From the seed begins the life of many plants. Miniature chamomile or sprawling maple, fragrant sunflower or juicy watermelon - they all grew out of small seeds.

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 dispersion. Spreading with the help of wind or animals, it is the seeds of plants that germinate and develop new territories. This ability causes plants.

External structure of the seed

As a result of the fertilization process are formed which determines the functions performed.

The size of the seeds of various plants varies considerably: from millimeter poppy seeds to half a meter in Seychelles palm.

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

The peel of the seed is formed from the ovule covers. This is a reliable protection of the seed from the 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 recess, which is the trace of the seed blade. Before the formation of the fetus, it connected the seed with 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 plant, therefore it consists of its miniature parts. They are the germinal root, the bud and the stalk. The stock of nutrients of the embryo is in the cotyledons. There is another plan for the structure of seeds in nature, when the embryo is located inside the endosperm. This is the supply of nutrients.

Ripened seeds can be at rest for a long time, which gives them advantages over disputes that germinate immediately after ripening and die if there are no conditions necessary for development.

In nature, all organs are quite diverse, including seeds. The structure determines their classification. Seeds that are in the endosperm, called protein. Another type of seed is called protein-free.

Seed composition

Studies have shown that all seeds are made of organic matter, most of which is vegetable protein or gluten. Most of this substance is contained in the 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 type of plant. So, sunflower seeds are rich in oils, wheat kernels are starch.

In addition to proteins, fats and carbohydrates, seeds also contain inorganic substances. First of all, it is water 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 irreplaceable.

Seeds of monocots and dicots

The presence of seeds is characteristic only for a certain systematic group of plants - seed. In turn, they are combined into two groups: the Gymnosperms and Angiosperms. Seeds of 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 additional protection for 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 particular group of plants is easy to determine. Considering the structure of the monocotyledonous seed, for example, a wheat kernel, you can make sure that only one cotyledon is present. The seedling of such a seed forms one germinal leaf.

Bean seeds are quite different. Their structure is characteristic of seeds of dicotyledonous plants: two cotyledons in the seed germ and two 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 a 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 do they not 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 increases by several times in volume, and the nutrients of the endosperm of the embryo dissolve. In this state, they become accessible to cells of the living embryo.

Important conditions for germination are also the access of oxygen, sunlight, optimum air temperature. It is usually 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 for the plants themselves, for animals and humans. For plants, they are a means of reproduction and settling on the earth's surface. With a supply of starch, fat and protein, the seeds serve as an excellent nutritional 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 sunflower seeds and corn. Yes, and the success of the future harvest depends largely 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. Such development they achieved precisely due to the presence of important generative organs - seeds.

Seeds are used for sexual reproduction of plants. The good news is that offspring receive genetic material from two different individuals. Combinations of genes become possible, leading to greater diversity than asexual reproduction. One of the main tasks of any individual is the preservation of offspring, its protection and feeding. Consider the structure of a plant seed in more detail to see how these functions are performed.

Seed structure

Angiospermous plants are characterized by the presence of seed coat. The peel protects the embryo from drying out and other environmental influences. It is thin (peas, beans) or thick (apricot, cherry).

The supply of nutrients - it is necessary to obtain all necessary for the growth and development of substances. They will be used until the plant comes out of the ground and can not use sunlight for photosynthesis - self-nutrition.

The tissue in which the nutrients are located is called the endosperm. It consists of large cells that contain starch, proteins and oils.

The germ is a future plant that is still in its infancy, but it already has:

• germinal root;
• gemmule;
• stalk.

The angiosperms in the endosperm contain special hormones (cytokines) that regulate the growth and development of individual parts of the embryo.

But in some groups of plants (for example, in orchids), the structure of a plant's seed differs from the others: a small embryo does not yet have differentiated organs. They develop after germination.

In addition to the embryo, seed lobes are located in the seed. One or two, depending on what kind of plant we have: monocot or dicot.

In the seed of a monocotyledonous plant, the embryo is located at the base of the seed, separated from the endosperm with the help of a modified cotyledon (shield). And during germination, it is not carried to the surface of the soil, the sprout comes out of the ground without seed.

An example of a monocotyledonous plant is wheat.

The structure of a plant seed in dicotyledons is slightly different: the germ sits between the cotyledons. During germination, they are removed from the ground at the top of the germ. Of course, after they fall off, revealing the top of the plant.

A bright representative of dicots - beans.

Seed functions

It is important to remember that seeds are the result of a long evolution of plants. And for many years they have successfully fulfilled all their functions:

• embryo protection - so that the offspring do not die from the influence of the environment, dense skin can withstand changes in temperature and humidity;
• nutrition of the future plant - the endosperm carries all the necessary substances for the development of the embryo;
• distribution - the seeds can have a rather intricate form for flying over long distances, or be surrounded by pulp, so that the animals serve as a “transport” for the plants.

Seed Structure - Video

Seed  - It is a reproductive organ, which in angiosperm plants is formed from the ovule, usually after double fertilization.

The structure of the seed.  Initially, the seed is inside the fruit, which protects it before germination. Each seed consists of the seed coat, the embryo and the storage tissues.

Testa  evolving from integuments (covers) ovuletherefore, it is diploid (2n). It is multi-layered and always in the seed. The thickness and density of the seed coat are related to the characteristics of the pericarp, so it can be soft, leathery, membranous or hard (woody). The seed coat protects the germ from mechanical damage, drying and premature germination. In addition, it can promote seed germination.

Germ  is a plant in its infancy and consists of germinal root, stalk, cotyledon and bud. An embryo develops from a zygote formed by the fusion of sperm with an egg cell (2n).

Storage tissue  Seed are endosperm and perisperm. Endosperm   formed as a result of double fertilization at the merger of the central nucleus of the embryo sac (2n) with the second sperm (1n). Therefore, the endosperm consists of triploid cells (3n). Perisperm   is a derivative of nucellus and consists of cells with a diploid set of chromosomes.

Types of seeds.Seed classification is based on the location of the spare nutrients. Distinguish four types of seeds   (fig. 22):

Fig. 22. Types of seeds:

BUT  - seeds with an endosperm that surrounds the embryo (poppy);

B- seeds with endosperm adjacent to the embryo (wheat); AT  - seeds with small endosperm (surrounds the embryo) and powerful perisperm (pepper); R  - seeds with perisperm (cockle);

D  - seeds with spare substances deposited in the cotyledons of the embryo (peas); 1   - seed coat; 2   - endosperm; 3   - spine; 4   - stalk; 5   - Pochechka; 6   - cotyledons; 7   - pericarp;

8   - perisperm

1) endosperm seeds   mainly characteristic of seeds of the class monocotyledonous, and also some dicotyledons (solanaceous, celery, poppy); spare nutrients are localized in the endosperm;

2) seeds with perisperma   characteristic of cloves, mariews, in which in the mature seed the endosperm is completely absorbed, and the perisperm remains and grows; the seed consists of the seed coat, the embryo and the perisperm;

3) seeds with endosperm and perisperma   they have black pepper, bean, water lily, in the seeds of which the endosperm is preserved and perisperm develops; the seed consists of the seed coat, the embryo, the endosperm and the perisperm;

4) seeds without endosperm and without perisperm   characteristic of legumes, pumpkin, asrovyh; in the process of development, the embryo completely absorbs the endosperm, therefore, the supply of nutrients is in the cotyledons of the embryo; in this case, the seed consists of the seed coat and the embryo.

The structure of the seed with endosperm.Such seeds are characteristic for plants of the class Monocots, for example for bluegrass (cereals). In the grain of wheat (swollen seeds) are distinguished abdominal side  (from the side of the groove) and the opposite - dorsal. At one of the poles of the seed, on the dorsal side, is germ. From the opposite pole there are hairs that retain the weevil in the soil and promote water supply to the endosperm of the seed (Fig. 23).

Fig. 23. The structure of the grain of wheat

(longitudinal section):

1 - hairs; 2   - the pericarp accrete with the seed coat; 3 - aleurone layer;

4 - a layer of spare starch ( 3 –4   - endosperm); 5   - shield; 6 - epiblast; 7 - A bud with leaves; 8   - coleoptile; 9   - spine;

10   - koleoriza (root vagina)

Outside, the weevil is covered with a thin, filmy layer that is difficult to separate from the inside of the weevil. It is a pericarp that has grown together with the seed coat, since the weevil is a single-seeded fruit. The structure of the pericarp and the rind of the seed is clearly visible when considering the microslide of the cross-section of the weevil.

The size of the embryo is insignificant compared with the size of the endosperm. This means that the spare substances are in the endosperm. It consists of two layers: aleurone and storage starch.

Germ  has the following parts:

– germinal root with root cap, koleorizu  (root vagina);

– germ stalk  and kidney  with a growing cone;

– coleoptile  (first germinal leaf) in the form of a colorless cap, with which it breaks through the layers of soil during germination;

– shield  (modified cotyledon) - by its location in the weevil forms a partition between the embryo and the endosperm; under the action of enzymes, the shield transfers the nutrients of the endosperm into an assimilable form and transfers them to the nutrition of the embryo;

– epiblast  located on the opposite side of the shield and is the second reduced cotyledons.

Seed structure without endosperm and without perisperm.  Such seeds are characteristic of legumes, pumpkin, aster. Consider this type of seed structure using the example of common bean (seeds that are swollen in water) (Fig. 24).

Fig. 24. The structure of the common bean seed:

1   - germinal root; 2   - micropyle; 3   - scar;

4   - seed suture; 5   - seed coat; 6   - Pochechka;

7   - embryonic stalk; 8   –– seedlings

Outside the seed is covered with a thick seed coat. It can be a different color. On the inner concave side of the seed are located the hem, micropyle and seed suture.

Scar- This is the place of attachment of the seed to the seed blade.

Micropile - a hole through which water and gases enter the seed. The micropile is located near the scar, on one line.

Seed stitch  - this is a trace from the accretion of the ovule with the seed blade. It is located on the side opposite to the micropill and also adjoins the hem.

Under the seed coat is germ.  There are the following parts:

– two large cotyledons  kidney-shaped; they are germinal leaves, where nutrients are deposited in the stock;

– germinal root;

– germ stalk;

– gemmulecovered with embryonic leaves.

The bean seed does not have endosperm, since the reserve substances are in the cotyledons. It consists of the seed coat and the embryo.

Back in school in the course of botany (grade 6), the structure of the seed was a fairly simple and memorable topic. In fact, this was the result of a long evolutionary process and has a complex and unique structure. In our article, we will consider the features of its structural parts, the structure of the dicotyledonous seed, and also determine the biological role of plant seeds.

The appearance of the seed in the process of evolution

Plants were not always capable of forming seeds. It is known that life originated in water, and the first plants were algae. They had a primitive structure and multiplied vegetatively - by parts of the thallus and with the help of specialized mobile cells - zoospores. The first natives on land were rhinophytes. They, like their future successors - the highest spore plants, multiplied with the help of spores. But water was necessary for the development of these specialized cells. Therefore, with a change in environmental conditions, their numbers also decreased.

The next evolutionary stage was the emergence of the seed. It was a huge step forward for the adaptation and distribution of many plant species. The external and internal structure of the seed determine reliable protection of the embryo, surrounded by a supply of water and nutrients. So, they increase the viability and species diversity of the flora of the planet.

Seed formation process

Consider this process on the example of a group of plants, which in the modern world is dominant. They are representatives. They all form a flower - the most important generative organ. In his pestle is an egg, and the anthers of the stamens contain sperm. After the pollination process, i.e. transfer of pollen from the anther stamens to the stigma of the pistil, sperm along the germinal tube are advanced into the ovary of the stamen, where the process of fusion of gametes takes place - fertilization. As a result, an embryo is formed. At the merger of the second sperm with the central germ cell, a reserve nutrient is formed. It is also called endosperm. The seed structure is completed by a durable outer shell. Such a structure is the basis for the development of the future plant organism.

External structure of seeds

As already mentioned, the seed is covered with peel outside. It is dense enough to protect the embryo inside from mechanical damage, temperature changes and the penetration of harmful microorganisms. But the color of seeds varies widely: from black to bright red. This structure of the seed is easy to explain. In some plants, color is used for masking. For example, so that the birds could not see them in the soil after planting. Other plants, on the contrary, are adapted to seed distribution with the help of various animals. Together with undigested food debris, they secrete them far beyond the habitat of the parent plant.

The internal structure of the seed

The main part of any seed is the germ. This is the future organism. Therefore, it consists of the same parts as the adult plant. This germinal root, stalk, leaf and bud. The structure of the seed of different plants may vary significantly. Most of these nutrients accumulate in the endosperm. This is the shell that surrounds the embryo around, protecting and nourishing it throughout the entire period of individual development. But there are cases when, during the process of ripening and germination of a seed, it completely consumes the substances of the endosperm. Then they accumulate mainly in the fleshy parts of the embryo. They are called cotyledons. Such a structure is typical, for example, for pumpkin or beans. But at shepherd's bag  the supply of substances is concentrated in the tissue of the germinal root. The seeds of various systematic groups of plants are also different.

Features of the Seeds of Gymnastics plants

The external and internal structure of the seed of this group of organisms is characterized by the fact that the process of formation and development of the embryo occurs on the surface of the seed coat. In addition to the main parts, the seeds of Gymnosperms have a pterygoid, membranous outgrowth. It helps to spread the seeds of these plants with the help of the wind.

Another feature of the Gymnoscious seeds is the duration of their formation. For them to become viable, four months to three years must pass. The process of ripening seeds occurs in cones. This is not a fruit at all. They are specialized modifications of the shoot. Some seeds of conifers are able to be stored in cones for decades. All this time they retain their vitality. In order for the seeds to fall into the ground, the scales of the cone unfold themselves. They are picked up by the wind, sometimes carrying over long distances. If the bumps are soft, externally resembling nuts, they are not revealed themselves, but with the help of birds. Especially love to feast on seeds of various types of jays. It also contributes to the resettlement of representatives of the Gymnastics Division.

The name of this systematic unit itself indicates that the embryo of the future plant is poorly protected. Indeed, the presence of endosperm guarantees only the development of the seed. But the cones of many plants are revealed during adverse development conditions. Once on the soil surface, the seeds are exposed to low temperatures and lack of moisture, so not all of them germinate and give rise to a new plant.

Features of Flowering Plant Seeds

Compared with the Gymnosperms, representatives of the Department of Flowers have a number of significant advantages. The formation of their seeds occurs in the ovary of flowers. This is the most extended part of the pistil, which gives rise to fruits. As a result, seeds develop inside them. They are circled by three layers of the pericarp, which are distinguished by their properties and functions. Consider their structure on the example of drupes plum. The outer leathery layer protects against mechanical damage, ensuring integrity. The middle one is juicy and meaty. It nourishes and provides the germ with the necessary moisture. The internal ossified layer is additional protection. As a result, seeds have all the necessary conditions for development and germination, even under adverse circumstances.

Monocot Seeds

The structure of the seed is very easy to determine. Their germ consists of only one cotyledon. These parts are also called germinal leaves. Monocots are all plants Onion and Lily. If the seeds of corn or wheat are germinated, soon one leaflet is formed from the surface of the soil of each grain. This is the cotyledons. Tried to split a grain of rice into several parts? Naturally, this is impossible. All because her embryo is formed of a single cotyledon.

Seeds of Dicots

Seeds Solanaceae, Astrovye, legumes, Cabbage and many others are somewhat different in structure. Even based on the name, it is easy to guess that their embryo consists of two cotyledons. This is a basic systematic feature. The structure of the seeds of dicotyledonous plants is easy to see with the naked eye. For example, a sunflower seed is easily divided into two equal parts. These are the cotyledons of its embryo. The structure of bichromatic seed can be seen on young shoots. Try to germinate the seeds of ordinary beans at home. And you will see two carpels that appear above the surface of the earth.

Seed germination conditions

The structure of the seeds of dicotyledonous plants, as well as representatives of other systematic units of this kingdom of nature, determines the presence of all the necessary substances for the development of the embryo. But other conditions are necessary for germination. For each plant they are completely different. First, it is a certain air temperature. For heat-loving plants it is +10 degrees Celsius. But winter wheat begins to develop already at + 1. Water is also needed. Thanks to her, the seed swells, which accelerates the processes of respiration and metabolism. Nutrients transfer to a form in which they can be absorbed by the embryo. The presence of air and a sufficient amount of sunlight are two more conditions for seed germination and the development of the whole plant, since without them photosynthesis is impossible.

Seeds and fruits

Each fruit contains seeds of higher plants almost identical. But the fruits are more diverse. Allocate dry and juicy fruits. They differ in the structure of the layers that are located around the seed. In juicy one of the layers of the pericarp necessarily fleshy. Plum, peach, apple, raspberry, strawberry ... These delicacies are loved by everyone precisely because they are juicy and sweet. In dry fruit, the pericarp is leathery or ossified. Its layers usually grow together into one that reliably protects the seeds inside. A box of poppies, a mustard pod, a grain of wheat has just such a structure.

The biological role of seeds

Most plants on the planet use seeds for breeding. The structure of the seeds of modern plants is the result of a long evolution. These generative organs contain the germ and the stock of substances that ensures its growth and development even in adverse conditions. Seeds have adaptations for distribution, which increases their chance of survival and resettlement.

So the seed is the result of the fertilization process. It is a structure consisting of an embryo, storage substances and protective skin. All its elements perform certain functions due to which the group of seed plants occupied a dominant position on the planet.