Flowering plants are a large and diverse group that dominates most terrestrial ecosystems. From the main flowering plants cultivated by man, his existence depends. But for flowering plants to appear, they must go through the stage of pollination and fertilization. How this happens, read this article.
Pollination
This process is carried out by transferring pollen from the stamens to the pestle. How does pollination and fertilization occur in flowering plants? This is done in two ways: self-pollination and cross-pollination. In the first case, the transfer of pollen grains to the pestle occurs in the same flower. So pollinated peas or tulips. In cross-pollination, the pollen of the flower of one plant is transferred to the pistil of another. Plants are pollinated most often by insects, in rare cases by wind (sedge and birch), birds and water.
As a result of pollination by insects, bright, clearly visible flowers are formed with a pleasant smell and nectaries, which produce a sweet liquid. Still such plants form a lot of pollen. It is an insect feed. They are attracted by the bright color or smell of flowers. When insects extract nectar, they touch the surface of pollen grains that adhere to their body, and when flying onto a flower of another plant, remain on the pestle. This is how insect pollination occurs. Many flowering plants are pollinated only by certain insects: fragrant tobacco - a nocturnal butterfly, creeping clover - a bee, and meadow - a bumblebee.
Cross-pollinated plants are better suited to changing environmental conditions. But the pollination process in this case depends on a number of factors. And self-pollination does not depend on anything. Weather conditions and the absence of intermediaries are not terrible for him.
Fertilization
A pollen grain, falling on the stigma of a pestle, begins to sprout gradually. From a vegetative cell, the development of a long pollen tube occurs. Growing up, she reaches the level of location of the ovary, and then the ovule. At the same time, a pair of sperm is formed, which penetrates the pollen tube. She, in turn, enters the ovule through the pollen duct. Then the tube at the very tip breaks and releases male sperm, which are immediately sent to the germinal membrane, it is called the sac. Here the eggs develop.
Next, the egg fertilizes with one sperm, and the formation of a zygote, from which a small embryo of a completely new organism of plant origin begins to form. At the same time, the second sperm merges with the zygote nucleus or with the polar nuclei. As a result, a triploid cell is formed, from which the endosperm arises. It is called nutrient tissue, which contains the reserves of the necessary substances for the normal development of the embryo of the future plant. This is how the sexual reproduction organs of flowering plants are presented.
When one sperm with an egg, and the other, with polar nuclei, merge together, this process is called double fertilization. It is peculiar only to flowering and is a unique feature of angiosperms. A fertilized ovule grows into a seed. As a result, the ovary of the pestle grows. In flowering plants, the fetus develops from the wall of the ovary.
Breeding
Any plant, reaching a certain size and passing the appropriate stages of development, begins to reproduce organisms of a similar kind. This is reproduction, which is a necessary property of life. All organisms thus prolong the existence of the species itself. There are sexual and asexual reproduction, which occurs with the participation of one individual. When plants develop specialized cells - spores, organisms begin to multiply.
This is characteristic of mosses, algae, ferns, plunders and horsetails. Spores are special small cells with a nucleus and cytoplasm that are coated. They are able to endure poor conditions for a long time. But, getting into a favorable environment, they quickly germinate and begin to form daughter plants, whose properties do not differ from the mother ones.
During sexual reproduction, the female and male germ cells merge, resulting in the formation of daughter organisms that are qualitatively different from the parent. Parental organisms of the female and male origin are already taking part here.
The structure and development of ovule plants
In the composition of the ovum, the dominant role is played by macrosporangia. It is in it that the laying of one mother cell occurs, from which macrospores are formed. Three things begin to die, and ultimately collapse. The fourth macrospore is the feminine, lengthens and its core is divided. Then, daughter nuclei move to different poles of a cell elongated in shape. Each nucleus formed is still divided twice.
In cells located near different poles, four nuclei are formed. This is called the embryo sac, in which there are eight haploid nuclei. Next, from each of the four nuclei, one of them follows to the center of the embryonic sac. There they merge, as a result of which they form a secondary nucleus - diploid.
Then, in the embryo sac, in the cytoplasm, partitions are formed between the nuclei at the cellular level. The bag becomes seven cells. Near one of its poles is the egg apparatus, which includes a large egg and two auxiliary cells. Antipode cells are located at the other pole, there are three in total. So, the bag now has six haploid cells and one diploid, with a secondary nucleus. It is located in the center of the germinal sac.
What is an ovary?
It is called the lower thickened part of the pestle with a cavity closed inside, in which the ovules are located. Pollen enters the ovule from the stigma of the pestle, which is protected from adverse conditions by the internal moist cavity. In the ovum, the development of female germ cells - ovules.
In flowering plants, the ovary develops from the wall of the ovary. fruit with seeds. The ovary of the flowers is multi-nested and single-nested. In the first case, it is divided into nests by partitions, and in the second - not. The ovary of flowering plants is also divided into single-seed and multi-seeded. It depends on the number of ovules in it: a plum, for example, has one, and a poppy has a lot.
What are the ovaries?
Types of ovaries of flowering plants are:
- Top. To the receptacle, it is attached freely, not fused with other departments in the flower. The walls of the ovary are formed from carpels. In flowering plants, the fetus develops from the wall of the ovary. An example is buttercup and cereal plants. These flowers are called subpestic or parapestic.
- The lower ovary is always under the receptacle. It is formed with the participation of other flower departments: the base of the sepals and stamens with petals, which in many flowers are attached to the top of the ovary. In flowering plants, the fruit develops from the wall of the ovary. An example is the Asteraceae, cactus and orchid plants. The flower is called suprastatic.
- Semi-low ovary. Its top does not grow together with other parts, so it is free. Flowers of this type are called semi-authentic. These are the types of ovaries of flowering plants.
Flowering plants
They are the most progressive group of plants, numbering two hundred and fifty thousand species, distributed throughout the planet Earth. The smallest plant is duckweed, whose diameter is one millimeter. She lives in the water. The largest flowering plants are trees, reaching a height of one hundred meters or more.
The appearance of flowering plants is due to the development of a special organ of reproduction - a flower. In some plants, it is painted in bright colors, in others it smells wonderful. Flowers are small and inconspicuous in plants similar to grass. Despite the huge variety of flowering plants, they all harmoniously fit into our lives: decorate gardens and parks, give the joy of communicating with them.
Flower structure
The flower is a complex system of organs that provides for the reproduction of plants by seeds. Its appearance led to the wide distribution of angiosperms (flowering) plants on Earth. A flower has many functions. With its participation, stamens with pollen grains, pistils with ovules are formed. It plays a major role in pollination, fertilization, and the formation of seeds and fruits.
The flower is a shortened, modified, limited shoot growth, bearing perianth, pistils and stamens. All angiosperms have similar in structure and different in shape flowers. Thus, adaptation to pollination occurs in various ways.
The flower may end on the main or side stems, the bare part of which under the flower itself is called the pedicels. It is greatly shortened or absent at all from sessile flowers. The pedicel passes into the receptacle, which is elongated, convex, concave or flat. It contains all parts of the flower. These are sepals with petals, stamens with a pestle, in the lower part of which an ovary is formed, in which there are ovules or ovules. A flower with such an ovary is more concave in the receptacle. If the ovary forms at the top of the pestle, the receptacle will be convex or flat.