Transport of substances across cell membranes. Transport of water, mineral salts and assimilates throughout the plant. Transpiration Plant transport system

Fats are broken down into glycerol and fatty acids by the enzyme lipase with the participation of water.

CH 2 OSOS 17 H 35 CH2OH

SNOSOS 17 H 33 + 3H 2 O → CHON + C 17 H 35 COOH + 2C 17 H 33 COOH

Steoric oleic

CH 2 OSOS 17 N 33 CH 2 OH

sterorinodiolein

Conversion of glycerol(Gl-n)

Gl-n → DOAP + FHA

PHA + DOAP → fructose 1,6 diphosphate (see Calvin's cycle)

PHA can also be completely oxidized to CO 2 and H 2 O through c. Krebs (PHA → PVC → Krebs c. → CO 2 + H 2 O). Here the connection between fat metabolism and carbohydrate metabolism is clearly visible.

Transformation of residential complex. β – oxidation is the main way of their decomposition. It consists in the sequential cleavage of the CH 3 -CO S-CoA molecule from the FA chain. That. the FA chain is shortened and ultimately it breaks down into CH 3 -CO S-CoA molecules with the formation of n FADH 2 and n NADH + H +, the oxidation of which leads to the production of Q β-oxidation occurs in the mitochondrial matrix.

Many high-molecular fatty acids are also capable of α-oxidation, when CO 2 is split off from the carboxyl group (but this is less common).

Glyoxylate cycle. When fats break down, many acetyl-CoA molecules are formed. Part of it can be used for the biosynthesis of carbohydrates through the glyoxylate cycle, which is a modified Krebs cycle. Before the formation of isocitric acid c. Krebs and glyoxylate go the same way. In the glyoxylate cycle, isocitric acid breaks down into glyoxylic acid (C -COOH) and succinic acid (CH2-COOH

CH2-COOH).

Succinic acid undergoes transformations as in c. Krebs, which leads to the formation of carbohydrates. Glyoxylic acid is the starting material for the synthesis of the amino acid glycine and formic acid. In addition, it condenses with another acetyl-CoA molecule to form malic acid, which undergoes further transformation as in c. Krebs (malic acid → PIKE).

The synthesis of carbohydrates using acetyl-CoA is one of the main purposes of the glyoxylate cycle.

The relationship of metabolism in plants.

In a plant organism, five main directions of metabolism can be defined:

A) carbohydrates;

B) lipids;

B) amino acids;

D) nitrogenous bases (purines and pyrimidines);

D) organic acids.

Naturally, the leading role belongs to proteins, which are synthesized from carbohydrates. Carbohydrates also serve as a starting material for the synthesis of fats, which, when oxidized, can be converted into carbohydrates.

Therefore, if a plant contains ↓ of any substance, then ↓ of another. For example, the content of B. leads to ↓ amount of carbohydrates. By adjusting growing conditions, you can influence the accumulation of certain groups of substances. A balance is maintained between all forms of substances, which is regulated by enzymes and controlled genetically.

Question 5. Transport of organic substances through the phloem.

Transport of organic compounds, which ensures the transfer of various metabolites, energy products and physiologically active substances both within the cell and between cells of plant tissues and organs, is an important link in the metabolism of the plant organism.

The main direction of transport is the outflow of photosynthesis products from leaves to other organs: stem, root, flowers, fruits, i.e. organs of consumption and storage of organic substances.

In plants there are donor-acceptor relationships. Those cells, tissues and organs in which organic substances are consumed are called attracting or accepting zones, and the centers of formation of metabolites subject to outflow into acceptor zones are donors . For example: leaf → root

donor products acceptor

The transport function is performed by elements of the plant’s vascular system, called phloem. The phloem elements of plant stems form a rather complex system consisting of parallel bundles of sieve tubes.

Organic substances move through the phloem in dissolved form in two directions - up and down; along the xylem, the flow is directed only upward. The simultaneous movement of substances through the phloem in opposite directions occurs through different sieve tubes.

Composition of phloem sap .

More than 80% of the substances are sucrose. Its concentration can be 1 mol/l, whereas in leaf mesophyll cells it is 10-30 times lower. Therefore, the transfer of sucrose from leaf cells to ST against a concentration gradient is carried out using active transport mechanisms, i.e. operation of pumps with energy consumption (usually in the form of ATP). Therefore, the transport of substances is closely related to respiration and is a highly energy-consuming process.

Nitrogenous substances are transported in the form of amino acids and their amides. Low molecular weight proteins were discovered. Contains small amounts organic acids, vitamins, phytohormones (stimulants); quite high concentration of ATP. There are many potassium ions from inorganic substances. pH of phloem sap is 8.0-8.5.

Amino acids and amides synthesized in the roots are transported in significant quantities through the xylem. The speed of movement of organic substances through the phloem is quite high: 20-100 cm/hour.

Methods for detecting phloem transport .

Radiodicators (C 14 , tritium hydrogen isotope, etc.). For example, transport of sucrose or amino acids occurs through parallel sieve tubes, both up and down simultaneously, but along each sieve tube in only one direction;

Experiments with ringing.

Juice flows out

Growth is slowing down

The mechanisms of phloem transport are not fully understood. Its intensity depends on the functional activity of CT satellite cells and external factors - temperature, NPK, H 2 O, CO 2, O 2, etc.

EXCHANGE AND TRANSPORT

PLANT WATER EXCHANGE

Indicators quantitatively characterizing transpiration(T).

Transpiration rate is the amount of water evaporated per unit time, calculated per unit leaf area (g/m 2 hour; g/dm 2 hour). The value is dynamic and varies widely depending on the type of plant, external conditions, physiological state and layering of leaves (see LPZ No. 8 and 10).

Transpiration coefficient is the amount of water consumed to form a unit of dry matter. It varies widely (from 110 to 1200). Average values are 200-330 g of water per 1 g of dry matter (or kg per kg, t per ton).

Transpiration productivity is the number of grams of dry matter formed by the evaporation of 1 liter of water. Average values are 2-3 g for C 3 plants and 6-8 g for C 4 plants.

Relative transpiration is the ratio of the intensity of transpiration to the intensity of evaporation from the open water surface (E). T 1 = T/E. T 1 is always less than one (see LPZ No. 10).

Ways to regulate transpiration. Transpiration rates are large and can be reduced without damage to plants.

Increased air humidity. For example, in protected ground conditions they carry out spraying plants, place containers with water;

Reduced wind speed. For example, shelterbelts and canopy crops (cucumbers and corn along the edges) are planted.

Maintaining optimal temperature conditions (watering, spraying, etc.).

Use of antitranspirants.

They are used when transplanting plants, as well as in conditions of lack of moisture. According to their mechanism of action, they can be divided into two groups: substances that cause the closure of stomata; substances that form films on the surface of leaves.

The first group includes abscisic acid (ABA) and its derivatives, which do not have a toxic effect on plants and cause the closure of stomata both when sprayed and when introduced through the roots with irrigation water.

The second group of substances - film-type antitranspirants - form mono- and polymolecular transparent and elastic films on the surface of the leaves, limiting the evaporation of water. The natural prototype of film antitranspirants is epicutylary wax, which regulates the diffusion of water vapor and CO 2. The effectiveness of antitranspirants is high. Thus, when transplanting deciduous trees, treating them with film-type antitranspirants reduced transpiration by 20-60% within 12-15 days, which significantly increased their survival rate and sales time.

Ways to Promote efficiency use of water by agricultural crops. crops.

To assess the efficiency of water use, determine water consumption coefficient or evapotranspiration rate. It is calculated as the ratio of water consumed for evapotranspiration to the created biomass or economically useful yield:

evapotranspiration, m 3 /ha

Biomass, t/ha

Evapotranspiration– this is the total water consumption during the growing season per 1 hectare of crops or plantings. This includes evaporation of water from the soil surface - evaporation and transpiration. In weedy crops, this will be transpiration of both cultivated plants and weeds.

The CV value varies widely and exceeds the values of transpiration coefficients, for example, from 380 to 2500.

The agronomist’s task is to create conditions under which the water consumption coefficient decreases. Paths:

Increasing soil fertility, strict adherence to the rules of agricultural technology.

With the correct use of fertilizers in crop rotation, the total moisture consumption for the formation of 1 centner of grain is reduced by 20-25%.

Reducing the EF value can be achieved in two ways: reducing the amount of evapotranspiration and increasing yield.

Evapotranspiration can be reduced by reducing transpiration, transpiration and evapotranspiration. We looked at ways to reduce transpiration earlier. In crops, this should include the fight against weeds, which consume a lot of water.

Reducing the extent of evaporation is achieved by maintaining the soil in a loose state (dry watering) and creating dense crops.

The simplest plant organisms, consisting of one cell or a small group of cells, do not have any transport system. The supply of each cell with the necessary starting materials is ensured by simple diffusion, in some cases supplemented by mechanisms of facilitated diffusion or active transport. Large and more complexly organized vascular plants have transport systems, but they are simpler than those of animals, and the principle of their structure is completely different. As we have already seen, most of the cells of a higher plant exchange gases with the external environment in a direct way - through the intercellular spaces. However, higher plants had to develop a system for delivering water from the roots located in the soil, where photosynthesis occurs, as well as a system for delivering organic substances synthesized in the leaves to the cells of the stem and roots, which need these substances for metabolic processes and growth.

In the spring, when there are no leaves yet, the bulk of the organic substances necessary for the growth and development of buds is supplied by xylem from the reserves of roots, trunks and stems. The movement of water through the xylem and nutrients through the phloem is called translocation. The physicochemical basis of these two processes is somewhat different: water and substances dissolved in it rise through the vessels and tracheids of the xylem, which do not contain living protoplasm, as a result of the joint action transpiration And root pressure, and nutrients are transported by the living cells of the phloem with amazing rapidity by mechanisms that are not yet completely understood.

Solutions moving through xylem and phloem are complex mixtures of many substances, organic and mineral, the composition of which can be very different in different plants, in different parts one plant and at different times of the year. Plant sap contains up to 98% water, as well as salts, sugars, amino acids, enzymes and other proteins, organic acids (citric, malic, etc.) and hormones (for example, indolylacetic acid). Plant juices, unlike blood plasma in animals, usually have a somewhat acidic reaction (pH from 7 to 4.6).

Stem and its functions

The stem (in trees - the trunk, branches and shoots) serves as a link between the roots, through which water and minerals enter the plant, and the leaves, in which nutrients are synthesized. The conductive tissues of the stem form a single whole with similar tissues of the root and leaf - these are the routes for the movement of substances. The cells of some stems contain chlorophyll and photosynthesis occurs in them; other cells are specialized for storing starch and other nutrients. The stem and branches support the leaves in such a position that as much sunlight as possible falls on them, and the flowers and fruits are in a position most favorable for reproduction. At the growth points of the stems, the primordia of leaves and flowers are formed.

In some cases, it is difficult for an inexperienced person to distinguish roots from stems, since in many plants the stems grow underground, and the roots are sometimes aboveground. Ferns and many herbaceous plants have underground stems called rhizomes. They grow just below the soil surface and produce above-ground leaves. Plants such as potatoes develop thickened underground stems - tubers, adapted for storing food supplies. The onion bulb is an underground stem surrounded by overlapping, tightly packed scale-like leaves. The structure of the roots and stems is different: only on the stems there are nodes from which leaves arise. The tip of the root is always covered with a root cap, while the apex of the stem is bare, unless it ends in an apical bud. In the stem, conducting tissues are usually arranged in the form of rings: phloem forms the outer ring, and xylem forms the inner; in the root, bundles of phloem tubes lie between the rays of the star-shaped xylem mass.

Plant stems are herbaceous or woody. Soft, green, quite thin grassy the stem is typical for annuals plants. Such plants are formed from a seed, develop, flower and produce seeds during one growing season, dying before the onset of winter. Other herbaceous plants are two-year-olds– their life cycle lasts 2 years. During the first growing season, nutrients are deposited in the roots of the plant. Then the leaves of the plant die, and the next year flowering stems develop from the top, which produce seeds. Examples of biennials are carrots and beets. Plants with soft and tender stems, supported primarily by turgor pressure, are called herbs.

Very different from herbaceous annuals and biennials woody perennials, living much longer than two years and having a thick, durable stem, or trunk, covered with a layer of cork. Tree - this is a woody-stemmed perennial plant that begins to branch at some distance from the soil surface and therefore has a main stem, or trunk. Shrubs, which include, for example, lilac, oleander and hawthorn, are woody perennials with many stems of approximately the same size starting at the surface of the soil.

According to the generally accepted opinion, woody stemmed plants are more primitive than herbaceous plants, since, judging by the available data, the first true seed plants on earth were woody stemmed perennial plants. In past geological epochs, such plants reached as far north as Greenland. But as a result of the cooling that occurred at the end of the Mesozoic, some of them became extinct, and many species were pushed towards the equator. Other plants have adapted to the cold - they have developed a life cycle in which growth and flowering are completed in one year - during the warm summer period, and cold-resistant seeds tolerate the harsh conditions of winter; in other words, such plants turned into herbs. The tissues of herbaceous stems are located around bundles of xylem and phloem, but the structural details differ in the two main groups of angiosperms, or flowering plants (Angiospermae): dicotyledons(Dicotyledoneae) and monocots(Monocotyledoneae). In the stem of a dicotyledon, such as sunflower or clover, bundles of xylem and phloem are arranged in a circle in such a way that the stem is divided into 3 concentric zones - outer cortex, vascular bundles and central core, consisting of colorless parenchyma cells, which are a receptacle for reserve substances.

During the first year of life, the stems of woody plants are similar in structure to the stems of herbaceous plants. However, by the end of the first growing season, additional cambium appears in the medullary rays, so that it ultimately forms a continuous ring running both between and within the vascular bundles. During each subsequent year, the cambium produces additional xylem and phloem; this phloem replaces the primary phloem and forms, immediately outside the cambium, a thin continuous sheath of nutrient-conducting tissue, and annual deposits of xylem form tree rings. The boundaries between them are noticeable to the eye, since the xylem vessels that appear in the spring are wider and appear lighter than the vessels that appear in the fall. Plant sap rises to the leaves only through the youngest, outer xylem vessels, forming sapwood; inner layers of dead hard xylem cells and fibers that form heartwood, increase the strength of the stem so that it can withstand the increasing weight of foliage as the tree grows.

The width of tree rings varies depending on climatic conditions, prevailing during the formation of this ring. Therefore, by looking at the rings of old trees, it is possible to determine what the climate was like at a certain period in the past - several years or even several thousand years ago.

Cambium also plays an important role in wound healing in plants. If the outer tissues of the stem are damaged, the cambium grows out of the damaged area and differentiates into new xylem, phloem, and cambium, each of these tissues continuing continuously with the corresponding tissue type in the undamaged part of the plant. In most woody plants, some cells of the outer cortex become meristematic and form secondary, or cork, cambium. These outer cells become impregnated with waterproof, waxy substances and eventually die and fall off, partly under the influence of wind and rain, and partly under the pressure of tissue growing from within.

In the stem of monocots, such as corn, the outer epidermis consists of thick-walled cells and is penetrated by stomata, similar to those of leaves. The epidermis and the cortical cells lying directly below it become thick-walled, lignify and turn into mechanical tissue. The vascular bundles are scattered throughout the stem, and are not arranged in a ring, as in dicotyledons. In the outer part of the stem, the bunches are smaller and more numerous. Each vascular bundle contains xylem and phloem, but lacks cambium; usually it is enclosed in a shell of sclerenchyma cells that have a supporting function. In some monocots, such as wheat and bamboo, the parenchyma cells in the center of the stem are destroyed, resulting in a central pith cavity!

In the spring, after the apical bud begins to grow, the covering scales move apart and fall off, leaving a ring of scars. These scars, which mark the position of the end of the stem at the end of the growth period, remain visible for many years. Thus, by counting the number of scars from apical buds, the age of the branch can be determined. The general appearance of a tree or shrub is determined by the position and distribution of apical and axillary buds and their comparative activity. In trees with a strong apical bud, for example, cedar or poplar, the shoots formed by the apical bud are much stronger than the axillary shoots; the result is a single straight main trunk. Plants with strong axillary buds are distinguished by a horizontal arrangement of branches and a spreading shape. On general form trees are also influenced by the direction and strength of the prevailing wind and the presence of other trees nearby.

In addition to apical and axillary buds, lentils and bud scars, other formations can be distinguished on the surface of the shoot. These include leaf scars, remaining after the leaf has fallen from the petiole, and fruit scars, occurring after fetal abscission. A leaf is an organ specially adapted for photosynthesis. Details of its structure have been described previously. Along the leaf petiole, bundles of xylem and phloem pass from the stem to the leaf wall, where they can branch repeatedly, forming a network of veins. The xylem vessels and tracheids are located on the upper side of each vein, and the phloem sieve tubes are located on the lower side.

Transpiration

Leaves, when exposed to air, lose moisture through evaporation, except for those periods when the air is saturated with water vapor. Solar heat causes water to evaporate from the surface of mesophyll cells, and the resulting water vapor diffuses out of the leaf through the stomata. This kind of water loss, called transpiration, can occur in all plant organs exposed to air, but it is mainly carried out by the leaves. At night, transpiration is very insignificant, since the stomata are usually closed and the evaporation of water from the surface of the mesophyll cells is slowed down due to the lower temperature. The stomata are also often closed in the second half of a hot sunny day. This significantly reduces transpiration and allows the plant to conserve water. When there is a sufficient supply of water to the plant, the stomata remain open and the plants release an amazing amount of moisture through transpiration. Only a small portion (1–2%) of the water absorbed by the roots is used in the process of photosynthesis. The rest of the moisture passes through the stomata in the form of water vapor during the process of transpiration. If the plant does not receive enough water from the roots, the guard cells of the stomata lose turgor and the stomata close, retaining water.

The numerous small openings of the stomata serve as an extremely efficient route for the diffusion of water vapor, oxygen and CO 2. Although the total area of these pores is only 1–3% of the entire surface of the leaf blade, the rate of diffusion through the stomata is only 25–50% lower than through an open surface equal to the surface of the leaf. In the sun, a plant transpires on average about 50 cm 3 of water per 1 m 2 of leaf surface in 1 hour. A corn plant consumes on average more than 200 liters of water during the growing season; a medium-sized tree transpires the same amount of water in just 1 day. The amount of water transpired varies greatly among different plants; It is estimated, for example, that 1 hectare of corn transpires 3,500,000 liters of water during the growing season, and 1 hectare of mature maple forest - approximately twice as much, while cacti in the Arizona desert consume no more than 2,750 liters of water per 1 hectare for the whole year. The amount of water evaporated by the leaves of trees in a forest also largely depends on precipitation, humidity and temperature in the area.

Transpiration facilitates the movement of water up the stem, contributes to the concentration in the leaves of dilute solutions of mineral salts absorbed by the roots and necessary for the synthesis of new cellular components, and also causes cooling of the leaves, similar to what happens in animals during the evaporation of sweat. Although a leaf absorbs about 75% of the sunlight falling on it, only about 3% of the absorbed light is used in the process of photosynthesis. The rest of the light energy is converted into heat and must be removed to avoid the death of leaf tissue. Part of this heat is spent on evaporation of water (540 kcal is consumed to convert 1 liter of water into water vapor), and part is removed by radiation and convection.

As a result of the evaporation of water from the surface of meyophyll cells, the concentration of substances dissolved in the cell sap increases and the cells become slightly hypertonic; they begin to receive water from neighboring cells with a high water content, and these latter, in turn, receive water from the tracheids and vessels of the leaf veins. Thus, during transpiration, water, due to the purely physical process of osmosis, penetrates from the xylem vessels of the veins through intermediate cells into the mesophyll cells closest to the air-filled intercellular spaces of the leaf, where its evaporation occurs. Consequently, water continuously flows from the soil into the conducting system of the root and rises along the stem and petiole to the veins of the leaf blade.

Movement of water

Many years ago, it was experimentally shown that in the stem, water and salts absorbed by the roots rise mainly through the tracheids and xylem vessels, while sugars and other organic substances move mainly through the sieve tubes of the phloem. If you make a cut along the entire circumference of the stem, crossing the phloem and cambium, but not affecting the xylem, the leaves will retain turgor for a long time and remain in good condition; therefore, water enters them through the xylem, since the phloem is completely cut off. Using a special technique, the xylem can be cut while leaving the phloem relatively intact; in this case, the leaves almost immediately wither and die, i.e. and these results indicate that water enters the leaves mainly through the xylem. Although the route of water transfer has long been known, the mechanism of this process is still not entirely clear. Any theory, to be considered acceptable, must explain the high rate of water flow, reaching 75-100 ml per minute in some plants, as well as the fact that water rises to the very tops of trees such as Douglas fir and sequoia, reaching heights of up to 125 m. To maintain such a column of water, a pressure of more than 12 atm is required; In addition, additional pressure is required to lift the water against friction in narrow channels. According to some estimates, the pressure required to lift water to the top of a tall tree can reach 30 atm. It could either be created at the base of the plant and push water upward, or created at its top and pull up family; The combined action of both these forces is also possible.

Root pressure. By cutting the stem of a well-watered tomato plant, you can see how juice will flow out of the stump for some time. If you attach a glass tube to the hemp and tie the junction tightly enough, the sap can rise in the tube to a height of 1 m or even higher. This suggests that there is a positive pressure at the root-stem boundary, called root pressure and created by forces acting at the root. When there is an abundance of moisture in the soil and high air humidity, which minimizes water loss due to evaporation from the leaves, water can come out under pressure from the ends of the leaf veins, forming droplets along the edges of the leaf. This phenomenon is called guttation, also indicates that, under certain conditions, xylem sap can be under pressure created by the roots.

The sap in the roots is hypertonic with respect to the soil solution; it is possible that this, at least in part, determines the root pressure. The movement of water from the soil through the epidermis, cortex, endoderm and pericycle of the root into its xylem and further up the xylem into the stem and leaves occurs “down” the concentration gradient and is carried out - at least in part - by simple diffusion. If the roots are killed or deprived of oxygen, root pressure will drop to zero; therefore, this pressure depends on some active process that requires energy. Many plant physiologists have come to the conclusion that root endodermal cells actively secrete water inward, towards the central cylinder, and that this is what largely determines root pressure.

At the first measurements of root pressure, low values were obtained, but later, when methods were developed that made it possible to cut the stem and “hermetically” attach the device to it without damaging the tissue, it was shown that root pressure can reach 6 - 10 atm or more even in a tomato, in experiments with which the water rises in the tube by less than 1 m.

In the spring, when there are no leaves yet, the only force causing the sap to rise up the stem is probably root pressure. Attempts to measure root pressure in conifers have not been successful; it is possible that in these plants it does not occur at all. If root pressure were their main force causing the rise of sap, then one would expect that sap would flow out under pressure from a punctured xylem vessel; however, after piercing such a vessel, on the contrary, the hissing of air entering inside is heard. It is possible that in some plants, under certain conditions, root pressure is actually involved in raising the sap up the stem, but it can hardly be considered the main factor operating in most plants most of the time.

Transpiration and linkage theory

Another force that could cause water to move up the stem is a "lift" from above, rather than a push from below. In leaves, water is consumed as a result of transpiration and in the process of photosynthesis, which, in addition, leads to the formation of osmotically active substances; these processes maintain the hypertonicity of the contents of the leaf cells in relation to the juice located in the veins. Leaf cells continually draw water from the upper xylem of the leaves and stem, causing the column of liquid in each conducting vessel to rise. The presence of this suction force can be demonstrated by connecting a cut shoot with a waterproof material to the end of a glass tube, the other end of which is immersed in a container of water; By introducing an air bubble into the tube, you can judge by its movement the speed of water movement.

The role of cohesion of water molecules in its ascent through the xylem was formulated in 1894 by Dixon and Joly, who predicted that a column of water should have great tensile strength. In a number of experiments, values were actually obtained that significantly exceeded the 30 atm required to raise water to the top of a sequoia tree. If you take a porous ceramic tube, pour water into it and immerse the lower end in mercury, then as a result of the evaporation of water, the mercury can rise up to 100 cm or more - significantly higher than it would rise under the influence of barometric pressure. To successfully demonstrate this phenomenon, the water must first be boiled to remove dissolved gases from which bubbles could form when the water column stretches.

Based on the theory of adhesion, it should be expected that during periods of intense transpiration, the diameter of the tree trunk will decrease. If the column of water in the xylem experiences tension, an inward force must act on the walls of each of the conducting vessels. The combined action of such forces on all channels in the active zone of wood would be sufficient to cause noticeable compression of the trunk during active transpiration. A similar effect was actually discovered: the thickness of the trunk of a majestic pine (Pinus radiata) subject to daily fluctuations with a minimum shortly after noon, when transpiration reaches its maximum.

Dixon and Joly's hypothesis is also supported by experiments that studied the absorption of water by tropical vines. Some of these vines climb the trunks. trees up to a height of 50 m or more. If you cut the vine stem near the base and lower it into a bucket of water, the plant begins to intensively absorb water. Rapid absorption of water is also observed if the bucket is replaced with a hermetically sealed vessel, although a vacuum is created in the vessel. At present, the theory of linkage is widely accepted, as it allows us to explain the rise of water in most plants under almost any conditions. The question of the mechanism of the initial formation of a water column remains unclear.

In any living or plant organism, tissue is formed by cells similar in origin and structure. Any tissue is adapted to perform one or several important functions for an animal or plant organism.

Types of tissues in higher plants

The following types of plant tissues are distinguished:

educational (meristem);
integumentary;
mechanical;
conductive;
basic;
excretory.

All these tissues have their own structural features and differ from each other in the functions they perform.

Fig.1 Plant tissue under a microscope

Educational plant tissue

Educational fabric- This is the primary tissue from which all other plant tissues are formed. It consists of special cells capable of multiple divisions. It is these cells that make up the embryo of any plant.

This tissue is retained in the adult plant. It is located:

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at the bottom of the root system and at the tops of the stems (ensures plant growth in height and development of the root system) - apical educational tissue;
inside the stem (ensures the plant grows in width and thickens) - lateral educational tissue;

Plant integumentary tissue

Covering tissue is a protective tissue. It is necessary in order to protect the plant from sudden changes in temperature, from excessive evaporation of water, from microbes, fungi, animals and from all kinds of mechanical damage.

The integumentary tissues of plants are formed by cells, living and dead, that are capable of allowing air to pass through, providing the gas exchange necessary for plant growth.

The structure of plant integumentary tissue is as follows:

first there is the skin or epidermis, which covers the leaves of the plant, stems and the most vulnerable parts of the flower; skin cells are living, elastic, they protect the plant from excessive moisture loss;
Next is the cork or periderm, which is also located on the stems and roots of the plant (where the cork layer is formed, the skin dies); The cork protects the plant from adverse environmental influences.

There is also a type of integumentary tissue known as crust. This is the strongest covering fabric, cork in in this case is formed not only on the surface, but also in depth, and its upper layers slowly die off. Essentially, the crust is made up of cork and dead tissue.

Fig. 2 Crust - a type of plant covering tissue

For the plant to breathe, cracks form in the crust, at the bottom of which there are special shoots, lentils, through which gas exchange occurs.

Mechanical plant tissue

Mechanical tissues give the plant the strength it needs. It is thanks to their presence that the plant can withstand strong gusts of wind and do not break under streams of rain or under the weight of fruits.

There are two main types of mechanical fabrics: bast and wood fibers.

Conductive plant tissues

Conductive fabric ensures the transport of water with minerals dissolved in it.

This tissue forms two transport systems:

upward(from roots to leaves);
downward(from leaves to all other parts of plants).

The ascending transport system consists of tracheids and vessels (xylem or wood), and vessels are more advanced conductors than tracheids.

In descending systems, the flow of water with photosynthesis products passes through sieve tubes (phloem or phloem).

Xylem and phloem form vascular-fibrous bundles - the “circulatory system” of the plant, which penetrates it completely, connecting it into one whole.

Main fabric

Ground tissue or parenchyma- is the basis of the entire plant. All other types of fabrics are immersed in it. This is living tissue and it does different functions. It is because of this that its different types are distinguished (information about the structure and functions different types main fabric is presented in the table below).

Types of main fabric	Where is it located in the plant?	Functions	Structure
Assimilation	leaves and other green parts of the plant	promotes the synthesis of organic substances	consists of photosynthetic cells
Storage	tubers, fruits, buds, seeds, bulbs, root vegetables	promotes the accumulation of organic substances necessary for plant development	thin-walled cells
Aquifer	stem, leaves	promotes water accumulation	loose tissue consisting of thin-walled cells
Airborne	stem, leaves, roots	promotes air circulation throughout the plant	thin-walled cells

Rice. 3 The main tissue or parenchyma of the plant

Excretory tissues

The name of this fabric indicates exactly what function it plays. These fabrics help saturate the fruits of plants with oils and juices, and also contribute to the release of a special aroma by the leaves, flowers and fruits. Thus, there are two types of this fabric:

endocrine tissue;
Exocrine tissue.

What have we learned?

For the biology lesson, 6th grade students need to remember that animals and plants consist of many cells, which, in turn, arranged in an orderly manner, form one or another tissue. We found out what types of tissues exist in plants - educational, integumentary, mechanical, conductive, basic and excretory. Each tissue performs its own strictly defined function, protecting the plant or providing all its parts with access to water or air.

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Plant transport systems

Unlike the complex transport system of higher animals, consisting of the heart and blood vessels, in higher plants this system is simpler and consists of xylem and phloem. Some plants also have a third subsystem containing latex – milky juice, rich in carbohydrates, fats and proteins, from which a number of valuable products are obtained, in particular rubber. By conductive elements xylem water and minerals move up the stem - from the roots to the leaves, and through the tubes phloem Nutrients synthesized in the leaves move down the stem and are used or stored in the stem itself and in the roots. However, nutrients can also move through the phloem from the bottom up (to the tips of the shoots and the ovaries and fruits located above). In the spring, when there are no leaves yet, the bulk of the organic substances necessary for the growth and development of buds is supplied by xylem from the reserves of roots, trunks and stems. The movement of water through the xylem and nutrients through the phloem is called translocation. The physicochemical basis of these two processes is somewhat different: water and substances dissolved in it rise through the vessels and tracheids of the xylem, which do not contain living protoplasm, as a result of the joint action transpiration And root pressure, and nutrients are transported by the living cells of the phloem with amazing rapidity by mechanisms that are not yet completely understood.

Solutions moving through xylem and phloem are complex mixtures of many substances, organic and mineral, the composition of which can be very different in different plants, in different parts of the same plant and at different times of the year. Plant sap contains up to 98% water, as well as salts, sugars, amino acids, enzymes and other proteins, organic acids (citric, malic, etc.) and hormones (for example, indolylacetic acid). Plant juices, unlike blood plasma in animals, usually have a somewhat acidic reaction (pH from 7 to 4.6).

Stem and its functions

The stem (in trees - the trunk, branches and shoots) serves as a link between the roots, through which water and minerals enter the plant, and the leaves, in which nutrients are synthesized. The conductive tissues of the stem form a single whole with similar tissues of the root and leaf - these are the routes for the movement of substances. The cells of some stems contain chlorophyll and photosynthesis occurs in them; other cells are specialized for storing starch and other nutrients. The stem and branches support the leaves in such a position that as much sunlight as possible falls on them, and the flowers and fruits 1 are in a position most favorable for reproduction. At the growth points of the stems, the primordia of leaves and flowers are formed.

com, while the apex of the stem is bare unless it ends in an apical bud.

In the stem, conducting tissues are usually arranged in the form of rings: phloem forms the outer ring, and xylem forms the inner; in the root, bundles of phloem tubes lie between the rays of the star-shaped xylem mass.

Very different from herbaceous annuals and biennials woody perennial plants, living much longer than two years and having a thick, durable stem, or trunk, covered with a layer of cork. Tree - this is a woody-stemmed perennial plant that begins to branch at some distance from the soil surface and therefore has a main stem, or trunk. Shrubs, which include, for example, lilac, oleander and hawthorn, are woody perennials with many stems of approximately the same size starting at the surface of the soil.

According to the generally accepted opinion, woody stemmed plants are more primitive than herbaceous plants, since, judging by the available data, the first true seed plants on earth were woody stemmed perennial plants. In past geological epochs, such plants reached as far north as Greenland. But as a result of the cooling that occurred at the end of the Mesozoic, some of them became extinct, and many species were pushed towards the equator. Other plants have adapted to the cold - they have developed a life cycle in which growth and flowering are completed in one year - during the warm season. summer period, and cold-resistant seeds tolerate harsh winter conditions; in other words, such plants turned into herbs. The tissues of herbaceous stems are located around bundles of xylem and phloem, but the structural details differ in the two main groups of angiosperms, or flowering plants (Angiospermae): dicotyledons(Dicotyledoneae) and monocots(Monocotyledoneae). In the stem of a dicotyledon, such as sunflower or clover, bundles of xylem and phloem are arranged in a circle in such a way that the stem is divided into 3 concentric zones - outer cortex, vascular bundles and central core, consisting of colorless parenchyma cells, which are a receptacle for reserve substances (Fig. 327).

During the first year of life, the stems of woody plants are similar in structure to the stems of herbaceous plants. However, by the end of the first growing season, additional cambium appears in the medullary rays, so that it ultimately forms a continuous ring running both between and within the vascular bundles. During each subsequent year, the cambium produces additional xylem and phloem; this phloem replaces the primary phloem and forms, immediately outside the cambium, a thin continuous sheath of nutrient-conducting tissue, and annual deposits of xylem form tree rings(Fig. 328). The boundaries between them are noticeable to the eye, since the xylem vessels that appear in the spring are wider and appear lighter than the vessels that appear in the fall. Plant sap rises to the leaves only through the youngest, outer xylem vessels, forming sapwood; inner layers of dead hard xylem cells and fibers that form heartwood, increase the strength of the stem so that it can withstand the increasing weight of foliage as the tree grows.

The width of tree rings varies depending on the climatic conditions that prevailed during the formation of a given ring. Therefore, by looking at the rings of old trees, it is possible to determine what the climate was like at a certain period in the past - several years or even several thousand years ago.

In the stem of monocots, such as corn, the outer epidermis consists of thick-walled cells and is penetrated by stomata, similar to those of leaves. The epidermis and the cortical cells lying directly below it become thick-walled, lignify and turn into mechanical tissue. The vascular bundles are scattered throughout the stem (Fig. 329), and are not arranged in a ring, as in dicotyledons. In the outer part of the stem, the bunches are smaller and more numerous. Each vascular bundle contains xylem and phloem, but lacks cambium; usually it is enclosed in a shell of sclerenchyma cells that have a supporting function. In some monocots, such as wheat and bamboo, the parenchyma cells in the center of the stem are destroyed, resulting in a central pith cavity!

In the spring, after the apical bud begins to grow, the covering scales move apart and fall off, leaving a ring of scars (Fig. 330). These scars, which mark the position of the end of the stem at the end of the growth period, remain visible for many years. Thus, by counting the number of scars from apical buds, the age of the branch can be determined.

The general appearance of a tree or shrub is determined by the position and distribution of apical and axillary buds and their comparative activity. In trees with a strong apical bud, for example, cedar or poplar, the shoots formed by the apical bud are much stronger than the axillary shoots; the result is a single straight main trunk. Plants with strong axillary buds are distinguished by a horizontal arrangement of branches and a spreading shape. The general appearance of a tree is also influenced by the direction and strength of the prevailing wind and the presence of other trees nearby.

In addition to apical and axillary buds, lentils and bud scars, other formations can be distinguished on the surface of the shoot. These include leaf scars ( rice. 330), remaining after the leaf falls from the petiole, and fruit scars, occurring after fetal abscission.

A leaf is an organ specially adapted for photosynthesis. Details of its structure have been described previously (section 46). Along the leaf petiole, bundles of xylem and phloem pass from the stem to the leaf wall, where they can branch repeatedly, forming a network of veins. The xylem vessels and tracheids are located on the upper side of each vein, and the phloem sieve tubes are located on the lower side.

Transpiration

Movement of water

Root pressure. By cutting the stem of a well-watered tomato plant, you can see how juice will flow out of the stump for some time. If you attach a glass tube to the hemp and tie the junction tightly enough, the sap can rise in the tube to a height of 1 m or even higher. This suggests that there is a positive pressure at the root-stem boundary, called root pressure and created by forces acting at the root. When there is an abundance of moisture in the soil and high air humidity, which minimizes water loss due to evaporation from the leaves, water can come out under pressure from the ends of the leaf veins, forming droplets along the edges of the leaf (Fig. 331). This phenomenon is called guttation, also indicates that, under certain conditions, xylem sap can be under pressure created by the roots.

Transpiration and linkage theory. Another force that could cause water to move up the stem is a "lift" from above, rather than a push from below. In leaves, water is consumed as a result of transpiration and in the process of photosynthesis, which, in addition, leads to the formation of osmotically active substances; these processes maintain the hypertonicity of the contents of the leaf cells in relation to the juice located in the veins. Leaf cells continually draw water from the upper xylem of the leaves and stem, causing the column of liquid in each conducting vessel to rise. The presence of this suction force can be demonstrated by connecting a cut shoot with a waterproof material to the end of a glass tube, the other end of which is immersed in a vessel of water (Fig. 332); By introducing an air bubble into the tube, you can judge by its movement the speed of water movement.

The water column in the xylem vessels, experiencing suction pressure from above, is in a somewhat stretched state; however, there is strong mutual cohesion between water molecules connected to each other by hydrogen bonds, and therefore the thin strands of water in the xylem vessels exhibit greater tensile strength. Thus, a tension is created in the upper part of the water column (mainly as a result of transpiration), which, due to the adhesion of water molecules, is transmitted along the entire length of the stem and roots and leads to a rise in the entire water column. The idea that water rises in plants under the influence of suction force resulting from transpiration was first expressed by Stephen Hayles at the beginning of the 18th century. The role of cohesion of water molecules in its ascent through the xylem was formulated in 1894 by Dixon and Joly, who predicted that a column of water should have great tensile strength. In a number of experiments, values were actually obtained that significantly exceeded the 30 atm required to raise water to the top of a sequoia tree. If you take a porous ceramic tube, pour water into it and immerse the lower end in mercury, then as a result of the evaporation of water, the mercury can rise up to 100 cm or more - significantly higher than it would rise under the influence of barometric pressure (Fig. 333). To successfully demonstrate this phenomenon, the water must first be boiled to remove dissolved gases from which bubbles could form when the water column stretches.

Based on the theory of adhesion, it should be expected that during periods of intense transpiration, the diameter of the tree trunk will decrease. If the column of water in the xylem experiences tension, a force directed inward should act on the walls of each of the conducting vessels. The combined action of such forces on all channels of the active zone of wood would be sufficient to cause a noticeable compression of the trunk during active transpiration. A similar effect was actually discovered: majestic pine trunk thickness (Pinus radiata) subject to daily fluctuations with a minimum shortly after noon, when transpiration reaches its maximum.

Transport systems of plants The simplest plant organisms, consisting of one cell or a small group of cells, do not have any transport system. The supply of each cell with the necessary starting materials is ensured simply

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Research

Plant transport system

MBOU Irkutsk Secondary School No. 37, 2nd grade

Head: PDO Sizenova Krestina Vladimirovna

Irkutsk 2017

CONTENT.

Introduction………………………………………………………………………………2

Theoretical part……………………………………………………….3

Practical part………………………………………………………..6

Conclusions………………………………………………………………………………..9

INTRODUCTION

Relevance: knowledge of the transport system will allow you to get flowers of unusual colors from boring white buds.

Purpose of the work: to study the movement of water and other substances through plants using an experiment that will not only give new knowledge about plants, but also the unusual color of the plant.

Tasks:

Study the structure of plants and their organs;

Find out how substances move in plants;

Conducting experiments to confirm the existence of a transport system.

Object of study: plant transport system

Subject of research: Chrysanthemum,

genus: Chrysanthemum (lat.Chrysanthemum )

family: Asteraceae (lat.Asteraceae ).

Research methodology:

I decided to divide my research into several stages:

Studying literature on the plant transport system;

Mastering chrysanthemum propagation methods;

Conducting experiments showing the presence of a transport system in plants.

THEORETICAL PART.

The movement of mineral and organic substances throughout the plant is very great importance, since this is the process by which the physiological interconnection of individual organs is carried out. So-called donor-acceptor connections are created between the organs that supply nutrients and the organs that consume them. The root serves as a donor of mineral nutrients, and the leaf serves as a donor of organic substances. In this regard, there are two main flows of nutrients in plants - ascending and descending.

The movement of water along the root bark occurs mainly along the apoplast, where it encounters less resistance, and only partially along the symplast. From the vessels of the stem, water enters the vessels of the leaf. Water moves from the stem through the petiole or leaf sheath and into the leaf. In the leaf blade, water-conducting vessels are located in the veins. The veins gradually branch out and become smaller. The denser the network of veins, the less resistance water encounters when moving to the mesophyll cells of the leaf.

A number of clarifications on the question of the paths and direction of movement of substances throughout the plant were made by studies using labeled atoms. Currently, scientists believe that the transport system in plants includes intracellular, short-range and long-distance transport. Short-range transport is the movement of substances between cells inside an organ through non-specialized tissues, for example, along the apoplast or symplast. Long-distance transport is the movement of substances between organs through specialized tissues - conducting bundles, i.e., through xylem and phloem. Together, xylem and phloem form a conducting system that permeates all plant organs and ensures continuous circulation of water and substances.

The movement of a substance through conducting plant tissues is called translocation. In vascular plants, these tissues are extremely specialized and are represented by xylem and phloem. The xylem carries out translocation mainly of water, mineral salts dissolved in it, as well as some organic nitrogen compounds and hormones; transport is directed from the roots to the aboveground organs of the plant. Phloem serves primarily to move solutions of organic and inorganic substances; Along the phloem, substances move mainly from leaves and storage organs to other parts of the plant, as a rule, to storage organs (roots, rhizomes, tubers, bulbs).Phloem transport can occur simultaneously in two directions. This "bidirectionality" is the resultone-way current in separate but adjacentsieve tubes connected to various donors and acceptors.

All consuming organs are provided, as a rule, by the donor closest to them. The upper photosynthetic vines supply the growing buds and the youngest leaves. The lower leaves provide roots. Fruits are provided from the leaves closest to them.

Stem and its functions

The stem (in trees - the trunk, branches and shoots) serves as a link between the roots, through which water and minerals enter the plant, and the leaves, in which nutrients are synthesized. The conductive tissues of the stem form a single whole with similar tissues of the root and leaf - these are the routes for the movement of substances. The cells of some stems contain chlorophyll and photosynthesis occurs in them; other cells are specialized for storing starch and other nutrients. At the growth points of the stems, the primordia of leaves and flowers are formed.

Plant stems are herbaceous or woody. The soft, green, rather thin herbaceous stem is typical of annual plants. Such plants develop from seed, flower and produce seeds during one growing season, dying before the onset of winter. Other herbaceous plants are biennials - their life cycle lasts 2 years.

Very different from herbaceous plants are woody perennial plants, which live much longer than two years and have a thick, durable stem, or trunk, covered with a layer of cork. During the first year of life, the stems of these plants are similar in structure to the stems of herbaceous plants. But by the end of the first growing season, additional cambium appears in the medullary rays, so that it subsequently forms a continuous ring passing both between the vascular bundles and within them. During each subsequent year, the cambium produces additional layers of xylem and phloem. This is how annual rings are formed in trees and shrubs. The boundaries between them are visible to the eye, since the xylem vessels that appear in the spring are wider and appear lighter than the vessels that appear in the fall.

Transpiration

Movement of water

Chrysanthemums as a subject of research.

Chrysanthemums ( lat.Chrysanthemum) - a genus of annual and perennial herbaceous plants of the familyAsteraceae , orCompositae . The plants are close to the genera Yarrow and Tansy, where many species of chrysanthemums often move.

The chrysanthemum is native to the countries of the temperate and northern zones of the Earth, but the largest number of plants still grow in Asia, Europe and Africa.

The name of the genus comes from the Greek. “χρῡσανθής” (golden-flowered), formed from two words “chrysos” (gold) and “anthemis” (flower), and is explained by the fact that the plants are characterized by the yellow color of the inflorescence.

Chrysanthemums grow mainly in the form of branched subshrubs, less often - in the form of herbaceous plants. The height of the bushes is from 50 cm to 1.5 m. The leaves are arranged in an alternate order, simple, whole, jagged, notched or dissected, various in size and shape, pubescent or not, mostly light green. The flowers are small, collected in a basket, in some species large, consisting, as a rule, of central tubular yellow flowers and ligulate marginal flowers, variously colored and usually arranged in a single row. In many hybrid varieties they are arranged in multi-rows and form a so-called “double” inflorescence. Shoots are glabrous/or pubescent. The fruit is an achene.

Chrysanthemums are propagated by seeds and cuttings.

Propagation by seeds. For early flowering, seeds are sown in March in common containers. As the seedlings grow, they are planted in pots. The substrate for planting is loose and nutritious.

Reproduction by cuttings. Chrysanthemums are successfully propagated by cuttings. Cuttings are taken from strong young shoots. Cut the cuttings carefully, under the leaf node, with a sharp tool. You can plant in various containers; pots with a diameter of 7-9 cm are suitable. For rooting, take a peat-humus mixture, which is sprinkled on top with a layer of sand about 2 cm thick. You can root in clean sand.

PRACTICAL PART.

First I needed to plant chrysanthemums. Having several cut chrysanthemum flowers from the bouquet, it was therefore easy to acquire cuttings.

1 II took the stems of the chrysanthemum, cut off all the leaves from them and pinched the top. I placed these stems in a glass of water and left them until young roots appeared.

2 For further cultivation, I selected a small, wide pot, since the roots grow wider than deep. I used universal soil, with a small amount of fertilizer. I placed pebbles on the bottom of the pot and mixed them with the soil. This will help avoid rotting of the root system. The pot was placed on sunny place in the SUN greenhouse.

3 When several strong roots appeared on the cuttings, I placed the shoots in moist soil to a depth of 3-5 cm. I sprinkled the roots with earth, but did not bury them too deeply. I wrapped the pot in plastic wrap for 2 weeks so that the roots could take root better.

Experience No. 1.

After the chrysanthemums took root, I began to water them with water with dissolved dye (Fig. 1). And I began to wait for my chrysanthemums to begin to bloom. Watering was carried out after the top layer of soil had dried.

Fig.1

Experience No. 2.

In order to make sure that water enters the leaves through the xylem, I conducted the following experiment. I placed a cut maple branch in the water where I dissolved the ink. Over time, the wood became colored, but the area closer to the bark, where the phloem is located, remained uncolored. From this experience, I was convinced that water flows through the xylem, and I also saw where xylem and phloem are located.

It takes quite a long time for chrysanthemums to grow and bloom, so I decided to conduct another experiment for which I used cut chrysanthemums that appeared at our house after the holiday.

Experience No. 3.

I placed each chrysanthemum stem in a separate container with water, where I added different dyes (Fig. 2). Soon I observed how the white inflorescences gradually began to acquire a different color, which corresponded to the color of the dye (Fig. 3). Over time, the flowers became completely colored (Fig. 4). This confirmed that water, together with all the substances dissolved in it, moves upward with a certain force.

Fig.2