Who is intrinsic to insemination? What is the advantage of internal fertilization?

Who is inherent in internal fertilization, what is the essence of this process, and what is its biological significance? These and many other questions you can answer when you get acquainted with our article.

What is sexual reproduction?

Reproduction is one of the properties of all living organisms. This process ensures the continuity of generations. Sexual reproduction creates new combinations of genetic material, and hence signs of organisms. It is this process that underlies heredity and variability.

Sex is called reproduction, during which gametes participate. These are specialized cells containing a haploid chromosome set. In nature, it is capable of carrying out both plants and animals.

The structure of gametes

The process of gamete fusion is fertilization. Internal or external fertilization is carried out only by the sex cells. Distinguish between male and female gametes - spermatozoa and ovules. They have significant differences in structure. Thus, female sex cells are not capable of movement and contain a sufficient supply of nutrients. This is due to the fact that it is on the basis of female gametes that the future organism develops. Male germ cells of plants are also incapable of movement, so the process of fertilization in these organisms is preceded by pollination.

Gametes are structures that have a single, or haploid, set of chromosomes. And this structure is not accidental. The fact is that an adult organism must possess a double (diploid) chromosome set. This is possible only with the fusion of haploid gametes.

External and internal insemination

Fertility is the connection of the genetic material of the germ cells. Depending on the place in which this process takes place, several types of it are distinguished. External fertilization takes place outside the body of the female. In nature it occurs in amphibians and fish. Internal fertilization is typical for typically terrestrial animals: reptiles, birds, mammals.

Peculiarities of external fertilization

External, or external, fertilization begins with the excretion of the germ cells outside. Therefore, the convergence of organisms is not necessary at all. Despite this, in nature there is often a cluster of breeding individuals. For example, fish or frogs when spawning.

External fertilization, internal or its intermediate type begins with the process of insemination. Its essence lies in the convergence of the sex cells. Scientists have found that with external fertilization, almost immediately after the contact of the cells, changes occur in the electrical impulses of the egg shells. And after 7 seconds the contents of gametes are already connected, resulting in a zygote. It is divided many times and a multicellular embryo is gradually being formed.

Female animals, which are characterized by external fertilization, simultaneously release a large number of eggs into the water. For example, the fish immediately rake several thousand eggs. Only a small part of them will be fertilized and turn into fry. The rest will become prey to aquatic animals.

What is the advantage of internal fertilization

Internal fertilization of animals occurs in the genital ducts of the female. There and there is a fixed egg. The spermatozoon approaches her as a result of sexual intercourse. It has already been established that in most cases only the nuclear substance of the male gamete penetrates into the egg cell. Its cytoplasm is practically not involved in the process of formation of a new organism.

The main advantage of internal fertilization is that the embryo is relatively independent of unfavorable environmental conditions. Its development takes place within the mother's body for a certain time. He provides the embryo with everything necessary: heat, moisture, oxygen, nutrients. In addition, with fertilization within the body, the probability of gamete fusion increases significantly, which causes the stability of the reproductive process in such individuals. For these reasons, the number of female gametes capable of fertilization is much less than in animals that release them into the environment.

A single egg is impregnated with one sperm. But why do many organisms have several individuals at once, or even dozens? This is possible in two ways. In the first case, several eggs emerge at once to fertilization, each of which is connected to a separate male gamete. In this case, the human being is born with fraternal twins. They can be either one or the same sex, but they are similar to each other no more than their own brothers and sisters. Odnoyaytsevye twins appear as a result of dividing the zygote into several parts. In this case, a man is born the children of the same sex, similar to each other as two drops of water.

Sexual reproduction of plants

In flowering plants, fertilization also takes place - internal fertilization. Representatives of this systematic unit have a number of features that are manifested during the sexual process. It is carried out by a generative organ - a flower. The process of fusion of gametes is preceded by pollination. Its essence lies in the transfer of male sex cells on the stigma of the pistil with the help of wind, insects, water or man.

Double Fertilization

Next, two sperm along with a germinating germinal tube descend into the lower expanded part of the pistil - the ovary. Here, a fusion of one sperm with a female gamete occurs, and the other with a central germ cell. Therefore, such a fertilization is called double. As a result, an embryo is formed, surrounded by a reserve nutrient with an endosperm and a membrane. In other words, the seed.

Such a process provided the current flowering plants with a dominant position on the planet. The egg and the embryo are securely protected by the walls of the ovary, and the seed contains the necessary supply of nutrients and water necessary for the growth and development of the adult plant.

Type of fertilization and the habitat of animals

It is easy to trace the dependence of the habitat of organisms and the type of their fertilization. Thus, the fusion of gametes in the external environment occurs in the water, where the embryo of organisms with external fertilization initially develops. And this process is possible only in a neutral or alkaline medium, and in acidic it becomes impossible.

The appearance of internal fertilization in the process of evolution is associated with the release of chordates to land. The life of representatives of this type outside the water became possible precisely because of this feature. Internal fertilization in reptiles occurs within the body of the female, where the embryo initially develops. It is in the egg, which contains a rich supply of substances and most are covered with dense membranes. The increase in the amount of yolk compensates for the absence of a larval stage in the ontogeny of reptiles. And the appearance of dense shells makes possible the development of eggs on land and reliably protects against drying and mechanical damage.

Ontogeny of multicellular animals

Zygote, which is formed as a result of fertilization, begins to divide many times. After a certain time, it already consists of a number of cells - blastomeres. Then the gastrula stage begins, which is characterized by the laying of the embryonic leaves. The process of development of the embryo by the formation of organs and their systems continues.

Individual development of multicellular animals includes embryonic and post-embryonic periods. In organisms with internal fertilization, the first of them occurs in the mother's body or inside the egg. This provides a higher level of development of animals, as well as their ability to live independently after birth. Since the birth of the postembryonic period begins. Fertilization, internal or external, determines the future type of development of organisms. In the first case, it occurs without the stage of the larva. However, the newborn is slightly different from the sexually mature. This type of development is called direct. But the fish and amphibians pass through the stage of the larva, during which they further develop, reaching the level of organization of adult representatives.

So, internal fertilization is the process of fusion of sex cells inside the female organism. In comparison with the external one, it has a number of significant advantages: a higher probability of gamete fusion, their independence from external conditions and provision of higher viability of future individuals.