It is with the seed that the life of many plants begins. Miniature chamomile or sprawling maple, fragrant sunflower or juicy watermelon - they all grew from a small seed.
What is a seed
A seed is a generative organ. In addition to the function of sexual reproduction, it fulfills an important function of plant settlement. Spread with the help of wind or animals, it is the seeds of plants that germinate and develop new territories. This ability is determined by the structure of the seed of the plant.
External structure of the seed
As a result of the fertilization process, seeds are formed whose structure determines the functions performed.
The seed size of various plants varies significantly: from millimeter poppy seeds to half-meter in Seychelles palm.
The shape of the seeds is also diverse, 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 peel of the seed is formed from the integument of the ovum. This is a reliable protection of the seed from lack of moisture and environmental hazards.
The protective cover can be painted in different colors. Looking at the concave side of the seed, it is easy to notice the indentation that follows from the placenta. Before the fetus formed, she connected the seed to the pericarp.
The internal structure of the seed
The second most important part of each seed is the germ. It is the forerunner of the future leaf-stem plant, therefore it consists of its miniature parts. They are the germinal root, kidney and stalk. The nutrient reserve of the embryo is in the cotyledons. There is also another plan of seed structure in nature when the embryo is inside the endosperm. This is the supply of nutrients.
Ripened seeds can be at rest for a long time, which gives them advantages over spores that germinate immediately after ripening and die if there are no conditions necessary for development.
In nature, all organs, including seeds, are quite diverse. The structure determines their classification. Seeds in which nutrients are found in the endosperm are called proteinaceous. Another type of seed is called proteinless.
Seed composition
Studies have shown that all seeds are made up of organic substances, most of which are plant protein or gluten. Most of this substance is found in cereal plants, from which I make flour and bake bread.
Also in the seeds is fat and carbohydrate starch. The percentage of these substances varies depending on the type of plant. So, sunflower seeds are rich in oils, wheat grains - in starch.
In addition to proteins, fats and carbohydrates, seeds also contain inorganic substances. This is primarily the water necessary for the development of the future plant, and mineral salts.
Regardless of quantity, each substance has its own significance for the development and growth of seeds and is indispensable.
Seeds of monocotyledonous and dicotyledonous plants
The presence of seeds is characteristic only for a certain systematic group of plants - seed. In turn, they are combined into two groups: Gymnosperms and Angiosperms. The seeds of gymnosperm coniferous plants are located on the scales of cones without coating. Therefore, 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.
Much more likely to germinate are seeds of angiosperms. Representatives of this group occupy a dominant position due to the presence of fruits that protect their seeds. The structure of each fetus provides reliable protection against cold and nutrition of the embryo.
The belonging of a plant to a certain group is easy to determine. Having examined the structure of a monocotyledonous seed, for example, a wheat grain, we can verify that there is only one cotyledon. The seedling of such a seed forms one germinal leaf.
Beans seeds are arranged in a completely different way. Their structure is characteristic of the seeds of dicotyledonous plants: two cotyledons in the seed embryo and two embryonic leaves. In addition to the structure of the embryo, there are other signs that determine the group of plants. This is the type of root system, the presence of cambium, the structure and venation of leaves, the shape of the leaves. But the structure of the seed is a defining feature.
Seed germination
Surely, every house has many seeds. Beans, peas, lentils, sunflower seeds, and even wheat are frequent guests in the kitchen. But why do not 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 of oxygen, sunlight, optimal air temperature. Usually it is above 0 degrees. But the seeds of winter cereals are specially treated with cold, and a 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 feed 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 of sunflower and corn. And the success of the future crop largely depends on the quality of the seed.
Seed plants are the most highly developed, complex in structure, vital processes, and occupy a dominant position in the plant world. They achieved this development precisely thanks to the presence of important generative organs - seeds.