Who is characterized by internal fertilization, what is the essence of this process, and what is its biological significance? You can answer these and many other questions when you get acquainted with our article.
Breeding is one of the properties of all livingorganisms. This process ensures the continuity of generations. Sexual reproduction creates new combinations of genetic material, and hence the signs of organisms. It is this process that underlies heredity and variation.
Sexual breeding is called, during whichgametes are participating. These are specialized cells containing the haploid chromosome set. In nature, it can carry out both plants and animals.
The process of gamete fusion is fertilization.Internal or external fertilization is carried out only by germ cells. There are male and female gametes - sperm and egg. They have significant differences in the structure. Thus, the female sex cells are not capable of movement and contain an adequate supply of nutrients. This is due to the fact that it is on the basis of female gametes that the future organism develops. The male germ cells of plants are also not capable of movement, therefore fertilization in these organisms is preceded by pollination.
Gametes are structures that are single,or haploid, a 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 only possible with the merger of haploid gametes.
Fertilization is a compound called geneticgerm cell material. Depending on the place in which this process takes place, there are several types of it. External fertilization occurs outside the body of the female. In nature, it is found in amphibians and fish. Internal fertilization is typical of typical land animals: reptiles, birds, mammals.
Outdoor, or external, fertilization begins.with excretion of germ cells. Therefore, the convergence of organisms in this case is not necessary. Despite this, there is often a cluster of breeding individuals in nature. For example, fish or frogs when spawning.
External fertilization, internal or hisintermediate type begin with the insemination process. Its essence lies in the convergence of germ cells. Scientists have found that with external fertilization almost immediately after contact of the cells, changes occur in the electrical impulses of the egg shells. And after 7 seconds, the gamete content is already connected, resulting in a zygote. It is divided many times and a multicellular germ is gradually formed.
Females of animals characterized by outdoorfertilization, simultaneously release a large number of eggs into the water. For example, fish throw several thousand eggs at once. Only a small part of them will be fertilized and become fry. The rest will become prey for aquatic animals.
Internal fertilization of animals occurs infemale genital ducts. There is a fixed egg. A sperm cell approaches it as a result of intercourse. It has already been established that in most cases only the nuclear substance of the male gamete penetrates the egg cell. Its cytoplasm practically does not participate in the process of formation of a new organism.
The main advantage of internal fertilizationis that the embryo is relatively independent of adverse environmental conditions. Its development takes place within the maternal organism for some time. It provides the embryo with everything necessary: heat, moisture, oxygen, nutrients. In addition, during fertilization inside the body, the probability of gamete fusion increases significantly, which makes the reproduction process stable in such individuals. For these reasons, the number of female gametes capable of fertilization is much lower compared with animals that release them into the environment.
Specific egg cell fertilizes onesperm. But why, in many organisms, several individuals, or even dozens, appear at once? This is possible in two ways. In the first case, several eggs come out to fertilization, each of which is connected to a separate male gamete. A person in this case is born fraternal twins. They can be both single and different sexes, and no more resemble each other than siblings. Identical twins appear as a result of dividing zygotes into several parts. In this case, a person gives birth to children of the same sex, similar to each other as two drops of water.
In flowering plants also occursfertilization is internal. Representatives of this systematic unit have a number of features that manifest themselves during the sexual process. It is carried out by the generative organ - the flower. The process of fusion of gametes is preceded by pollination. Its essence lies in the transfer of male germ cells on the stigma of the pistil with the help of wind, insects, water or humans.
Next, two sperm with germinatinggerminal tube descend into the lower extended part of the pistil - the ovary. This is where one sperm merges with the female gamete, and the other with the central germ cell. Therefore, such fertilization is called double. As a result, an embryo is formed, surrounded by a spare nutrient by the endosperm and the shell. In other words, the seed.
Such a process has provided modern floweringplants dominant position on the planet. The egg cell and the embryo are reliably protected by the ovary walls, and the seed contains the necessary supply of nutrients and water necessary for the growth and development of an adult plant.
It is easy to trace the dependence of the habitatorganisms and their type of fertilization. Thus, the fusion of gametes in the environment occurs in the water, where the embryo of organisms with external fertilization initially develops. Moreover, this process is possible only in a neutral or alkaline medium, and in acidic it becomes impossible.
Появление внутреннего оплодотворения в процессе evolution is associated with the release of chordates to land. The life of representatives of this type out of the water became possible precisely because of this feature. Inner fertilization in reptiles occurs inside 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 shells. An increase in the amount of yolk compensates for the absence of the larval stage in the ontogenesis of reptiles. And the appearance of dense shells makes it possible to develop eggs on land and reliably protects against drying and mechanical damage.
The zygote that is formed as a resultfertilization, begins to repeatedly share. After a certain time, it already consists of a number of cells - blastomeres. Next, the stage of the gastrula begins, which is characterized by the laying of germ layers. The development of the embryo continues with the formation of organs and their systems.
Individual development of multicellular animalsincludes embryonic and post-embryonic periods. In organisms with internal fertilization, the first of these occurs in the maternal organism or inside the egg. This provides a higher level of development of animals, as well as their ability to live independently after birth. From the moment of birth, the postembryonic period begins. Fertilization, internal or external, determines the future type of development of organisms. In the first case, it occurs without the larva stage. In this case, the newborn individual is slightly different from the mature. This type of development is called direct. But fish and amphibians pass through the larva stage, during which they additionally develop, reaching the level of organization of adult representatives.
So internal fertilization is a process.merger of germ cells within the body of the female. Compared to the external one, it has several significant advantages: a higher probability of gamete fusion, their independence from external conditions, and ensuring a higher viability of future individuals.
