Fertilization is the fusion of two cells, resulting in the formation of a new cell, giving rise to another organism of the same genus or species. What is double fertilization in flowering 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. Each pair of chromosomes has one paternal and one maternal cell. The essence of the fertilization process is to restore the diploid set of chromosomes and combine the hereditary material of the parents. Their offspring will be more viable, as it combines the most useful qualities from father and mother.
Fertilization - what is it?
This is the process of stimulating the egg to develop as a result of the union of the nuclei. Fertilization - what is it? This is an irreversible process that occurs as a result of the fusion of heterosexual gametes and the union of their nuclei. A fertilized egg does not undergo this procedure a second time.
But there are plants that reproduce a new generation only with the help of a female gamete without fertilization. This reproduction is called virgin. It is noteworthy that these two methods of reproduction in one plant species can alternate.
Double fertilization of flowering plants
The germ cells of both beginnings are called gametes. Moreover, the eggs are female, and the sperm are male, which are motionless in the seed plants and motile in the spore. Fertilization - what is it? This is the appearance of a special cell - a zygote, containing hereditary signs of sperm and egg.
Flowering plants have complex fertilization, which is called double fertilization, because, in addition to the egg, another special cell is fertilized. The formation of sperm occurs in the dust grains of pollen, and their maturation is carried out in the stamens, more precisely in their anthers. The ovum is formed by ovules located in the ovary of the pestle. When the egg is fertilized with sperm, seeds begin to develop from the ovum.
For fertilization in flowering to occur, you must first pollinate the plant, that is, dust particles of pollen must get on the stigma of the pestle. Once on the stigma, they begin to grow inside the ovary, resulting in the formation of a pollen tube. At the same time, two spermatozoa form in a speck of dust. They do not stand still, but begin to advance towards the pollen tube, which penetrates the ovule. Here, as a result of division and lengthening of one cell, the formation of an embryonic sac occurs.
It is needed for the location of an egg and another cell in it, in which a double set of hereditary information is concentrated. After this, the pollen tube grows into the embryo sac and one sperm merges with the egg, resulting in the formation of a zygote, and the other with a special cell. The development of the fetus comes from the zygote. The second fusion forms nutrient tissue, or endosperm, necessary for the nutrition of 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 within its limits - their paired.
- To provide material continuity between generations following the sequence.
- Combine the hereditary properties of two parents in one form or genus.
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.
Angiosperm Fertilization
This process was first described by the German scientist Strasbourg in the second half of the nineteenth century. Fertilization of angiosperms occurs as a result of the fusion of two nuclei of different gametes: male and female. Their cytoplasm is not involved in fertilization. In fact, fertilization occurs when sperm merges with the nucleus of the egg.
Sperm are pollen grains or pollen tubes. The grain begins to germinate after it falls on the stigma. The start time of this process is different for each plant, as is the time of fertilization. For example, beet pollen grains germinate after two hours, and corn - instantly. The first sign of 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.
A pollen tube with sperm moving along it grows and eventually bursts. All its contents are inside the embryo sac. One of the sperm that penetrated here is introduced into the egg and merges with its haploid nucleus. Fertilization - what is it? This is a fusion of two nuclei: sperm and egg cells. 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 diploid nucleus merge, a certain set of chromosomes is formed, of which two are of maternal origin, and one of the paternal origin. Thus, the double fertilization of organisms of plant origin 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
- Great adaptability to growth in different conditions.
- Double fertilization, allowing you to have a supply of substances necessary for normal seed germination.
- The presence of a triploid endosperm.
- The formation of ovules inside the ovary, in which the walls of the pestle protect them from damage.
- The development of the fetus of angiosperms from the ovary.
- Finding a seed inside a fetus whose walls are its protection.
- The presence of a flower makes it possible to pollinate plants with insects.
Due to the above characteristics, angiosperms occupy a dominant position in the world.
Feature of fertilization of angiosperms
It follows from the fact that these plants have double fertilization. A unique feature is represented by a phenomenon called xenia. Its meaning is that pollen directly affects the properties and signs of the endosperm. For example, take corn.
It happens with yellow and white seeds. Their color depends on the shade of the endosperm. When pollinating female flowers of white-corn maize with yellow-pollen pollen, its color will still be yellow, although the development of endosperm occurs on a plant with white grains.
What role do flowering plants play?
These plants comprise 13,000 genera and 250,000 species. They are widely distributed around the world. Flowering plants are key components of the biosphere that produce organic substances that bind carbon dioxide and produce oxygen. Pasture food chains start with them. Man uses many varieties of flowering plants for food. They build houses and make various household materials.
Not without them, and medicine. Certain species of angiosperms are dominant on the planet, they play a decisive role in the formation of vegetation cover and the creation of the main part of terrestrial phytomass. Ultimately, it is these plants that determine the possibility of the very existence of man on earth as a biological species.