Photosynthesis intensity

In plant physiology, two concepts are used: true and observed photosynthesis. This is due to the following considerations. The rate or intensity of photosynthesis is characterized by the amount of CO 2 absorbed by a unit of leaf surface per unit of time. The determination of the intensity of photosynthesis is carried out by the gasometric method by changing (reducing) the amount of CO 2 in a closed chamber with a leaf. However, along with photosynthesis, the process of respiration takes place, during which CO 2 is released. Therefore, the results obtained give an idea of ​​the intensity of the observed photosynthesis. To obtain the value of true photosynthesis, it is necessary to make a correction for respiration. Therefore, before the experiment, the intensity of respiration is determined in the dark, and then the intensity of the observed photosynthesis. Then the amount of CO 2 released during respiration is added to the amount of CO 2 absorbed in the light. Introducing this amendment, consider that the intensity of respiration in the light and in the dark is the same. But these corrections cannot give an estimate of true photosynthesis, because, firstly, when the leaf is darkened, not only true photosynthesis, but also photorespiration is excluded; secondly, the so-called dark breathing is actually dependent on light (see below).

Therefore, in all experimental work on the photosynthetic gas exchange of the leaf, preference is given to data on the observed photosynthesis. A more accurate method for studying the intensity of photosynthesis is the method of labeled atoms (the amount of absorbed 14 CO 2 is measured).

In the case when it is difficult to recalculate the amount of absorbed CO 2 per unit surface (coniferous, seeds, fruits, stem), the data obtained are referred to a mass unit. Given that the photosynthetic coefficient (the ratio of the volume of released oxygen to the volume of absorbed CO 2 equal to one, the rate of observed photosynthesis can be estimated by the number of milliliters of oxygen released by a unit of leaf area in 1 hour.

To characterize photosynthesis, other indicators are also used: quantum consumption, quantum yield of photosynthesis, assimilation number.

Quantum consumption is the ratio of the number of absorbed quanta to the number of assimilated CO 2 molecules. The reciprocal is named quantum yield.

Assimilation number- this is the ratio between the amount of CO 2 and the amount of chlorophyll that is contained in the leaf.

Speed ​​(intensity) photosynthesis is one of the most important factors affecting the productivity of agricultural crops, and hence the yield. Therefore, the elucidation of the factors on which photosynthesis depends should lead to the improvement of agrotechnical measures.

Theoretically, the rate of photosynthesis, like the rate of any multistage biochemical process, should be limited by the rate of the slowest reaction. So, for example, dark reactions of photosynthesis require NADPH and ATP, so dark reactions depend on light reactions. In low light, the rate of formation of these substances is too low to provide top speed dark reactions, so light will be the limiting factor.

The principle of limiting factors can be formulated as follows: with the simultaneous influence of several factors, the speed of a chemical process is limited by the factor that is closest to the minimum level (a change in this factor will directly affect this process).

This principle was first established by F. Blackman in 1915. Since then, it has been repeatedly shown that different factors, such as CO 2 concentration and illumination, can interact with each other and limit the process, although often one of them still dominates. Illumination, CO 2 concentration and temperature are the main external factors affecting the rate of photosynthesis. However, the water regime, mineral nutrition, etc. are also of great importance.

Light. When evaluating the effect of light on a particular process, it is important to distinguish between the influence of its intensity, quality (spectral composition), and exposure time to light.

In low light, the rate of photosynthesis is proportional to the light intensity. Gradually, other factors become limiting, and the increase in speed slows down. On a clear summer day, the illumination is approximately 100,000 lux, and 10,000 lux is enough to saturate photosynthesis with light. Therefore, light can usually be an important limiting factor in shading conditions. At very high light intensity, the discoloration of chlorophyll sometimes begins, and this slows down photosynthesis; however, in nature, plants exposed to such conditions are usually protected from it in one way or another (thick cuticle, drooping leaves, etc.).

The dependence of the intensity of photosynthesis on illumination is described by a curve, which is called the light curve of photosynthesis (Fig. 2.26).

Rice. 2.26. The dependence of the intensity of photosynthesis on illumination (light curve of photosynthesis): 1 is the rate of CO2 release in the dark (respiration rate); 2 – compensation point of photosynthesis; 3 – light saturation position

In low light, more CO 2 is released during respiration than it is bound during photosynthesis, so the beginning of the light curve with the abscissa axis is compensation point photosynthesis, which shows that in this case, photosynthesis uses exactly as much CO 2 as it is released during respiration. In other words, over time there comes a moment when photosynthesis and respiration will exactly balance each other, so that the visible exchange of oxygen and CO 2 will stop. The light compensation point is the light intensity at which the total gas exchange is zero.

Light curves are not the same for all plants. Plants that grow outdoors sunny places, the absorption of CO 2 increases until the light intensity is equal to the total solar illumination. In plants that grow in shaded areas (for example, oxalis), CO 2 uptake increases only at low light intensity.

All plants in relation to the intensity of light are divided into light and shade, or light-loving and shade-tolerant. Most agricultural plants are photophilous.

At shade-tolerant plants, firstly, light saturation occurs at weaker illumination, and secondly, in them the compensation point of photosynthesis occurs earlier, i.e., at lower illumination (Fig. 2.27).

The latter is due to the fact that shade-tolerant plants are characterized by low respiration intensity. In low light conditions, the intensity of photosynthesis is higher in shade-tolerant plants, and in strong light, on the contrary, in photophilous plants.

The intensity of the light also affects chemical composition end products of photosynthesis. The higher the illumination, the more carbohydrates are formed; in low light - more organic acids.

Experiments in laboratory conditions have shown that the quality of photosynthesis products is also affected by a sharp transition "darkness - light" and vice versa. At first, after turning on the light of high intensity, non-carbohydrate products are predominantly formed due to the lack of NADPH and ATP, and only after a while carbohydrates begin to form. Conversely, after the light is turned off, the leaves do not immediately lose their ability to photosynthesize, because for several minutes a supply of ATP and NADP remains in the cells.

After turning off the light, the synthesis of carbohydrates is first inhibited, and only then organic substances and amino acids. The main reason for this phenomenon is due to the fact that the inhibition of the conversion of FHA into PHA (and through it into carbohydrates) occurs earlier than the inhibition of FHA into PEP (and through it into alanine, malate, and aspartate).

The ratio of the forming products of photosynthesis is also affected by the spectral composition of light. Under the influence of blue light in plants, the synthesis of malate, aspartate and other amino acids and proteins increases. This response to blue light was found in both C 3 plants and C 4 plants.

The spectral composition of light also affects the intensity of photosynthesis (Fig. 2.28). Rice. 2.28. The action spectrum of photosynthesis in wheat leaves

Action spectrum is the dependence of the effectiveness of the chemical (biological) action of light on its wavelength. The intensity of photosynthesis in different parts of the spectrum is not the same. The maximum intensity is observed when plants are illuminated with those rays that are absorbed to the maximum by chlorophylls and other pigments. The intensity of photosynthesis is highest in red rays, because it is proportional not to the amount of energy, but to the number of quanta.

From the overall photosynthesis equation:

6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2

it follows that 686 kcal is needed to form 1 mole of glucose; this means that 686: 6 = 114 kcal is needed to assimilate 1 mole of CO 2. The energy reserve of 1 quantum of red light (700 nm) is 41 kcal/enstein, and blue (400 nm) 65 kcal/enstein. The minimum quantum consumption when illuminated with red light is 114:41 ≈ 3, while in reality 8–10 quanta are spent. Thus, the efficiency of using red light is 114/41 8 = 34%, and blue 114/65 8 = 22%.

CO 2 concentration. Dark reactions require carbon dioxide, which is included in organic compounds. Under normal field conditions, it is CO 2 that is the main limiting factor. The concentration of CO 2 in the atmosphere is 0.045%, but if you increase it, you can increase the rate of photosynthesis. With a short-term effect, the optimal concentration of CO 2 is 0.5%, however, with a long-term effect, damage to plants is possible, therefore, the optimum concentration in this case is lower - about 0.1%. Already now, some greenhouse crops, such as tomatoes, have begun to be grown in an atmosphere enriched with CO 2 .

A group of plants that absorb CO 2 from the atmosphere much more efficiently and therefore produce higher yields, the so-called C 4 plants, is of great interest at present.

AT artificial conditions the dependence of photosynthesis on the concentration of CO 2 is described in a carbon dioxide curve, which resembles the light curve of photosynthesis (Fig. 2.29).

At a CO 2 concentration of 0.01%, the rate of photosynthesis is equal to the rate of respiration (compensation point). Carbon dioxide saturation occurs at 0.2–0.3% CO 2, and in some plants, even at these concentrations, a slight increase in photosynthesis is observed.

Rice. 2.29. The dependence of the intensity of photosynthesis of pine needles on the concentration of CO 2 in the air

Under natural conditions, the dependence of photosynthesis on CO 2 concentration is described only by the linear part of the curve. It follows that the provision of plants with CO 2 under natural conditions is a factor that limits the yield. Therefore, it is advisable to grow plants indoors with a high content of CO 2 .

Temperature has a noticeable effect on the process of photosynthesis, since the dark, and partly light reactions of photosynthesis are controlled by enzymes. The optimum temperature for temperate plants is usually around 25°C.

The uptake and recovery of CO 2 in all plants increases with increasing temperature until some optimum level is reached. In most plants of the temperate zone, a decrease in the intensity of photosynthesis begins after 30 ° C, in some southern species after 40 o C. In high heat (50-60 o C), when enzyme inactivation begins, and the coordination of various reactions is disturbed, photosynthesis quickly stops. As the temperature rises, the rate of respiration increases much faster than the rate of natural photosynthesis. This affects the amount of observed photosynthesis. The dependence of the intensity of the observed photosynthesis on temperature is described by a temperature curve, in which three main points are distinguished: minimum, optimum, and maximum.

The minimum is the temperature at which photosynthesis begins, the optimum is the temperature at which photosynthesis is the most stable and reaches the highest speed, the maximum is the temperature after which photosynthesis stops (Fig. 2.30).

Rice. 2.30. The dependence of the intensity of photosynthesis on the temperature of the leaf: 1 - cotton; 2 – sunflower; 3 - sorghum

Influence of oxygen. More than half a century ago, a seemingly paradoxical phenomenon was noted. Air oxygen, which is a product of photosynthesis, is also its inhibitor: the release of oxygen and the absorption of CO 2 fall as the concentration of O 2 in the air increases. This phenomenon was named after its discoverer - the Warburg effect. This effect is inherent in all C 3 -plants. And only in the leaves of C 4 -plants it could not be detected. It is now firmly established that the nature of the Warburg effect is associated with the oxygenase properties of the main enzyme of the Calvin cycle, RDF-carboxylase. With a high concentration of oxygen, photorespiration begins. It has been established that when the concentration of O 2 is reduced to 2–3%, phosphoglycolate is not formed, and the Warburg effect also disappears. Thus, both of these phenomena, the manifestation of the oxygenase properties of RDF-carboxylase and the formation of glycolate, as well as a decrease in photosynthesis in the presence of O2, are closely related to each other.

A very low content of O 2 or a complete absence, as well as an increase in concentration to 25–30%, inhibits photosynthesis. For most plants, a slight decrease in the natural concentration (21%) of O 2 activates photosynthesis.

Effect of tissue hydration. As already noted, water participates in the light stage of photosynthesis as a hydrogen donor for CO2 reduction. However, the role of the photosynthesis-limiting factor is played not by the minimum amount of water (approximately 1% of the incoming water), but by the water that is part of the cell membranes and is the medium for all biochemical reactions, activates the enzymes of the dark phase. In addition, the degree of opening of the stomata depends on the amount of water in the guard cells, and the turgor state of the whole plant determines the location of the leaves in relation to the sun's rays. The amount of water indirectly affects the change in the rate of starch deposition in the stroma of the chloroplast and even changes in the structure and arrangement of thylakoids in the stroma.

The dependence of the intensity of photosynthesis on the water content of plant tissues, as well as the dependence on temperature, is described by a transition curve that has three main points: minimum, optimum, and maximum.

With dehydration, not only the intensity of photosynthesis changes, but also the qualitative composition of photosynthesis products: less malate, sucrose, and organic acids are synthesized; more - glucose, fructose alanine and other amino acids.

In addition, it was found that with a lack of water, ABA, a growth inhibitor, accumulates in the leaves.

Chlorophyll concentration, as a rule, is not a limiting factor, however, the amount of chlorophyll can decrease with various diseases (powdery mildew, rust, viral diseases), lack of minerals and with age (during normal aging). When the leaves turn yellow, they are said to become chlorotic, and the phenomenon itself is called chlorosis. Chlorotic spots on leaves are often a symptom of a disease or mineral deficiency.

Chlorosis can also be caused by a lack of light, since light is needed for the final stage of chlorophyll biosynthesis.

mineral elements. For the synthesis of chlorophyll, mineral elements are also needed: iron, magnesium and nitrogen (the last two elements are included in its structure), therefore they are especially important for photosynthesis. Potassium is also important.

For the normal functioning of the photosynthetic apparatus, the plant must be provided with necessary quantity(optimal) mineral elements. Magnesium, in addition to being a part of chlorophyll, is involved in the action of conjugating proteins in the synthesis of ATP, affects the activity of carboxylation reactions and the reduction of NADP +.

Iron in reduced form is necessary for the processes of biosynthesis of chlorophyll and iron-containing compounds of chloroplasts (cytochromes, ferredoxin). Iron deficiency disrupts cyclic and non-cyclic photophosphorylation, pigment synthesis, and changes in the structure of chloroplasts.

Manganese and chlorine take part in the photooxidation of water.

Copper is part of plastocyanin.

Nitrogen deficiency affects not only the formation of pigment systems and chloroplast structures, but also the amount and activity of RDP carboxylase.

With a lack of phosphorus, photochemical and dark reactions of photosynthesis are disturbed.

Potassium plays a multifunctional role in the ionic regulation of photosynthesis, with its deficiency in chloroplasts, the structure of the grana is destroyed, the stomata open weakly in the light and do not close enough in the dark, the water regime of the leaf worsens, i.e., all photosynthesis processes are disrupted.

Plant age. Only after the creation of phytotrons, where it is possible to grow plants under controlled conditions, was it possible to obtain reliable results. It was found that in all plants only at the very beginning life cycle When the photosynthetic apparatus is formed, the intensity of photosynthesis increases, very quickly reaches a maximum, then decreases slightly and then changes very little. For example, in cereals, photosynthesis reaches its maximum intensity during the tillering phase. This is explained by the fact that the maximum photosynthetic activity of the leaf coincides with the end of the period of its formation. Then aging begins and photosynthesis decreases.

The intensity of photosynthesis depends primarily on the structure of chloroplasts. As chloroplasts age, thylakoids are destroyed. Prove this using the Hill reaction. It goes worse, the older the chloroplasts. Thus, it was shown that the intensity is determined not by the amount of chlorophyll, but by the structure of the chloroplast.

AT optimal conditions humidity and nitrogen nutrition, the decrease in photosynthesis with age occurs more slowly, since under these conditions chloroplasts age more slowly.

genetic factors. The processes of photosynthesis to a certain extent depend on the heredity of the plant organism. The intensity of photosynthesis is different in plants of different systematic groups and life forms. In herbs, the intensity of photosynthesis is higher than in woody plants (Table 2.5).

The intensity of photosynthesis depends on a number of factors. First, on the wavelength of light. The process proceeds most effectively under the action of the waves of the blue-violet and red parts of the spectrum. In addition, the rate of photosynthesis is affected by the degree of illumination, and up to a certain point the rate of the process increases in proportion to the amount of light, then the note is no longer dependent on it.

Another factor is the concentration of carbon dioxide. The higher it is, the more intense the process of photosynthesis. Under normal conditions, the lack of carbon dioxide is the main limiting factor, since in atmospheric air contains a small percentage. However, under greenhouse conditions, this deficiency can be eliminated, which will favorably affect the rate of photosynthesis and the growth rate of plants.

An important factor in the intensity of photosynthesis is temperature. All photosynthesis reactions are catalyzed by enzymes, for which the optimal temperature range is 25-30 ° C. At more low temperatures the rate of action of enzymes is sharply reduced.

Water - important factor affecting photosynthesis. However, it is impossible to quantify this factor, since water is involved in many other metabolic processes occurring in the plant cell.

The Importance of Photosynthesis. Photosynthesis is a fundamental process in living nature. Thanks to him, from inorganic substances - carbon dioxide and water - with the participation of energy sunlight green plants synthesize organic substances necessary for the life of all life on Earth. The primary synthesis of these substances ensures the implementation of the processes of assimilation and dissimilation in all organisms.

The products of photosynthesis - organic substances - are used by organisms:

• to build cells;
• as a source of energy for life processes.

Man uses substances created by plants:

• as food (fruits, seeds, etc.);
• as an energy source (coal, peat, wood);
• as a building material.

Mankind owes its existence to photosynthesis. All fuels on Earth are products of photosynthesis. Using fossil fuels, we get the energy stored as a result of photosynthesis by ancient plants that existed in past geological epochs.

Simultaneously with the synthesis of organic substances, a by-product of photosynthesis, oxygen, is released into the Earth's atmosphere, which is necessary for the respiration of organisms. Without oxygen, life on our planet is impossible. Its reserves are constantly spent on products of combustion, oxidation, respiration occurring in nature. According to scientists, without photosynthesis, the entire supply of oxygen would be used up within 3,000 years. Therefore, photosynthesis is of the greatest importance for life on Earth.

For many centuries, biologists have tried to unravel the mystery of the green leaf. For a long time it was believed that plants create nutrients from water and minerals. This belief is connected with the experiment of the Dutch researcher Anna van Helmont, conducted back in the 17th century. He planted a willow tree in a tub, accurately measuring the mass of the plant (2.3 kg) and dry soil (90.8 kg). For five years, he only watered the plant, adding nothing to the soil. After five years, the mass of the tree increased by 74 kg, while the mass of the soil decreased by only 0.06 kg. The scientist concluded that the plant forms all substances from water. Thus, one substance was established that the plant absorbs during photosynthesis.

The first attempt to scientifically determine the function of a green leaf was made in 1667 by the Italian naturalist Marcello Malpighi. He noticed that if the first germinal leaves are torn off from pumpkin seedlings, then the plant stops developing. Studying the structure of plants, he made an assumption: under the influence of sunlight, some transformations occur in the leaves of the plant and water evaporates. However, these assumptions were ignored at the time.

After 100 years, the Swiss scientist Charles Bonnet conducted several experiments by placing a leaf of a plant in water and lighting it with sunlight. Only he made an incorrect conclusion, believing that the plant does not participate in the formation of bubbles.

The discovery of the role of the green leaf belongs to the English chemist Joseph Priestley. In 1772, while studying the importance of air for burning substances and breathing, he set up an experiment and found out that plants improve the air and make it suitable for breathing and burning. After a series of experiments, Priestley noticed that plants improve the air in the light. He was the first to suggest the role of light in the life of plants.

In 1800, the Swiss scientist Jean Senebier scientifically explained the essence of this process (by that time Lavoisier had already discovered oxygen and studied its properties): plant leaves decompose carbon dioxide and release oxygen only under the action of sunlight.

In the second half of the 19th century, an alcohol extract was obtained from the leaves of green plants. This substance is called chlorophyll.

German naturalist Robert Mayer discovered that plants absorb sunlight and turn it into energy. chemical bonds organic substances (the amount of carbon stored in the plant in the form of organic substances directly depends on the amount of light falling on the plant).

Kliment Arkadyevich Timiryazev, a Russian scientist, studied the influence of various parts of the sunlight spectrum on the process of photosynthesis. He managed to establish that it is in the red rays that photosynthesis proceeds most efficiently, and to prove that the intensity of this process corresponds to the absorption of light by chlorophyll.

K.A. Timiryazev emphasized that by assimilating carbon, the plant also assimilates sunlight, converting its energy into the energy of organic substances.

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Green leaf is the source of life on our planet. If it were not for green plants, there would be neither animals nor people on Earth. One way or another, plants serve as a source of food for the entire animal kingdom.

A person uses the energy not only of the sun's rays falling on the earth now, but also of those that fell on it tens and hundreds of millions of years ago. After all, coal, oil, and peat are chemically altered remains of plants and animals that lived in those distant times.

In recent decades, the attention of leading specialists in a number of branches of natural science has been riveted to the problem of photosynthesis, its various aspects are being comprehensively and deeply studied in many laboratories around the world. Interest is determined primarily by the fact that photosynthesis is the basis of the energy exchange of the entire biosphere.

The intensity of photosynthesis depends on many factors. light intensity , necessary for the greatest efficiency of photosynthesis, is different for different plants. In shade-tolerant plants, the maximum activity of photosynthesis is reached at about half of full sunlight, and in photophilous plants - almost at full sunlight.

Many shade-tolerant plants do not develop palisade (columnar) parenchyma in the leaves, and there is only spongy (lily of the valley, hoof). In addition, these plants have larger leaves and larger chloroplasts.

Also affects the rate of photosynthesis temperature environment . The highest intensity of photosynthesis is observed at a temperature of 20–28 °C. With a further increase in temperature, the intensity of photosynthesis decreases, and the intensity of respiration increases. When the rates of photosynthesis and respiration coincide, they speak of compensation point.

The compensation point changes depending on the intensity of the light, the rise and fall of the temperature. For example, in cold-resistant brown algae, it corresponds to a temperature of about 10 ° C. Temperature affects, first of all, chloroplasts, in which the structure changes depending on temperature, which is clearly visible in an electron microscope.

It is very important for photosynthesis carbon dioxide content in the air surrounding the plant. The average concentration of carbon dioxide in the air is 0.03% (by volume). A decrease in carbon dioxide content adversely affects the yield, and its increase, for example, to 0.04%, can increase the yield by almost 2 times. A more significant increase in concentration is harmful to many plants: for example, at a carbon dioxide content of about 0.1%, tomato plants get sick, their leaves begin to curl. In greenhouses and greenhouses, you can increase the carbon dioxide content by releasing it from special cylinders or letting dry carbon dioxide evaporate.

Light of different wavelengths also affects the intensity of photosynthesis in different ways. For the first time, the intensity of photosynthesis in different rays of the spectrum was studied by the physicist W. Daubeny, who showed in 1836 that the rate of photosynthesis in a green leaf depends on the nature of the rays. Methodical errors during the experiment led him to wrong conclusions. The scientist placed a segment of an elodea shoot in a test tube with water cut up, illuminated the test tube by passing sunlight through colored glasses or colored solutions, and took into account the intensity of photosynthesis by the number of oxygen bubbles coming off the cut surface per unit time. Daubeny came to the conclusion that the intensity of photosynthesis is proportional to the brightness of the light, and the brightest rays at that time were considered yellow. John Draper (1811-1882), who studied the intensity of photosynthesis in various beams of the spectrum emitted by a spectroscope, adhered to the same point of view.

The role of chlorophyll in the process of photosynthesis was proved by the outstanding Russian botanist and plant physiologist K.A. Timiryazev. Having spent in 1871-1875. a series of experiments, he found that green plants most intensively absorb the rays of the red and blue parts of the solar spectrum, and not yellow, as was thought before him. Absorbing the red and blue part of the spectrum, chlorophyll reflects green rays, which is why it appears green.

Based on these data, the German plant physiologist Theodor Wilhelm Engelmann in 1883 developed a bacterial method for studying the assimilation of carbon dioxide by plants.

He suggested that if you place a cell of a green plant together with aerobic bacteria in a drop of water and illuminate them with differently colored rays, then the bacteria should concentrate in those parts of the cell in which carbon dioxide is most decomposed and oxygen is released. To test this, Engelman somewhat improved the light microscope by mounting a prism above the mirror, which decomposed the sunlight into separate components of the spectrum. As a green plant, Engelman used the green alga Spirogyra, whose large cells contain long spiral chromatophores.

Having placed a piece of algae in a drop of water on a glass slide, Engelman introduced some aerobic bacteria there, after which he examined the preparation under a microscope. It turned out that in the absence of a prism, the prepared preparation was illuminated with even white light, and the bacteria were evenly distributed along the entire area of ​​the algae. In the presence of a prism, the beam of light reflected from the mirror was refracted, illuminating the area of ​​the algae under the microscope with light of different wavelengths. After a few minutes, the bacteria concentrated on those areas that were illuminated with red and blue light. Based on this, Engelman concluded that the decomposition of carbon dioxide (and, hence, the release of oxygen) in green plants is observed in additional to the main color (i.e. green) rays - red and blue.

Data received on modern equipment, fully confirm the results obtained by Engelman more than 120 years ago.

The light energy absorbed by chlorophyll takes part in the reactions of the first and second stages of photosynthesis; reactions of the third stage are dark; occurs without the participation of light. Measurements have shown that the process of reducing one oxygen molecule requires a minimum of eight quanta of light energy. Thus, the maximum quantum yield of photosynthesis, i.e. the number of oxygen molecules corresponding to one quantum of light energy absorbed by the plant is 1/8, or 12.5%.

R. Emerson and colleagues determined the quantum yield of photosynthesis when plants are illuminated with monochromatic light of various wavelengths. It was found that the yield remains constant at 12% in most of the visible spectrum, but decreases sharply near the far red region. This decrease in green plants begins at a wavelength of 680 nm. At lengths greater than 660 nm, only chlorophyll absorbs light. a; chlorophyll b has a maximum absorption of light at 650 nm, and at 680 nm practically does not absorb light. At a wavelength greater than 680 nm, the quantum yield of photosynthesis can be brought up to maximum value 12% provided that the plant is simultaneously illuminated also by light with a wavelength of 650 nm. In other words, if the light absorbed by chlorophyll a supplemented by light absorbed by chlorophyll b, then the quantum yield of photosynthesis reaches a normal value.

The increase in the intensity of photosynthesis during simultaneous illumination of a plant with two beams of monochromatic light of different wavelengths compared to its intensity observed under separate illumination by the same beams is called Emerson effect. Experiments with various combinations of far red light and light with more short length waves over green, red, blue-green and brown algae showed that the greatest increase in photosynthesis is observed if the second beam with a shorter wavelength is absorbed by auxiliary pigments.

In green plants, such auxiliary pigments are carotenoids and chlorophyll. b, in red algae - carotenoids and phycoerythrin, in blue-green algae - carotenoids and phycocyanin, in brown algae - carotenoids and fucoxanthin.

Further study of the process of photosynthesis led to the conclusion that auxiliary pigments transfer from 80 to 100% of the light energy absorbed by them to chlorophyll. a. Thus, chlorophyll a accumulates light energy absorbed by the plant cell, and then uses it in the photochemical reactions of photosynthesis.

It was later discovered that chlorophyll a is present in a living cell in the form of forms with different absorption spectra and different photochemical functions. One form of chlorophyll a, whose absorption maximum corresponds to a wavelength of 700 nm, belongs to the pigment system, called photosystem I, the second form of chlorophyll a with an absorption maximum of 680 nm, belongs to photosystem II.

So, a photoactive pigment system was discovered in plants, which absorbs light especially strongly in the red region of the spectrum. It begins to act even in low light. In addition, there is another known regulatory system, which selectively absorbs and uses for photosynthesis blue color. This system works in sufficiently strong light.

It has also been established that the photosynthetic apparatus of some plants largely uses red light for photosynthesis, while others use blue light.

To determine the intensity of photosynthesis of aquatic plants, you can use the method of counting oxygen bubbles. In the light, the process of photosynthesis takes place in the leaves, the product of which is oxygen, which accumulates in the intercellular spaces. When cutting the stem, excess gas begins to be released from the cut surface in the form of a continuous flow of bubbles, the rate of formation of which depends on the intensity of photosynthesis. This method is not very accurate, but it is simple and gives a visual representation of the dependence of the photosynthesis process on external conditions.

Experience 1. Dependence of photosynthesis productivity on light intensity

Materials and equipment: elodea; aqueous solutions of NaHCO 3 , (NH 4) 2 CO 3 or mineral water; settled tap water; glass rod; threads; scissors; 200 W electric lamp; clock; thermometer.

1. For the experiment, healthy shoots of elodea about 8 cm long of intense green color with an intact tip were selected. They were cut under water, tied with a thread to a glass rod and lowered upside down into a glass of water at room temperature (the water temperature should remain constant).

2. For the experiment, we took settled tap water enriched with CO 2 by adding NaHCO 3 or (NH 4) 2 CO 3, or mineral water, and exposed a glass with an aquatic plant to a bright light. We observed the appearance of air bubbles from the cut of the plant.

3. When the bubble flow became uniform, the number of bubbles released in 1 min was counted. The counting was carried out 3 times with a break of 1 min, the data were recorded in a table, and the average result was determined.

4. The glass with the plant was removed from the light source by 50–60 cm and the steps indicated in paragraph 3 were repeated.

5. The results of the experiments were compared and a conclusion was drawn about the different intensity of photosynthesis in bright and weak light.

The results of the experiments are presented in table 1.

Conclusion: at the used light intensities, the intensity of photosynthesis increases with increasing light intensity, i.e. the more light, the better photosynthesis goes.

Table 1. Dependence of photosynthesis on light intensity

Experience 2. Dependence of the productivity of photosynthesis on the spectral composition of light

Materials and equipment: elodea; a set of light filters (blue, orange, green); seven tall wide-mouth jars; settled tap water; scissors; 200 W electric lamp; clock; thermometer; test tubes.

1. The test tube was filled to 2/3 of the volume with settled tap water and placed in it. aquatic plant top down. The stem was cut under water.

2. A blue light filter (circular) was placed in a high wide-mouth jar, a test tube with a plant was placed under the filter, and the jar was exposed to bright light so that it fell on the plant, passing through the light filter. We observed the appearance of air bubbles from the cut of the plant stem.

3. When the bubble flow became uniform, the number of bubbles released in 1 min was counted. The calculation was carried out 3 times with a break of 1 min, the average result was determined, the data were entered into the table.

4. The blue light filter was replaced with a red one and the steps indicated in paragraph 3 were repeated, making sure that the distance from the light source and the water temperature remained constant.

5. The results of the experiments were compared and a conclusion was made about the dependence of the intensity of photosynthesis on the spectral composition of light.

The results of the experiment are presented in table 2.

Conclusion: the process of photosynthesis in orange light is very intensive, in blue it slows down, and in green it practically does not go.

Table 2. Dependence of the productivity of photosynthesis on the spectral composition of light

experience number	light filter	First dimension	Second dimension	third dimension	Mean
	Orange

Experience 3. The dependence of the intensity of photosynthesis on temperature

Materials and equipment: elodea; three tall wide-mouth jars; settled tap water; scissors; test tubes; 200 W electric lamp; clock; thermometer.

1. A 2/3 test tube was filled with settled tap water and an aquatic plant was placed in it with the top down. The stem was cut off under water.

2. Settled tap water of different temperatures (from 14°C to 45°C) was poured into three wide-mouth jars, a test tube with a plant was placed in a jar of medium temperature water (for example, 25°C), and the device was exposed to bright light. We observed the appearance of air bubbles from the cut of the plant stem.

3. After 5 min, the number of bubbles released in 1 min was counted. The calculation was carried out 3 times with a break of 1 min, the average result was determined, the data were entered into the table.

4. The test tube with the plant was transferred to a jar with water of a different temperature and the steps indicated in paragraph 3 were repeated, making sure that the distance from the light source and the water temperature remained constant.

5. The results of the experiments were compared and a written conclusion was made about the effect of temperature on the intensity of photosynthesis.

The results of the experiment are presented in table 3.

Conclusion: in the studied temperature range, the intensity of photosynthesis depends on temperature: the higher it is, the better photosynthesis proceeds.

Table 3. Temperature dependence of photosynthesis

As a result of our study, we made the following conclusions.

1. The photoactive pigment system absorbs light especially strongly in the red region of the spectrum. Blue rays are quite well absorbed by chlorophyll and very little green, which explains the green color of plants.

2. Our experiment with a branch of elodea convincingly proves that the maximum intensity of photosynthesis is observed when illuminated with red light.

3. The rate of photosynthesis depends on temperature.

4. Photosynthesis depends on the intensity of light. The more light, the better photosynthesis goes.

The results of such work may be of practical importance. In greenhouses with artificial lighting, by selecting the spectral composition of light, you can increase the yield. At the Agrophysical Institute in Leningrad in the late 1980s. in the laboratory of B.S. Moshkov, using special lighting modes, 6 tomato crops per year (180 kg / m 2) were obtained.

Plants require light rays of all colors. How, when, in what sequence and proportion to supply it with radiant energy is a whole science. The prospects for light culture are very great: from laboratory experiments, it can turn into an industrial year-round production of vegetable, green, ornamental and medicinal crops.

LITERATURE

1. Genkel P.A. Plant Physiology: Proc. allowance for an optional course for the 9th grade. - M: Education, 1985. - 175 p., ill.
2. Kretovich V.L. Biochemistry of plants: Textbook for biol. faculties of universities. – M.: graduate School, 1980. - 445 p., ill.
3. Raven P., Evert R., Eichhorn S. Modern botany: In 2 volumes: Per. from English. - M.: Mir, 1990. - 344 p., ill.
4. Salamatova T.S. Plant cell physiology: Tutorial. - L .: Publishing House of Leningrad University, 1983. - 232 p.
5. Taylor D., Green N., Stout W. Biology: In 3 volumes: Per. from English / Ed. R. Sopera - M .: Mir, 2006. - 454 p., ill.
6. http://sc.nios.ru (drawings and diagrams)

Of all the factors simultaneously affecting the process of photosynthesis limiting will be the one that is closer to the minimum level. It installed Blackman in 1905. Different factors can be limiting, but one of them is the main one.

1. In low light, the rate of photosynthesis is directly proportional to the light intensity. Light is the limiting factor in low light conditions. At high light intensity, chlorophyll becomes discolored and photosynthesis slows down. Under such conditions in nature, plants are usually protected (thick cuticle, pubescent leaves, scales).

1. The dark reactions of photosynthesis require carbon dioxide, which is included in organic matter, is a limiting factor in the field. The concentration of CO 2 in the atmosphere varies from 0.03-0.04%, but if you increase it, you can increase the rate of photosynthesis. Some greenhouse crops are now grown with increased CO 2 content.
2. temperature factor. Dark and some light reactions of photosynthesis are controlled by enzymes, and their action depends on temperature. The optimum temperature for plants in the temperate zone is 25 °C. With each increase in temperature by 10 °C (up to 35 °C), the reaction rate doubles, but due to the influence of a number of other factors, plants grow better at 25 °C.
3. Water- source material for photosynthesis. Lack of water affects many processes in cells. But even temporary wilting leads to serious crop losses. Reasons: when withering, the stomata of plants close, and this interferes with the free access of CO 2 for photosynthesis; with a lack of water in the leaves of some plants accumulates abscisic acid. It is a plant hormone - a growth inhibitor. In laboratory conditions, it is used to study the inhibition of the growth process.
4. Chlorophyll concentration. The amount of chlorophyll can decrease with powdery mildew, rust, viral diseases, mineral deficiencies and age (with normal aging). When the leaves turn yellow, chlorotic phenomena or chlorosis. The reason may be a lack of minerals. For the synthesis of chlorophyll, Fe, Mg, N and K are needed.
5. Oxygen. A high concentration of oxygen in the atmosphere (21%) inhibits photosynthesis. Oxygen competes with carbon dioxide for the active site of the enzyme involved in CO 2 fixation, which reduces the rate of photosynthesis.
6. Specific inhibitors. The best way to kill a plant is to suppress photosynthesis. To do this, scientists have developed inhibitors - herbicides- dioxins. For example: DHMM - dichlorophenyldimethylurea- inhibits the light reactions of photosynthesis. Successfully used to study the light reactions of photosynthesis.
7. Environmental pollution. Gases of industrial origin, ozone and sulfur dioxide, even in small concentrations, severely damage the leaves of a number of plants. To sour gas lichens are very sensitive. Therefore, there is a method lichen indications– determination of environmental pollution by lichens. Soot clogs the stomata and reduces the transparency of the leaf epidermis, which reduces the rate of photosynthesis.

6. Plant life factors, heat, light, air, water Plants throughout their lives are constantly in interaction with external environment. Plant requirements for life factors are determined by the heredity of plants, and they are different not only for each species, but also for each variety of a particular crop. That is why a deep knowledge of these requirements makes it possible to correctly establish the structure of sown areas, the rotation of crops, the placement crop rotations.
For normal life, plants need light, heat, water, nutrients, including carbon dioxide and air.
The main source of light for plants is solar radiation. Although this source is beyond human influence, the degree of use of the sun's light energy for photosynthesis depends on the level of agricultural technology: sowing methods (rows directed from north to south or from east to west), differentiated seeding rates, tillage, etc.
Timely thinning of plants and the destruction of weeds improve the illumination of plants.
Heat in plant life, along with light, is the main factor in plant life and necessary condition for biological, chemical and physical processes in the soil. Each plant at various phases and stages of development makes certain, but unequal requirements for heat, the study of which is one of the tasks of plant physiology and scientific agriculture. heat in plant life affects the rate of development in each stage of growth. The task of agriculture also includes the study of the thermal regime of the soil and methods of its regulation.
Water in plant life and nutrients, with the exception of carbon dioxide coming from both the soil and the atmosphere, are the soil factors of plant life. Therefore, water and nutrients are called elements of soil fertility.
Air in plant life(atmospheric and soil) is necessary as a source of oxygen for the respiration of plants and soil microorganisms, as well as a source of carbon that the plant absorbs during photosynthesis. In addition, Air in the life of plants is necessary for microbiological processes in the soil, as a result of which the organic matter of the soil is decomposed by aerobic microorganisms with the formation of soluble mineral compounds of nitrogen, phosphorus, potassium and other plant nutrients.

7 . Indicators of photosynthetic productivity of crops

A crop is created in the process of photosynthesis, when organic matter is formed in green plants from carbon dioxide, water and minerals. The energy of the sun's beam is converted into the energy of plant biomass. The efficiency of this process and ultimately the yield depend on the functioning of the crop as a photosynthetic system. In field conditions, sowing (cenosis) as a set of plants per unit area is a complex dynamic self-regulating photosynthetic system. This system includes many components that can be considered as subsystems; it is dynamic, as it constantly changes its parameters over time; self-regulating, since, despite various influences, sowing changes its parameters in a certain way, maintaining homeostasis.

Indicators of photosynthetic activity of crops. Seeding is an optical system in which leaves absorb PAR. In the initial period of plant development, the assimilation surface is small and a significant part of the PAR passes by the leaves and is not captured by them. With an increase in the area of ​​leaves, their absorption of solar energy also increases. When the leaf surface index* is 4...5, i.e. the area of ​​leaves in the crop is 40...50 thousand m 2 /ha, the absorption of PAR by the leaves of the crop reaches a maximum value - 75...80% of the visible, 40% of total radiation. With a further increase in leaf area, PAR absorption does not increase. In crops where the course of formation of the leaf area is optimal, the absorption of PAR can be on average 50...60% of the incident radiation during the growing season. PAR absorbed by the plant cover is the energy basis for photosynthesis. However, only part of this energy is accumulated in the crop. The PAR utilization factor is usually determined in relation to the PAR incident on the vegetation cover. If the biomass yield in central Russia accumulates 2...3% of PAR sowing, then the dry weight of all plant organs will be 10...15 t/ha, and the possible yield will be 4...6 t of grain per 1 ha . In sparse crops, the PAR utilization factor is only 0.5...1.0%.

Considering crops as a photosynthetic system, the dry biomass yield generated by growing season, or its growth over a certain period depends on the value of the average leaf area, the duration of the period and the net productivity of photosynthesis for this period.

Y \u003d FP NPF,

where Y is the yield of dry biomass, t/ha;

FP - photosynthetic potential, thousand m 2 - days / ha;

NPP - net productivity of photosynthesis, g/(m2 - days).

Photosynthetic potential is calculated by the formula

where Sc is the average leaf area for the period, thousand m 2 /ha;

T is the duration of the period, days.

The main indicators for the cenosis, as well as the yield, are determined per unit area - 1 m 2 or 1 ha. So, the leaf area is measured in thousand m 2 / ha. In addition, they use such an indicator as the leaf surface index. The main part of the assimilation surface is made up of leaves, it is in them that photosynthesis takes place. Photosynthesis can also occur in other green parts of plants - stems, awns, green fruits, etc., but the contribution of these organs to total photosynthesis is usually small. It is customary to compare crops with each other, as well as different states of one crop in dynamics in terms of leaf area, identifying it with the concept of "assimilation surface". The dynamics of the area of ​​leaves in the crop follows a certain regularity. After germination, the leaf area slowly increases, then the growth rate increases. By the time the formation of side shoots stops and the plants grow in height, the leaf area reaches its maximum value during the growing season, then it begins to gradually decrease due to the yellowing and death of the lower leaves. By the end of the growing season in the crops of many crops (cereals, legumes), green leaves on the plants are absent. The leaf area of ​​various agricultural plants can vary greatly during the growing season depending on the conditions of water supply, nutrition, and agricultural practices. Maximum area leaves in arid conditions reaches only 5 ... 10 thousand m 2 / ha, and with excessive moisture and nitrogen nutrition, it can exceed 70 thousand m 2 / ha. It is believed that with a leaf surface index of 4...5, sowing as an optical photosynthesizing system works in optimal mode, absorbing the largest number PAR. With a smaller area of ​​leaves, a part of the PAR is not captured by the leaves. If the leaf area is more than 50000 m2/ha, then the upper leaves shade the lower ones, and their share in photosynthesis sharply decreases. Moreover, the upper leaves "feed" the lower ones, which is unfavorable for the formation of fruits, seeds, tubers, etc. The dynamics of the leaf area shows that different stages during the growing season, sowing as a photosynthetic system functions differently (Fig. 3). During the first 20...30 days of vegetation, when the average leaf area is 3...7 thousand m 2 /ha, most of the PAR is not captured by the leaves, and therefore the PAR utilization factor cannot be high. Further, the area of ​​leaves begins to increase rapidly, reaching a maximum. As a rule, this occurs in bluegrasses in the phase of the milky state of the grain, in cereal legumes in the phase of full filling of seeds in the middle tier, in perennial herbs in the flowering phase. Then the leaf area begins to decrease rapidly. At this time, the redistribution and outflow of substances from the vegetative organs to the generative ones prevail. The duration of these periods and their ratio is influenced by various factors, including agrotechnical ones. With their help, it is possible to regulate the process of increasing the area of ​​leaves and the duration of periods. In arid conditions, the density of plants, and hence the area of ​​leaves, is deliberately reduced, since with a large area of ​​leaves, transpiration increases, plants suffer more from a lack of moisture, and yields decrease.

Research

Topic: The influence of various factors on the rate of photosynthesis

Work manager:Logvin Andrey Nikolaevich, biology teacher

village Shelokhovskaya

2009

Introduction - page 3

Chapter 1. Photosynthesis - page 4

Chapter 2. Abiotic factors - light and temperature. Their role in plant life - page 5

2.1. Light - page 5

2.2. Temperature - page 6

2.3. Gas composition of air - page 7

Chapter 3. The influence of various factors on the rate of photosynthesis - p.983.1. Starch test method - page 9

3.2. Dependence of photosynthesis on light intensity – page 10

3.3. The dependence of the intensity of photosynthesis on temperature - page 11

3.4. The dependence of the intensity of photosynthesis on the concentration of carbon dioxide in the atmosphere - page 12

Conclusion - page 12

Sources of information - page 13

Doing

Life on earth depends on the sun. The receiver and accumulator of the energy of solar rays on Earth are the green leaves of plants as specialized organs of photosynthesis. Photosynthesis is a unique process of creating organic substances from inorganic ones. This is the only process on our planet associated with the conversion of the energy of sunlight into the energy of chemical bonds contained in organic substances. In this way, the energy of sunlight received from space, stored by green plants in carbohydrates, fats and proteins, ensures the vital activity of the entire living world - from bacteria to humans.

An outstanding Russian scientist of the late XIX - early XX century. Kliment Arkadyevich Timiryazev (1843-1920) called the role of green plants on Earth cosmic.

K.A. Timiryazev wrote: “All organic substances, no matter how diverse they may be, wherever they are found, whether in a plant, animal or person, passed through the leaf, originated from substances produced by the leaf. Outside the leaf, or rather outside the chlorophyll grain, there is no laboratory in nature where organic matter is isolated. In all other organs and organisms, it is transformed, transformed, only here it is formed again from inorganic matter.

The relevance of the chosen topic is due to the fact that we all depend on photosynthetic plants and it is necessary to know how to increase the intensity of photosynthesis.

Object of study- houseplants

Subject of study– influence of various factors on the rate of photosynthesis.

Goals:

1. Systematization, deepening and consolidation of knowledge on plant photosynthesis and abiotic environmental factors.

2. To study the dependence of the rate of photosynthesis on the intensity of illumination, temperature and concentration of carbon dioxide in the atmosphere.

Tasks:

1. To study the literature on plant photosynthesis, to generalize and deepen knowledge about the influence of abiotic factors on plant photosynthesis.
2. To study the influence of various factors on the rate of photosynthesis.

Research hypothesis:The rate of photosynthesis increases with increasing light intensity, temperature and carbon dioxide concentration in the atmosphere.

Research methods:

1. Study and analysis of literature
2. Observation, comparison, experiment.

Chapter 1. Photosynthesis.

The process of formation of organic substances by cells of green plants and cyanobacteria with the participation of light. In green plants, it occurs with the participation of pigments (chlorophylls and some others) present in the chloroplasts and chromatophores of cells. From substances poor in energy (carbon monoxide and water), carbohydrate glucose is formed and free oxygen is released.

Photosynthesis is based on a redox process: electrons are transferred from a donor-reductant (water, hydrogen, etc.) to an acceptor (carbon monoxide, acetate). A reduced substance (carbohydrate glucose) and oxygen are formed if water is oxidized. There are two phases of photosynthesis:

Light (or light-dependent);

Dark.

In the light phase there is an accumulation of free atoms of hydrogen, energy (ATP is synthesized). dark phasephotosynthesis - a series of successive enzymatic reactions, and above all reactions of carbon dioxide binding (penetrates the leaf from the atmosphere). As a result, carbohydrates are formed, first monosaccharides (hexose), then saccharides and polysaccharides (starch). The synthesis of glucose goes with the absorption of a large amount of energy (ATP synthesized in the light phase is used). To remove excess oxygen from carbon dioxide, hydrogen is used, which is formed in the light phase and is in an unstable combination with a hydrogen carrier (NADP). Excess oxygen is due to the fact that in carbon dioxide the number of oxygen atoms is twice as large as the number of carbon atoms, and in glucose the number of carbon and oxygen atoms is equal.

Photosynthesis is the only process in the biosphere that leads to an increase in the energy of the biosphere due to an external source - the Sun and ensures the existence of both plants and all heterotrophic organisms.

Less than 1-2% of solar energy goes into crops.

Losses: incomplete absorption of light; limiting the process at the biochemical and physiological levels.

Ways to increase the efficiency of photosynthesis:

Providing plants with water;

Providing minerals and carbon dioxide;

Creation of crop structure favorable for photosynthesis;

Selection of varieties with high photosynthesis efficiency.

Chapter 2. Abiotic factors - light and temperature.

Their role in plant life.

Abiotic factorsall elements of inanimate nature that affect the body are called. Among them, the most important are light, temperature, humidity, air, mineral salts, etc. They are often combined into groups of factors: climatic, soil, orographic, geological, etc.

In nature, it is difficult to separate the action of one abiotic factor from another; organisms always experience their combined influence. However, for convenience of study, abiotic factors are usually considered separately.

2.1. Light

Among the numerous factors, light as a carrier of solar energy is one of the main ones. Without it, the photosynthetic activity of green plants is impossible. At the same time, the direct effect of light on protoplasm is fatal to the organism. Therefore, many morphological and behavioral properties of organisms are due to the action of light.

The sun radiates an enormous amount of energy into outer space, and although the Earth accounts for only one two millionth part of the solar radiation, it is enough to heat and light our planet. Solar radiation is electromagnetic waves of various lengths, as well as radio waves with a length of no more than 1 cm.

Among the solar energy penetrating the Earth's atmosphere, there are visible rays (there are about 50%), warm infrared rays (50%) and ultra-violet rays(about 1%). For ecologists, qualitative features of light are important: wavelength (or color), intensity (effective energy in calories) and duration of exposure (length of days).

Visible rays (we call them sunlight) consist of rays of different colors and different wavelengths. Light is of great importance in the life of the entire organic world, since the activity of animals and plants is associated with it - photosynthesis proceeds only under conditions of visible light.

In the life of organisms, not only visible rays are important, but also other types of radiant energy that reach the earth's surface: ultraviolet and infrared rays, electromagnetic (especially radio waves) and even gamma and X radiation. For example, ultraviolet rays with a wavelength of 0.38-0.40 microns have a large photosynthetic activity. These rays, especially when presented in moderate doses, stimulate the growth and reproduction of cells, promote the synthesis of highly active biological compounds, increasing the content of vitamins and antibiotics in plants, and increase the resistance of plant cells to various diseases.

Among all the rays of sunlight, rays are usually distinguished, one way or another affecting plant organisms, especially the process of photosynthesis, accelerating or slowing down its course. These rays are called physiologically active radiation (PAR for short). The most active among the PARs are: orange-red (0.65-0.68 microns), blue-violet (0.40-0.50 microns) and near ultraviolet (0.38-0.40 microns). Yellow-green rays (0.50-0.58 microns) are absorbed the least, and infrared rays are almost not absorbed. Only far infrared rays with a wavelength of more than 1.05 microns take part in the heat exchange of plants and therefore have some positive effect, especially in places with low temperatures.

Green plants need light for the formation of chlorophyll, the formation of the granal structure of chloroplasts; it regulates the work of the stomatal apparatus, affects gas exchange and transpiration, activates a number of enzymes, stimulates the biosynthesis of proteins and nucleic acids. Light affects cell division and elongation, growth processes and the development of plants, determines the timing of flowering and fruiting, and has a shaping effect. But light is of the greatest importance in the air nutrition of plants, in their use of solar energy in the process of photosynthesis.

2.2. Temperature

The thermal regime is one of essential conditions the existence of organisms, since all physiological processes are possible only at certain temperatures. The arrival of heat on the earth's surface is provided by the sun's rays and is distributed over the earth depending on the height of the sun above the horizon and the angle of incidence of the sun's rays. Therefore, the thermal regime is not the same at different latitudes and at different height above sea level.

The temperature factor is characterized by pronounced seasonal and daily fluctuations. This action of the factor in a number of regions of the Earth has an important signal value in the regulation of the timing of the activity of organisms, ensuring their daily and seasonal mode of life.

In characterizing the temperature factor, its extreme indicators, the duration of their action, and also how often they are repeated are very important. A change in temperature in habitats that goes beyond the threshold tolerance of organisms is accompanied by their mass death.

The significance of temperature for the vital activity of organisms is manifested in the fact that it changes the rate of physicochemical processes in cells. Temperature affects the anatomical and morphological features of organisms, affects the course of physiological processes, growth, development, behavior, and in many cases determines the geographical distribution of plants.

2.3. Gas composition of air.

In addition to the physical properties of the air environment, its chemical features are extremely important for the existence of terrestrial organisms. The gas composition of air in the surface layer of the atmosphere is quite homogeneous in terms of the content of the main components (nitrogen - 78.1, oxygen - 21.0, argon - 0.9, carbon dioxide - 0.03% by volume) due to the high diffusion capacity of gases and constant mixing by convection and wind currents. However, various impurities of gaseous, droplet-liquid and solid (dust) particles entering the atmosphere from local sources can be of significant environmental importance.

The high oxygen content contributed to an increase in the metabolism of terrestrial organisms compared to primary aquatic ones. Oxygen, due to its constantly high content in the air, is not a factor limiting life in the terrestrial environment. Only in places, under specific conditions, is a temporary deficit created, for example, in accumulations of decaying plant residues, stocks of grain, flour, etc.

The content of carbon dioxide can vary in certain areas of the surface layer of air within fairly significant limits. For example, if there is no wind in the center big cities its concentration increases tenfold. Diurnal changes in the carbon dioxide content in the surface layers are regular, associated with the rhythm of plant photosynthesis, and seasonal, due to changes in the intensity of respiration of living organisms, mainly the microscopic population of soils. Increased air saturation with carbon dioxide occurs in zones of volcanic activity, near thermal springs and other underground outlets of this gas. In high concentrations, carbon dioxide is toxic. In nature, such concentrations are rare.

In nature, the main source of carbon dioxide is the so-called soil respiration. Carbon dioxide diffuses from the soil into the atmosphere, especially vigorously during rain.

AT modern conditions a powerful source of additional amounts of CO 2 human activity to burn fossil fuels into the atmosphere.

The low content of carbon dioxide inhibits the process of photosynthesis. Under indoor conditions, the rate of photosynthesis can be increased by increasing the concentration of carbon dioxide; this is used in the practice of greenhouses and greenhouses. However, excessive amounts of CO 2 lead to poisoning of plants.

Air nitrogen for most inhabitants of the terrestrial environment is an inert gas, but a number of microorganisms (nodule bacteria, Azotobacter, clostridia, blue-green algae, etc.) have the ability to bind it and involve it in the biological cycle.

Local impurities entering the air can also significantly affect living organisms. This is especially true for toxic gaseous substances - methane, sulfur oxide (IV), carbon monoxide (II), nitrogen oxide (IV), hydrogen sulfide, chlorine compounds, as well as particles of dust, soot, etc., polluting the air in industrial areas. The main modern source of chemical and physical pollution of the atmosphere is anthropogenic: the work of various industrial enterprises and transport, soil erosion, etc. Sulfur oxide (S0 2 ), for example, is poisonous to plants even in concentrations from one fifty-thousandth to one millionth of the volume of air. Around industrial centers that pollute the atmosphere with this gas, almost all vegetation dies. Some plant species are particularly sensitive to S0 2 and serve as a sensitive indicator of its accumulation in the air. For example, lichens die even with traces of sulfur oxide (IV) in the surrounding atmosphere. Their presence in the forests around large cities testifies to the high purity of the air. The resistance of plants to impurities in the air is taken into account when selecting species for landscaping settlements. Sensitive to smoke, e.g. spruce and pine, maple, linden, birch. The most resistant are thuja, Canadian poplar, American adhesives, elderberry and some others.

Chapter 3. Influence of various factors on the rate of photosynthesis.

The rate of photosynthesis depends on both light intensity and temperature. The limiting factors of photosynthesis can also be the concentration of carbon dioxide, water, mineral nutrition elements involved in the construction of the photosynthetic apparatus and being the initial components for the photosynthesis of organic matter.

When determining the intensity of photosynthesis, two groups of methods are used: 1) gasometric - registering the amount of absorbed carbon dioxide or released oxygen; 2) methods for accounting for the amount of organic matter formed during photosynthesis.

A simple and visual method of "starch test". The method is based on the detection and assessment of the amount of starch accumulated during photosynthesis using a solution of iodine in potassium iodide.

3.1. Method of "starch test"

Target . Familiarize yourself with the "starch test" method.

Experience methodology.

Water the plant generously, put it in a warm dark place (in a closet or drawer), or darken individual leaves with dark bags of thick black paper. In the dark, the leaves gradually lose starch, which is hydrolyzed to sugars and used for respiration, growth, and is discharged to other organs.

After 3 - 4 days. check the destarching of the leaves. To do this, cut out pieces from a dark sheet, place in a test tube with water (2 - 3 ml) and boil for 3 minutes to kill the cells and increase the permeability of the cytoplasm. Then drain the water and boil several times in ethyl alcohol (2-3 ml each), changing the solution every 1-2 minutes until a piece of leaf tissue is discolored (you need to boil in a water bath, as alcohol can flare up when using an alcohol lamp!). Drain the last portion of the alcohol, add some water to soften the leaf tissues (they become brittle in alcohol), place a piece of tissue in a Petri dish and treat with iodine solution. With complete starching-painting, there is no blue coloration and it is possible to set up an experiment with such leaves. If there is even a small amount of starch, the leaf should not be handled, as this will make it difficult to observe the formation of starch. Destarching should be extended for another 1-2 days.

Leaves devoid of starch must be cut from the plant, renew the cut under water and lower the petiole into a test tube with water. It is better to work with cut leaves, since the newly formed starch in this case does not flow to other organs.

The leaves are placed in various conditions, provided for by the objectives of this work. For starch accumulation, leaves should be kept at least 30-40 cm away from a 100-200 W lamp and avoid overheating with a fan. After 1 - 1.5 hours, cut out three pieces of fabric of the same shape (circle, square) from the leaves of each option, process in the same way as when checking for completeness of starching. Depending on the conditions of the experiment, different amounts of starch will accumulate in the leaves, which can be determined by the degree of its blueness. Since the accumulation of starch in individual parts of the leaf may vary, at least three pieces are taken from it to analyze its content. To evaluate the results, average values ​​from three repetitions are used.

The degree of blue leaf is estimated in points:

dark blue - 3;

medium blue - 2;

faint blue - 1;

no color - 0.

3.2. Dependence of photosynthesis on light intensity.

Target . Determine the dependence of photosynthesis on the intensity of illumination.

Experience methodology.

Pelargonium leaves, prepared for the experiment, place: one in complete darkness; the second - to diffused daylight; the third - to a bright light. After the specified time, determine the presence of starch in the leaves.

Draw a conclusion about the effect of light intensity on the rate of photosynthesis.

Working process.

Plentifully watered geranium, put in a warm dark place (in a closet).

After 3 days, the destarching of the leaves was checked. To do this, cut out pieces from a dark sheet, placed in a test tube with water (2 - 3 ml) and boiled for 3 minutes to kill the cells and increase the permeability of the cytoplasm. Then the water was drained and boiled in a water bath several times in ethyl alcohol (2-3 ml each), changing the solution every 1-2 minutes, until a piece of leaf tissue became discolored. They poured out the last portion of alcohol, added a little water to soften the leaf tissues (they become brittle in alcohol), placed a piece of tissue in a Petri dish and treated with an iodine solution.

We observe complete destarching - there is no blue coloration.

Leaves devoid of starch were cut from the plant, the cut was renewed under water, and the petiole was lowered into a test tube with water. Geranium leaves, prepared for the experiment, were placed: one in total darkness; the second - to diffused daylight; the third - to a bright light.

After 1 hour, three pieces of tissue of the same shape were cut out from the leaves of each variant, processed in the same way as when checking for completeness of starch removal.

Result.

The degree of leaf blueness in the dark is 0 points, in diffused light - 1 point, in bright light - 3 points.

Conclusion. With increasing light intensity, the rate of photosynthesis increased.

3.3. The dependence of the intensity of photosynthesis on temperature.

Target . Determine the dependence of photosynthesis on temperature.

Experience methodology.

Place the prepared pelargonium leaves at an equal distance from a powerful light source: one in the cold (between the window frames), the other in room temperature. After the specified time, determine the presence of starch.

Draw a conclusion about the effect of temperature on the rate of photosynthesis.

Working process.

Leaves devoid of starch were placed at an equal distance from the lamp: one in the cold (between the window frames), the other at room temperature. After 1 hour, three pieces of tissue of the same shape were cut out from the leaves of each variant, processed in the same way as when checking for completeness of starch removal.

Result.

The degree of leaf blueness in the cold is 1 point, at room temperature - 3 points.

Conclusion. As the temperature increases, the rate of photosynthesis increases.

3.4. The dependence of the intensity of photosynthesis on the concentration of carbon dioxide in the atmosphere.

Target. Determine the dependence of the intensity of photosynthesis on the concentration of carbon dioxide in the atmosphere

Experience methodology.

Pelargonium leaves, prepared for work, put in a vessel with water, and the vessel - on a piece of glass under a glass cap. There also place a small cup with 1-2 g of soda, in which add 3-5 ml of 10% sulfuric or hydrochloric acid. Cover the joint between the glass and the cap with plasticine. Leave the other sheet in the classroom. In this case, the illumination and temperature of both leaves should be the same. After the specified time, take into account the starch accumulated in the leaves, draw a conclusion about the effect of CO2 concentration on the intensity of photosynthesis.

Working process.

Geranium leaves, prepared for work, were placed in a vessel with water, and the vessel was placed on a piece of glass under a glass cap. A small cup with 2 g of soda was also placed there, into which add 5 ml of 10% hydrochloric acid. The joint between the glass and the cap was covered with plasticine. Another sheet was left in the classroom. At the same time, the illumination and temperature of both leaves are the same.

Result.

The degree of blue leaf in the classroom - 2 points, under the cap - 3 points.

Conclusion. As the concentration of carbon dioxide in the atmosphere increases, the rate of photosynthesis increases.

Conclusion

Having done the practical part research work, we concluded that our hypothesis was confirmed. Indeed, the intensity of photosynthesis depends on temperature, illumination, carbon dioxide content in the atmosphere.

Information sources.

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