Reproduction is the ability of organisms to reproduce their own kind. Reproduction is one of the key features of all living things, so it is necessary to understand the biological significance of fertilization. This issue has now been studied at a high level, from the main stages to molecular and genetic mechanisms.
What is fertilization
Fertilization is a natural biological process of the fusion of two germ cells: male and female. Male gametes are called spermatozoa, while female gametes are called eggs.
The next step after the fusion of germ cells is the formation of a zygote, which can be considered a new living organism. The zygote begins to divide by mitosis, increasing the number of its constituent cells. The embryo develops from the zygote.
There are a large number of types of eggs and methods of crushing. All of them depend on the taxonomic affiliation of the living organism under consideration, as well as the degree of its evolutionary development.
What is the biological significance of fertilization
Reproduction is the main adaptation for procreation. The future of the species depends on the reproductive abilities of the species in question, so different animals and plants have their own ways of adapting to improve the quality of the whole process.
For example, wolves and lionesses always protect their offspring from potential predators. This increases the survival rate of the cubs and guarantees their adaptability to living conditions in the future. Fish lay a large number of eggs because the chance of external fertilization in the aquatic environment is quite low. As a result, out of thousands of potential fry, only a few hundred develop.
The biological significance of fertilization is that two germ cells from different organisms merge and form a zygote that carries the genetic characteristics of both parents. This explains the dissimilarity of relatives to each other. And this is good, because changing the gene pool of any population is an evolutionary adaptive mechanism. The offspring, generation after generation, become better than their parents. In conditions of a gradual change in the environment (climate change, the emergence of new external factors), adaptive skills are always appropriate.
And what is the biological significance of fertilization at the biochemical level? Let's take a look:
- This is the final formation of the egg.
- This is the determination of the sex of the future embryo due to the corresponding genes brought by male gametes.
- Finally, fertilization plays a rolein the restoration of a diploid set of chromosomes, since germ cells are individually haploid.
Propagation of flowering plants
Plants have some reproductive characteristics compared to animals. Representatives of angiosperms, which are characterized by double fertilization (discovered by the Russian scientist Navashin in 1898), require special attention.
The structures that determine sex in flowering plants are stamens and pistils. Pollen, which consists of a large number of grains, ripens in the stamens. One grain contains two cells: vegetative and generative. The pollen grain is covered with two shells, and the outer one always has some outgrowths and indentations.
The pistil is a pear-shaped structure consisting of a stigma, style and ovary. One or more ovules are formed in the ovary, inside which the female germ cells will mature.
When a pollen grain hits the stigma of a pistil, the vegetative cell begins to form a pollen tube. This canal is relatively long and ends at the micropyle of the ovule. At the same time, the generative cell divides by mitosis and forms two spermatozoa, which, through the pollen tube, enter the tissue of the ovule.
Why two sperm? How does the biological significance of fertilization in plants differ from the same process in animals? The fact is that the embryo sac of the ovule is represented by seven cells, among which there is a haploidfemale gamete and diploid central cell. Both will merge with the incoming sperm, forming a zygote and an endosperm, respectively.
Biological significance of double fertilization in plants
Seed formation is an important feature of reproduction in angiosperms. To fully mature in the soil, it needs a large amount of nutrients, which will include various enzymes, carbohydrates and other organic / inorganic components.
The endosperm in angiosperms is triploid, since the diploid central cell of the embryo sac has merged with the haploid sperm. This is the biological significance of fertilization in plants: the triple set of chromosomes contributes to a high rate of increase in the mass of endosperm tissue. As a result, the seed receives a lot of nutrients and energy reserves for germination.
Types of seeds
Depending on the fate of the endosperm, there are two main types of seeds:
- Seeds of monocot plants. They clearly show a well-developed endosperm, which occupies a larger volume. The cotyledon is reduced and presented in the form of a shield. This type of seed is typical for all representatives of cereals.
- Seeds of dicotyledonous plants. Here, the endosperm is either absent or remains in the form of small accumulations of tissue on the periphery. The nutritional function of such seeds is performed by two large cotyledons. Examples of plants: peas, beans, tomatoes, cucumbers,potatoes.
Conclusions
Of course, it would be a mistake to call such fertilization double, since we now know the main features and functions of this process. When the central cell fuses with sperm, no zygote is formed, and the resulting genetic set becomes triple. After all, a seed does not consist of two independent embryos.
However, the biological significance of double fertilization is really great. Seeds require a large amount of organic and inorganic substances during germination, and this problem is solved by the formation of a triploid endosperm.
