In the plant world, the most perfect and numerous group is the department of angiosperms or flowering plants. These include all plants that are equipped with an organ of seed reproduction - a flower. In total, there are more than 350 thousand different plant species on the planet, and of these, ¾ of them belong to angiosperms. They can easily grow in water, arid deserts and cover the lands of the steppes with a multi-colored carpet. This article will look at the life cycle of angiosperms that have adapted perfectly to various environmental conditions and are distributed from the icy Arctic to Antarctica.
Definition
Angiosperms or flowering plants are plants whose seed reproduction organ is a flower. These include herbs, flowers, shrubs and trees. Flowers develop male and female gametes.(reproductive cells). Seeds are located inside the ovary, in fruits, hence the name - angiosperms. Flowers vary in shape, size, structure and color. In some plants they are pollinated by the wind, in others by insects. The growing season is also different for everyone - from a few weeks (for ephemera) to hundreds of years (for oak). All angiosperms have different heights. There are many plants with erect trunks, but there are creeping, creeping and climbing stems. The root system and leaves are quite diverse. Despite this difference, there is a definite life cycle of angiosperms. All plants are grouped according to their characteristic features. The main criterion of taxonomy is the degree of relationship between plants. All flowering plants are divided into two classes - dicots and monocots.
They are of great importance both in nature and in the life of the individual. Some of them are eaten by humans, while others are fed to domestic and wild animals. Vegetable raw materials are used in various industries. Ornamental plants are used for landscaping, woody plants for construction, medicinal plants for traditional and folk medicine.
The development cycle of angiosperms
There is a change of generations. Meiosis produces spores, while gametes are the result of mitosis. Both those and others are formed in a flower. Therefore, it is called the organ of sexual and asexual reproduction. In pollen grains (microspores), male gametes are formed in large quantities, which are carried by insects or wind tostigma.
This phenomenon allows angiosperms to do without floating spermatozoa. At all stages of development, both embryos and spermatozoa with eggs are under the reliable protection of saprophyte tissues. The result is a high viability of flowering representatives of the flora.
Flower structure
The cycle of angiosperms is the alternation of generations of gametophyte (sexual) and sporophyte (asexual), which is represented by an ordinary plant, consisting of a stem, root, leaves and flower.
The corolla of the petals of the latter and the green sepals are protection for the female part of the flower (pistil) and the male part (stamens). The pistil includes a stigma, a style and an ovary with an egg. The stamens are endowed with the ability to produce pollen, which, once in the ovary, fertilizes the egg. As a result, a seed is formed. The fruit that protects the seed and allows it to spread comes from the ovary.
Features of angiosperms
The exclusivity of these plants is as follows:
- Double fertilization. From one seed, after contact with the egg, a zygote arises. Further, an embryo is formed from it. From the second, a triploid cell is formed, subsequently leading to the development of an endosperm containing nutrients.
- Pollen initially enters the stigma of the pistil and further into the pollen entrance of the ovule. The latter is protected from damage, as it is enclosed in the pistil cavity of the ovary.
- The presence of a flower makes it possible to reproduce by seeds.
- The female gametophyte is the embryo sac, while the male gametophyte is the pollen grain. They develop quite quickly and are greatly simplified, unlike other plants. On the other hand, they are under constant protection and depend on the sporophyte.
- The life cycle of angiosperms is dominated by the diploid sporophyte.
Variety
The variety of life forms and sizes of angiosperms strikes the imagination of the individual. For example, Wolffian duckweed is considered the smallest representative, its diameter is about one millimeter. And on the other side - a giant eucalyptus, reaching a height of one hundred meters. Thus, among the flowering ones there are:
- herbs;
- shrubs;
- trees;
- shrubs;
- lianas and others.
The first three are considered the main ones. Shrubs and trees are perennial. Some tree species can live for more than a thousand years. There are many annuals among herbaceous plants. During the growing season, they go through the entire life cycle of angiosperms. Briefly, this can be described as follows:
- Grow from seeds.
- Blossom.
- Grow seeds.
- Die off.
There are quite a lot of perennial and biennial grass species in nature. In cases where they grow in places where winters are cold, the green ground part dies off during the cold season. However, tubers or rhizomes remain in the ground, having some reservenutrients. In spring, a new green part of the plant is formed. It is important to remember that biennial plants bear fruit and bloom only in the second year, and then the plant dies. And perennials delight with flowering every year. Here is such a different life span of angiosperms. In addition, among flowering plants there are saprophytes, parasites and semi-parasites that have completely lost the ability to photosynthesize.
Main differences in the reproduction of angiosperms and gymnosperms
The exclusivity of angiosperms is the presence of a flower in which spores appear and hatch, forming a female and male sexual generation with gametes, and pollination, gynogenesis and seed development are also carried out. In angiosperms, gametophytes, seeds are formed in pistils and stamens, and not in cones, as in gymnosperms. In angiosperms, the ovules are formed inside the pistil, unlike the gymnosperms. Thanks to this, they are safely hidden and protected from bad environmental conditions. After fertilization, a seed is formed from the ovule, and the fruit arises from the bottom of the pistil. The next difference is the double fertilization of flowering plants, i.e., the endosperm is formed in them after, and in gymnosperms before fertilization. In addition, vegetative parthenogenesis occurs only in angiosperms. Thus, the life cycle of angiosperms is somewhat different than that of the gymnosperms of the plant world.
The difference between sexual and vegetative reproduction
Flowering plants are characterized by both sexual and vegetative reproduction. The first is related to the flower, soas it is considered a reproductive organ. From the zygote formed as a result of the fusion of gametes, the embryo of a new plant subsequently develops.
And with the vegetative method of reproduction, new representatives are formed due to the regeneration of leaves, shoots, roots, i.e. vegetative organs.
Gymnosperms
When they reproduce, these plant species produce seeds, not spores. In addition, they do not form fruits, and their seeds are not protected and are located on the surface of the cone scales. Larch, pine, spruce are the most famous instances of gymnosperms. For the most part, needles (needles) instead of leaves. A large group among the gymnosperms are conifers, and they are also represented by vines, trees and shrubs. Herbs in the department of gymnosperms are absent. All gymnosperms are evergreen perennials with a long lifespan. Seeds develop from ovules, which have nutrients in the skin, this is considered an important advantage over spore plants.
Gymnosperm cycle
The life cycle of gymnosperms and angiosperms has some differences. In the former, the asexual generation dominates, and the gametophyte develops on the sporophyte. Let us consider in more detail the development of gymnosperms using the example of an evergreen tree (pine). An adult plant is a sporophyte. Spores ripen in the so-called sporangia located in cones. Moreover, male and female differ in color: the first is yellow, and the second is red in the first year. At the endspring (in May) and at the beginning of the first summer month, male spores fall out of their houses and, with the help of the wind, move to cones of the opposite kind. The female spores germinate inside the sporangia, forming a bud with two organs. It is in them that the development of the egg takes place, that is, the growth is a gametophyte. He is the new generation of pine and at the same time the mother organism for the future embryo. The male gametophyte is the pollen that produces sperm.
In the first year, the gametes of both sexes are immature, so there is no fertilization. Female cones close after pollination, and male and female gametes develop in them throughout the year. A year later, fertilization takes place in female greenish and lignified cones. The first cell of the sporophyte is the zygote, which divides and forms from new cells an embryo that has a root and a shoot, i.e., vegetative organs. A shell forms around it and nutrients are deposited. This is how the seed is formed in the female cone. In the third year, they turn brown and open. As a result, the seeds fall into the soil and germinate, a young pine sporophyte appears.
Conclusion
More than 350 families, about thirteen thousand genera and more than three hundred thousand species of angiosperms are known. These autotrophic organisms are an essential component of the Earth's shell.
Flowering plants dominate gymnosperms. They make it possible for the animal world to exist. It has been proven that some groups of animals originated only afterThe earth was filled with angiosperms. This is perhaps the only group represented among higher plants, whose specimens were able to re-master the marine environment, i.e., together with algae, various species of flowering plants live in s alt water.
