fact that they can combine different ways of reproduction.

Of course, sexual and asexual reproduction of such organisms is very different. The table of species of reproduction will help to understand what is the fundamental difference.

It is clear that the sexual forms of reproduction of organisms are more perfect. But the sexless method guarantees the rapid reproduction of a large number of offspring. At sexual reproduction the number of daughter organisms grows not so intensively.