Photosynthesis takes place. The process of photosynthesis in plant leaves. Functions of plant cell parts

Photosynthesis is the process of synthesis of organic substances from inorganic ones using light energy. In the vast majority of cases, photosynthesis is carried out by plants using cellular organelles such as chloroplasts containing green pigment chlorophyll.

If plants were not capable of synthesizing organic matter, then almost all other organisms on Earth would have nothing to eat, since animals, fungi and many bacteria cannot synthesize organic substances from inorganic ones. They only absorb ready-made ones, split them into simpler ones, from which they again assemble complex ones, but already characteristic of their body.

This is the case if we talk about photosynthesis and its role very briefly. To understand photosynthesis, we need to say more: what specific inorganic substances are used, how does synthesis occur?

Photosynthesis requires two inorganic substances - carbon dioxide (CO 2) and water (H 2 O). The first is absorbed from the air by above-ground parts of plants mainly through stomata. Water comes from the soil, from where it is delivered to photosynthetic cells by the plant's conducting system. Also, photosynthesis requires the energy of photons (hν), but they cannot be attributed to matter.

In total, photosynthesis produces organic matter and oxygen (O2). Typically, organic matter most often means glucose (C 6 H 12 O 6).

Organic compounds are mostly composed of carbon, hydrogen and oxygen atoms. They are found in carbon dioxide and water. However, during photosynthesis, oxygen is released. Its atoms are taken from water.

Briefly and generally, the equation for the reaction of photosynthesis is usually written as follows:

6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2

But this equation does not reflect the essence of photosynthesis and does not make it understandable. Look, although the equation is balanced, in it the total number of atoms in free oxygen is 12. But we said that they come from water, and there are only 6 of them.

In fact, photosynthesis occurs in two phases. The first one is called light, second - dark. Such names are due to the fact that light is needed only for the light phase, the dark phase is independent of its presence, but this does not mean that it occurs in the dark. The light phase occurs on the membranes of the thylakoids of the chloroplast, and the dark phase occurs in the stroma of the chloroplast.

During the light phase, CO 2 binding does not occur. All that occurs is the capture of solar energy by chlorophyll complexes, its storage in ATP, and the use of energy to reduce NADP to NADP*H 2 . The flow of energy from light-excited chlorophyll is provided by electrons transmitted along the electron transport chain of enzymes built into the thylakoid membranes.

The hydrogen for NADP comes from water, which is decomposed by sunlight into oxygen atoms, hydrogen protons and electrons. This process is called photolysis. Oxygen from water is not needed for photosynthesis. Oxygen atoms from two water molecules combine to form molecular oxygen. The reaction equation for the light phase of photosynthesis briefly looks like this:

H 2 O + (ADP+P) + NADP → ATP + NADP*H 2 + ½O 2

Thus, the release of oxygen occurs during the light phase of photosynthesis. The number of ATP molecules synthesized from ADP and phosphoric acid per photolysis of one water molecule can be different: one or two.

So, ATP and NADP*H 2 come from the light phase to the dark phase. Here, the energy of the first and the reducing power of the second are spent on the binding of carbon dioxide. This stage of photosynthesis cannot be explained simply and concisely because it does not proceed in such a way that six CO 2 molecules combine with hydrogen released from NADP*H 2 molecules to form glucose:

6CO 2 + 6NADP*H 2 →C 6 H 12 O 6 + 6NADP
(the reaction occurs with the expenditure of energy ATP, which breaks down into ADP and phosphoric acid).

The given reaction is just a simplification to make it easier to understand. In fact, carbon dioxide molecules bind one at a time, joining the already prepared five-carbon organic substance. An unstable six-carbon organic substance is formed, which breaks down into three-carbon carbohydrate molecules. Some of these molecules are used to resynthesize the original five-carbon substance to bind CO 2 . This resynthesis is ensured Calvin cycle. A minority of carbohydrate molecules containing three carbon atoms exit the cycle. All other organic substances (carbohydrates, fats, proteins) are synthesized from them and other substances.

That is, in fact, three-carbon sugars, not glucose, come out of the dark phase of photosynthesis.

Plants, like all living organisms, require various substances to live, grow and develop. They come from the environment external to the plant. Various chemical processes take place in plant cells, as a result of which other substances characteristic of the plant are formed from the incoming substances.

From the soil, the plant uses its roots to absorb water with inorganic (mineral) substances dissolved in it. And in the green parts of plants, mainly in the leaves, organic substances are formed. The process of plants forming organic substances from inorganic ones is called photosynthesis.

Photosynthesis is a very complex multi-stage process, consisting of two main stages:

• Stage 1(light phase) A prerequisite is the participation of solar energy! The process begins with light. It activates chlorophyll (a substance found in chloroplasts). And activated chlorophyll breaks down the water molecule into hydrogen and oxygen. Oxygen is released into the air.
• Stage 2(dark phase) This stage of photosynthesis is called dark, because here all processes occur without the participation of light. At this stage, in the course of many chemical reactions involving carbon dioxide and active components obtained during the first stage of photosynthesis, organic matter (carbohydrate) is formed - sugar (glucose).

What inorganic substances are necessary for photosynthesis? These are carbon dioxide and water. Carbon dioxide is found in the air. There is about 0.03% of it there. Carbon dioxide is released into the air during the respiration process of almost all living organisms. Therefore, despite the fact that there is little of it in the air, and plants constantly absorb it from there, the amount of carbon dioxide is constantly replenished. In addition, industry and cars, among other things, emit carbon dioxide into the air. Water for photosynthesis comes from the soil through the suction zone of the roots.

What organic substances are formed during photosynthesis? This is glucose. Glucose is a carbohydrate. It is sweet and is part of the sugar molecule. As we know, there are three main groups of organic substances: proteins, fats and carbohydrates. Don't plants really need proteins and fats? Needed. However, they are not formed during the process of photosynthesis, but later, as a result of various biochemical reactions occurring in various plant cells and organs. Including in the roots. These reactions involve glucose and other chemical compounds. Excess glucose is converted into starch in plants and stored in special organs (for example, tubers).

What inorganic substances are formed during photosynthesis? This is oxygen. It is released into the air. Oxygen is used by living organisms during the process of respiration.

How does the process of photosynthesis occur? The process of photosynthesis requires sunlight to take place. light. He contains energy, which is converted by plants into the energy of chemical bonds in the glucose molecule. A special pigment is involved in the process of photosynthesis chlorophyll, which is found in the chloroplasts of plant cells. It is chlorophyll that gives plants their green color. It absorbs the entire spectrum of visible radiation except green, which it reflects. We see objects in the color that is reflected by them.

Thus, photosynthesis is the process of formation of organic substances from inorganic ones for the purpose of storing light energy in chemical bonds, which occurs with the help of a special pigment (in plants it is chlorophyll).

Since sunlight is so important for plants, they try to catch as much of it as possible. For this purpose, special adaptations have developed in the process of evolution. The leaves of the plants are usually flat and wide. Their skin is thin and transparent. Usually the leaves on the plant are arranged so as not to shade each other.

The entire complex step-by-step process of photosynthesis occurs uninterruptedly in the chloroplasts while the green leaves receive solar energy. Glucose is almost immediately converted into other carbohydrates, such as starch. These organic substances flow through the sieve tubes of the bast from the leaves to all parts of the plant: to the buds, generative organs. From glucose and minerals in plant cells, through a process of numerous transformations, other organic substances are formed, including proteins and fats. All these organic substances go towards the growth and development of the plant - that is, to build its body, and are also deposited in storage tissues and used during respiration.

Photosynthesis is the synthesis of organic compounds in the leaves of green plants from water and atmospheric carbon dioxide using solar (light) energy adsorbed by chlorophyll in chloroplasts.

Thanks to photosynthesis, visible light energy is captured and converted into chemical energy, which is stored (stored) in organic substances formed during photosynthesis.

The date of discovery of the process of photosynthesis can be considered 1771. The English scientist J. Priestley drew attention to changes in the composition of the air due to the vital activity of animals. In the presence of green plants, the air again became suitable for both breathing and combustion. Subsequently, the work of a number of scientists (Y. Ingenhaus, J. Senebier, T. Saussure, J.B. Boussingault) established that green plants absorb CO 2 from the air, from which organic matter is formed with the participation of water in the light. It was this process that in 1877 the German scientist W. Pfeffer called photosynthesis. The law of conservation of energy formulated by R. Mayer was of great importance for revealing the essence of photosynthesis. In 1845, R. Mayer proposed that the energy used by plants is the energy of the Sun, which plants convert into chemical energy through the process of photosynthesis. This position was developed and experimentally confirmed in the research of the remarkable Russian scientist K.A. Timiryazev.

The main role of photosynthetic organisms:

1) transformation of the energy of sunlight into the energy of chemical bonds of organic compounds;

2) saturation of the atmosphere with oxygen;

As a result of photosynthesis, 150 billion tons of organic matter are formed on Earth and about 200 billion tons of free oxygen are released per year. It prevents an increase in the concentration of CO2 in the atmosphere, preventing overheating of the Earth (greenhouse effect).

The atmosphere created by photosynthesis protects living things from harmful short-wave UV radiation (the oxygen-ozone shield of the atmosphere).

Only 1-2% of solar energy is transferred into the harvest of agricultural plants; losses are due to incomplete absorption of light. Therefore, there is a huge prospect of increasing productivity through the selection of varieties with high efficiency of photosynthesis and the creation of a crop structure favorable for light absorption. In this regard, the development of theoretical foundations for controlling photosynthesis is becoming especially relevant.

The importance of photosynthesis is enormous. Let us only note that it supplies fuel (energy) and atmospheric oxygen necessary for the existence of all living things. Therefore, the role of photosynthesis is planetary.

The planetarity of photosynthesis is also determined by the fact that thanks to the cycle of oxygen and carbon (mainly) the current composition of the atmosphere is maintained, which in turn determines the further maintenance of life on Earth. We can further say that the energy that is stored in the products of photosynthesis is essentially the main source of energy that humanity now has.

Total reaction of photosynthesis

CO 2 +H 2 O = (CH 2 O) + O 2 .

The chemistry of photosynthesis is described by the following equations:

Photosynthesis – 2 groups of reactions:

light stage (depends on illumination)

dark stage (depends on temperature).

Both groups of reactions occur simultaneously

Photosynthesis occurs in the chloroplasts of green plants.

Photosynthesis begins with the capture and absorption of light by the pigment chlorophyll, found in the chloroplasts of green plant cells.

This turns out to be enough to shift the absorption spectrum of the molecule.

The chlorophyll molecule absorbs photons in the violet and blue, and then in the red part of the spectrum, and does not interact with photons in the green and yellow part of the spectrum.

That's why chlorophyll and plants look green - they simply cannot take advantage of the green rays and leave them to wander around the world (thus making it greener).

Photosynthetic pigments are located on the inner side of the thylakoid membrane.

Pigments are organized into photosystems(antenna fields for capturing light) - containing 250–400 molecules of different pigments.

The photosystem consists of:

reaction center photosystems (chlorophyll molecule A),

antenna molecules

All pigments in the photosystem are capable of transferring excited state energy to each other. The photon energy absorbed by one or another pigment molecule is transferred to a neighboring molecule until it reaches the reaction center. When the resonance system of the reaction center goes into an excited state, it transfers two excited electrons to the acceptor molecule and thereby becomes oxidized and acquires a positive charge.

In plants:

photosystem 1(maximum light absorption at a wavelength of 700 nm - P700)

photosystem 2(maximum light absorption at a wavelength of 680 nm - P680

Differences in absorption optima are due to slight differences in pigment structure.

The two systems work in tandem, like a two-part conveyor called non-cyclic photophosphorylation .

Summary equation for non-cyclic photophosphorylation:

Ф - symbol of phosphoric acid residue

The cycle begins with photosystem 2.

1) antenna molecules capture the photon and transmit excitation to the active center molecule P680;

2) the excited P680 molecule donates two electrons to cofactor Q, while it is oxidized and acquires a positive charge;

Cofactor(cofactor). A coenzyme or any other substance necessary for an enzyme to perform its function

Coenzymes (coenzymes)[from lat. co (cum) - together and enzymes], organic compounds of non-protein nature participating in the enzymatic reaction as acceptors of individual atoms or atomic groups cleaved by the enzyme from the substrate molecule, i.e. to carry out the catalytic action of enzymes. These substances, in contrast to the protein component of the enzyme (apoenzyme), have a relatively small molecular weight and, as a rule, are thermostable. Sometimes coenzymes mean any low-molecular substances, the participation of which is necessary for the catalytic action of the enzyme to occur, including ions, for example. K + , Mg 2+ and Mn 2+ . Enzymes are located. in the active center of the enzyme and, together with the substrate and functional groups of the active center, form an activated complex.

Most enzymes require the presence of a coenzyme to exhibit catalytic activity. The exception is hydrolytic enzymes (for example, proteases, lipases, ribonuclease), which perform their function in the absence of a coenzyme.

The molecule is reduced by P680 (under the action of enzymes). In this case, water dissociates into protons and molecular oxygen, those. water is an electron donor, which ensures the replenishment of electrons in P 680.

PHOTOLYSIS WATER- splitting of a water molecule, in particular during photosynthesis. Due to photolysis of water, oxygen is produced, which is released by green plants in the light.

DEFINITION: Photosynthesis is the process of formation of organic substances from carbon dioxide and water, in light, with the release of oxygen.

The process of photosynthesis involves:

1) chloroplasts,

3) carbon dioxide,

5) temperature.

In higher plants, photosynthesis occurs in chloroplasts - oval-shaped plastids (semi-autonomous organelles) containing the pigment chlorophyll, thanks to the green color of which parts of the plant also have a green color.

In algae, chlorophyll is contained in chromatophores (pigment-containing and light-reflecting cells). Brown and red algae, which live at considerable depths where sunlight does not reach well, have other pigments.

If you look at the food pyramid of all living things, photosynthetic organisms are at the very bottom, among the autotrophs (organisms that synthesize organic substances from inorganic ones). Therefore, they are a source of food for all life on the planet.

During photosynthesis, oxygen is released into the atmosphere. In the upper layers of the atmosphere, ozone is formed from it. The ozone shield protects the Earth's surface from harsh ultraviolet radiation, thanks to which life was able to emerge from the sea onto land.

Oxygen is necessary for the respiration of plants and animals. When glucose is oxidized with the participation of oxygen, mitochondria store almost 20 times more energy than without it. This makes the use of food much more efficient, which has led to high metabolic rates in birds and mammals.

A more detailed description of the process of photosynthesis in plants

Progress of photosynthesis:

The process of photosynthesis begins with light hitting chloroplasts - intracellular semi-autonomous organelles containing green pigment. When exposed to light, chloroplasts begin to consume water from the soil, splitting it into hydrogen and oxygen.

Part of the oxygen is released into the atmosphere, the other part goes to oxidative processes in the plant.

Sugar combines with nitrogen, sulfur and phosphorus coming from the soil, in this way green plants produce starch, fats, proteins, vitamins and other complex compounds necessary for their life.

Photosynthesis occurs best under the influence of sunlight, but some plants can be content with artificial lighting.

A complex description of the mechanisms of photosynthesis for the advanced reader

Until the 60s of the 20th century, scientists knew only one mechanism for carbon dioxide fixation - through the C3-pentose phosphate pathway. However, recently a group of Australian scientists was able to prove that in some plants the reduction of carbon dioxide occurs through the C4-dicarboxylic acid cycle.

In plants with a C3 reaction, photosynthesis occurs most actively under conditions of moderate temperature and light, mainly in forests and dark places. Such plants include almost all cultivated plants and most vegetables. They form the basis of the human diet.

In plants with a C4 reaction, photosynthesis occurs most actively under conditions of high temperature and light. Such plants include, for example, corn, sorghum and sugar cane, which grow in warm and tropical climates.

Plant metabolism itself was discovered quite recently, when it was discovered that in some plants that have special tissues for storing water, carbon dioxide accumulates in the form of organic acids and is fixed in carbohydrates only after a day. This mechanism helps plants save water.

How does the process of photosynthesis occur?

The plant absorbs light using a green substance called chlorophyll. Chlorophyll is found in chloroplasts, which are found in stems or fruits. There is a particularly large amount of them in leaves, because due to its very flat structure, the leaf can attract a lot of light, and therefore receive much more energy for the process of photosynthesis.

After absorption, chlorophyll is in an excited state and transfers energy to other molecules of the plant body, especially those that are directly involved in photosynthesis. The second stage of the photosynthesis process takes place without the mandatory participation of light and consists of obtaining a chemical bond with the participation of carbon dioxide obtained from air and water. At this stage, various very useful substances for life, such as starch and glucose, are synthesized.

These organic substances are used by the plants themselves to nourish its various parts, as well as to maintain normal life functions. In addition, these substances are also obtained by animals by eating plants. People also get these substances by eating foods of animal and plant origin.

Conditions for photosynthesis

Photosynthesis can occur both under the influence of artificial light and sunlight. As a rule, plants “work” intensively in nature in the spring and summer, when there is a lot of necessary sunlight. In autumn there is less light, the days are shortened, the leaves first turn yellow and then fall off. But as soon as the warm spring sun appears, green foliage reappears and green “factories” will resume their work again to provide the oxygen so necessary for life, as well as many other nutrients.

Alternative definition of photosynthesis

Photosynthesis (from ancient Greek photo-light and synthesis - connection, folding, binding, synthesis) is the process of converting light energy into the energy of chemical bonds of organic substances in the light by photoautotrophs with the participation of photosynthetic pigments (chlorophyll in plants, bacteriochlorophyll and bacteriorhodopsin in bacteria ). In modern plant physiology, photosynthesis is more often understood as a photoautotrophic function - a set of processes of absorption, transformation and use of the energy of light quanta in various endergonic reactions, including the conversion of carbon dioxide into organic substances.

Phases of photosynthesis

Photosynthesis is a rather complex process and includes two phases: light, which always occurs exclusively in the light, and dark. All processes occur inside the chloroplasts on special small organs - thylakodia. During the light phase, a quantum of light is absorbed by chlorophyll, resulting in the formation of ATP and NADPH molecules. The water then breaks down, forming hydrogen ions and releasing an oxygen molecule. The question arises, what are these incomprehensible mysterious substances: ATP and NADH?

ATP is a special organic molecule found in all living organisms and is often called the “energy” currency. It is these molecules that contain high-energy bonds and are the source of energy in any organic synthesis and chemical processes in the body. Well, NADPH is actually a source of hydrogen, it is used directly in the synthesis of high-molecular organic substances - carbohydrates, which occurs in the second, dark phase of photosynthesis using carbon dioxide.

Light phase of photosynthesis

Chloroplasts contain a lot of chlorophyll molecules, and they all absorb sunlight. At the same time, light is absorbed by other pigments, but they cannot carry out photosynthesis. The process itself occurs only in some chlorophyll molecules, of which there are very few. Other molecules of chlorophyll, carotenoids and other substances form special antenna and light-harvesting complexes (LHC). They, like antennas, absorb light quanta and transmit excitation to special reaction centers or traps. These centers are located in photosystems, of which plants have two: photosystem II and photosystem I. They contain special chlorophyll molecules: respectively, in photosystem II - P680, and in photosystem I - P700. They absorb light of exactly this wavelength (680 and 700 nm).

The diagram makes it more clear how everything looks and happens during the light phase of photosynthesis.

In the figure we see two photosystems with chlorophylls P680 and P700. The figure also shows the carriers through which electron transport occurs.

So: both chlorophyll molecules of two photosystems absorb a light quantum and become excited. The electron e- (red in the figure) moves to a higher energy level.

Excited electrons have very high energy; they break off and enter a special chain of transporters, which is located in the membranes of thylakoids - the internal structures of chloroplasts. The figure shows that from photosystem II from chlorophyll P680 an electron goes to plastoquinone, and from photosystem I from chlorophyll P700 to ferredoxin. In the chlorophyll molecules themselves, in place of electrons after their removal, blue holes with a positive charge are formed. What to do?

To compensate for the lack of an electron, the chlorophyll P680 molecule of photosystem II accepts electrons from water, and hydrogen ions are formed. In addition, it is due to the breakdown of water that oxygen is released into the atmosphere. And the chlorophyll P700 molecule, as can be seen from the figure, makes up for the lack of electrons through a system of carriers from photosystem II.

In general, no matter how difficult it is, this is exactly how the light phase of photosynthesis proceeds; its main essence is the transfer of electrons. You can also see from the figure that in parallel with electron transport, hydrogen ions H+ move through the membrane, and they accumulate inside the thylakoid. Since there are a lot of them there, they move outward with the help of a special conjugating factor, which is orange in the picture, shown on the right and looks like a mushroom.

Finally, we see the final step of electron transport, which results in the formation of the aforementioned NADH compound. And due to the transfer of H+ ions, energy currency is synthesized - ATP (seen on the right in the figure).

So, the light phase of photosynthesis is completed, oxygen is released into the atmosphere, ATP and NADH are formed. What's next? Where is the promised organic matter? And then comes the dark stage, which consists mainly of chemical processes.

Dark phase of photosynthesis

For the dark phase of photosynthesis, carbon dioxide – CO2 – is an essential component. Therefore, the plant must constantly absorb it from the atmosphere. For this purpose, there are special structures on the surface of the leaf - stomata. When they open, CO2 enters the leaf, dissolves in water and reacts with the light phase of photosynthesis.

During the light phase in most plants, CO2 binds to a five-carbon organic compound (which is a chain of five carbon molecules), resulting in the formation of two molecules of a three-carbon compound (3-phosphoglyceric acid). Because The primary result is precisely these three-carbon compounds; plants with this type of photosynthesis are called C3 plants.

Further synthesis in chloroplasts occurs rather complexly. It ultimately forms a six-carbon compound, from which glucose, sucrose or starch can subsequently be synthesized. In the form of these organic substances, the plant accumulates energy. In this case, only a small part of them remains in the leaf, which is used for its needs, while the rest of the carbohydrates travel throughout the plant, arriving where energy is most needed - for example, at the growth points.

1. Is photosynthesis a process of plastic or energy metabolism? Why?

Photosynthesis refers to the processes of plastic metabolism because accompanied by:

● by the synthesis of complex organic compounds from simpler substances, namely: glucose (C 6 H 12 O 6) is synthesized from inorganic substances (H 2 O and CO 2);

● absorption of light energy.

2. In which organelles of a plant cell does photosynthesis occur? What is a photosystem? What function do photosystems perform?

Photosynthesis occurs in green plastids - chloroplasts.

Photosystems are special pigment-protein complexes located in the membranes of chloroplast thylakoids. There are two types of photosystems – photosystem I and photosystem II. Each of them includes a light-harvesting antenna formed by pigment molecules, a reaction center and electron carriers.

The light-harvesting antenna functions like a funnel: pigment molecules absorb light and transfer all the collected energy to the reaction center, where the trap molecule represented by chlorophyll a is located. Having absorbed energy, the trap molecule goes into an excited state and gives one of its electrons to a special carrier, i.e. oxidizes. Thus, photosystems perform the function of absorbing light and converting light energy into chemical energy.

3. What is the importance of photosynthesis on Earth? Why would the existence of the biosphere be impossible without phototrophic organisms?

Photosynthesis is the only process on the planet during which the light energy of the Sun is converted into the energy of chemical bonds of synthesized organic substances. In this case, the starting compounds for the synthesis of organic substances are energy-poor inorganic substances - carbon dioxide and water.

Organic compounds formed during photosynthesis are transferred as part of food from phototrophic organisms to herbivores, then to carnivores, being a source of energy and building material for the synthesis of other substances, for the formation of new cells and structures. Consequently, thanks to the activity of phototrophs, the nutritional needs of heterotrophic organisms are satisfied.

In addition, photosynthesis is a source of molecular oxygen necessary for the respiration of most living organisms. The ozone layer is formed and maintained from oxygen, protecting living organisms on the planet from the harmful effects of short-wave ultraviolet radiation. Thanks to photosynthesis, a relatively constant CO 2 content in the atmosphere is maintained.

4. Characterize the light and dark phases of photosynthesis according to the plan:

1) location of the leak; 2) starting materials; 3) ongoing processes; 4) final products.

What products of the light phase of photosynthesis are used in the dark phase?

Light phase of photosynthesis.

1) Place of leakage: thylakoid membranes.

2) Starting substances: H 2 O, oxidized NADP (NADP +), ADP, H 3 PO 4. Photosynthetic pigments (chlorophylls, etc.) are also necessary for the light phase to occur, but they cannot be called the initial substances of the light phase.

3) Occurring processes: absorption of light by photosystems, photolysis of water, transport of electrons to the outside of the thylakoid and accumulation of protons inside the thylakoid (i.e., the appearance of an electrochemical potential on the thylakoid membrane), ATP synthesis, reduction of NADP +.

4) End products: ATP, reduced NADP (NADP H+H +), by-product - molecular oxygen (O 2).

Dark phase of photosynthesis.

1) Place of leakage: chloroplast stroma.

2) Initial substances: CO 2, ATP, reduced NADP (NADP H+H +).

3) Ongoing processes: glucose synthesis (reduction of CO 2 to organic substances), during which ATP hydrolysis and NADP H+H + oxidation occur.

4) End products: glucose (C 6 H 12 O 6), oxidized NADP (NADP +), ADP, H 3 PO 4.

In the dark phase of photosynthesis, light phase products such as NADP H+H + (serves as a source of hydrogen atoms for the synthesis of glucose) and ATP (serves as a source of energy for the synthesis of glucose) are used.

5. Compare photosynthesis and aerobic respiration. Indicate similarities and differences.

Similarities:

● Complex multi-stage processes involving enzymes.

● Photosynthesis and the final (oxygen) stage of aerobic respiration occur in double-membrane organelles (chloroplasts and mitochondria, respectively).

● Redox processes, which are accompanied by the transfer of electrons along the electron transport chains of the internal membranes of the corresponding organelles, the appearance of a potential difference on these membranes, the work of ATP synthetase and ATP synthesis.

Differences:

● The process of photosynthesis refers to plastic metabolism because is accompanied by the synthesis of organic substances from inorganic ones and occurs with the absorption of light energy. The process of aerobic respiration refers to energy metabolism, since complex organic substances are broken down and the energy contained in them is released.

● Photosynthesis occurs only in the cells of phototrophic organisms, and aerobic respiration occurs in the cells of most living organisms (including phototrophs).

● Various starting materials and final products. If we consider the summary equations of photosynthesis and aerobic respiration, we can see that the products of photosynthesis are actually the starting materials for aerobic respiration and vice versa.

● NAD and FAD serve as carriers of hydrogen atoms in the process of respiration, and NADP in photosynthesis.

And (or) other significant features.

6. A person consumes approximately 430 g of oxygen per day. An average-sized tree absorbs about 30 kg of carbon dioxide per year. How many trees are needed to provide one person with oxygen?

● In a year, a person consumes: 430 g × 365 = 156,950 g of oxygen.

● Let's calculate the chemical amount of carbon dioxide absorbed per year by one tree:

M (CO 2) = 12 + 16 × 2 = 44 g/mol. n (CO 2) = m: M = 30,000 g: 44 g/mol ≈ 681.8 mol.

● Summary equation of photosynthesis:

6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2

The absorption of 6 moles of carbon dioxide is accompanied by the release of 6 moles of oxygen. This means that, absorbing 681.8 moles of carbon dioxide per year, the tree releases 681.8 moles of oxygen.

● Let’s find the mass of oxygen released by the tree per year:

M (O 2) = 16 × 2 = 32 g/mol. m (O 2) = n × M = 681.8 mol × 32 g/mol = 21,817.6 g

● Let's determine how many trees are needed to provide one person with oxygen. Number of trees = 156,950 g: 21,817.6 ≈ 7.2 trees.

Answer: To provide one person with oxygen, on average, 7.2 trees will be needed (acceptable answers would be “8 trees” or “7 trees”).

7. Researchers divided wheat plants into two groups and grew them in the laboratory under the same conditions, except that the plants in the first group were illuminated with red light, and the plants in the second group were illuminated with green light. In which group of plants did photosynthesis proceed more intensively? What is this connected with?

Photosynthesis proceeded more intensely in plants illuminated with red light. This is due to the fact that the main photosynthetic pigments - chlorophylls - intensively absorb red light (as well as the blue-violet part of the spectrum), and reflect green, which determines the green color of these pigments.

8*. What experiment can be used to prove that the oxygen released during photosynthesis is formed precisely from water molecules, and not from molecules of carbon dioxide or any other substance?

If water labeled with radioactive oxygen is used to carry out photosynthesis (the molecules contain oxygen radionuclide instead of the stable nuclide 16 O), then the radioactive label can be detected in the released molecular oxygen. If you use any other substance containing oxygen radionuclide for photosynthesis, then the released O2 will not contain a radioactive label. In particular, radioactive oxygen contained in the molecules of absorbed carbon dioxide will be found in the synthesized organic substances, but not in the composition of O 2.

*Tasks marked with an asterisk require students to put forward various hypotheses. Therefore, when marking, the teacher should focus not only on the answer given here, but take into account each hypothesis, assessing the biological thinking of students, the logic of their reasoning, the originality of ideas, etc. After this, it is advisable to familiarize students with the answer given.