Fertilization - what is it and how does it happen? Double fertilization in flowering plants

Fertilization is the process of the fusion of two cells, resulting in the formation of a new cell that gives rise to another organism of the same genus or species. What is double fertilization in flowering plants? Plants and how it happens, read this article.

The essence of fertilization

It occurs as a result of the fusion of two cells, female and male, and the appearance of a diploid zygote. In each pair of chromosomes, there is one paternal and one maternal cell. The essence of the process of fertilization is to restore the diploid set of chromosomes and combine the hereditary material of the parents. Their offspring will be more viable, as it will combine the most useful qualities from the father and mother.

Fertilization - what is it?

This is the process of inducing the egg to develop as a result of the unification of the nuclei. Fertilization - what is it? This is an irreversible process that occurs as a result of the fusion of heterogeneous gametes and the union of their nuclei. The fertilized egg is not subjected to this procedure a second time.

But there are plants that reproduce the new generation only with the help of female gametes without fertilization. Such reproduction is called virgin. It is noteworthy that these two ways of reproduction in one plant species can alternate.

Double fertilization of flowering plants

The sex cells of both origins are called gametes. And female eggs are female, and male ones are spermatozoa, which are immobile in seed plants, and in sporic plants they are mobile. Fertilization - what is it? This is the appearance of a special cell - the zygote, containing hereditary signs of the sperm and the ovum.

Flowering plants have a complex fertilization, which is called double, since, in addition to the egg, another special cell is impregnated. The formation of spermatozoa occurs in the dust of pollen, and their maturation is carried out in stamens, more precisely in their anthers. The place of egg formation is the ovipules located in the pestle's ovary. When the egg is impregnated with sperm, seeds start to develop from the ovule.

To fertilize the flowering plants, first you need to pollinate the plant, that is, on the stigma of the pistil must get a speck of pollen. Once on the stigma, they begin to germinate inside the ovary, resulting in the formation of a pollen tube. Simultaneously, two spermatozoa are formed in the speck of dust. They do not stand still, but begin to move toward the pollen tube, which penetrates the ovule. Here, as a result of division and lengthening of one cell, an embryo sac forms.

It is necessary for the location in it of an egg and another cell in which a double set of hereditary information is concentrated. After this, the pollen tube germinates into the embryonic sac and merges one sperm with the egg, which results in the formation of a zygote, and the other with a special cell. The development of the embryo comes from the zygote. The second fusion forms the nutrient tissue, or endosperm, necessary for feeding the embryo during the growth period.

What is needed for the existence of each plant species?

• First of all, it is necessary to restore the diploid set of chromosomes, and in its limits - their pairs.
• Ensure material continuity between generations, the next sequence.
• Combine in one form or gender the hereditary properties of two parents.

All this is done at the genetic level. In order for fertilization to take place, the maturation of the maternal and paternal gametes must occur simultaneously.

Fertilization in angiosperms

This process was first described by the German scientist Strasburger in the second half of the nineteenth century. Fertilization angiosperms occurs as a result of the fusion of two nuclei of different gametes: with males and females. Their cytoplasm does not participate in fertilization. The actual fertilization occurs when the sperm merges with the core of the egg.

The place of origin of spermatozoa is pollen grains or pollen tubes. The grain begins to germinate after it reaches the stigma. The time of the beginning of this process for each plant is different, as is the time of fertilization. For example, pollen beet seeds germinate in two hours, and corn - instantly. The first sign of the germination of grain is its increase in volume. Usually one pollen grain forms one tube. But some plants do not obey this rule and form several tubes, of which only one reaches its development.

The pollen tube with sperm moving along it grows and eventually breaks. All its contents are inside the embryo sac. One of the sperm penetrated here is introduced into the egg and merges with its haploid nucleus. Fertilization - what is it? This is the fusion of two nuclei: the sperm and the ovum. The fertilized egg begins to divide, two new cells are obtained. They are divided into four and so on. Thus, multiple division occurs, as a result of which the embryo of the plant develops.

Angiosperms after the fertilization process have the ability to develop an additional organ called endosperm. This is nothing but the nutrient medium of the embryo. When the second sperm and the diploid nucleus merge, a definite set of chromosomes is formed, of which two are of parent origin, and one of the father's. Thus, double fertilization of plant organisms occurs when one sperm merges with the egg and the other with the nucleus of the cell located in the center.

Distinctive features of angiosperms

• Greater adaptability to growth in different conditions.
• Double fertilization, allowing to have a stock of substances necessary for normal germination of seeds.
• Presence of triploid endosperm.
• The formation of ovules inside the ovary, in which the walls of the pestle protect them from damage.
• Development of the fetus of angiosperms from the ovary.
• Finding the seed inside the fruit, the walls of which are its protection.
• The presence of a flower makes it possible to pollinate plants with insects.

Due to the listed characteristics angiosperms occupy the dominant position in the world.

Peculiarity of insemination of angiosperms

It follows from the fact that these plants have a double fertilization. A unique feature is represented by a phenomenon called Xenia. Its meaning lies in the fact that pollen directly affects the properties and signs of endosperm. For example, take the corn.

It happens with yellow and white seeds. Their color depends on the shade of the endosperm. When pollination of female flowers of white-grained maize with pollen of yellow-grained variety, its color will still be yellow, although the development of endosperm occurs on a plant with white grains.

What is the role of flowering plants?

These plants have 13,000 genera and 250,000 species. They are widely distributed around the world. Flowering plants are the key components of the biosphere, producing organic substances that bind carbon dioxide and release oxygen. Pasture food chains start with them. Many species of flowering plants people use for food. They build dwellings and make various household materials.

Do not do without them and medicine. Individual species of angiosperms are dominant on the planet, they are given a decisive role in the formation of the vegetation cover and the creation of the main part of the terrestrial phytomass. Ultimately, it is these plants that determine the possibility of the very existence of man on earth as a species of the biological.