Photosynthesis occurs in the cells of which tissue. The concept of photosynthesis, where and what happens in the light phase of photosynthesis. The importance of photosynthesis in human life

Photosynthesis- this 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, the energy of visible light is captured and converted into chemical energy stored (stored) in organic substances formed during photosynthesis.

The date of the discovery of the process of photosynthesis can be considered 1771. The English scientist J. Priestley drew attention to the change 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. Later, the work of a number of scientists (J. Ingengauz, J. Senebier, T. Saussure, J. B. Bussengo) found 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. Of great importance for revealing the essence of photosynthesis was the law of conservation of energy, formulated by R. Mayer. In 1845, R. Mayer suggested that the energy used by plants is the energy of the Sun, which plants convert into chemical energy during photosynthesis. This position was developed and experimentally confirmed in the studies 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 on Earth, 150 billion tons of organic matter are formed 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 the Earth from overheating (greenhouse effect).

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

Only 1-2% of solar energy passes into the crop of agricultural plants, the losses are due to incomplete absorption of light. Therefore, there is a huge prospect of increasing yields due to the selection of varieties with high photosynthesis efficiency, the creation of a crop structure favorable for light absorption. In this regard, the development of theoretical foundations for the control of photosynthesis becomes especially relevant.

The importance of photosynthesis is gigantic. We 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 planetary nature of photosynthesis is also determined by the fact that due to the circulation of oxygen and carbon (mainly) the modern composition of the atmosphere is maintained, which in turn determines the further maintenance of life on Earth. It can be said further that the energy that is stored in the products of photosynthesis is, in essence, the main source of energy that humanity now has at its disposal.

Total reaction of photosynthesis

SO 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 (depending on temperature).

Both groups of reactions proceed simultaneously

Photosynthesis takes place in the chloroplasts of green plants.

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

This is sufficient 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 parts of the spectrum.

Therefore, chlorophyll and plants look green - they simply cannot take advantage of the green rays in any way and leave them to walk around in the wide world (thus making it greener).

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

The 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 the neighboring molecule until it reaches the reaction center. When the resonant system of the reaction center goes into an excited state, it transfers two excited electrons to the acceptor molecule and thereby oxidizes and acquires a positive charge.

In plants:

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

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

Differences in absorption optima are due to slight differences in the structure of the pigments.

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

Summary equation for non-cyclic photophosphorylation:

F - symbol for a phosphoric acid residue

The cycle begins with photosystem 2.

1) antenna molecules trap a photon and transfer excitation to the P680 active center molecule;

2) the excited P680 molecule donates two electrons to the 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 with enzymes], organic compounds of non-protein nature, participating in the enzymatic reaction as acceptors of individual atoms or atomic groups that are cleaved off by the enzyme from the substrate molecule, i.e. for 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 weight substances, the participation of which is necessary for the manifestation of the catalytic action of the enzyme, including ions, for example. K + , Mg 2+ and Mn 2+ . Offers are located. in the active site of the enzyme and together with the substrate and functional groups of the active site form an activated complex.

For the manifestation of catalytic activity, most enzymes require the presence of a coenzyme. 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). The water then 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 the water molecule, in particular in the process of photosynthesis. Due to the photolysis of water, oxygen is released, which is released by green plants in the light.

The most important organic process, without which the existence of all living beings on our planet would be in question, is photosynthesis. What is photosynthesis? known to everyone from school. Roughly speaking, this is the process of formation of organic substances from carbon dioxide and water, which occurs in the light and is accompanied by the release of oxygen. A more complex definition is as follows: photosynthesis is the process of converting light energy into the energy of chemical bonds of substances of organic origin with the participation of photosynthetic pigments. In modern practice, photosynthesis is usually understood as a set of processes of absorption, synthesis and use of light in a number of endergonic reactions, one of which is the conversion of carbon dioxide into organic substances. And now let's find out in more detail how photosynthesis proceeds and what phases this process is divided into!

general characteristics

Chloroplasts, which every plant has, are responsible for photosynthesis. What are chloroplasts? These are oval plastids that contain a pigment such as chlorophyll. It is chlorophyll that determines the green color of plants. In algae, this pigment is present in the composition of chromatophores - pigment-containing light-reflecting cells of various shapes. Brown and red algae, which live at considerable depths where sunlight does not reach well, have different pigments.

Substances of photosynthesis are part of autotrophs - organisms capable of synthesizing organic substances from inorganic substances. They are the lowest step of the food pyramid, therefore they are included in the diet of all living organisms on the planet Earth.

Benefits of Photosynthesis

Why is photosynthesis needed? Oxygen released from plants during photosynthesis enters the atmosphere. Rising into its upper layers, it forms ozone, which protects the earth's surface from strong solar radiation. It is thanks to the ozone screen that living organisms can comfortably stay on land. In addition, as you know, oxygen is needed for the respiration of living organisms.

Process progress

It all starts with the fact that light enters the chloroplasts. Under its influence, organelles draw water from the soil, and also divide it into hydrogen and oxygen. Thus, two processes take place. Photosynthesis of plants begins at the moment when the leaves have already absorbed water and carbon dioxide. Light energy accumulates in thylakoids - special compartments of chloroplasts, and divides the water molecule into two components. Part of the oxygen goes to the respiration of the plant, and the rest goes into the atmosphere.

Then carbon dioxide enters the pyrenoids - protein granules surrounded by starch. This is where hydrogen comes in. Mixing with each other, these substances form sugar. This reaction also proceeds with the release of oxygen. When sugar (the general name for simple carbohydrates) is mixed with nitrogen, sulfur and phosphorus that enter the plant from the soil, starch (a complex carbohydrate), proteins, fats, vitamins and other substances necessary for plant life are formed. In the vast majority of cases, photosynthesis occurs in natural light conditions. However, artificial lighting can also participate in it.

Until the 60s of the twentieth century, science was aware of one mechanism for the reduction of carbon dioxide - along the C 3 -pentose phosphate pathway. Recently, Australian scientists have shown that in some plant species this process can proceed through the C 4 -dicarboxylic acid cycle.

Plants that reduce carbon dioxide via the C3 pathway perform best in moderate temperatures and low light, in forests or dark places. These plants include the lion's share of cultivated plants and almost all the vegetables that form the basis of our diet.

In the second class of plants, photosynthesis proceeds most actively under conditions of high temperature and strong illumination. This group includes plants that grow in tropical and warm climates, such as corn, sugar cane, sorghum, and so on.

Plant metabolism, by the way, was discovered quite recently. Scientists were able to find out that some plants have special tissues to conserve water reserves. Carbon dioxide accumulates in them in the form of organic acids and passes into carbohydrates only after 24 hours. This mechanism gives plants the opportunity to conserve water.

How is the process going?

We already know in general terms how the process of photosynthesis proceeds and what kind of photosynthesis happens, now let's get to know it more deeply.

It all starts with the fact that the plant absorbs light. Chlorophyll helps her in this, which in the form of chloroplasts is located in the leaves, stems and fruits of the plant. The main amount of this substance is concentrated in the leaves. The thing is that due to its flat structure, the sheet attracts a lot of light. And the more light, the more energy for photosynthesis. Thus, the leaves in the plant act as a kind of locators that capture the light.

When light is absorbed, chlorophyll is in an excited state. It transfers energy to other plant organs that are involved in the next stage of photosynthesis. The second stage of the process takes place without the participation of light and consists in a chemical reaction involving water obtained from the soil and carbon dioxide obtained from the air. At this stage, carbohydrates are synthesized, which are essential for the life of any organism. In this case, they not only feed the plant itself, but are also transmitted to the animals that eat it. People also get these substances by eating plant or animal products.

Process phases

Being a rather complex process, photosynthesis is divided into two phases: light and dark. As the name implies, the first phase requires the presence of solar radiation, while the second does not. During the light phase, chlorophyll absorbs a quantum of light, forming ATP and NADH molecules, without which photosynthesis is impossible. What are ATP and NADH?

ATP (adenositriphosphate) is a nucleic coenzyme that contains high-energy bonds and serves as an energy source in any organic transformation. The conjunction is often referred to as the energy volute.

NADH (nicotinamide adenine dinucleotide) is a source of hydrogen that is used to synthesize carbohydrates with the participation of carbon dioxide in the second phase of a process such as photosynthesis.

light phase

Chloroplasts contain many chlorophyll molecules, each of which absorbs light. Other pigments also absorb it, but they are not capable of photosynthesis. The process takes place only in part of the chlorophyll molecules. The remaining molecules form antenna and light-harvesting complexes (LSCs). They accumulate light quanta and transfer them to reaction centers, which are also called traps. Reaction centers are located in photosystems, of which there are two in a photosynthetic plant. The first contains a chlorophyll molecule capable of absorbing light with a wavelength of 700 nm, and the second - 680 nm.

So, two types of chlorophyll molecules absorb light and are excited, which contributes to the transition of electrons to a higher energy level. Excited electrons, which have a large amount of energy, break off and enter the carrier chain located in the thylakoid membranes (internal structures of chloroplasts).

Electron transition

An electron from the first photosystem passes from chlorophyll P680 to plastoquinone, and an electron from the second system to ferredoxin. At the same time, a free place is formed at the place of detachment of electrons in the chlorophyll molecule.

To make up for the shortage, the P680 chlorophyll molecule accepts electrons from water, forming hydrogen ions. And the second chlorophyll molecule makes up for the shortage through the carrier system from the first photosystem.

This is how the light phase of photosynthesis proceeds, the essence of which is the transfer of electrons. Parallel to the electron transport, the movement of hydrogen ions through the membrane takes place. This leads to their accumulation inside the thylakoid. Accumulating in large quantities, they are released outside with the help of a conjugating factor. The result of electron transport is the formation of the NADH compound. And the transfer of a hydrogen ion leads to the formation of the energy currency ATP.

At the end of the light phase, oxygen enters the atmosphere, and ATP and NADH are formed inside the petal. Then the dark phase of photosynthesis begins.

dark phase

This phase of photosynthesis requires carbon dioxide. The plant constantly absorbs it from the air. For this purpose, there are stomata on the surface of the leaf - special structures that, when opened, absorb carbon dioxide. Entering the inside of the leaf, it dissolves in water and participates in the processes of the light phase.

During the light phase in most plants, carbon dioxide binds to an organic compound that contains 5 carbon atoms. As a result, a pair of molecules of a three-carbon compound called 3-phosphoglyceric acid is formed. It is because this compound is the primary result of the process that plants with this type of photosynthesis are called C 3 plants.

Further processes taking place in chloroplasts are very difficult for inexperienced laymen. The end result is a six-carbon compound that synthesizes simple or complex carbohydrates. It is in the form of carbohydrates that the plant stores energy. A small part of the substances remains in the leaf and fulfills its needs. The remaining carbohydrates circulate throughout the plant and go to the places where they are most needed.

Photosynthesis in winter

Many at least once in their lives wondered where oxygen comes from in the cold season. Firstly, oxygen is produced not only by deciduous plants, but also by coniferous and marine plants. And if deciduous plants freeze in winter, then conifers continue to breathe, although less intensively. Secondly, the oxygen content in the atmosphere does not depend on whether the trees have shed their leaves. Oxygen occupies 21% of the atmosphere, anywhere on our planet at any time of the year. This value does not change, since the air masses move very quickly, and winter does not come at the same time in all countries. And, thirdly, in winter in the lower layers of the air that we inhale, the oxygen content is even greater than in summer. The reason for this phenomenon is the low temperature, due to which oxygen becomes denser.

Conclusion

Today we remembered what photosynthesis is, what chlorophyll is, and how plants release oxygen by absorbing carbon dioxide. Of course, photosynthesis is the most important process in our life. It reminds us of the need to respect nature.

27-Feb-2014 | One Comment | Lolita Okolnova

Photosynthesis- the process of formation of organic substances from carbon dioxide and water in the light with the participation of photosynthetic pigments.

Chemosynthesis- a method of autotrophic nutrition, in which the oxidation reactions of inorganic compounds serve as an energy source for the synthesis of organic substances from CO 2

Usually, all organisms capable of synthesizing organic substances from inorganic substances, i.e. organisms capable of photosynthesis and chemosynthesis, refer to .

Some are traditionally classified as autotrophs.

We briefly talked about in the course of considering the structure of a plant cell, let's take a look at the whole process in more detail ...

The essence of photosynthesis

(total equation)

The main substance involved in the multi-step process of photosynthesis - chlorophyll. It is it that transforms solar energy into chemical energy.

The figure shows a schematic representation of the chlorophyll molecule, by the way, the molecule is very similar to the hemoglobin molecule ...

Chlorophyll is built into chloroplast grana:

Light phase of photosynthesis:

(carried out on thylakoid membranes)

• Light, hitting the chlorophyll molecule, is absorbed by it and brings it into an excited state - an electron that is part of the molecule, having absorbed the energy of light, goes to a higher energy level and participates in synthesis processes;
• Under the action of light, the splitting (photolysis) of water also occurs:

At the same time, oxygen is removed to the external environment, and protons accumulate inside the thylakoid in the "proton reservoir"

2H + + 2e - + NADP → NADP H 2

NADP is a specific substance, a coenzyme, i.e. a catalyst, in this case a carrier of hydrogen.

• synthesized (energy)

Dark phase of photosynthesis

(occurs in the stroma of chloroplasts)

actual glucose synthesis

a cycle of reactions occurs in which C 6 H 12 O 6 is formed. These reactions use the energies of ATP and NADP·H 2 formed in the light phase; In addition to glucose, other monomers of complex organic compounds are formed during photosynthesis - amino acids, glycerol and fatty acids, nucleotides

Please note: this phase is dark is called not because it goes at night - glucose synthesis occurs, in general, around the clock, but the dark phase no longer needs light energy.

“Photosynthesis is the process upon which all manifestations of life on our planet ultimately depend.”

K.A. Timiryazev.

As a result of photosynthesis, about 150 billion tons of organic matter are formed on Earth and about 200 billion tons of free oxygen are released per year. In addition, plants involve billions of tons of nitrogen, phosphorus, sulfur, calcium, magnesium, potassium and other elements in the circulation. Although a green leaf uses only 1-2% of the light falling on it, organic matter and oxygen in general are created by the plant.

Chemosynthesis

Chemosynthesis is carried out due to the energy released during the chemical reactions of oxidation of various inorganic compounds: hydrogen, hydrogen sulfide, ammonia, iron oxide (II), etc.

According to the substances included in the metabolism of bacteria, there are:

• sulfur bacteria - microorganisms of water bodies containing H 2 S - sources with a very characteristic odor,
• iron bacteria,
• nitrifying bacteria - oxidize ammonia and nitrous acid,
• nitrogen-fixing bacteria - enrich the soil, extremely increase yields,
• hydrogen-oxidizing bacteria

But the essence remains the same - this is also

How to explain such a complex process as photosynthesis, briefly and clearly? Plants are the only living organisms that can produce their own food. How do they do it? For growth, they receive all the necessary substances from the environment: carbon dioxide - from the air, water and - from the soil. They also need energy from sunlight. This energy triggers certain chemical reactions during which carbon dioxide and water are converted into glucose (nutrition) and photosynthesis is. Briefly and clearly, the essence of the process can be explained even to school-age children.

"Together with the Light"

The word "photosynthesis" comes from two Greek words - "photo" and "synthesis", a combination which in translation means "together with light". The solar energy is converted into chemical energy. Chemical equation of photosynthesis:

6CO 2 + 12H 2 O + light \u003d C 6 H 12 O 6 + 6O 2 + 6H 2 O.

This means that 6 carbon dioxide molecules and twelve water molecules are used (along with sunlight) to produce glucose, resulting in six oxygen molecules and six water molecules. If we represent this in the form of a verbal equation, we get the following:

Water + sun => glucose + oxygen + water.

The sun is a very powerful source of energy. People always try to use it to generate electricity, insulate houses, heat water, and so on. Plants "figured out" how to use solar energy millions of years ago because it was necessary for their survival. Photosynthesis can be briefly and clearly explained as follows: plants use the light energy of the sun and convert it into chemical energy, the result of which is sugar (glucose), the excess of which is stored as starch in the leaves, roots, stems and seeds of the plant. The energy of the sun is transferred to the plants, as well as to the animals that these plants eat. When a plant needs nutrients for growth and other life processes, these reserves are very useful.

How do plants absorb solar energy?

Talking about photosynthesis briefly and clearly, it is worth touching on the question of how plants manage to absorb solar energy. This is due to the special structure of the leaves, which includes green cells - chloroplasts, which contain a special substance called chlorophyll. This is what gives the leaves their green color and is responsible for absorbing the energy of sunlight.

Why are most leaves wide and flat?

Photosynthesis takes place in the leaves of plants. The surprising fact is that plants are very well adapted to trap sunlight and absorb carbon dioxide. Due to the wide surface, much more light will be captured. It is for this reason that solar panels, which are sometimes installed on the roofs of houses, are also wide and flat. The larger the surface, the better the absorption.

What else is important for plants?

Just like humans, plants also need nutrients and nutrients to stay healthy, grow and perform well. They get minerals dissolved in water from the soil through their roots. If the soil lacks mineral nutrients, the plant will not develop normally. Farmers often test the soil to make sure it has enough nutrients for crop growth. Otherwise resort to the use of fertilizers containing essential minerals for plant nutrition and growth.

Why is photosynthesis so important?

Explaining photosynthesis briefly and clearly for children, it is worth mentioning that this process is one of the most important chemical reactions in the world. What are the reasons for such a loud statement? First, photosynthesis feeds plants, which in turn feed all other living things on the planet, including animals and humans. Secondly, as a result of photosynthesis, oxygen necessary for respiration is released into the atmosphere. All living things breathe in oxygen and breathe out carbon dioxide. Luckily, plants do the opposite, which is why they are very important for humans and animals to breathe.

Amazing process

Plants, it turns out, also know how to breathe, but, unlike humans and animals, they absorb carbon dioxide from the air, not oxygen. Plants also drink. That's why you need to water them, otherwise they will die. With the help of the root system, water and nutrients are transported to all parts of the plant body, and carbon dioxide is absorbed through small holes in the leaves. The trigger for starting a chemical reaction is sunlight. All the resulting metabolic products are used by plants for nutrition, oxygen is released into the atmosphere. This is how you can briefly and clearly explain how the process of photosynthesis occurs.

Photosynthesis: light and dark phases of photosynthesis

The process under consideration consists of two main parts. There are two phases of photosynthesis (description and table - below). The first is called the light phase. It occurs only in the presence of light in thylakoid membranes with the participation of chlorophyll, electron carrier proteins, and the enzyme ATP synthetase. What else does photosynthesis hide? Light and replace each other as day and night come on (Calvin cycles). During the dark phase, the production of the same glucose, food for plants, occurs. This process is also called the light-independent reaction.

Conclusion

From all of the above, the following conclusions can be drawn:

• Photosynthesis is the process that makes it possible to obtain energy from the sun.
• The light energy of the sun is converted into chemical energy by chlorophyll.
• Chlorophyll gives plants their green color.
• Photosynthesis occurs in the chloroplasts of plant leaves.
• Carbon dioxide and water are essential for photosynthesis.
• Carbon dioxide enters the plant through tiny holes, stomata, and oxygen exits through them.
• Water is absorbed into the plant through its roots.
• Without photosynthesis, there would be no food in the world.

Plants obtain water and minerals from their roots. Leaves provide organic plant nutrition. Unlike roots, they are not in the soil, but in the air, therefore they carry out not soil, but air nutrition.

From the history of the study of air nutrition of plants

Knowledge about plant nutrition has been accumulating gradually.

About 350 years ago, the Dutch scientist Jan Helmont first set up an experiment on the study of plant nutrition. In a clay pot with soil, he grew a willow, adding only water there. The scientist carefully weighed the fallen leaves. Five years later, the mass of willow, together with fallen leaves, increased by 74.5 kg, and the mass of soil decreased by only 57 g. Based on this, Helmont came to the conclusion that all substances in the plant are formed not from soil, but from water. The opinion that the plant increases in size only due to water persisted until the end of the 18th century.

In 1771, the English chemist Joseph Priestley studied carbon dioxide, or "spoiled air" as he called it, and made a remarkable discovery. If you light a candle and cover it with a glass cap, then, after burning a little, it will go out.

A mouse under such a cap begins to suffocate. However, if a mint branch is placed under the cap along with the mouse, then the mouse does not suffocate and continues to live. This means that plants "correct" the air spoiled by the breath of animals, that is, they turn carbon dioxide into oxygen.

In 1862, the German botanist Julius Sachs proved through experiments that green plants not only release oxygen, but also create organic substances that serve as food for all other organisms.

Photosynthesis

The main difference between green plants and other living organisms is the presence in their cells of chloroplasts containing chlorophyll. Chlorophyll has the ability to capture the sun's rays, the energy of which is necessary to create organic substances. The process of formation of organic matter from carbon dioxide and water with the help of solar energy is called photosynthesis (Greek: pholos light). In the process of photosynthesis, not only organic substances are formed - sugars, but also oxygen is released.

Schematically, the process of photosynthesis can be depicted as follows:

Water is absorbed by the roots and moves through the conducting system of the roots and stem to the leaves. Carbon dioxide is a constituent of air. It enters the leaves through open stomata. The structure of the leaf contributes to the absorption of carbon dioxide: the flat surface of the leaf blades, which increases the area of ​​contact with air, and the presence of a large number of stomata in the skin.

Sugars formed as a result of photosynthesis are converted into starch. Starch is an organic substance that does not dissolve in water. Who is easy to detect with an iodine solution.

Evidence of starch formation in leaves exposed to light

Let us prove that in the green leaves of plants, starch is formed from carbon dioxide and water. To do this, consider the experiment, which at one time was staged by Julius Sachs.

A houseplant (geranium or primrose) is kept for two days in the dark so that all the starch is used up for vital processes. Then several leaves are covered on both sides with black paper so that only part of them is covered. During the day, the plant is exposed to light, and at night it is additionally illuminated with a table lamp.

After a day, the studied leaves are cut off. To find out in which part of the leaf starch has formed, the leaves are boiled in will (so that the starch grains swell), and then kept in hot alcohol (the chlorophyll dissolves and the leaf becomes discolored). Then the leaves are washed in water and treated with a weak solution of iodine. Tc parts of the leaves that were in the light acquire a blue color from the action of iodine. This means that the starch was formed in the cells of the illuminated part of the leaf. Therefore, photosynthesis occurs only in the presence of light.

Evidence for the need for carbon dioxide for photosynthesis

To prove that carbon dioxide is necessary for the formation of starch in the leaves, the houseplant is also previously kept in the dark. Then one of the leaves is placed in a flask with a small amount of lime water. The flask is closed with a cotton swab. The plant is exposed. Carbon dioxide is absorbed by lime water, so it will not be in the flask. The leaf is cut off, and, just as in the previous experiment, it is examined for the presence of starch. It is aged in hot water and alcohol, treated with iodine solution. However, in this case, the result of the experiment will be different: the sheet does not turn blue, because. it does not contain starch. Therefore, for the formation of starch, in addition to light and water, carbon dioxide is needed.

Thus, we answered the question of what kind of food the plant receives from the air. Experience has shown that it is carbon dioxide. It is necessary for the formation of organic matter.

Organisms that independently create organic substances to build their body are called autotrophs (Greek autos - self, trofe - food).

Evidence for the formation of oxygen during photosynthesis

To prove that during photosynthesis, plants release oxygen into the external environment, consider the experiment with the aquatic plant Elodea. Elodea shoots are lowered into a vessel with water and covered with a funnel from above. Place a test tube filled with water at the end of the funnel. The plant is exposed to light for two to three days. Elodea exudes gas bubbles when exposed to light. They accumulate at the top of the tube, displacing water. In order to find out what kind of gas it is, the test tube is carefully removed and a smoldering splinter is introduced into it. The torch flares up brightly. This means that oxygen has accumulated in the flask, supporting combustion.

Space role of plants

Plants containing chlorophyll are able to absorb solar energy. Therefore, K.A. Timiryazev called their role on Earth cosmic. Part of the solar energy stored in organic matter can be stored for a long time. Coal, peat, oil are formed by substances that were created by green plants in ancient geological times and absorbed the energy of the Sun. By burning natural combustible materials, a person releases the energy stored millions of years ago by green plants.

Photosynthesis (Tests)

1. Organisms that form organic substances only from organic ones:

1.heterotrophs

2. autotrophs

3.chemotrophs

4. mixotrophs

2. In the light phase of photosynthesis, the following occurs:

1.formation of ATP

2.formation of glucose

3.carbon dioxide release

4.formation of carbohydrates

3. During photosynthesis, oxygen is formed, which is released in the process:

1.Protein biosynthesis

2.photolysis

3.excitation of the chlorophyll molecule

4.Compound carbon dioxide and water

4. As a result of photosynthesis, light energy is converted into:

1. thermal energy

2.Chemical energy of inorganic compounds

3. electrical energy thermal energy

4.chemical energy of organic compounds

5. Respiration in anaerobes in living organisms proceeds in the process:

1.oxygen oxidation

2.photosynthesis

3.fermentation

4.Chemosynthesis

6. The end products of carbohydrate oxidation in the cell are:

1.ADP and water

2.ammonia and carbon dioxide

3.water and carbon dioxide

4.ammonia, carbon dioxide and water

7. At the preparatory stage of the breakdown of carbohydrates, hydrolysis occurs:

1. cellulose to glucose

2. proteins to amino acids

3.DNA to nucleotides

4.fats to glycerol and carboxylic acids

8. Enzymes provide oxygen oxidation:

1.Digestive tract and lysosomes

2. cytoplasm

3.mitochondria

4.plastid

9. During glycolysis, 3 mol of glucose is stored in the form of ATP:

10. Two moles of glucose underwent complete oxidation in an animal cell, while carbon dioxide was released:

11. In the process of chemosynthesis, organisms convert the energy of oxidation:

1.sulfur compounds

2.organic compounds

3.starch

12. One gene corresponds to information about the molecule:

1.amino acids

2.starch

4.nucleotide

13. The genetic code consists of three nucleotides, which means it:

1. specific

2. redundant

3.universal

4.triplet

14. In the genetic code, one amino acid corresponds to 2-6 triplets, this manifests itself:

1.continuity

2. redundancy

3.versatility

4.specificity

15. If the nucleotide composition of DNA is ATT-CHC-TAT, then the nucleotide composition of i-RNA:
1.TAA-CHTs-UTA

2.UAA-GCG-AUA

3.UAA-CHC-AUA

4.UAA-CHC-ATA

16. Protein synthesis does not occur on own ribosomes in:

1.tobacco mosaic virus

2. Drosophila

3.ant

4.Vibrio cholerae

17. Antibiotic:

1. is a protective blood protein

2.synthesizes a new protein in the body

3.is a weakened pathogen

4.inhibits protein synthesis of the pathogen

18. The section of the DNA molecule where replication occurs has 30,000 nucleotides (both strands). For replication you will need:

19. How many different amino acids can one t-RNA transport:

1.always one

2.always two

3.always three

4. Some may carry one, some may carry several.

20. The DNA region from which transcription occurs contains 153 nucleotides; a polypeptide is encoded in this region from:

1.153 amino acids

2.51 amino acids

3.49 amino acids

4.459 amino acids

21. During photosynthesis, oxygen is formed as a result of

1. photosynthesis water

2.​ decomposition of carbon gas

3. reduction of carbon dioxide to glucose

4. ATP synthesis

During the process of photosynthesis,

1. synthesis of carbohydrates and release of oxygen

2. Evaporation of water and absorption of oxygen

3. gas exchange and lipid synthesis

4. carbon dioxide release and protein synthesis

23. In the light phase of photosynthesis, the energy of sunlight is used to synthesize molecules

1. lipids

2. proteins

3. nucleic acid

24. Under the influence of the energy of sunlight, the electron rises to a higher energy level in the molecule

1. squirrel

2. glucose

3. chlorophyll

4. protein biosynthesis

25. A plant cell, like an animal cell, receives energy in the process. .

1. Oxidation of organic substances

2. protein biosynthesis

3. lipid synthesis

4. Nucleic acid synthesis

Photosynthesis takes place in the chloroplasts of plant cells. Chloroplasts contain the pigment chlorophyll, which is involved in the process of photosynthesis and gives plants their green color. It follows that photosynthesis occurs only in the green parts of plants.

Photosynthesis is the process of forming organic matter from inorganic matter. In particular, glucose is an organic substance, and water and carbon dioxide are inorganic.

Sunlight is also essential for photosynthesis to take place. The energy of light is stored in the chemical bonds of organic matter. This is the main point of photosynthesis: to bind energy, which will later be used to maintain the life of a plant or animals that will eat this plant. Organic matter is only a form, a way to store solar energy.

When photosynthesis proceeds in cells, various reactions take place in chloroplasts and on their membranes.

Not all of them need light. Therefore, there are two phases of photosynthesis: light and dark. The dark phase does not require light and can occur at night.

Carbon dioxide enters the cells from the air through the surface of the plant. Water flows from the roots down the stem.

As a result of the process of photosynthesis, not only organic matter is formed, but also oxygen. Oxygen is released into the air through the surface of the plant.

The glucose formed as a result of photosynthesis is transferred to other cells, turns into starch (is stored), and is used for life processes.

The main organ in which photosynthesis takes place in most plants is the leaf. It is in the leaves that there are many photosynthetic cells that make up the photosynthetic tissue.

Since sunlight is important for photosynthesis, leaves usually have a large surface area. In other words, they are flat and thin. In order for the light to reach all the leaves, in plants they are arranged so that they almost do not obscure each other.

So, for the process of photosynthesis to take place, carbon dioxide, water and light. The products of photosynthesis are organic matter (glucose) and oxygen. Photosynthesis takes place in chloroplasts, which are most found in leaves.

In plants (mainly in their leaves), photosynthesis takes place in the light. This is a process in which the organic substance glucose (a type of sugar) is formed from carbon dioxide and water. Further, glucose in the cells is converted into a more complex substance, starch. Both glucose and starch are carbohydrates.

In the process of photosynthesis, not only organic matter is produced, but oxygen is also released as a by-product.

Carbon dioxide and water are inorganic substances, while glucose and starch are organic.

Therefore, it is often said that photosynthesis is the process of formation of organic substances from inorganic substances in the light. Only plants, some single-celled eukaryotes, and some bacteria are capable of photosynthesis. There is no such process in the cells of animals and fungi, so they are forced to absorb organic substances from the environment. In this regard, plants are called autotrophs, and animals and fungi are called heterotrophs.

The process of photosynthesis in plants takes place in chloroplasts, which contain the green pigment chlorophyll.

So, for photosynthesis to take place, you need:

chlorophyll,

carbon dioxide.

The process of photosynthesis produces:

organic matter,

oxygen.

Plants are adapted to capture light. In many herbaceous plants, the leaves are collected in the so-called basal rosette, when the leaves do not shade each other. Trees are characterized by leaf mosaic, in which the leaves grow in such a way as to obscure each other as little as possible. In plants, leaf blades can turn towards the light due to the bending of the leaf petioles. With all this, there are shade-loving plants that can only grow in the shade.

Waterfor photosynthesisarrivesinto the leavesfrom the rootsalong the stem. Therefore, it is important that the plant receives enough moisture. With a lack of water and certain minerals, the process of photosynthesis is inhibited.

Carbon dioxidetaken for photosynthesisdirectlyout of thin airleaves. Oxygen, which is produced by the plant during photosynthesis, on the contrary, is released into the air. Gas exchange is facilitated by intercellular spaces (gaps between cells).

The organic substances formed in the process of photosynthesis are partly used in the leaves themselves, but mainly flow into all other organs and turn into other organic substances, are used in energy metabolism, and are converted into reserve nutrients.

Photosynthesis

Photosynthesis- the process of synthesis of organic substances due to the energy of light. Organisms that are capable of synthesizing organic substances from inorganic compounds are called autotrophic. Photosynthesis is characteristic only of cells of autotrophic organisms. Heterotrophic organisms are not able to synthesize organic substances from inorganic compounds.
The cells of green plants and some bacteria have special structures and complexes of chemicals that allow them to capture the energy of sunlight.

The role of chloroplasts in photosynthesis

In plant cells there are microscopic formations - chloroplasts. These are organelles in which energy and light are absorbed and converted into the energy of ATP and other molecules - energy carriers. The grains of chloroplasts contain chlorophyll, a complex organic substance. Chlorophyll captures the energy of light for use in the biosynthesis of glucose and other organic substances. Enzymes necessary for the synthesis of glucose are also located in chloroplasts.

Light phase of photosynthesis

A quantum of red light absorbed by chlorophyll puts an electron into an excited state. An electron excited by light acquires a large supply of energy, as a result of which it moves to a higher energy level. An electron excited by light can be compared to a stone raised to a height, which also acquires potential energy. He loses her by falling from a height. The excited electron, as if in steps, moves along the chain of complex organic compounds embedded in the chloroplast. Moving from one stage to another, the electron loses energy, which is used for the synthesis of ATP. The electron that wasted energy returns to chlorophyll. A new portion of light energy again excites the chlorophyll electron. It again follows the same path, spending energy on the formation of ATP molecules.
Hydrogen ions and electrons, necessary for the reduction of energy carrier molecules, are formed during the splitting of water molecules. The breakdown of water molecules in chloroplasts is carried out by a special protein under the influence of light. This process is called photolysis of water.
Thus, the energy of sunlight is directly used by the plant cell for:
1. excitation of chlorophyll electrons, the energy of which is further spent on the formation of ATP and other energy carrier molecules;
2. photolysis of water, supplying hydrogen ions and electrons to the light phase of photosynthesis.
In this case, oxygen is released as a by-product of photolysis reactions.

The stage during which, due to the energy of light, energy-rich compounds are formed - ATP and energy carrier molecules, called light phase of photosynthesis.

Dark phase of photosynthesis

Chloroplasts contain five-carbon sugars, one of which is ribulose diphosphate, is a carbon dioxide acceptor. A special enzyme binds five-carbon sugar with carbon dioxide in the air. In this case, compounds are formed that, due to the energy of ATP and other energy carrier molecules, are reduced to a six-carbon glucose molecule.

Thus, the light energy converted during the light phase into the energy of ATP and other energy carrier molecules is used to synthesize glucose.

These processes can take place in the dark.
It was possible to isolate chloroplasts from plant cells, which carried out photosynthesis in a test tube under the action of light - they formed new glucose molecules, while absorbing carbon dioxide. If the illumination of chloroplasts was stopped, then the synthesis of glucose was also suspended. However, if ATP and reduced energy carrier molecules were added to chloroplasts, then glucose synthesis resumed and could proceed in the dark. This means that light is really needed only for the synthesis of ATP and the charging of energy carrier molecules. Absorption of carbon dioxide and the formation of glucose in plants called dark phase of photosynthesis because she can walk in the dark.
Intense lighting, increased carbon dioxide in the air lead to an increase in the activity of photosynthesis.

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