Seed. Its development and education. Types of seeds and their structure What does a seed consist of?

.(Source: “Biological Encyclopedic Dictionary.” Editor-in-chief M. S. Gilyarov; Editorial Board: A. A. Babaev, G. G. Vinberg, G. A. Zavarzin and others - 2nd ed., corrected . - M.: Sov.

.(Source: “Biology. Modern illustrated encyclopedia.” Chief editor A. P. Gorkin; M.: Rosman, 2006.)

See what “SEED” is in other dictionaries:

Wed. a substance containing an animal or plant germ. From the seed comes the tree, from the tree the fruit, from the fruit the seed. As is the seed, so is the tribe, and vice versa. Every past brings its own seed. | Descendants, descending generation. To everyone, like a seed... ... Dahl's Explanatory Dictionary

Cycad seeds are large. Elliptical, oblong ovoid or spherical in shape, they usually have a length of 3-4 cm with a thickness of 2-3 cm. But some species have either smaller or larger seeds. So, zamia seeds... ... Biological encyclopedia

SEED, gen. and dates seed, seed, seed, pl. seeds, seeds, cf. 1. The reproductive organ of a plant, the grain from which a new plant develops. The seed develops from the ovule. The nucleus of the seed contains the embryo. The plant produced seeds. Breeding... ... Ushakov's Explanatory Dictionary

Grain, seed. Cm … Synonym dictionary

Modern encyclopedia

In botany, the organ of reproduction, dispersal and survival of unfavorable conditions in seed plants. Develops from an ovule, usually after fertilization. In a seed, there is an embryo, a peel (shell) and, in many plants, tissues with reserve... ... Big Encyclopedic Dictionary

Seed... The initial part of complex words, introducing the meaning of the word: seed 1., 4. (cotyledon, seminal effusion, ovule, etc.). Ephraim's explanatory dictionary. T. F. Efremova. 2000... Modern explanatory dictionary of the Russian language by Efremova

Seed- (botanical), organ of reproduction and dispersal in seed plants. Develops from an ovule, usually after fertilization. In angiosperms the seed is enclosed in the fruit, in gymnosperms it is formed openly on the seed scales and... ... Illustrated Encyclopedic Dictionary

SEED, a part of flowering plants (Angiosperms) containing the embryo and food reserves. Formed in the OVY by FERTILIZATION of the female GAMETE. Nutrients can be stored in a special tissue called ENDOSPERM, or... ... Scientific and technical encyclopedic dictionary

SEED, me, plural. mena, myan, menam, cf. 1. Reproductive organ in plants, grain. Hemp village 2. pl. Grains intended for sowing. Garden seeds. Leave the plant to seed (to get seeds from it for sowing). 3. trans., what... ... Ozhegov's Explanatory Dictionary

A flowering plant begins its life as a seed. Plant seeds vary in shape, color, size, weight, but they all have a similar structure.

The grain of wheat is not a seed, but a fruit. The fruit tissue in the grain is represented only by a filmy outer layer, called the fruit membrane. The rest of the grain is the seed.

The structure of a monocot seed can be clearly seen using the example of wheat. In wheat, the grains are fruits - caryopsis containing only one seed. The majority of the grain is occupied by endosperm, a special storage tissue containing organic substances. The embryo is located on the side of the endosperm. It consists of an embryonic root, an embryonic stalk, an embryonic bud and a modified cotyledon located on the border with the endosperm. During seed germination, this cotyledon facilitates the flow of nutrients from the endosperm to the embryo.

Structure of a monocot seed (wheat)

The structure of the seed of a dicotyledonous plant

The structure of the seed of a dicotyledonous plant is easier to consider using the example of a bean, which consists of an embryo and a seed coat. After removing the seed coat, the embryo is exposed, which consists of an embryonic root, an embryonic stalk, two massive cotyledons and a bud enclosed between them. Cotyledons are the first modified leaves of the embryo. In beans and many other plants, they contain a supply of nutrients, which are then used to feed the seedling, and also perform a protective function in relation to the bud.

The structure of the seed of a dicotyledonous plant (beans)

Determination of inorganic substances in seeds

Target: identify inorganic substances in the seed.

What we do: put some dry seeds (wheat) at the bottom of the test tube and heat them over the fire. Condition: the test tube must be held horizontally over the fire so that its upper part remains cold.

What we see: Soon drops of water can be seen on the inner walls in the cold part of the test tube.

Result: drops of water are the result of cooling of water vapor released from the seeds.

What we do: We continue to heat the test tube.

What we see: brown gases appear. The seeds are charred.

Result: When the seeds are completely burned, only a little ash remains. There is not much of it in the seeds - from 1.5 to 5% of dry weight.

Conclusion: the seeds contain flammable organic and non-flammable mineral (ash).

Determination of organic matter in seeds

It is known that flour is obtained by grinding wheat grains in a mill.

Target: Let's find out the composition of organic substances included in wheat seeds.

What we do: Let's take some wheat flour, add water to it and make a small lump of dough. Wrap the lump of dough in gauze and rinse thoroughly in a vessel with water.

What we see: the water in the vessel became cloudy, and a small sticky lump remained in the gauze.

What we do: drop 1-2 drops of iodine solution into a glass of water.

What we see: the liquid in the vessel turned blue.

Result: The water being tested turns blue, which means there is starch in it.

On the gauze in which the dough was, a viscous sticky mass remained - gluten, or vegetable protein.

Conclusion: The seeds contain vegetable protein and starch - these are organic substances. Organic substances are mainly deposited in the seeds. Different plants have them in different quantities.

Determination of vegetable fats in plant seeds

In addition to protein and starch from organic substances, the seeds also contain vegetable fats.

Target: prove that the seeds contain vegetable fats.

What we do: Place the sunflower seed between two sheets of white paper (Fig. 1). Then press the blunt end of a pencil onto the seed (Fig. 2).

What we see: a greasy stain appeared on the paper (Fig. 3).

General conclusion: organic substances are formed in the body and, when heated, become charred and then burned, turning into gaseous substances. The inorganic substances that make up the seed do not burn or char.

Life processes of a germinating seed

Seed germination

Seed germination is an important indicator of the quality of the seeds themselves. It is not difficult to define it.

Target: learn to determine seed germination.

What they do: count out 100 seeds in a row from the seed material, without choice, lay them out on wet filter paper or on moistened sand (or on a wet cloth).

What we see: After 3-4 days, count the number of sprouted seeds and see how well the seeds germinate.

After 7-10 days, the number of sprouted seeds is again counted and final germination is monitored.

Germination is assessed as a percentage, calculating the number of germinated percent out of 100 sown.

Conclusion: The higher the number of sprouted seeds, the better the quality of the seed material.

Seed germination

There are seeds that, when germinated, bring cotyledon leaves to the surface of the soil (beans, cucumber, pumpkin, beets, birch, maple, aster, marigolds) - this is above-ground germination of the seed.

In other plants, during germination, the cotyledons do not come to the surface of the soil (peas, nasturtium, fava beans, oak, chestnut); they are classified as plants with underground germination.

Conditions necessary for seed germination

To do this, you can do a little experiment.

Target: What conditions are necessary for seeds to begin to germinate?

What we do: Let's take three glasses and put a few grains of wheat at the bottom of each. In the first one, we will leave the seeds as they are (there will only be air in it). In the second, pour in enough water so that it only wets the seeds, but does not cover them completely. Fill the third glass halfway. Cover all three glasses with glass and leave in the light. This is the beginning of our experience.

In about 4-5 days we will analyze the result.

What we see: in the first, the seeds remained unchanged, in the second they swelled and sprouted, and in the third they only swelled, but did not germinate.

Result: experience shows that seeds easily absorb water and swell, increasing in volume. In this case, organic substances (proteins and starch) become soluble. Thus, the seed begins active life from a dormant state. However, if, as in the third glass, air does not have access to the seeds, then although they swell, they do not germinate. The seeds sprouted only in the second glass, where they had access to both water and air. There were no changes in the first glass, since no moisture reached the seeds.

Conclusion: Seeds require moisture and air for germination.

Effect of temperature on seed germination

Target: Let us confirm experimentally that in addition to moisture and oxygen, temperature conditions also influence seed germination.

What we do: put several bean seeds (equal amounts) in two glasses and pour in water so that it only moistens the seeds, but does not cover them completely. Cover the glasses with glass. We will leave one glass in the room at a temperature of +18-19ºС, and put the other in the cold (refrigerator), where the temperature is not higher than +3-4ºС.

In 4-5 days, we will check the results.

Result: the seeds sprouted only in the glass that was standing in the room.

Conclusion: therefore, for seed germination a certain ambient temperature is also necessary.

Breathing Seeds

The need for air is explained by the fact that seeds respire, that is, they absorb oxygen from the air and release carbon dioxide into the environment.

Target: experimentally prove that plants absorb oxygen from the air and release carbon dioxide.

What we do: Let's take two glass flasks. Place a small amount of swollen pea seeds in one, and leave the other empty. Cover both flasks with glass.

After a day, take a burning splinter and bring it into an empty flask.

What we see: the splinter continues to burn. Place in a flask with seeds. The light went out.

It has been scientifically proven that oxygen in the air supports combustion and is absorbed during respiration. Carbon dioxide does not support combustion and is released during breathing.

Conclusion: experience showed that germinating seeds (like a living organism) absorbed oxygen (O 2) from the air that was in the flask and released carbon dioxide (CO 2). Make sure the seeds are breathing.

Dry seeds, if they are alive, also breathe, but for them this process is very weak.

Transformation of substances in a germinating seed

Seed germination is accompanied by complex biochemical and anatomical and physiological processes. As soon as water begins to flow into the seeds, respiration sharply increases in them and enzymes are activated. Under their influence, reserve nutrients are hydrolyzed, turning into a mobile, easily digestible form. Fats and starch are converted into organic acids and sugars, proteins into amino acids. Moving into the embryo from storage organs, nutrients become a substrate for the synthesis processes that begin in it, primarily new nucleic acids and enzymatic proteins necessary for the beginning of growth. The total amount of nitrogen substances remains at the same level even when the energy breakdown of proteins occurs, because amino acids and aspargine accumulate.

The starch content decreases sharply, but the amount of soluble sugars does not increase. Sugar is spent on the respiration process, which occurs very energetically in a germinating seed. As a result of respiration, energy-rich compounds are formed - ADP and ATP, carbon dioxide, water and thermal energy are released. Part of the sugars is spent on the formation of fiber and hemicelluloses necessary for the construction of new cell membranes.

A significant amount of mineral substances present in the seed remains constant during germination. Cations found in seeds regulate colloidal chemical processes and osmotic pressure in new cells.

The influence of nutrient reserves in the seed on the development of seedlings

The growth of the embryo and its transformation into a seedling occurs due to the division and growth of its cells. The larger the seeds, the more reserve substances they contain and the better the seedlings grow.

Target: Determine experimentally whether seed size affects seedling growth.

What we do: Sow the largest pea seeds in one container with soil, and the small ones in another. After some time, compare the seedlings.

The result is obvious.

Conclusion: Large seeds develop into more powerful plants that produce the highest yield. There are more and more cells as they receive nutrients, grow and divide again.

Target: Let us empirically test the statement that for growth, especially at first, seedlings use substances stored in the seeds themselves.

What we do: We take swollen bean seeds of the same size and remove one cotyledon (1) from one seed, 1.5 cotyledons (2) from another, and leave both cotyledons (3) from the third for control.

We place all of them in containers, as shown in the figure.

In 8-10 days.

What we see: It is noticeable that a seedling with two cotyledons turned out to be larger and stronger than a seedling with one cotyledon or a seedling with half a cotyledon.

Conclusion: Thus, high seed quality is a necessary condition for obtaining a good harvest.

Plant dormancy period

The dormant period is a necessary condition for seed germination. Dormancy may be forced, due to the lack of conditions necessary for germination (temperature, humidity). An example of seed dormancy is dry seeds.

Organic dormancy is determined by the properties of the seed itself. The term “peace” has a conditional meaning. In most cases, metabolic processes occur in such seeds (respiration, sometimes embryo growth), but germination is inhibited. Seeds that are in organic dormancy, even under conditions favorable for germination, do not germinate at all or germinate poorly.

The ability of seeds to be in forced or organic dormancy was developed in plants in the process of evolution as a means of surviving a season unfavorable for seedling growth. In this way, a supply of seeds is created in the soil.

The main reasons preventing seed germination:

• waterproofness of the peel, due to the presence in it of a palisade layer of thick-walled cells, cuticle (waterproof waxy film);
• the presence in the pericarp of substances that inhibit (slow down) germination;
• underdevelopment of the embryo;
• physiological mechanism of germination inhibition.

Sowing time and seed placement depth

The depth of seed placement depends on their size. The larger the seeds, the deeper they are sown. Large seeds have more reserve nutrients and are enough for the development and growth of seedlings while they emerge from great depths.

Small seeds are sown to a depth of - to 2 cm, medium - from 2 to 4 cm, and large seeds - from 4 to 6 cm.

The depth of seed placement also depends on the properties of the soil. Seeds are planted deeper in sandy soils than in clay soils. The upper layers of loose sandy soils dry out quickly, and when planted shallowly, the seeds do not receive enough moisture. On dense clay soils there is enough moisture in the upper layers, but there is little air in the lower layers. When planted deeply, the seeds suffocate because they lack oxygen.

Seed is a reproductive organ that in angiosperms is formed from the ovule, usually after double fertilization.

The structure of the seed. Initially, the seed is inside the fruit, which protects it until it germinates. Each seed consists of a seed coat, an embryo and storage tissues.

Testa develops from integuments (covers) of the ovule, so it is diploid (2n). It is multi-layered and is always present 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, filmy or hard (woody). The seed coat protects the embryo from mechanical damage, drying out and premature germination. In addition, it can promote seed germination.

Germ is a plant in its infancy and consists of embryonic root, stalk, cotyledons and buds. The embryo develops from a zygote formed as a result of the fusion of a sperm with an egg (2n).

Storage tissues The seeds are endosperm and perisperm. Endosperm is formed as a result of double fertilization when the central nucleus of the embryo sac (2n) merges 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. The classification of seeds is based on the location of reserve nutrients. Distinguish four types of seeds (Fig. 22):

Rice. 22. Types of seeds:

A– seeds with endosperm that surrounds the embryo (poppy);

B– seeds with endosperm adjacent to the embryo (wheat); IN– seeds with a small endosperm (surrounds the embryo) and a powerful perisperm (pepper); G– seeds with perisperm (pupa);

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

8 – perisperm

1) seeds with endosperm mainly characteristic of seeds of the monocot class, as well as some dicotyledons (nightshade, celery, poppy); reserve nutrients are localized in the endosperm;

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

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

4) seeds without endosperm and without perisperm characteristic of legumes, pumpkin, aster; during development, the embryo completely absorbs the endosperm, so the supply of nutrients is in the cotyledons of the embryo; in this case, the seed consists of a seed coat and an embryo.

The structure of a seed with endosperm. Such seeds are characteristic of plants of the Monocot class, for example, bluegrass (cereals). In the wheat grain (swollen seeds) there are ventral side(from the side of the groove) and the opposite - dorsal. On one of the poles of the seed, on the dorsal side, there is embryo. On the opposite pole there are hairs that hold the grain in the soil and contribute to the supply of water to the endosperm of the seed (Fig. 23).

Rice. 23. Structure of wheat grain

(longitudinal section):

1 – hairs; 2 – pericarp fused with the seed coat; 3 – aleurone layer;

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

10 – coleorhiza (root sheath)

The outside of the grain is covered with a thin filmy layer, which is difficult to separate from the inside of the grain. This is the pericarp fused with the seed coat, since the caryopsis is a single-seeded fruit. The structure of the pericarp and seed coat is clearly visible when examining a microscopic specimen of a cross section of a grain.

The size of the embryo is small compared to the size of the endosperm. This means that reserve substances are located in the endosperm. It consists of two layers: aleurone and storage starch.

Germ has the following parts:

– embryonic root with root cap, coleorhiza(root sheath);

– germ stalk And kidney with a growth cone;

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

– shield(modified cotyledon) - according to its location in the grain, it forms a partition between the embryo and the endosperm; under the influence of enzymes, the scutum converts the nutrients of the endosperm into an digestible form and transfers them to the nutrition of the embryo;

– epiblast located on the side opposite the scutellum and is the second reduced cotyledon.

The structure of a seed without endosperm and without perisperm. Such seeds are typical for legumes, pumpkin, and aster. Let us consider this type of seed structure using the example of common beans (seeds swollen in water) (Fig. 24).

Rice. 24. Structure of the common bean seed:

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

4 – seed suture; 5 – seed coat; 6 – kidney;

7 – embryonic stalk; 8 –cotyledons

The outside of the seed is covered with a thick seed coat. It can be of different colors. On the inner concave side of the seed there is a hilum, micropyle and seed suture.

Rib- This is the place where the seed is attached to the achene.

Micropyle- a hole through which water and gases enter the seed. The micropyle is located next to the scar, on the same line.

Seed suture- this is a trace from the fusion of the ovule with the peduncle. It is located on the side opposite to the micropyle and is also adjacent to the scar.

Under the seed coat is embryo. The following parts are distinguished:

– two large cotyledons kidney-shaped; they are the germ leaves where nutrients are deposited;

– germinal root;

– germ stalk;

– gemmule, covered with germ layers.

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

Seeds of flowering plants vary in shape and size: they can reach several tens of centimeters (palm trees) and be almost indistinguishable (orchids, broomrape).

Shape: spherical, elongated spherical, cylindrical. Thanks to this shape, minimal contact of the seed surface with the environment is ensured. This allows the seeds to more easily tolerate unfavorable conditions.

Seed structure

The outside of the seed is covered with a seed coat. The surface of the seeds is usually smooth, but it can also be rough, with spines, ribs, hairs, papillae and other outgrowths of the seed coat. All these formations are adaptation to seed dispersal.

A scar and pollen passage are visible on the surface of the seeds. Rib- trace from the peduncle, with the help of which the seed was attached to the wall of the ovary, pollen passage stored as a small hole in the seed coat.

The main part of the seed is located under the skin. embryo. Many plants have specialized storage tissue in their seeds - endosperm. In those seeds that do not have endosperm, nutrients are deposited in the cotyledons of the embryo.

The structure of seeds of monocotyledonous and dicotyledonous plants is not the same. A typical dicotyledonous plant is beans, and a typical monocotyledonous plant is rye.

The main difference in the structure of seeds of monocotyledonous and dicotyledonous plants is the presence of two cotyledons in the embryo in dicotyledonous plants and one in monocotyledonous plants.

Their functions are different: in dicotyledonous seeds the cotyledons contain nutrients, they are thick and fleshy (beans).

In monocots, the only cotyledon is the scutellum - a thin plate located between the embryo and the endosperm of the seed and tightly adjacent to the endosperm (rye). When the seed germinates, the scutellum cells absorb nutrients from the endosperm and supply them to the embryo. The second cotyledon is reduced or absent.

Conditions for seed germination

Seeds of flowering plants can withstand unfavorable conditions for a long time, preserving the embryo. Seeds with a living embryo can germinate and give rise to a new plant; they are called germinated. Seeds with a dead embryo become not germinating they cannot germinate.

For seed germination, a set of favorable conditions is necessary: ​​the presence of a certain temperature, water, air access.

Temperature. The range of temperature variations at which seeds can germinate depends on their geographic origin. “Northerners” need a lower temperature than people from southern countries. Thus, wheat seeds germinate at temperatures from 0° to +1°C, and corn seeds - at + 12°C. This must be taken into account when setting sowing dates.

The second condition for seed germination is availability of water. Only well-moistened seeds can germinate. The need for water for seed swelling depends on the composition of nutrients. Seeds rich in proteins (peas, beans) absorb the greatest amount of water, and seeds rich in fat (sunflower) absorb the least amount of water.

Water, penetrating through the spermatic opening (pollen opening) and through the seed coat, removes the seed from the dormant state. First of all, breathing sharply increases and enzymes are activated. Under the influence of enzymes, reserve nutrients are converted into a mobile, easily digestible form. Fats and starch are converted into organic acids and sugars, and proteins into amino acids.

Breathing Seeds

Active respiration of swelling seeds requires access to oxygen. During breathing, heat is generated. Raw seeds have more active respiration than dry seeds. If raw seeds are folded in a thick layer, they quickly heat up and their embryos die. Therefore, only dry seeds are poured into storage and stored in well-ventilated areas. For sowing, larger and more complete seeds should be selected without admixture of weed seeds.

Seeds are cleaned and sorted using sorting and grain cleaning machines. Before sowing, the quality of the seeds is checked: germination, viability, humidity, infestation with pests and diseases.

When sowing, it is necessary to take into account the depth of seed placement in the soil. Small seeds should be sown at a depth of 1-2cm (onions, carrots, dill), large ones - at a depth of 4-5cm (beans, pumpkin). The depth of seed placement also depends on the type of soil. In sandy soils they sow somewhat deeper, and in clay soils - shallower. In the presence of a set of favorable conditions, germinating seeds begin to germinate and give rise to new plants. Young plants that develop from a seed embryo are called seedlings.

In the seeds of any plant, germination begins with the elongation of the embryonic root and its exit through the pollen passage. At the moment of germination, the embryo feeds heterotrophically, using the nutrient reserves contained in the seed.

In some plants, during germination, the cotyledons are carried above the soil surface and become the first assimilation leaves. This aboveground type of germination (pumpkin, maple). In others, the cotyledons remain underground and are a source of nutrition for the seedling (pea). Autotrophic nutrition begins after the appearance of shoots with green leaves above the ground. This underground type of germination.