Transport of nutrients in plants and animals. Transport of substances within a plant Transport of substances within a plant

Cells exchange various substances with their environment as a result of diffusion. However, the transfer of substances by ordinary diffusion over long distances is inefficient; there is a need for specialized transport systems. Such a transfer from one place to another is carried out due to the pressure difference in these places. All transported substances move at the same speed, in contrast to diffusion, where each substance moves at its own speed depending on the concentration gradient.

In animals, four main types of transport can be distinguished: the digestive, respiratory, circulatory, and lymphatic systems. Some of them have been described earlier, we will move on to others in the following paragraphs.

In vascular plants, the movement of substances is carried out through two systems: xylem (water and mineral salts) and phloem (organic substances). The movement of substances along the xylem is directed from the roots to the aerial parts of the plant; The phloem moves nutrients away from the leaves.

Osmosis is one of the most important mechanisms for the transport of substances in a plant. Osmosis is the movement of solvent molecules (such as water) from areas of higher concentration to areas of lower concentration across a semi-permeable membrane. This process is similar to normal diffusion, but is faster. Numerically, osmosis is characterized osmotic pressure- the pressure that must be applied to prevent the osmotic entry of water into the solution.

In plants, the role of such semipermeable membranes is played by the plasma membrane and the tonoplast (the membrane surrounding the vacuole). If the cell comes into contact with a hypertonic solution (that is, a solution in which the concentration of water is less than in the cell itself), then water begins to flow out of the cell. This process is called plasmolysis. The cell shrinks. Plasmolysis is reversible: if such a cell is placed in a hypotonic solution (with a higher water content), then water will begin to flow inside, and the cell will swell again. In this case, the internal parts of the cell (protoplast) exert pressure on the cell wall. In a plant cell, swelling is stopped by a rigid cell wall. Animal cells do not have rigid walls, and plasma membranes are too delicate; a special mechanism is needed to regulate osmosis.

We emphasize once again that osmotic pressure is a potential value rather than a real one. It becomes real only in some cases - for example, when it is measured. It must also be remembered that water moves in the direction from a lower osmotic pressure to a higher one.

The main mass of water is absorbed by young zones of plant roots in the area of ​​root hairs - tubular outgrowths of the epidermis. Thanks to them, the water-absorbing surface is significantly increased. Water enters the root by osmosis and moves up to the xylem along the apoplast (along the cell walls), the symplast (along the cytoplasm and plasmodesmata), and also through the vacuoles. It should be noted that in the cell walls there are strips called Caspari belts. They consist of waterproof suberin and prevent the movement of water and substances dissolved in it. In these places, water is forced to pass through the plasma membranes of the cells; it is believed that in this way plants are protected from the penetration of toxic substances, pathogenic fungi, etc.

The second important force involved in the rise of water is root pressure. It is 1–2 atm (in exceptional cases, up to 8 atm). This value, of course, is not enough to ensure the movement of fluid alone, but its contribution in many plants is undeniable.

Getting through the xylem into the leaves, water and minerals are distributed through a branched network of vascular bundles through the cells. Movement along the leaf cells is carried out, as in the root, in three ways: along the apoplast, symplast and vacuoles. For its needs, the plant uses less than 1% of the water it absorbs, the rest eventually evaporates through the wax layer on the surface of the leaves and stems - the cuticle (about 10% water) - and special pores - stomata (90% water). Herbaceous plants lose about a liter of water per day, and in large trees this figure can reach hundreds of liters. Evaporation of water (transpiration) is carried out due to the energy of the sun. The easiest way to observe transpiration is to cover the potted plant with a cap; droplets of liquid will collect on the inner surface of the cap.

Many factors influence the rate of evaporation; both external conditions (light, temperature, humidity, presence of wind, availability of water in the soil), and structural features of the leaves (leaf surface area, cuticle thickness, number of stomata). A number of external factors lead to a decrease in the diffusion of water from the leaves, others (for example, lack of light or strong wind) cause the stomata to close (due to the work of special guard cells). Plants of arid regions have special adaptations to reduce transpiration: stomata sunk deep into leaves, dense pubescence of hairs or scales, thick waxy coating, turning leaves into spines or needles, and others. Autumn leaf fall in temperate latitudes is also designed to reduce water evaporation when cold weather sets in.

Some minerals, having fulfilled their useful function, can move further up or down the phloem. This happens, for example, before shedding the leaves, when the beneficial substances accumulated by the leaves are stored, being deposited in other parts of the plant.

Multicellular plants have another transport system, designed to distribute the products of photosynthesis - phloem. Unlike xylem, organic matter can be transported up and down the phloem. 90% of the transported substances are sucrose, which practically does not participate directly in the metabolism of the plant and therefore is an ideal carbohydrate for transport. The speed of movement of sugar is usually 20-100 cm / h; in a day, several kilograms of sugar (in dry mass) can pass through the trunk of a large tree.

How such large flows of nutrients can flow in thin phloem sieve tubes (their diameter does not exceed 30 μm) is not entirely clear. Apparently, substances are distributed along the phloem by a mass current, and not by diffusion. Possible transport mechanisms are conventional pressure or electroosmosis.

If the phloem is damaged, the sieve tubes become clogged as a result of the deposition of callose on the sieve plates. Irreversible nutrient leakage usually stops within minutes of injury.

In multicellular organisms, cells of different tissues are distant from each other. Therefore, they have formed a transport system that provides the flow of gases and nutrients to all organs and tissues.

The movement of substances in a plant

To find out how the transport system of plants works, we will conduct two experiments.

Experience 1. Poplar (maple, willow) shoots are placed in a vessel with water tinted with red ink. After two days, we will make several longitudinal and transverse sections of the stem. On all sections we will see that only the wood has been stained. The bark and core remained unpainted. This means that water with dissolved substances rises through the wood of the stem, through the vessels.

Experience 2. Place two shoots in a vessel with water and expose to light. Previously, one of
we will remove the bark ring (3 cm wide), stepping back from the end of the shoot 8-10 cm. After 3-4 weeks, adventitious roots will develop in the shoots. In an intact shoot, roots form at the lower end. In a shoot with an annular cut, adventitious roots will develop over the bare section of the stem. There will be no roots under the annular cut, since by removing the ring of bark, we damaged the sieve tubes. Organic substances from the leaves, moving along the bast, reached the cut point and accumulated here. This contributed to the development of adventitious roots.

Thus, experience proves that organic substances move along the bark of the stem, sieve tubes of the bast. They move to all organs of the plant - roots, underground shoots, tops of above-ground shoots, flowers, fruits, seeds.

Transport of substances in animals

Just as substances are transported through the conducting system of a plant, the circulatory system ensures the transfer of oxygen and nutrients to all organs and tissues of animals. Carbon dioxide and harmful substances enter the blood from the tissues. The release of blood from carbon dioxide occurs in the respiratory organs, and from harmful substances - in the excretory organs.

The main organ of the circulatory system, providing its transport function, is the heart. It plays the role of a pump that provides blood circulation. The heart pumps blood through the blood vessels.

Warm-blooded and cold-blooded animals

In frogs, lizards, snakes, crocodiles, turtles, the blood mixes in one of the sections of the heart. As a result, blood, poor in oxygen, enters all organs. Such animals are cold-blooded. Their body temperature depends on environment. In birds and mammals, oxygenated blood does not mix with blood carrying carbon dioxide and harmful substances. An increase in the oxygen content in the blood ensures the release of a large amount of energy, due to which these animals have a constant body temperature and are warm-blooded. This allows them to more easily endure adverse environmental conditions and widely spread around the planet.

Question 1. What is the importance of the transport of substances for multicellular living organisms?

The transport of substances for multicellular organisms is involved in almost all vital processes: respiration - hemoglobin carries oxygen to each cell for its respiration, and then carbon dioxide leaves our body through the lungs; nutrition - the movement of food through the gastrointestinal tract.

Question 2. Recall the structural features of a plant cell and explain how and thanks to what structures substances move from one cell to another in the tissues of a plant organism.

The cell consists of a shell with pores, inside a viscous substance-cytoplasm, it contains a nucleus with a nucleolus and vacuoles.

The movement of substances (in the form of solutions) occurs through the cell membrane, thanks to the pores - these are thinner sections of the cell membrane.

Question 3. Find out what substances move inside plants in the process of metabolism, and sign their names in the figure.

1 - water with minerals dissolved in it,

2 - oxygen

3 - carbon dioxide

4 - dissolved organic matter

Question 4. What is the difference between the transport of substances in lower and higher plants?

The transport of substances in both lower and higher plants differs in that: in higher plants, the transport of water, mineral and organic substances is carried out through roots and vessels along conductive tissues, while in lower plants there are no tissues and substances move between cells.

Question 5. Fill in the table "Transport of substances in higher plants."

Question 6*. In early spring, birch sap is collected from notches on a birch trunk. What do you think it is in terms of composition and where does it come from if there are no leaves on the plant yet?

Birch sap is purified water from the soil of the earth processed and passed through the birch root system already with the addition of trace elements from the birch trunk.

Question 7*. In winter, hares gnawed the bark of a young cherry, and after a while it turned out that the tree had died. Suggest why and how this happened.

Hares damaged blood vessels and sieve tubes. The transport of substances was disrupted, because of this the tree died.

Question 8. Look at the picture and read the description of the experience depicted in it. They took two glasses of water, left clean water in one, and added a few drops of red ink to the other. One plant of the same species with white flowers was placed in each glass. Five hours later, in the second glass, some parts of the plant were stained.

Answer the questions:

1) What process can be studied using this experiment?

With the help of this experiment, it is possible to study the process of transport of substances.

2) What parts (organs) of the plant are stained?

Leaves and flowers of plants were painted.

3) What structures of these organs stained most intensively and why?

The flower petals were the most intensely stained. Since they were originally white, their coloration is most noticeable.

4) Is it possible to return the original color to the plant organs? Justify the answer.

This plant can certainly be returned to its original appearance, you just need to return ordinary water, when the colored substances leave the plant, it will become its normal color.

Question 9*. Explain the results of the ringed branch experiment described in the textbook on p.114. Why do you think damage to the bark of trees is dangerous for their life?

In the bark of a tree, sieve tubes pass through which the substances necessary for life pass. If the bark is damaged, the tubes are also damaged. Accordingly, the supply of nutrients is reduced, which has a detrimental effect on the plant.

For the implementation of vital processes, plants need water and mineral (inorganic) substances dissolved in it. A plant can get them mainly from moist soil. The roots are responsible for the absorption of water in plants. However, it is not so much the roots that need water as the leaves and other above-ground organs of the plant (developing buds, shoots, flowers, fruits). Therefore, in higher plants, in the process of evolution, a conducting system was developed that ensures the transport of substances. It has the most complex structure in angiosperms.

For the movement of water and minerals both along the stem, and along the leaves and in the roots, they are responsible vessels. They are dead cells. The upward movement of water and minerals is provided by root pressure and the evaporation of water from the leaves.

In woody plants, the vessels are found in the wood of the stems. This can be verified by placing a branch in a tinted aqueous solution. After some time, on the cross cut, you can see that only the wood will be painted. This means that water and minerals dissolved in it move only along it.

Movement along the stem of organic matter

In the green leaves of plants, photosynthesis occurs, during which organic substances are synthesized. From these substances, other organic substances are subsequently synthesized, which are used in various life processes and for energy production.

Organic substances are needed not only by the green parts of the plant, but also by other organs and tissues. In addition, part of the organic matter is stored in reserve. Therefore, in plants, not only the movement of water and minerals, but also the transport of organic substances is carried out. Usually it goes in the opposite direction from the flow of the aqueous solution.

Organic matter in angiosperms moves along sieve tubes. These are living cells, their transverse partitions, with which they come into contact with each other, look like a sieve.

In woody plants, sieve tubes are located in the bast, which is a part of the bark located closer to the cambium (wood is located on the inside of the cambium).

If the bark of the stem of a plant is damaged deep enough, and this prevents the outflow of organic substances, then so-called nodules, or outgrowths, form on the trunk. They accumulate organic matter. At their expense, a wound plug is formed on the damage to the trunk. Further, roots and buds can begin to develop in this place.

Organic substances in plants often accumulate in various organs and tissues (roots, stems, pith). In the spring, these substances are used to ensure that the plant has leaves and new shoots. To do this, stored organic matter must dissolve in water and move to where they are needed. And it turns out that at this time organic substances move not through sieve tubes, but through vessels with water and minerals.

Question 1.
To maintain normal life, the body needs nutrients (minerals, water, organic compounds) and oxygen. Usually these substances move through the vessels (through the vessels of wood and bast in plants and through the blood vessels in animals). In cells, substances move from organelle to organelle. Substances are transported into the cell from the intercellular substance. Waste and unnecessary substances are removed from the cells and then through the excretory organs from the body. Thus, the transport of substances in the body is necessary for normal metabolism and energy.

Question 2.
In unicellular organisms, substances are transported by the movement of the cytoplasm. So, in an amoeba, the cytoplasm flows from one part of the body to another. The nutrients contained in it move and are carried throughout the body. In ciliates shoes - a unicellular organism with a constant body shape - the movement of the digestive vesicle and the distribution of nutrients throughout the cell is achieved by continuous circular motion of the cytoplasm.

Question 3.
Cardiovascular the system ensures the continuous movement of blood, which is necessary for all organs and tissues. Through this system, organs and tissues receive oxygen, nutrients, water, mineral salts, hormones that regulate the functioning of the body enter the organs with blood. From the organs into the blood comes carbon dioxide, decay products. In addition, the circulatory system maintains a constant body temperature, ensures the constancy of the internal environment of the body ( homeostasis), the relationship of organs, provides gas exchange in tissues and organs. The circulatory system also performs a protective function, since the blood contains antibodies and antitoxins.

Question 4.
Blood is a fluid connective tissue. It consists of plasma and formed elements. Plasma is a liquid intercellular substance, shaped elements are blood cells. Plasma makes up 50-60% of blood volume and is 90% water. The rest is organic (about 9.1%) and inorganic (about 0.9%) plasma substances. Organic substances include proteins (albumin, gamma globulin, fibrinogen, etc.), fats, glucose, urea. Due to the presence of fibrinogen in the plasma, blood is capable of clotting - an important protective reaction that saves the body from blood loss.

Question 5.
Blood is made up of plasma and formed elements. Plasma is a liquid intercellular substance, shaped elements are blood cells. Plasma makes up 50-60% of blood volume and is 90% water. The rest is organic (about 9.1%) and inorganic
(about 0.9%) plasma matter. Organic substances include proteins (albumin, gamma globulin, fibrinogen, etc.), fats, glucose, urea. Due to the presence of fibrinogen in the plasma, blood is capable of clotting - an important protective reaction that saves the body from blood loss.
The formed elements of blood are erythrocytes - red blood cells, leukocytes - white blood cells and platelets - platelets.

Question 6.
stomata represent a gap that is located between two bean-shaped (trailing) cells. The guard cells are located above the large intercellular in loose leaf tissue. Stomata are usually located on the underside of the leaf blade, and in aquatic plants (water lily, capsule) - only on the top. A number of plants (cereals, cabbage) have stomata on both sides of the leaf.

Question 7.
To maintain normal life, the plant absorbs CO 2 (carbon dioxide) from the atmosphere with its leaves and water with mineral salts dissolved in it from the soil with its roots.
The roots of plants are covered, like fluff, with root hairs that absorb the soil solution. Thanks to them, the suction surface increases tens and even hundreds of times.
The movement of water and minerals in plants is carried out due to two forces: root pressure and evaporation of water by leaves. Root pressure - the force that causes a one-way supply of moisture from the roots to the shoots. Evaporation of water by leaves is a process that occurs through the stomata of leaves and maintains a continuous flow of water with minerals dissolved in it through the plant in an upward direction.

Question 8.
Organic substances synthesized in the leaves flow to all organs of the plant but to the sieve tubes of the bast and form a downward current. In woody plants, the movement of nutrients in the horizontal plane occurs with the participation of core rays.

Question 9.
With the help of root hairs, water and minerals are absorbed from soil solutions. The shell of the root hair cells is thin - this facilitates absorption.
root pressure- the force that causes a one-sided supply of moisture from the roots to the shoots. Root pressure develops when the osmotic pressure in the root vessels exceeds the osmotic pressure of the soil solution. Root pressure, along with evaporation, is involved in the movement of water in the plant body.

Question 10.
The evaporation of water from a plant is called transpiration. Water evaporates through the entire surface of the plant body, but especially intensively through the stomata in the leaves. The meaning of evaporation: it takes part in the movement of water and solutes through the body of the plant; promotes carbohydrate nutrition of plants; protects plants from overheating.