It is from the seed that the life of many plants begins. Miniature chamomile or spreading maple, fragrant sunflower or juicy watermelon - they all grew from a small seed.
What is a seed
The seed is a generative organ. In addition to the function of sexual reproduction, it performs an important function of plant settlement. Spreading with the help of wind or animals, it is the seeds of plants that germinate and develop new territories. This ability determines the structure of the plant seed.
External structure of the seed
As a result of the fertilization process, seeds are formed, the structure of which determines the functions performed.
The size of the seeds of various plants varies greatly: from millimeter poppy seeds to half a meter in the Seychellois palm.
The shape of the seeds is also varied, but more often it is rounded. Typically, bean seeds, whose structure is typical, serve as an example of the study of this generative organ.
The seed coat is formed from the integument of the ovule. This is a reliable protection of the seed from lack of moisture and dangerous environmental factors.
Protective cover can be dyeddifferent colors. Looking at the concave side of the seed, it is easy to notice the depression, which is a trace from the seed stalk. Before the fruit was formed, she connected the seed with the pericarp.
Internal structure of a seed
The second most important part of every seed is the germ. It is the forerunner of the future leafy plant, therefore it consists of its miniature parts. They are the germinal root, bud and stalk. The nutrient reserve of the embryo is in the cotyledons. There is also another plan for the structure of seeds in nature, when the embryo is inside the endosperm. This is the supply of nutrients.
Mature seeds can be dormant for a long time, which gives them advantages over spores that germinate immediately after ripening and die if there are no necessary conditions for development.
In nature, all organs are quite diverse, including seeds. The structure determines their classification. Seeds in which nutrients are in the endosperm are called proteinaceous. Another type of seed is called protein-free.
Seed Composition
Studies have shown that all seeds are composed of organic matter, most of which is vegetable protein or gluten. Most of this substance is found in cereal plants, from which I make flour and bake bread.
The seeds also contain fat and carbohydrate starch. The percentage of these substances varies depending on the type of plant. So, sunflower seeds are richoils, wheat grains - starch.
In addition to proteins, fats and carbohydrates, seeds also contain inorganic substances. This is, first of all, the water necessary for the development of the future plant, and mineral s alts.
Regardless of quantity, each substance has its own importance for the development and growth of seeds and is irreplaceable.
Seeds of monocots and dicots
The presence of seeds is characteristic only for a certain systematic group of plants - seed plants. In turn, they are combined into two groups: gymnosperms and angiosperms. Seeds of gymnosperms of conifers are located on the scales of cones without coating. That is why they have such a name. In February, seeds fall on bare snow, the structure of which does not provide for additional protection of the embryo from adverse conditions.
The seeds of angiosperms are much more likely to germinate. Representatives of this group occupy a dominant position due to the presence of fruits that protect their seeds. The structure of each fruit provides reliable protection from the cold and nutrition of the embryo.
It is easy to determine whether a plant belongs to a certain group. Having considered the structure of a monocotyledonous seed, for example, a grain of wheat, one can be convinced that there is only one cotyledon. The sprout of such a seed forms one germ layer.
Bean seeds are arranged quite differently. Their structure is typical for the seeds of dicotyledonous plants: two cotyledons in the seed embryo and twogerm layers. In addition to the structure of the embryo, there are other signs that determine the group of plants. This is the type of the root system, the presence of cambium, the structure and venation of the leaves, the shape of the leaves. But the structure of the seed is the defining feature.
Seed germination
Surely, every house has a lot of seeds. Beans, peas, lentils, sunflower seeds, and even wheat are frequent guests in the kitchen. But why don't they form seedlings? The answer is simple: certain conditions are necessary for their germination. The most important of these is water. When it penetrates, the seed swells and increases several times in volume, and the nutrients of the endosperm of the embryo dissolve. In this state, they become available to the cells of a living embryo.
Important conditions for germination are also access to oxygen, sunlight, optimal air temperature. Usually it is above 0 degrees. But the seeds of winter cereals are specially treated with cold, and the negative temperature is a necessary condition for the development of their seeds.
The role of seeds in nature and human life
Seeds are of great importance both for the plants themselves and for animals and humans. For plants, they are a means of reproduction and settlement on the earth's surface. With a supply of starch, fat and protein, the seeds serve as an excellent nutritious food for animals and birds. For humans, they are also a food product. It is impossible to imagine the life of people without bread made from cereal seeds or without vegetable oil from seeds.sunflower and corn. And the success of the future harvest largely depends on the quality of the seed.
Seed plants are the most highly developed, complex in structure, life processes, and occupy a dominant position in the plant world. They achieved such development precisely due to the presence of important generative organs - seeds.
