Seeds: structure. External and internal structure of the seed

It is from the seed that the life of many plants begins. Miniature chamomile or spreading maple, fragrant sunflower or a juicy watermelon - they all grew from a small seed.

What is the seed

The seed is a generative organ. In addition to the function of sexual reproduction, it performs an important function of plant dispersal. Propagating with the help of wind or animals, it is the plant seeds that germinate and develop new territories. This ability determines the structure of the seed of the plant.

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 considerably: from millimeter seeds of poppies to half-meters in the Seychellois palm.

The shape of the seeds is also diverse, but more often it is round. Usually, bean seeds, the structure of which is typical, serve as an example of the study of this generative organ.

The seed coat is formed from the covers of the ovule. This is a reliable protection of the seed from lack of moisture and dangerous environmental factors.

The protective cover can be painted in different colors. Considering the concave side of the seed, it is easy to notice the groove, which is a trace from the seed stem. Before the formation of the fetus, she connected the seed with the pericarp.

The internal structure of the seed

The second most important part of each seed is the embryo. It is the forerunner of the future leafy plants, therefore it consists of its miniature parts. They are the embryonic root, the kidney and the stem. The nutrient supply 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.

Ripened seeds can be in a state of rest for a long time, which gives them advantages over spores that germinate immediately after maturing and die if there are no conditions necessary for the 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 protein-free.

Seed Composition

Studies have shown that all seeds consist of organic substances, most of which are plant protein or gluten. Most of this substance is contained in cereals, 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 plant species. So, sunflower seeds are rich in oils, wheat grains - starch.

In addition to proteins, fats and carbohydrates, the seeds also contain inorganic substances. This is primarily water, which is necessary for the development of the future plant, and mineral salts.

Regardless of the 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. Seeds of gymnosperms of coniferous plants are located on scales of cones without covering. Therefore they have such a name. In February, the bare snow falls seeds, the structure of which does not provide additional protection of the embryo from adverse conditions.

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 fetus provides reliable protection against cold and nutrition of the embryo.

Belonging to a certain group of plants is easy to determine. Having considered the structure of a monocotyledon, for example, a grain of wheat, one can be convinced of the presence of only one cotyledon. The germ of this seed forms one germinal leaf.

The bean seeds are completely different. Their structure is characteristic of seeds of dicotyledonous plants: two cotyledons in the embryo of the seed and two embryonic leaves. In addition to the structure of the embryo, there are other signs that determine the group of plants. This 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 the defining feature.

Germination of seeds

Surely, every house has a lot of seeds. Beans, peas, lentils, sunflower seeds, and even wheat are frequent guests in the kitchen. But why do not they form sprouts? 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 several times increases in volume, and the nutrients of the endosperm of the embryo dissolve. In this state, they become available to the cells of the living germ.

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 plants themselves, for animals and for humans. For plants, they are a means of reproduction and dispersal over the earth's surface. Having a stock of starch, fat and protein, the seeds serve as an excellent nutritious food for animals and birds. For man, they are also a food product. It is impossible to imagine the life of people without bread made from seeds of cereals or without vegetable oil from sunflower seeds 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, processes of vital activity, and occupy a dominant position in the plant world. This development they have achieved precisely because of the presence of important generative organs - seeds.