§ 1 Features of the root structure

One of the main functions of the plant root is to absorb water and minerals dissolved in it from the soil. In connection with this function, the root has features of both external and internal structure. Let's take a closer look. All types of roots in the root system: main, lateral, adventitious, have similarities in structure.

All roots branch, grow at the top and never have leaves on them. The root tip is protected by a cap of several layers of dead cells - the root cap. Its function is to protect the root division zone from mechanical damage. The cells of the cap are constantly renewed due to division; these are cells of educational tissue - meristems. Some meristem cells add new layers to both the root and the root cap.

Behind the division zone there is an elongation zone, where cells no longer grow, but only stretch. In this zone, the root lengthens and pushes the division zone forward. Further from the stretch zone is the suction zone. It is a section of the root densely covered with root hairs. A root hair is an outgrowth of a root epidermal cell, that is, the integumentary layer. These cells increase the absorption surface of soil solutions. The suction zone can gradually move along the root: new ones appear at the leading edge of this zone. root hairs, and in the back, the old ones are gradually dying off. As a result of this process, the suction zone slowly moves deeper into the soil. There are also two more zones on the root: branching, where lateral roots are formed, and the conduction zone, located above. The conduction zone is responsible for the transport of water and minerals to the aboveground organs of the plant and transport organic matter from the stem to the root, and also serves as a support.

§ 2 Movement of water through the plant

How does each plant cell get water from the soil? Water is absorbed from the soil by root hairs due to the build-up of pressure inside these cells. This phenomenon called root pressure. Next, from the cells with root hairs, the aqueous solution seeps into the root cells and, moving from cell to cell, enters the vessels. Through the vessels of the root, water rises first to the stem, and through the vessels of the stem - to the leaves of the plant.

Water moves upward through the vessels of the conducting tissue (xylem), thanks not only to root pressure, but also due to the evaporation of water in the leaves. Lack of water in the leaves causes surface tension in xylem vessels, which is capable of pulling up the entire column of water, creating a massive flow. Further along the xylem, water disperses throughout the plant and is used for metabolic processes, substances, photosynthesis and evaporation.

§ 3 Roots of moisture-loving and drought-resistant plants

The roots of moisture-loving and drought-resistant plants differ in length, thickness and location in the soil. The roots of some plants can reach depths of up to 15 meters, thereby reaching the exit groundwater in dry areas. For example, sunflower roots reach 3 meters. Thanks to the main root that quickly penetrates deep and a strong branching system of lateral roots and roots, sunflower can withstand drought and absorb well nutrients and soil moisture. But in a cucumber, the root depth often remains at a depth of no more than half a meter and the root is located “in breadth”, occupying a certain area.

Like all cells, root cells need respiration. They absorb oxygen from the soil and release it into carbon dioxide. Therefore, for many cultivated plants, methods are used to enrich the soil with oxygen - loosening, plowing, harrowing.

In warm soil, roots absorb moisture better than in cold soil. Therefore, for heat-loving plants in our garden, we use cover for the beds - peat or film.

Have you noticed that many gardeners who grow tomatoes transplant seedlings in the spring by pinching off the top of the root. Why do they do this? In order for the plant to develop faster, a lot of water and nutrition are needed.

These processes will be provided by powerful root system. And the development of root branching occurs when the main root does not grow in length, which is why it is pinched.

§ 4 Brief summary on the topic of the lesson

1. The structure of the root is interconnected with its main function - absorbing water and carrying it to the shoot of the plant.

2. In external structure The root can be divided into the following zones: division zone (with root cap), elongation zone, absorption zone, branching zone and conduction zone.

3. The root absorbs water due to root pressure and the force of evaporation from the surface of the leaves.

4. For root development, the following are needed: soil moisture, oxygen and heat.

Images used:

Water supplied by the roots quickly moves through the plant to the leaves. The question arises, how water moves through a plant? The water absorbed by the root hairs travels a distance of several millimeters through living cells, and then enters the dead xylem vessels.

Movement of water through living cells possible thanks to the presence sucking force, increasing from the root hair to living cells adjacent to the xylem vessels. The same distribution of suction force is present in living leaf cells (Fig. 124).

When water moves through living leaf cells, the suction force of each subsequent cell should differ by 0.1 atm. In one of the experiments it was possible to establish that in the leaf ivy in the third cell from the vein there was a suction force equal to 12.1 atm, and in the 210th cell - 32.6 atm. Thus, to overcome the resistance of 207 cells, the difference in suction force was 20.5 atm, i.e. just about 0.1 atm for each cell. From these data it follows that the resistance to the osmotic movement of water through living cells is about 1 atm by 1 mm path traversed by water. From this it becomes clear why plants that do not have blood vessels (mosses, lichens), don't reach large sizes. Only in connection with the appearance tracheid(ferns and gymnosperms) and vessels(angiosperms) in the process of evolution, it became possible for the plant to reach a height of several tens and even over a hundred meters ( eucalyptus, redwoods).

Only a small part of its path in the plant water passes through living cells - in the roots and then in the leaves. Most The water passes through the vessels of the root, stem and leaf. The evaporation of water from the surface of the leaves creates the presence of suction force in the cells of the leaf and root and maintains the constant movement of water throughout the plant. Therefore, the leaves of plants are called upper end motor, unlike the root system of a plant, - lower end motor, which pumps water into the plant.

About the meaning water movement By dead cells wood - vessels and tracheids - can be judged from this experience.

If we cut a branch of any herbaceous plant and place it in water, then the water will flow to the leaves, moving through the vessels due to evaporation from their surface. If you clog the cavities of the vessels by immersing the branch in molten gelatin, and then, when the gelatin is drawn into the vessels and hardens, scrape it off the cut surface and lower the branch into water, then the leaves will quickly wither. This experience shows that water cannot quickly move through living parenchyma cells to the leaves.

By evaporating water from the surface of their leaves, plants automatically draw water through the vessels. The more intense the transpiration, the more water the plant sucks. The suction effect of transpiration can easily be detected if a cut branch is hermetically sealed in the upper end of a glass tube filled with water, the lower end of which is immersed in a cup of mercury. As the water evaporates, mercury will be drawn into the tube to take its place (Fig. 125). The rise of mercury ends with air released from the intercellular spaces, which interrupts the communication of vessels with water. Usually, however, in such an experiment it is possible to raise mercury to a significant height. The operation of the upper end motor plays a significant role big role for the plant compared to the bottom, since it occurs automatically, due to energy sun rays, heating the sheet and increasing evaporation. The operation of the lower end motor is associated with the expenditure of energy due to the consumption of assimilates accumulated during photosynthesis. However, in the spring, when the foliage has not yet blossomed, or in humid shady habitats where transpiration is very low, the root system plays the main role in the movement of water, pumping water into the plant. Material from the site

Suction force The volume of leaves is so large that if you cut a leafy branch, you will see water not flowing out, but being sucked in. In tall trees, this sucking of water by the leaves is transmitted down tens of meters. At the same time, it is known that any suction pump cannot lift water to a height exceeding 10 m, since the weight of this water column will correspond atmospheric pressure and be balanced by it. The observed difference between the suction pump and the plant stem depends on the adhesion of water to the walls of the vessels. Experiments with sporangium ring fern showed that the adhesion force of water here is 300-350 atm. As is known, the ring on a fern sporangium consists of dead cells, the inner and side walls of which are thick and the outer walls are thin. When sporangia mature, these cells, filled with water, lose it and decrease in size. In this case, the thin wall is drawn inward and the ends of the thick walls are brought closer together. It turns out like a tense spring, trying to tear the water away from the walls. When the water comes off, the spring straightens and the spores are thrown out with force from the sporangium, as if from a throwing machine. This separation of water can be caused by immersing sporangia in concentrated solutions of certain salts. Measurements showed that the force producing water separation turned out to be approximately 350 atm. From the foregoing it is clear that the solid columns of water filling the vessels are strongly spaded due to the force of adhesion. Weight of a column of water in 100 m height corresponds to only 10 atm. Thus, the enormous adhesive force allows the water in plant stems to rise to a height significantly higher than the barometric one. Root pressure and the suction action of leaves move the water current to a considerable height. Great importance at the same time, they also have transverse partitions in the vessels, since the air entering the vessels is isolated from both common system Only small areas are excluded from water supply.

Water speed in vessels is relatively small. For deciduous trees it averages 20 cm 3 per hour for 1 cm 2 cross-sections of wood, and for conifers only 5 cm 3 per hour. At the same time, blood moves through the arteries at a speed of 40-50 cm 3 per second, and water through water mains is 100 cm 3 by 1 cm 2 sections per second.

Water absorption by the root and its transport in flowering plants

The special course “Plant Physiology” is intended for students studying biology in depth (11th grade, 34 hours). The special course program provides for the study of the section “Movement of substances throughout the plant” in four lessons on the topics “Absorption of water by the root and its transport in flowering plant"," Transpiration and its physiological role ", " Absorption of minerals by the root and transport of ions in flowering plants ", " Transport of organic substances in flowering plants ".

The lesson “Absorption of water by roots and its transport in flowering plants” is designed for 40–45 minutes. In the 10th grade, students study a special course “Anatomy and Morphology of Plants” (34 hours), so in the 11th grade, questions about the anatomy and morphology of plants are only repeated during the lesson. On lessons general biology and chemistry, schoolchildren have already learned the concepts osmosis, osmotic pressure, therefore, these questions are only repeated during this lesson.

Lesson objectives. Update knowledge about the structure of root hairs, xylem, water molecules, the concepts of osmosis, osmotic pressure, cahesion, adhesion, etc. Consider physiological mechanisms absorption of water by the roots. To study the mechanism of water movement in flowering plants. Improve students' skills in working with laboratory equipment and conducting experiments. Develop intellectual abilities, logical thinking, cognitive independence skills of students.

Equipment: live plants, plant shoots, test tubes, magnifying glasses, vegetable oil, ink, Vaseline, glass and rubber tubes, scalpel and tables “Root structure”, “ Cellular structure leaf”, “Structure of the stem”.

Experiments laid down by students on the eve of the lesson

The experiments we offer are widely known, because... are included in the basic school curriculum, but students’ explanation of the results obtained should be more scientific and in-depth, corresponding to the level of 11th grade students studying biology in depth. The teacher assigns several students, and each of them creates their own experience (in this lesson three experiments are demonstrated, which means that three schoolchildren will be involved in their production).

Experience No. 1

Take a plant grown in damp sawdust, shake off its root system and place its roots in a test tube of water. Pour oil on top of the water to prevent evaporation. Mark the water level on the wall of the test tube. After a day, note the water level again and compare it with the original. Draw a conclusion from the results obtained.

Experience No. 2

For a young balsam plant, cut the stem 3–5 cm above the root collar. Lubricate the stump around with Vaseline and put a rubber tube on it. Connect its free end to a glass tube (Fig. 1). Before demonstrating the experiment, water the soil in the pot with warm water. What are you observing? What do the experimental results indicate?

Rice. 1. Experiment demonstrating root pressure

Experience No. 3

Place a shoot of a tree or shrub in a vessel with water tinted with ink. Every other day, use a dissecting knife (scalpel) to cut off the lower part (about 1–2 cm) of the shoot. Examine the cross-section with a magnifying glass. Which layer of the stem is colored? Explain the results of the experiment.

DURING THE CLASSES

I. Learning new material

1. Movement of substances in plants

Any organism, and especially a complex one, needs metabolism with the environment, metabolism between the cells of the body and metabolism within cells. This is possible only if there is transport of substances within the body.
What processes in a living organism ensure the transport of substances to long distances?

Suggested answers. Transport of substances over short distances is ensured by physical processes diffusion (including osmosis), active transport and cytoplasmic currents. (Students studied these processes in the 10th grade in general biology lessons.)

Teacher. Indeed, single-celled organisms and in those multicellular organisms in which the ratio of body surface to its volume is sufficiently large, these methods of transport work well.
How substances are transported in large and, compared to single-celled organisms, is more complex organized organisms, because diffusion alone is clearly not enough for these purposes?

Suggested answers. In organisms whose cells are very distant from each other and from environment, special transport systems arise over long distances, guaranteeing the rapid movement of necessary substances.

Teacher. What transport systems in animals and plants do you know?

Suggested answers. Animals have a circulatory system, and plants have a conducting system formed by xylem and phloem.

Teacher. You correctly named the so-called circulatory systems of animals and plants. They provide reliable transport of substances to these organisms.
Thus, transport of substances is the delivery of necessary compounds to certain organs and tissues using special systems. We will study the plant's ability to transport organic and inorganic substances, because without their transportation, its normal functioning would be impossible. The process of movement of substances through the conducting tissues of a plant is called translocation.

2. Substances transported by plants

Teacher. List the most important groups of substances that must be transported by the plant.

Suggested answers. Water, gases, mineral salts, organic substances.

Teacher. You correctly named the main groups of substances transported by the plant. Now let's try to trace the path of these substances in the plant body.

I suggest you, based on your knowledge of the structure of plant tissues and organs, fill out the table “Movement of substances in plants.” The diagram located on your tables will help you fill out the table (Fig. 3).

Rice. 3. Scheme of circulation of water, inorganic ions and assimilates in the plant. Water and inorganic ions absorbed by the root move upward along the xylem with the transpiration current. Most of them are transported to the leaves. In leaves, a significant amount of water and inorganic ions moves into the phloem and is removed from them along with sucrose in the assimilate flow. The letter A indicates places specialized in the absorption and assimilation of starting materials from external environment. The letters Z and P indicate the places of loading and unloading, respectively, O - the points at which the exchange between xylem and phloem occurs

Teacher ( checking table completion). You filled out the table correctly, naming the substances transported by the plant and indicating the route of these substances. Now you have to become more familiar with the mechanism of water transport in plants. The path of water in a plant begins from the root.

3. Water absorption by the plant root

Demonstration of experiment No. 1. The student who started it on the eve of the lesson talks about the experiment and its results. From the results of the experiment, the conclusion follows that water is absorbed by the root of the plant.

Teacher. Remember which root structures absorb water and what their structure is ( table demonstration "Root structure").

Suggested answers. The root structures that absorb water are root hairs located in the suction zone. They are cytoplasmic outgrowths of cells of the root epidermis.

Teacher. The cytoplasm of the root hair and the soil solution are separated from each other by a membrane. What causes water to penetrate the root hair membrane?

Suggested answers. Based on knowledge of osmosis, it can be assumed that water molecules move from an area where their concentration is high (from a solution with low osmotic pressure) to where their concentration is low (into a solution with a higher osmotic pressure). This means that the cytoplasm of the cells that form the root hairs is more concentrated than the soil solution. This is what ensures a kind of diffusion of water molecules from the soil into the root cells.

Teacher. You have correctly identified the reason for the absorption of water by the roots. Nowadays, physiologists, when they want to describe the tendency of water molecules to move from one place to another, use the term “water potential.” Water moves from an area of ​​higher water potential to an area of ​​lower water potential, i.e. from soil to root. The process of water absorption by the root is reflected in Fig. 2., it is also on your tables. The water potential gradient is also maintained due to the movement of water through the xylem, but we will talk about this a little later.
Thus, water is absorbed by root hairs due to the difference in water potential of the soil solution and cell cytoplasm forming root hairs. The water then passes through the root bark into the xylem and up through it to the leaves.

Rice. 2. Scheme of the main pathways for the movement of water and inorganic ions from the soil through the epidermis and bark into the xylem. Water moves mainly along the apoplast until it reaches the endoderm, where apoplastic movement is blocked by the Casparian belts. Casparian belts force water to cross plasma membranes and protoplasts of endodermal cells on its way to the xylem. Passing through plasma membrane on the inner surface of the endodermis, water can again follow the apoplastic path to the cavities of the xylem elements. Inorganic ions are actively absorbed by epidermal cells and then move along the symplast through the cortex into parenchyma cells, from which they are pumped into xylem elements

Demonstration of experiment No. 2. The student who started it on the eve of the lesson talks about the experiment and its results. The liquid collected in the glass tube indicates the root's ability to create pressure. Probably, it is precisely due to this pressure that the above-ground organs of the plant are supplied with water.

Teacher. The correct assumption was made about the ability of the root to create pressure, which is called root pressure. It is 100–200 kPa. In some plants, root pressure causes liquid droplets to be released through the hydathodes.
What are hydathodes and what is the process of releasing droplet-liquid moisture called?

Suggested answers. Hydathodes are water stomata of plants, and the process of releasing liquid droplets through them is called guttation. (Students were introduced to this concept when studying excretory tissues of plants in the 10th grade.)

Teacher. You correctly remembered the name of the process of releasing water droplets through hydathodes. It was also true that due to root pressure, water rises up the stem. But a problem arises: the flow of liquid, rising upward, must overcome greater pressure than the root is capable of developing, that is, root pressure alone is usually not enough to ensure the movement of water up the xylem. What other force causes water to rise? Now we have to solve this problem by becoming familiar with the mechanism of water rising through the xylem.

4. Rise of water through the xylem

Demonstration of experiment No. 3. The third student, who also started the experiment on the eve of the lesson, talks about the experiment and its results. A cross section of the stem examined with a magnifying glass clearly shows that the wood layer has become colored (secondary wood is called xylem). From the results of the experiment it follows that xylem is the water-conducting tissue of the plant, and that it is through it that water rises from the root to the leaves of the plant.

Teacher. Experience clearly confirms the idea that xylem in the plant body conducts water. ( Demonstration of the table “Structure of the stem”.)
Remember what the structure of xylem is.

Suggested answers. The xylem of flowering plants consists of two types of structures that transport water - tracheids and tracheae (vessels). Xylem vessels are dead tubes with a narrow lumen.

Teacher. It has been correctly said that xylem vessels are dead tubes with a narrow lumen. Their diameter varies from 0.01 to 0.2 mm. Large quantities water is transported through the xylem relatively quickly. For example, in tall trees, water rising speeds of up to 8 m/h were recorded. But let’s return to the previously identified problem. What forces do you think ensure that water flows up the stem?

Suggested answers. Logic suggests two possibilities: water is pushed out from below (but we have already talked about root pressure and concluded that this alone is not enough to ensure the upward xylem current) or it is pulled from above.

Teacher. Because root pressure alone is not capable of lifting water to the top big tree, let's dwell on the hypothesis that suggests that water “stretches” through the entire plant, especially since this hypothesis is confirmed by the available data.
To study the mechanism of water movement through xylem, I suggest you read the text that is on each of you’s desks. After reading, be sure to answer the questions about the text.

Reading text

The theory of water movement is known as the theory of cohesion (you became familiar with this concept when studying the structure and properties of water in the 10th grade in general biology lessons) - tension. According to this theory, the rise of water from the roots is due to the evaporation of water from the cells of the leaf (remember the structure of the leaf). Evaporation leads to a decrease in the water potential of cells adjacent to the xylem. Therefore, water enters these cells from xylem sap, which has a higher water potential, and reaches the ends of the leaf veins, from where it evaporates (the mechanism of evaporation will be studied in the next lesson).
The xylem vessels are filled with water, and as the water leaves the vessels, tension is created in the water column. It is transmitted down the stem all the way from leaf to root due to the adhesion (cohesion) of water molecules. (Think about why water molecules tend to “stick” to each other.)
Because of cohesion, the tensile strength of water is high enough to prevent its molecules from separating under the tension required to lift water through the xylem of a tall tree and create a mass current. In this case, water enters the base of such a column in the roots from neighboring root cells.
In addition, water molecules tend to stick to the walls of vessels under the influence of adhesion (sticking) forces that are electrical in nature.
Cell membranes, along which water moves, attract water very effectively, which provides maximum benefits for water adhesion and creates the conditions for cohesiveness.

Questions to the text

1. What is the name of the theory of water movement through xylem?
2. Why do water molecules tend to “stick” to each other?
3. Why do they say that the energy for the movement of water and mineral salts throughout the plant is supplied not by the plant, but directly by the Sun?

Suggested answers. The theory of water movement through xylem is called the “adhesion-cohesion” theory.
Water molecules are polar and attract each other electrical forces, and are then held together by hydrogen bonds.
The energy for the movement of water is supplied by the Sun, because... heating the leaves promotes the separation of water molecules from water flow xylem, and this creates tension in the water column, which is transmitted down the stem due to cohesion.

Teacher. So, the movement of water in the body of a plant is possible due to the exceptional ability of its molecules for cohesion and adhesion, which plants use so skillfully. Thus, we answered the question about the reasons for the movement of water up the stem.

This concludes the material for today's lesson.

II. Consolidation of knowledge

Define the following concepts: transport of substances, xylem, phloem, translocation, osmosis, osmotic pressure, water potential, root pressure, hydathodes, guttation, cohesion, adhesion.

III. Homework

Learn theoretical material. Answer the following questions orally.

Explain why water rises to the tops tall trees, whereas with a mechanical pump it can be raised to a height of no more than 10 m.

The plant loses water due to the negative water potential of the atmosphere. How would you explain this statement?

Farmers rarely fertilize their crops during drought because they have learned from experience that doing so can be harmful. Explain why this is so.

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Phylogenetically, the root arose later than the stem and leaf - in connection with the transition of plants to life on land and probably originated from root-like underground branches. The root has neither leaves nor in a certain order located kidneys. It is characterized by apical growth in length, its lateral branches arise from internal tissues, the growth point is covered with a root cap. The root system is formed throughout life plant organism. Sometimes the root can serve as a storage site for nutrients. In this case, it changes.

Types of roots

The main root is formed from the embryonic root during seed germination. Lateral roots extend from it.

Adventitious roots develop on stems and leaves.

Lateral roots are branches of any roots.

Each root (main, lateral, adventitious) has the ability to branch, which significantly increases the surface of the root system, and this helps to better strengthen the plant in the soil and improve its nutrition.

Types of root systems

There are two main types of root systems: taproot, which has a well-developed main root, and fibrous. The fibrous root system consists of large number adventitious roots of equal size. The entire mass of roots consists of lateral or adventitious roots and has the appearance of a lobe.

The highly branched root system forms a huge absorbing surface. For example,

• the total length of winter rye roots reaches 600 km;
• length of root hairs - 10,000 km;
• the total root surface is 200 m2.

This is many times the area of ​​the aboveground mass.

If the plant has a well-defined main root and adventitious roots develop, then a root system is formed mixed type(cabbage, tomato).

External structure of the root. Internal structure of the root

Root zones

Root cap

The root grows in length from its apex, where the young cells of the educational tissue are located. The growing part is covered with a root cap, which protects the root tip from damage and facilitates the movement of the root in the soil during growth. Last function is carried out due to the property of the outer walls of the root cap being covered with mucus, which reduces friction between the root and soil particles. They can even push soil particles apart. The cells of the root cap are living and often contain starch grains. The cells of the cap are constantly renewed due to division. Participates in positive geotropic reactions (direction of root growth towards the center of the Earth).

Cells of the division zone are actively dividing, the length of this zone is different types and at different roots of the same plant is not the same.

Behind the division zone is an extension zone (growth zone). The length of this zone does not exceed a few millimeters.

As linear growth completes, the third stage of root formation begins—its differentiation; a zone of cell differentiation and specialization (or a zone of root hairs and absorption) is formed. In this zone, the outer layer of the epiblema (rhizoderm) with root hairs, the layer of the primary cortex and the central cylinder are already distinguished.

Root hair structure

Root hairs are highly elongated outgrowths of the outer cells covering the root. The number of root hairs is very large (per 1 mm2 from 200 to 300 hairs). Their length reaches 10 mm. Hairs form very quickly (in young apple tree seedlings in 30-40 hours). Root hairs are short-lived. They die off after 10-20 days, and new ones grow on the young part of the root. This ensures the development of new soil horizons by the roots. The root continuously grows, forming more and more new areas of root hairs. Hairs can not only absorb ready-made solutions of substances, but also contribute to the dissolution of certain soil substances and then absorb them. The area of ​​the root where the root hairs have died is able to absorb water for a while, but then becomes covered with a plug and loses this ability.

The hair shell is very thin, which facilitates the absorption of nutrients. Almost the entire hair cell is occupied by a vacuole, surrounded by a thin layer of cytoplasm. The nucleus is at the top of the cell. A mucous sheath is formed around the cell, which promotes the gluing of root hairs to soil particles, which improves their contact and increases the hydrophilicity of the system. Absorption is facilitated by the secretion of acids (carbonic, malic, citric) by root hairs, which dissolve mineral salts.

Root hairs also play a mechanical role - they serve as support for the root tip, which passes between the soil particles.

Under a microscope, a cross section of the root in the absorption zone shows its structure at the cellular and tissue levels. On the surface of the root there is rhizoderm, under it there is bark. The outer layer of the cortex is the exodermis, inward from it is the main parenchyma. Its thin-walled living cells perform a storage function, conducting nutrient solutions in a radial direction - from the suction tissue to the vessels of the wood. They also contain the synthesis of a number of organic substances vital for the plant. The inner layer of the cortex is the endoderm. Nutrient solutions entering the central cylinder from the cortex through endodermal cells pass only through the protoplast of cells.

The bark surrounds the central cylinder of the root. It borders on a layer of cells that retain the ability to divide for a long time. This is a pericycle. Pericycle cells give rise to lateral roots, adventitious buds and secondary educational tissues. Inward from the pericycle, in the center of the root, there are conductive tissues: bast and wood. Together they form a radial conductive bundle.

The root vascular system conducts water and minerals from the root to the stem (upward flow) and organic matter from the stem to the root (downward flow). It consists of vascular-fibrous bundles. The main components of the bundle are sections of the phloem (through which substances move to the root) and xylem (through which substances move from the root). The main conducting elements of phloem are sieve tubes, xylem is trachea (vessels) and tracheids.

Root life processes

Transport of water in the root

Absorption of water by root hairs from the soil nutrient solution and conduction of it in a radial direction along the cells of the primary cortex through passage cells in the endoderm to the xylem of the radial vascular bundle. The intensity of water absorption by root hairs is called suction force (S), it is equal to the difference between osmotic (P) and turgor (T) pressure: S=P-T.

When the osmotic pressure is equal to the turgor pressure (P=T), then S=0, water stops flowing into the root hair cell. If the concentration of substances in the soil nutrient solution is higher than inside the cell, then water will leave the cells and plasmolysis will occur - the plants will wither. This phenomenon is observed in conditions of dry soil, as well as with excessive application of mineral fertilizers. Inside the root cells, the suction force of the root increases from the rhizoderm towards the central cylinder, so water moves along a concentration gradient (i.e. from a place with a higher concentration to a place with a lower concentration) and creates root pressure, which raises the column of water through the xylem vessels , forming an ascending current. This can be found on leafless trunks in the spring when the “sap” is collected, or on cut stumps. The flow of water from wood, fresh stumps, and leaves is called “crying” of plants. When the leaves bloom, they also create a suction force and attract water to themselves - a continuous column of water is formed in each vessel - capillary tension. Root pressure is the lower driver of water flow, and the suction force of the leaves is the upper one. This can be confirmed using simple experiments.

Absorption of water by roots

Target: find out the basic function of the root.

What we do: plant grown on wet sawdust, shake off its root system and lower its roots into a glass of water. Pour a thin layer over the water to protect it from evaporation. vegetable oil and mark the level.

What we see: After a day or two, the water in the container dropped below the mark.

Result: consequently, the roots sucked up the water and brought it up to the leaves.

You can also do one more experiment to prove the absorption of nutrients by the root.

What we do: cut off the stem of the plant, leaving a stump 2-3 cm high. We put a rubber tube 3 cm long on the stump, and on the upper end we put a curved glass tube 20-25 cm high.

What we see: The water in the glass tube rises and flows out.

Result: this proves that the root absorbs water from the soil into the stem.

Does water temperature affect the intensity of water absorption by roots?

Target: find out how temperature affects root function.

What we do: one glass should be with warm water(+17-18ºС), and the other with cold (+1-2ºС).

What we see: in the first case, water is released abundantly, in the second - little, or stops altogether.

Result: this is proof that temperature greatly influences root function.

Warm water is actively absorbed by the roots. Root pressure increases.

Cold water is poorly absorbed by the roots. In this case, root pressure drops.

Mineral nutrition

The physiological role of minerals is very great. They are the basis for synthesis organic compounds, as well as factors that change physical state colloids, i.e. directly affect the metabolism and structure of the protoplast; act as catalysts for biochemical reactions; affect cell turgor and protoplasm permeability; are centers of electrical and radioactive phenomena in plant organisms.

It has been established that normal plant development is possible only if there are three non-metals in the nutrient solution - nitrogen, phosphorus and sulfur and four metals - potassium, magnesium, calcium and iron. Each of these elements has individual meaning and cannot be replaced by another. These are macroelements, their concentration in the plant is 10 -2 -10%. For normal development plants need microelements, the concentration of which in the cell is 10 -5 –10 -3%. These are boron, cobalt, copper, zinc, manganese, molybdenum, etc. All these elements are present in the soil, but sometimes in insufficient quantities. Therefore, mineral and organic fertilizers are added to the soil.

The plant grows and develops normally if the environment surrounding the roots contains all the necessary nutrients. This environment for most plants is soil.

Breathing of roots

For normal growth and development of the plant, it is necessary that the root receives Fresh air. Let's check if this is true?

Target: Does the root need air?

What we do: Let's take two identical vessels with water. Place developing seedlings in each vessel. Every day we saturate the water in one of the vessels with air using a spray bottle. Pour a thin layer of vegetable oil onto the surface of the water in the second vessel, as it delays the flow of air into the water.

What we see: After some time, the plant in the second vessel will stop growing, wither, and eventually die.

Result: The death of the plant occurs due to a lack of air necessary for the root to breathe.

Root modifications

Some plants store reserve nutrients in their roots. They accumulate carbohydrates, mineral salts, vitamins and other substances. Such roots grow greatly in thickness and acquire an unusual appearance. Both the root and the stem are involved in the formation of root crops.

Roots

If reserve substances accumulate in the main root and at the base of the stem of the main shoot, root vegetables (carrots) are formed. Plants that form root crops are mostly biennials. In the first year of life, they do not bloom and accumulate a lot of nutrients in the roots. On the second, they quickly bloom, using the accumulated nutrients and forming fruits and seeds.

Root tubers

In dahlia, reserve substances accumulate in adventitious roots, forming root tubers.

Bacterial nodules

The lateral roots of clover, lupine, and alfalfa are peculiarly modified. Bacteria settle in young lateral roots, which promotes absorption nitrogen gas soil air. Such roots take on the appearance of nodules. Thanks to these bacteria, these plants are able to live in nitrogen-poor soils and make them more fertile.

Stilates

Ramp, which grows in the intertidal zone, develops stilted roots. They hold large leafy shoots on unstable muddy soil high above the water.

Air

Tropical plants living on tree branches develop aerial roots. They are often found in orchids, bromeliads, and some ferns. Aerial roots hang freely in the air without reaching the ground and absorb moisture from rain or dew that falls on them.

Retractors

In bulbous and corm plants, such as crocuses, among the numerous thread-like roots there are several thicker, so-called retractor roots. By contracting, such roots pull the corm deeper into the soil.

Columnar

Ficus plants develop columnar above-ground roots, or supporting roots.

Soil as a habitat for roots

Soil for plants is the medium from which it receives water and nutrients. The amount of minerals in the soil depends on specific features maternal rock, the activity of organisms, from the life activity of the plants themselves, from the type of soil.

Soil particles compete with roots for moisture, retaining it on their surface. This is the so-called bound water, which is divided into hygroscopic and film. It is held in place by the forces of molecular attraction. The moisture available to the plant is represented by capillary water, which is concentrated in small pores of the soil.

An antagonistic relationship develops between moisture and the air phase of the soil. The more large pores there are in the soil, the better the gas regime of these soils, the less moisture the soil retains. The most favorable water-air regime is maintained in structural soils, where water and air exist simultaneously and do not interfere with each other - water fills the capillaries inside the structural units, and air fills the large pores between them.

The nature of the interaction between plant and soil is largely related to the absorption capacity of the soil - the ability to hold or bind chemical compounds.

Soil microflora decomposes organic matter to more simple connections, participates in the formation of soil structure. The nature of these processes depends on the type of soil, chemical composition plant residues, physiological properties microorganisms and other factors. Soil animals take part in the formation of soil structure: annelids, insect larvae, etc.

As a result of a combination of biological and chemical processes a complex complex of organic substances is formed in the soil, which is combined with the term “humus”.

Water culture method

What salts the plant needs, and what effect they have on its growth and development, was established through experience with aquatic crops. The water culture method is the cultivation of plants not in soil, but in aqueous solution mineral salts. Depending on the goal of the experiment, you can exclude a particular salt from the solution, reduce or increase its content. It was found that fertilizers containing nitrogen promote plant growth, those containing phosphorus promote the rapid ripening of fruits, and those containing potassium promote the rapid outflow of organic matter from leaves to roots. In this regard, it is recommended to apply fertilizers containing nitrogen before sowing or in the first half of summer; those containing phosphorus and potassium - in the second half of summer.

Using the water culture method, it was possible to establish not only the plant’s need for macroelements, but also to clarify the role of various microelements.

Currently, there are cases where plants are grown using hydroponics and aeroponics methods.

Hydroponics is the growing of plants in containers filled with gravel. A nutrient solution containing the necessary elements is fed into the vessels from below.

Aeroponics is the air culture of plants. With this method, the root system is in the air and is automatically (several times within an hour) sprayed with a weak solution of nutrient salts.

First, by reading a textbook, encyclopedias and articles on the Internet, I learned what the structure of flower plants looks like

The organs of a flower plant are shoots, roots, flowers, fruits with seeds. And they all consist of various types tissue: educational, integumentary, mechanical, conductive, basic. All these fabrics perform various functions in plant life.

Transport of water in flowering plants

In order for a plant to grow, certain conditions must be met: light, heat, water, nutrition. The active movement of substances in plants occurs through conducting tissues. Water and minerals dissolved in it move in the plant from the roots to the flower through vessels. Water enters the plant through the root hairs, then the water rises under pressure through the vessels of the root. Once in the leaves, water evaporates from the surface of the cells and is released into the atmosphere in the form of steam. This process ensures a continuous upward flow of water through the plant.

But what forces ensure the movement of water current up the stem in a glass of water? It can be assumed that the water is pushed out from below or is pulled from above. Over short distances, the transport of substances is ensured by the physical processes of diffusion. Water molecules move from an area where their concentration is high to where their concentration is low.