Test for preparation for the Unified State Exam - "photosynthesis". Sequence of photosynthesis processes in green plants (in chronological order) Factors influencing the rate of photosynthesis

Every living thing on the planet needs food or energy to survive. Some organisms feed on other creatures, while others can produce their own nutrients. They produce their own food, glucose, in a process called photosynthesis.

Photosynthesis and respiration are interconnected. The result of photosynthesis is glucose, which is stored as chemical energy in. This stored chemical energy results from the conversion of inorganic carbon (carbon dioxide) to organic carbon. The process of breathing releases stored chemical energy.

In addition to the products they produce, plants also need carbon, hydrogen and oxygen to survive. Water absorbed from the soil provides hydrogen and oxygen. During photosynthesis, carbon and water are used to synthesize food. Plants also need nitrates to make amino acids (an amino acid is an ingredient for making protein). In addition to this, they need magnesium to produce chlorophyll.

The note: Living things that depend on other foods are called . Herbivores such as cows and plants that eat insects are examples of heterotrophs. Living things that produce their own food are called. Green plants and algae are examples of autotrophs.

In this article you will learn more about how photosynthesis occurs in plants and the conditions necessary for this process.

Definition of photosynthesis

Photosynthesis is the chemical process by which plants, some algae, produce glucose and oxygen from carbon dioxide and water, using only light as an energy source.

This process is extremely important for life on Earth because it releases oxygen, on which all life depends.

Why do plants need glucose (food)?

Like humans and other living things, plants also require nutrition to survive. The importance of glucose for plants is as follows:

Glucose produced by photosynthesis is used during respiration to release energy that the plant needs for other vital processes.
Plant cells also convert some of the glucose into starch, which is used as needed. For this reason, dead plants are used as biomass because they store chemical energy.
Glucose is also needed to make other chemicals such as proteins, fats and plant sugars needed to support growth and other important processes.

Phases of photosynthesis

The process of photosynthesis is divided into two phases: light and dark.

Light phase of photosynthesis

As the name suggests, light phases require sunlight. In light-dependent reactions, energy from sunlight is absorbed by chlorophyll and converted into stored chemical energy in the form of the electron carrier molecule NADPH (nicotinamide adenine dinucleotide phosphate) and the energy molecule ATP (adenosine triphosphate). Light phases occur in thylakoid membranes within the chloroplast.

Dark phase of photosynthesis or Calvin cycle

In the dark phase or Calvin cycle, excited electrons from the light phase provide energy for the formation of carbohydrates from carbon dioxide molecules. The light-independent phases are sometimes called the Calvin cycle due to the cyclical nature of the process.

Although dark phases do not use light as a reactant (and, as a result, can occur during the day or night), they require the products of light-dependent reactions to function. Light-independent molecules depend on the energy carrier molecules ATP and NADPH to create new carbohydrate molecules. Once energy is transferred, the energy carrier molecules return to the light phases to produce more energetic electrons. In addition, several dark phase enzymes are activated by light.

Diagram of photosynthesis phases

The note: This means that the dark phases will not continue if the plants are deprived of light for too long, as they use the products of the light phases.

The structure of plant leaves

We cannot fully study photosynthesis without knowing more about the structure of the leaf. The leaf is adapted to play a vital role in the process of photosynthesis.

External structure of leaves

Square

One of the most important characteristics of plants is the large surface area of their leaves. Most green plants have wide, flat, and open leaves that are capable of capturing as much solar energy (sunlight) as is needed for photosynthesis.

Central vein and petiole

The central vein and petiole join together and form the base of the leaf. The petiole positions the leaf so that it receives as much light as possible.

Leaf blade

Simple leaves have one leaf blade, while complex leaves have several. The leaf blade is one of the most important components of the leaf, which is directly involved in the process of photosynthesis.

Veins

A network of veins in the leaves transports water from the stems to the leaves. The released glucose is also sent to other parts of the plant from the leaves through the veins. Additionally, these leaf parts support and keep the leaf blade flat for greater capture of sunlight. The arrangement of the veins (venation) depends on the type of plant.

Leaf base

The base of the leaf is its lowest part, which is articulated with the stem. Often, at the base of the leaf there are a pair of stipules.

Leaf edge

Depending on the type of plant, the edge of the leaf can have different shapes, including: entire, jagged, serrate, notched, crenate, etc.

Leaf tip

Like the edge of the leaf, the tip comes in various shapes, including: sharp, rounded, obtuse, elongated, drawn-out, etc.

Internal structure of leaves

Below is a close diagram of the internal structure of leaf tissues:

Cuticle

The cuticle acts as the main, protective layer on the surface of the plant. As a rule, it is thicker on the top of the leaf. The cuticle is covered with a wax-like substance that protects the plant from water.

Epidermis

The epidermis is a layer of cells that is the covering tissue of the leaf. Its main function is to protect the internal tissues of the leaf from dehydration, mechanical damage and infections. It also regulates the process of gas exchange and transpiration.

Mesophyll

Mesophyll is the main tissue of a plant. This is where the process of photosynthesis occurs. In most plants, the mesophyll is divided into two layers: the upper one is palisade and the lower one is spongy.

Defense cages

Guard cells are specialized cells in the epidermis of leaves that are used to control gas exchange. They perform a protective function for the stomata. Stomatal pores become large when water is freely available, otherwise the protective cells become sluggish.

Stoma

Photosynthesis depends on the penetration of carbon dioxide (CO2) from the air through the stomata into the mesophyll tissue. Oxygen (O2), produced as a by-product of photosynthesis, leaves the plant through the stomata. When the stomata are open, water is lost through evaporation and must be replaced through the transpiration stream by water absorbed by the roots. Plants are forced to balance the amount of CO2 absorbed from the air and the loss of water through the stomatal pores.

Conditions required for photosynthesis

The following are the conditions that plants need to carry out the process of photosynthesis:

Carbon dioxide. A colorless, odorless, natural gas found in the air and has the scientific name CO2. It is formed during the combustion of carbon and organic compounds, and also occurs during respiration.
Water. A clear, liquid chemical that is odorless and tasteless (under normal conditions).
Light. Although artificial light is also good for plants, natural sunlight generally provides better conditions for photosynthesis because it contains natural ultraviolet radiation, which has a positive effect on plants.
Chlorophyll. It is a green pigment found in plant leaves.
Nutrients and minerals. Chemicals and organic compounds that plant roots absorb from the soil.

What is produced as a result of photosynthesis?

Glucose;
Oxygen.

(Light energy is shown in parentheses because it is not matter)

The note: Plants obtain CO2 from the air through their leaves, and water from the soil through their roots. Light energy comes from the Sun. The resulting oxygen is released into the air from the leaves. The resulting glucose can be converted into other substances, such as starch, which is used as an energy store.

If factors that promote photosynthesis are absent or present in insufficient quantities, the plant can be negatively affected. For example, less light creates favorable conditions for insects that eat the leaves of the plant, and a lack of water slows it down.

Where does photosynthesis occur?

Photosynthesis occurs inside plant cells, in small plastids called chloroplasts. Chloroplasts (mostly found in the mesophyll layer) contain a green substance called chlorophyll. Below are other parts of the cell that work with the chloroplast to carry out photosynthesis.

Structure of a plant cell

Functions of plant cell parts

: provides structural and mechanical support, protects cells from, fixes and determines cell shape, controls the rate and direction of growth, and gives shape to plants.
: provides a platform for most enzyme-controlled chemical processes.
: acts as a barrier, controlling the movement of substances into and out of the cell.
: as described above, they contain chlorophyll, a green substance that absorbs light energy through the process of photosynthesis.
: a cavity within the cell cytoplasm that stores water.
: contains a genetic mark (DNA) that controls the activities of the cell.

Chlorophyll absorbs light energy needed for photosynthesis. It is important to note that not all color wavelengths of light are absorbed. Plants primarily absorb red and blue wavelengths - they do not absorb light in the green range.

Carbon dioxide during photosynthesis

Plants take in carbon dioxide from the air through their leaves. Carbon dioxide leaks through a small hole at the bottom of the leaf - the stomata.

The lower part of the leaf has loosely spaced cells to allow carbon dioxide to reach other cells in the leaves. This also allows the oxygen produced by photosynthesis to easily leave the leaf.

Carbon dioxide is present in the air we breathe in very low concentrations and is a necessary factor in the dark phase of photosynthesis.

Light during photosynthesis

The leaf usually has a large surface area so it can absorb a lot of light. Its upper surface is protected from water loss, disease and exposure to weather by a waxy layer (cuticle). The top of the sheet is where the light hits. This mesophyll layer is called palisade. It is adapted to absorb a large amount of light, because it contains many chloroplasts.

During light phases, the process of photosynthesis increases with more light. More chlorophyll molecules are ionized and more ATP and NADPH are generated if light photons are concentrated on a green leaf. Although light is extremely important in the photophases, it should be noted that excessive amounts can damage chlorophyll, and reduce the process of photosynthesis.

Light phases are not very dependent on temperature, water or carbon dioxide, although they are all needed to complete the process of photosynthesis.

Water during photosynthesis

Plants obtain the water they need for photosynthesis through their roots. They have root hairs that grow in the soil. Roots are characterized by a large surface area and thin walls, allowing water to pass through them easily.

The image shows plants and their cells with enough water (left) and lack of it (right).

The note: Root cells do not contain chloroplasts because they are usually in the dark and cannot photosynthesize.

If the plant does not absorb enough water, it wilts. Without water, the plant will not be able to photosynthesize quickly enough and may even die.

What is the importance of water for plants?

Provides dissolved minerals that support plant health;
Is a medium for transportation;
Maintains stability and uprightness;
Cools and saturates with moisture;
Makes it possible to carry out various chemical reactions in plant cells.

The importance of photosynthesis in nature

The biochemical process of photosynthesis uses energy from sunlight to convert water and carbon dioxide into oxygen and glucose. Glucose is used as building blocks in plants for tissue growth. Thus, photosynthesis is the method by which roots, stems, leaves, flowers and fruits are formed. Without the process of photosynthesis, plants will not be able to grow or reproduce.

Producers

Due to their photosynthetic ability, plants are known as producers and serve as the basis of almost every food chain on Earth. (Algae are the equivalent of plants in). All the food we eat comes from organisms that are photosynthetics. We eat these plants directly or eat animals such as cows or pigs that consume plant foods.

Base of the food chain

Within aquatic systems, plants and algae also form the basis of the food chain. Algae serve as food for, which, in turn, act as a source of nutrition for larger organisms. Without photosynthesis in aquatic environments, life would not be possible.

Carbon dioxide removal

Photosynthesis converts carbon dioxide into oxygen. During photosynthesis, carbon dioxide from the atmosphere enters the plant and is then released as oxygen. In today's world, where carbon dioxide levels are rising at alarming rates, any process that removes carbon dioxide from the atmosphere is environmentally important.

Nutrient cycling

Plants and other photosynthetic organisms play a vital role in nutrient cycling. Nitrogen in the air is fixed in plant tissue and becomes available for the creation of proteins. Micronutrients found in soil can also be incorporated into plant tissue and become available to herbivores further up the food chain.

Photosynthetic dependence

Photosynthesis depends on the intensity and quality of light. At the equator, where sunlight is plentiful all year round and water is not a limiting factor, plants have high growth rates and can become quite large. Conversely, photosynthesis occurs less frequently in the deeper parts of the ocean because light does not penetrate these layers, resulting in a more barren ecosystem.

All living organisms living on Earth are open systems that depend on the supply of matter and energy from the outside. The process of consuming matter and energy is called food . Chemicals are necessary to build the body, energy is necessary to carry out life processes. There are two types of nutrition of living organisms: autotrophic and heterotrophic, and three groups of organisms according to the type of nutrition: autotrophs, heterotrophs and mixotrophs.

Classification of living organisms by type of nutrition

Type	Characteristic	Organisms
Autotrophs	Organisms that use carbon dioxide as a carbon source. In other words, these are organisms capable of creating organic substances from inorganic ones - carbon dioxide, water, mineral salts	Plants and some bacteria
Heterotrophs	Organisms that use organic compounds as a carbon source	Animals, fungi and most bacteria
Mixotrophs	Organisms with a mixed type of nutrition, which, depending on living conditions, can both synthesize organic substances from inorganic ones and feed on ready-made organic compounds	Insectivorous plants, representatives of the department of euglena algae, etc.

Depending on the source of energy, autotrophs are divided into photoautotrophs and chemoautotrophs.

Classification of autotrophs depending on the energy source

According to the method of obtaining food, heterotrophs are divided into phagotrophs (holozoans) and osmotrophs.

Classification of heterotrophs according to the method of obtaining food

According to the state of the food source, heterotrophs are divided into biotrophs and saprotrophs.

Metabolism- the totality of all chemical reactions occurring in a living organism. The importance of metabolism is to create the substances necessary for the body and provide it with energy.

Components of metabolism

The processes of plastic and energy metabolism are inextricably linked. All synthetic (anabolic) processes require energy supplied through dissimilation reactions. The breakdown reactions themselves (catabolism) occur only with the participation of enzymes synthesized during the assimilation process.

The role of ATP in metabolism

The energy released during the breakdown of organic matter is not immediately used by the cell, but is stored in the form of high-energy compounds, usually in the form of adenosine triphosphate (ATP). By its chemical nature, ATP is a mononucleotide.

ATP (adenosine triphosphoric acid)- a mononucleotide consisting of adenine, ribose and three phosphoric acid residues, interconnected by high-energy bonds.

These bonds store energy, which is released when they are broken:
ATP + H 2 O → ADP + H 3 PO 4 + Q 1
ADP + H 2 O → AMP + H 3 PO 4 + Q 2
AMP + H 2 O → adenine + ribose + H 3 PO 4 + Q 3,
where ATP is adenosine triphosphoric acid; ADP - adenosine diphosphoric acid; AMP - adenosine monophosphoric acid; Q 1 = Q 2 = 30.6 kJ; Q 3 = 13.8 kJ.
The supply of ATP in the cell is limited and is replenished through the process of phosphorylation. Phosphorylation- addition of a phosphoric acid residue to ADP (ADP + P → ATP). It occurs at varying rates during respiration, fermentation and photosynthesis. ATP is renewed extremely quickly (in humans, the lifespan of one ATP molecule is less than 1 minute).
The energy accumulated in ATP molecules is used by the body in anabolic reactions (biosynthesis reactions). The ATP molecule is a universal storer and carrier of energy for all living beings.

Energy exchange

The energy necessary for life is obtained by most organisms as a result of oxidation processes of organic substances, that is, as a result of catabolic reactions. The most important compound that acts as fuel is glucose.
In relation to free oxygen, organisms are divided into three groups.

Classification of organisms in relation to free oxygen

In obligate aerobes and facultative anaerobes, in the presence of oxygen, catabolism occurs in three stages: preparatory, oxygen-free and oxygen. As a result, organic substances break down into inorganic compounds. In obligate anaerobes and facultative anaerobes, when there is a lack of oxygen, catabolism occurs in the first two stages: preparatory and oxygen-free. As a result, intermediate organic compounds are formed, still rich in energy.

Stages of catabolism

1. The first stage is preparatory- consists of the enzymatic breakdown of complex organic compounds into simpler ones. Proteins are broken down into amino acids, fats into glycerol and fatty acids, polysaccharides into monosaccharides, nucleic acids into nucleotides. In multicellular organisms, this occurs in the gastrointestinal tract; in unicellular organisms, in lysosomes under the influence of hydrolytic enzymes. The energy released in this process is dissipated in the form of heat. The resulting organic compounds either undergo further oxidation or are used by the cell to synthesize its own organic compounds.
2. Second stage - incomplete oxidation (oxygen-free)- consists in the further breakdown of organic substances, carried out in the cytoplasm of the cell without the participation of oxygen. The main source of energy in the cell is glucose. The oxygen-free, incomplete oxidation of glucose is called glycolysis. As a result of glycolysis of one glucose molecule, two molecules of pyruvic acid (PVA, pyruvate) CH 3 COCOOH, ATP and water are formed, as well as hydrogen atoms, which are bound by the NAD + carrier molecule and stored in the form of NADH.
The total formula of glycolysis is as follows:
C 6 H 12 O 6 + 2H 3 PO 4 + 2ADP + 2NAD+ → 2C 3 H 4 O 3 + 2H 2 O + 2ATP + 2NAD N.
Further in the absence of oxygen in the environment Glycolysis products (PVC and NADH) are processed either into ethyl alcohol - alcoholic fermentation(in yeast and plant cells when there is a lack of oxygen)
CH 3 COCOOH → CO 2 + CH 3 COH
CH 3 SON + 2NAD H → C 2 H 5 OH + 2NAD + ,
or into lactic acid - lactic acid fermentation (in animal cells with a lack of oxygen)
CH 3 COCOOH + 2NAD H → C 3 H 6 O 3 + 2NAD + .
In the presence of oxygen in the environment the products of glycolysis undergo further breakdown to final products.
3. The third stage is complete oxidation (respiration)- consists of the oxidation of PVC to carbon dioxide and water, carried out in mitochondria with the obligatory participation of oxygen.
It consists of three stages:
A) formation of acetyl coenzyme A;
B) oxidation of acetyl coenzyme A in the Krebs cycle;
B) oxidative phosphorylation in the electron transport chain.

A. At the first stage, PVC is transferred from the cytoplasm to mitochondria, where it interacts with matrix enzymes and forms 1) carbon dioxide, which is removed from the cell; 2) hydrogen atoms, which are delivered by carrier molecules to the inner membrane of the mitochondrion; 3) acetyl coenzyme A (acetyl-CoA).
B. At the second stage, acetyl coenzyme A is oxidized in the Krebs cycle. The Krebs cycle (tricarboxylic acid cycle, citric acid cycle) is a chain of sequential reactions during which one molecule of acetyl-CoA produces 1) two molecules of carbon dioxide, 2) an ATP molecule and 3) four pairs of hydrogen atoms transferred to the molecules - transporters - NAD and FAD. Thus, as a result of glycolysis and the Krebs cycle, the glucose molecule is split into CO 2, and the energy released in this case is spent on the synthesis of 4 ATP and accumulates in 10 NADH and 4 FADH 2.
B. In the third stage, hydrogen atoms with NADH and FADH 2 are oxidized by molecular oxygen O 2 to form water. One NADH is capable of forming 3 ATP, and one FADH is capable of forming 2 –2 ATP. Thus, the energy released in this case is stored in the form of another 34 ATP.
This process proceeds as follows. Hydrogen atoms are concentrated near the outside of the inner mitochondrial membrane. They lose electrons, which are transferred through a chain of carrier molecules (cytochromes) of the electron transport chain (ETC) to the inner side of the inner membrane, where they combine with oxygen molecules:
O 2 + e - → O 2 - .
As a result of the activity of enzymes in the electron transport chain, the inner mitochondrial membrane is charged negatively from the inside (due to O 2 -), and positively charged from the outside (due to H +), so that a potential difference is created between its surfaces. Molecules of the enzyme ATP synthetase, which have an ion channel, are built into the inner membrane of mitochondria. When the potential difference across the membrane reaches a critical level, positively charged H + particles begin to be pushed through the ATPase channel by the force of the electric field and, once on the inner surface of the membrane, interact with oxygen, forming water:
1/2O 2 - +2H + → H 2 O.
The energy of hydrogen ions H + transported through the ion channel of the inner mitochondrial membrane is used to phosphorylate ADP into ATP:
ADP + P → ATP.
This formation of ATP in mitochondria with the participation of oxygen is called oxidative phosphorylation.
The overall equation for the breakdown of glucose during cellular respiration is:
C 6 H 12 O 6 + 6O 2 + 38H 3 PO 4 + 38ADP → 6CO 2 + 44H 2 O + 38ATP.
Thus, during glycolysis, 2 ATP molecules are formed, during cellular respiration - another 36 ATP molecules, in total, with complete oxidation of glucose - 38 ATP molecules.

Plastic exchange

Plastic metabolism, or assimilation, is a set of reactions that ensure the synthesis of complex organic compounds from simpler ones (photosynthesis, chemosynthesis, protein biosynthesis, etc.).
Heterotrophic organisms build their own organic matter from organic food components. Heterotrophic assimilation is essentially reduced to the rearrangement of molecules:
organic food substances (proteins, fats, carbohydrates) → simple organic molecules (amino acids, fatty acids, monosaccharides) → body macromolecules (proteins, fats, carbohydrates).
Autotrophic organisms are capable of completely independently synthesizing organic substances from inorganic molecules consumed from the external environment. In the process of photo- and chemosynthesis, simple organic compounds are formed, from which macromolecules are subsequently synthesized:
inorganic substances (CO 2, H 2 O) → simple organic molecules (amino acids, fatty acids, monosaccharides) → macromolecules of the body (proteins, fats, carbohydrates).

Photosynthesis

Photosynthesis- synthesis of organic compounds from inorganic ones using light energy.

The overall equation for photosynthesis is:

Photosynthesis occurs with the participation photosynthetic pigments, which have the unique property of converting the energy of sunlight into chemical bond energy in the form of ATP. Photosynthetic pigments are protein-like substances. The most important pigment is chlorophyll. In eukaryotes, photosynthetic pigments are embedded in the inner membrane of plastids; in prokaryotes, they are embedded in invaginations of the cytoplasmic membrane.
The structure of the chloroplast is very similar to the structure of the mitochondrion. The inner membrane of grana thylakoids contains photosynthetic pigments, as well as electron transport chain proteins and ATP synthetase enzyme molecules.
The process of photosynthesis consists of two phases: light and dark.
1. Light phase of photosynthesis occurs only in the light in the membrane of the grana thylakoids.
This includes the absorption of light quanta by chlorophyll, the formation of an ATP molecule and the photolysis of water.
Under the influence of a light quantum (hv), chlorophyll loses electrons, passing into an excited state:

These electrons are transferred by carriers to the outer surface of the thylakoid membrane, that is, facing the matrix, where they accumulate.
At the same time, photolysis of water occurs inside the thylakoids, that is, its decomposition under the influence of light:

The resulting electrons are transferred by carriers to chlorophyll molecules and reduce them. Chlorophyll molecules return to a stable state.
Hydrogen protons formed during photolysis of water accumulate inside the thylakoid, creating an H + reservoir. As a result, the inner surface of the thylakoid membrane is charged positively (due to H +), and the outer surface is charged negatively (due to e -). As oppositely charged particles accumulate on both sides of the membrane, the potential difference increases. When the potential difference reaches a critical value, the electric field force begins to push protons through the ATP synthetase channel. The energy released in this case is used to phosphorylate ADP molecules:
ADP + P → ATP.

The formation of ATP during photosynthesis under the influence of light energy is called photophosphorylation.
Hydrogen ions, once on the outer surface of the thylakoid membrane, meet electrons there and form atomic hydrogen, which binds to the hydrogen carrier molecule NADP (nicotinamide adenine dinucleotide phosphate):
2Н + + 4е – + NADP + → NADPH 2 .
Thus, during the light phase of photosynthesis, three processes occur: the formation of oxygen due to the decomposition of water, the synthesis of ATP and the formation of hydrogen atoms in the form of NADPH 2. Oxygen diffuses into the atmosphere, and ATP and NADPH 2 participate in the processes of the dark phase.
2. Dark phase of photosynthesis occurs in the chloroplast matrix both in the light and in the dark and represents a series of sequential transformations of CO 2 coming from the air in the Calvin cycle. Dark phase reactions are carried out using the energy of ATP. In the Calvin cycle, CO 2 combines with hydrogen from NADPH 2 to form glucose.
In the process of photosynthesis, in addition to monosaccharides (glucose, etc.), monomers of other organic compounds are synthesized - amino acids, glycerol and fatty acids. Thus, thanks to photosynthesis, plants provide themselves and all living things on Earth with the necessary organic substances and oxygen.

Comparative characteristics of photosynthesis and respiration of eukaryotes

Sign	Photosynthesis	Breath
Reaction equation	6CO 2 + 6H 2 O + light energy → C 6 H 12 O 6 + 6O 2	C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + energy (ATP)
Starting materials	Carbon dioxide, water
Reaction products	Organic matter, oxygen	Carbon dioxide, water
Importance in the cycle of substances	Synthesis of organic substances from inorganic substances	Decomposition of organic substances to inorganic ones
Conversion of energy	Conversion of light energy into the energy of chemical bonds of organic substances	Conversion of the energy of chemical bonds of organic substances into the energy of high-energy bonds of ATP
Key Stages	Light and dark phase (including Calvin cycle)	Incomplete oxidation (glycolysis) and complete oxidation (including Krebs cycle)
Location of the process	Chloroplasts	Hyaloplasm (incomplete oxidation) and mitochondria (complete oxidation)

Genetic information in all organisms is stored in the form of a specific sequence of DNA nucleotides (or RNA in RNA viruses). Prokaryotes contain genetic information in the form of a single DNA molecule. In eukaryotic cells, genetic material is distributed in several DNA molecules organized into chromosomes.
DNA consists of coding and non-coding regions. Coding regions code for RNA. Non-coding regions of DNA perform structural function, allowing sections of genetic material to be packaged in a particular way, or regulatory function by participating in the inclusion of genes that direct protein synthesis.
The coding regions of DNA are genes. Gene - a section of a DNA molecule encoding the synthesis of one mRNA (and, accordingly, a polypeptide), rRNA or tRNA.
The region of the chromosome where the gene is located is called locus . The set of genes in the cell nucleus is genotype , a set of genes of a haploid set of chromosomes - genome , a set of extranuclear DNA genes (mitochondria, plastids, cytoplasm) - plasmon .
The implementation of information recorded in genes through protein synthesis is called expression (manifestation) of genes. Genetic information is stored as a specific sequence of DNA nucleotides and is realized as a sequence of amino acids in a protein. RNA acts as intermediaries and carriers of information. That is, the implementation of genetic information occurs as follows:
DNA → RNA → protein.
This process is carried out in two stages:
1) transcription;
2) broadcast.

Transcription(from lat. transcriptio- rewriting) - synthesis of RNA using DNA as a template. As a result, mRNA, tRNA and rRNA are formed. The transcription process requires a lot of energy in the form of ATP and is carried out by the enzyme RNA polymerase.

At the same time, not the entire DNA molecule is transcribed, but only its individual segments. Such a segment ( transcripton) begins promoter- a section of DNA where RNA polymerase attaches and where transcription begins and ends terminator- a section of DNA containing a signal for the end of transcription. Transcripton is a gene from the point of view of molecular biology.
Transcription, like replication, is based on the ability of the nitrogenous bases of nucleotides to bind complementarily. During transcription, the double strand of DNA is broken, and RNA synthesis is carried out along one DNA strand.

During the process of transcription, the sequence of DNA nucleotides is copied onto the synthesized mRNA molecule, which acts as a template in the process of protein biosynthesis.
Prokaryotic genes consist only of coding nucleotide sequences.

Eukaryotic genes consist of alternating coding ( exons) and non-coding ( introns) plots.

After transcription, portions of the mRNA corresponding to the introns are removed during splicing, which is an integral part of processing.

Processing- the process of formation of mature mRNA from its precursor pre-mRNA. It includes two main events. 1. Attaching short sequences of nucleotides to the ends of the mRNA, indicating the start and end of translation. 2. Splicing- removal of uninformative mRNA sequences corresponding to DNA introns. As a result of splicing, the molecular weight of mRNA decreases by 10 times.
Broadcast(from lat. translation- translation) - synthesis of a polypeptide chain using mRNA as a template.

All three types of RNA are involved in translation: mRNA is the information matrix; tRNAs deliver amino acids and recognize codons; rRNA together with proteins form ribosomes, which hold mRNA, tRNA and protein and carry out the synthesis of the polypeptide chain.

Broadcast stages

Stage	Characteristic
Initiation	Assembly of the complex involved in the synthesis of the polypeptide chain. The small ribosomal subunit binds to the initiator met-t RNA, and then with m rn k, after which the formation of a whole ribosome occurs, consisting of small and large subparticles.
Elongation	Elongation of the polypeptide chain. The ribosome moves along the RNA, which is accompanied by multiple repetitions of the cycle of adding the next amino acid to the growing polypeptide chain.
Termination	Completion of the synthesis of the polypeptide molecule. The ribosome reaches one of the three stop codons m RNA, and since t does not exist RNA with anticodons complementary to stop codons, the synthesis of the polypeptide chain stops. It is released and separated from the ribosome. Ribosomal subparticles dissociate, separate from mRNA and can take part in the synthesis of the next polypeptide chain.

Template synthesis reactions

self-duplication of DNA (replication);
formation of mRNA, tRNA and rRNA on a DNA molecule (transcription);
protein biosynthesis into mRNA (translation).

What all these reactions have in common is that a DNA molecule in one case or an mRNA molecule in another acts as a matrix on which identical molecules are formed. Matrix synthesis reactions are the basis for the ability of living organisms to reproduce their own kind.
Regulation of gene expression. The body of a multicellular organism is made up of a variety of cell types. They differ in structure and function, that is, they are differentiated. The differences are manifested in the fact that in addition to the proteins necessary for any cell of the body, cells of each type also synthesize specialized proteins: keratin is formed in the epidermis, hemoglobin is formed in erythrocytes, etc. Cellular differentiation is caused by a change in the set of expressed genes and is not accompanied by any irreversible changes in the structure of the DNA sequences themselves.

Cell division

Chromosome set

Chromosome set - a set of chromosomes contained in the nucleus. Depending on the chromosome set, cells are somatic and sexual.

Somatic and germ cells

Cell cycle

Cell cycle (cell life cycle) - the existence of a cell from the moment of its origin as a result of the division of the mother cell until its own division or death. The duration of the cell cycle depends on the type of cell, its functional state and environmental conditions. The cell cycle includes a mitotic cycle and a resting period.

IN rest period (G 0) the cell performs its inherent functions and chooses its future fate - it dies or returns to the mitotic cycle. In continuously reproducing cells, the cell cycle coincides with the mitotic cycle, and there is no rest period.
Mitotic cycle consists of four periods: presynthetic (postmitotic) - G 1, synthetic - S, postsynthetic (premitotic) - G 2, mitosis - M. The first three periods are the preparation of the cell for division ( interphase), the fourth period is the division itself (mitosis).

Interphase - preparing the cell for division.

Interphase periods

Eukaryotic cell division

The basis for reproduction and individual development of organisms is cell division.
Eukaryotic cells have three ways of dividing:

amitosis (direct division),
mitosis (indirect division),
meiosis (reduction division).

Amitosis- a rare method of cell division, characteristic of aging or tumor cells. In amitosis, the nucleus is divided by constriction and uniform distribution of the hereditary material is not ensured. After amitosis, the cell is not able to enter into mitotic division.

Mitosis- a type of cell division in which daughter cells receive genetic material identical to that contained in the mother cell. As a result of mitosis, one diploid cell produces two diploid cells, genetically identical to the mother one.

Phases of mitosis

Phases	Number of chromosomes and chromatids	Processes
Prophase	2n4c	Chromosomes spiral, centrioles (in animal cells) diverge to the poles of the cell, the nuclear membrane disintegrates, nucleoli disappear, and a spindle begins to form.
Metaphase	2n4c	Chromosomes, consisting of two chromatids, are attached by their centromeres(primary constrictions) to the filaments of the spindle. Moreover, they are all located in the equatorial plane. This structure is called metaphase plate.
Anaphase	2n2c	Centromeres divide, and the filaments of the spindle stretch the chromatids separated from each other to opposite poles. Now separated chromatids are called daughter chromosomes.
Telophase	2n2c	Daughter chromosomes reach the cell poles, despiral, spindle filaments are destroyed, a nuclear membrane is formed around the chromosomes, and the nucleoli are restored. The two nuclei formed are genetically identical. This is followed by cytokinesis(cytoplasmic division), which results in the formation of two daughter cells. Organelles are distributed more or less evenly between them.

Biological significance of mitosis:

genetic stability is achieved;
the number of cells in the body increases;
the body grows;
Phenomena of regeneration and asexual reproduction are possible in some organisms.

Meiosis

Meiosis- a type of cell division accompanied by a reduction in the number of chromosomes. As a result of meiosis, one diploid cell produces four haploid cells, genetically different from the maternal one. During meiosis, two cell divisions occur (the first and second meiotic divisions), and the doubling of the number of chromosomes occurs only before the first division.

Phases of meiosis

Phases	Number of chromosomes and chromatids	Processes
Prophase I	2n4c	Processes similar to those of prophase of mitosis occur. In addition, homologous chromosomes, represented by two chromatids, come closer and “stick together” with each other. This process is called conjugation. In this case, an exchange of sections of homologous chromosomes occurs - crossing over(crossing of chromosomes), that is, the exchange of hereditary information. After conjugation, homologous chromosomes are separated from each other.
Metaphase I	2n4c	Processes similar to those of metaphase of mitosis occur.
Anaphase I	1n2c	Unlike anaphase of mitosis, centromeres do not divide and not one chromatid from each chromosome moves to the poles of the cell, but one chromosome, consisting of two chromatids and held together by a common centromere.
Telophase I	1n2c	Two cells with a haploid set are formed.
Interphase	1n2c	Short. DNA replication (doubling) does not occur and, therefore, diploidity is not restored.
Prophase II	1n2c
Metaphase II	1n2c	Similar to processes during mitosis.
Anaphase II	1n1c	Similar to processes during mitosis.
Telophase II	1n1c	Similar to processes during mitosis.

Biological significance of meiosis:

basis of sexual reproduction;
the basis of combinative variability.

Prokaryotic cell division

Prokaryotes do not have mitosis or meiosis. Bacteria reproduce asexually - cell division using constrictions or partitions, less often budding. These processes are preceded by the doubling of the circular DNA molecule.
In addition, bacteria are characterized by a sexual process - conjugation. During conjugation through a special channel formed between two cells, a DNA fragment of one cell is transferred to another cell, that is, the hereditary information contained in the DNA of both cells changes. Since the number of bacteria does not increase, for correctness the concept of “sexual process” is used, but not “sexual reproduction”.

ATP synthesis
effect of light on chlorophyll
consumption of ATP on the reactions of glucose synthesis from CO 2 and H 2 O
transfer of electrons by plastoquinones to the outer surface of thylakoids
photolysis of water
accumulation of H+ protons on the inner surface of thylakoids
proton slipping through the ATP synthetase channel
reduction of Mn by photolysis enzymes to oxidation state +7

Order of viral reproduction stages (in chronological order).

adsorption stage
stage of assembly (self-organization) of viral particles
injection stage
replication of viral nucleic acid molecules
lysis stage
synthesis of virus-specific proteins and enzymes

The sequence of chemical elements according to their concentration in the cell (descending order).

gold
carbon
potassium
iron
silver

The sequence of chemical elements in accordance with their concentration in the cell (ascending).

carbon
magnesium

A sequence reflecting the structure of the cell cytolemma from the outer to the inner layer (in chronological order).

hydrophobic zone of lipids
protein molecules
glycocalyx polysaccharides
hydrophilic zone of lipid molecules

A sequence reflecting the structure of the mitochondrion from the outer layer to the inner (in chronological order).

matrix
outer membrane
mushroom bodies
intermembrane space
inner membrane
fold of the inner membrane

Sequence of processes during pinocytosis (in chronological order).

detachment of the pinocytotic vesicle from the cytolemma
entry of external molecules to glycocalyx receptors
transportation of molecules attached from outside to areas of the cytoplasm
invagination of the cytolemma with attached molecules
bringing the edges of the invagination closer together and closing them

The sequence of links in the chain of energy flow in a heterotroph cell (ascending).

energy of sun
various forms of work
heterotrophs
autotrophs
organic matter

12. Sequence of reactions of the light phase of photosynthesis (in chronological order).

1. abstraction of an electron from a chlorophyll molecule and its transfer by a carrier molecule to the outer membrane of chloroplasts

2. illumination of chloroplasts by sunlight

3. excitation of a chlorophyll molecule under the action of a photon

4. the occurrence of a potential difference between the two surfaces of the chloroplast membrane due to the concentration of electrons and protons on them

5. decomposition of water molecules into oxygen and a positively charged proton

13. Sequence of stages of energy metabolism.

oxidation of pyruvic acid to carbon dioxide and water
synthesis of 36 ATP molecules
entry of organic substances into the cell
breakdown of glucose to pyruvic acid
splitting biopolymers into monomers
synthesis of two ATP molecules

14. Sequence of phenomena and processes occurring in the process of protein synthesis (in chronological order).

joining of two tRNA molecules with amino acids to mRNA
addition of an amino acid to tRNA
synthesis of mRNA on a DNA template
movement of mRNA from the nucleus to the ribosome
interaction of amino acids attached to mRNA, formation of a peptide bond
stringing ribosomes onto mRNA
delivery of amino acids to the ribosome

15. Sequence of DNA replication (in chronological order).

binding of destabilizing proteins to DNA strands
removal of RNA primer
destruction of hydrogen bonds between nitrogenous bases
completion of the 3' ends of linear DNA molecules
RNA primer formation
formation of daughter DNA strands

Sequence of stages of the cell life cycle (in chronological order).

synthetic period (S)
mitosis
presynthetic period(G 1)
premitotic period(G 2)

17. Sequence of phenomena and processes occurring in preparation for and during mitosis (in chronological order).

despiralization of chromosomes
attachment of chromosomes to spindle strands
doubling of cellular DNA
formation of interphase nuclei of daughter cells
chromosome spiralization
divergence of daughter chromatids to the cell poles

Sequence of processes in metaphase of mitosis (in chronological order).

completion of movement of chromosomes to the spindle
completion of the process of separation of sister chromatids from each other
alignment of chromosomes in the equatorial plane of the spindle
attachment of centriole kinetochores to the filaments of the mitotic apparatus
formation of a metaphase plate of chromosomes (the so-called mother star)

1) providing all living things with organic substances

2) splitting biopolymers into monomers

3) oxidation of organic substances to carbon dioxide and water

4) solar energy conversion

5) enriching the atmosphere with oxygen necessary for breathing

6) enrichment of soil with nitrogen salts

1) conversion of solar energy into ATP energy

2) formation of excited electrons of chlorophyll

3) carbon dioxide fixation

4) formation of starch

5) conversion of ATP energy into glucose energy

The source of hydrogen for the reduction of carbon dioxide during photosynthesis is

1) hydrochloric acid 2) carbonic acid 3) water 4) carbohydrate glucose

In the process of chemosynthesis, unlike photosynthesis,

1) organic substances are formed from inorganic ones

2) the energy of oxidation of inorganic substances is used

3) organic substances are broken down into inorganic ones

4) carbon dioxide is the source of carbon

Establish the sequence of processes occurring during photosynthesis.

1) excitation of chlorophyll electrons 2) ATP synthesis

3) CO2 fixation 4) absorption of light quanta by chlorophyll molecules

The light phase of photosynthesis uses energy from sunlight to synthesize molecules.

1) lipids 2) proteins 3) nucleic acids 4) ATP

When exposed to energy from sunlight, an electron rises to a higher energy level in the molecule

1) protein 2) glucose 3) chlorophyll 4) carbon dioxide

During the process of photosynthesis occurs

1) synthesis of carbohydrates and release of oxygen 2) evaporation of water and absorption of oxygen

3) gas exchange and lipid synthesis 4) release of carbon dioxide and protein synthesis

Red algae (purple algae) live at great depths. Despite this, photosynthesis occurs in their cells. Explain how photosynthesis occurs if the water column absorbs rays from the red-orange part of the spectrum.

In the dark phase of photosynthesis, in contrast to the light phase,

1) photolysis of water 2) reduction of carbon dioxide to glucose

3) synthesis of ATP molecules using the energy of sunlight 4) combination of hydrogen with the NADP+ transporter

5) use of the energy of ATP molecules for the synthesis of carbohydrates 6) formation of starch molecules from glucose

In a chlorophyll molecule, an electron moves to a higher energy level under the influence of energy

1) light quanta 2) AMP molecules 3) water photolysis 4) ATP molecules

Enzymes involved in the process of photosynthesis are embedded in membranes

1) mitochondria 2) endoplasmic reticulum 3) lysosomes 4) granules of chloroplasts

Atomic hydrogen is released during photosynthesis due to the splitting of molecules

1) water 2) glucose 3) fats 4) proteins

Establish a correspondence between the feature of the process and its type.

PROCESS FEATURE PROCESS TYPE

A) occurs in chloroplasts 1) photosynthesis

B) consists of light and dark phases 2) glycolysis

C) pyruvic acid is formed

D) occurs in the cytoplasm

D) the final product is glucose

E) breakdown of glucose

The process of photosynthesis occurs intensively in the leaves of plants. Does it occur in ripe and unripe fruits? Explain your answer.

In plant cells, unlike animal cells, there is

1) chemosynthesis 2) phagocytosis 3) photosynthesis 4) pinocytosis

The peculiarities of metabolism in plants compared to animals are that what happens in their cells

1) chemosynthesis 2) energy metabolism 3) photosynthesis 4) protein biosynthesis

Photosynthesis can occur in plant cells that contain

1) cell walls 2) chromosomes 3) chloroplasts 4) cytoplasm

Photolysis of water is initiated during photosynthesis by energy

1) solar 2) ATP 3) thermal 4) mechanical

Trace the path of hydrogen in the light and dark stages of photosynthesis from the moment of its formation to the synthesis of glucose.

The energy of the molecule's electrons is used to form ATP molecules during photosynthesis.

1) NADP+ 2) glucose 3) chlorophyll 4) water

Photosynthesis, unlike protein biosynthesis, occurs in cells

1) any organism 2) containing chloroplasts

Establish the correct sequence of photosynthesis processes.

1) stimulation of chlorophyll 2) synthesis of glucose

3) connection of electrons with NADP + and H + 4) fixation of carbon dioxide

5) photolysis of water

What process does not occur during the light phase of photosynthesis?

1) ATP synthesis 2) NADPH 2 synthesis 3) photolysis of water 4) glucose synthesis

Establish a correspondence between the characteristic and the life process of the plant to which it is attributed.

CHARACTERISTICS LIFE PROCESS

A) glucose is synthesized 1) photosynthesis

B) organic substances are oxidized 2) respiration

B) oxygen is released

D) carbon dioxide is formed

D) occurs in mitochondria

E) accompanied by energy absorption

Oxygen molecules during photosynthesis are formed due to the decomposition of molecules

1) glucose 2) water 3) ATP 4) carbon dioxide

How is the energy of sunlight converted in the light and dark phases of photosynthesis into the energy of chemical bonds of glucose? Explain your answer.

In the synthesis of what substance do hydrogen atoms participate in the dark phase of photosynthesis?

1) ATP 2) NADP 2H 3) glucose 4) water

During the process of photosynthesis, plants

1) provide themselves with organic substances

2) oxidize complex organic substances to simple ones

3) absorb oxygen and release carbon dioxide

4) consume the energy of organic substances

The transition of electrons to a higher energy level occurs in the light phase of photosynthesis in molecules

1) chlorophyll 2) water 3) carbon dioxide 4) glucose

- synthesis of organic substances from carbon dioxide and water with the obligatory use of light energy:

6CO 2 + 6H 2 O + Q light → C 6 H 12 O 6 + 6O 2.

In higher plants, the organ of photosynthesis is the leaf, and the organelles of photosynthesis are the chloroplasts (structure of chloroplasts - lecture No. 7). The membranes of chloroplast thylakoids contain photosynthetic pigments: chlorophylls and carotenoids. There are several different types of chlorophyll ( a, b, c, d), the main one is chlorophyll a. In the chlorophyll molecule, a porphyrin “head” with a magnesium atom in the center and a phytol “tail” can be distinguished. The porphyrin “head” is a flat structure, is hydrophilic and therefore lies on the surface of the membrane that faces the aqueous environment of the stroma. The phytol “tail” is hydrophobic and due to this retains the chlorophyll molecule in the membrane.

Chlorophylls absorb red and blue-violet light, reflect green light and therefore give plants their characteristic green color. Chlorophyll molecules in thylakoid membranes are organized into photosystems. Plants and blue-green algae have photosystem-1 and photosystem-2, while photosynthetic bacteria have photosystem-1. Only photosystem-2 can decompose water to release oxygen and take electrons from the hydrogen of water.

Photosynthesis is a complex multi-step process; photosynthesis reactions are divided into two groups: reactions light phase and reactions dark phase.

Light phase

This phase occurs only in the presence of light in thylakoid membranes with the participation of chlorophyll, electron transport proteins and the enzyme ATP synthetase. Under the influence of a quantum of light, chlorophyll electrons are excited, leave the molecule and enter the outer side of the thylakoid membrane, which ultimately becomes negatively charged. Oxidized chlorophyll molecules are reduced, taking electrons from water located in the intrathylakoid space. This leads to the breakdown or photolysis of water:

H 2 O + Q light → H + + OH - .

Hydroxyl ions give up their electrons, becoming reactive radicals.OH:

OH - → .OH + e - .

OH radicals combine to form water and free oxygen:

4NO. → 2H 2 O + O 2.

In this case, oxygen is removed to the external environment, and protons accumulate inside the thylakoid in the “proton reservoir”. As a result, the thylakoid membrane, on the one hand, is charged positively due to H +, and on the other, due to electrons, it is charged negatively. When the potential difference between the outer and inner sides of the thylakoid membrane reaches 200 mV, protons are pushed through the ATP synthetase channels and ADP is phosphorylated to ATP; Atomic hydrogen is used to restore the specific carrier NADP + (nicotinamide adenine dinucleotide phosphate) to NADPH 2:

2H + + 2e - + NADP → NADPH 2.

Thus, in the light phase, photolysis of water occurs, which is accompanied by three important processes: 1) ATP synthesis; 2) the formation of NADPH 2; 3) the formation of oxygen. Oxygen diffuses into the atmosphere, ATP and NADPH 2 are transported into the stroma of the chloroplast and participate in the processes of the dark phase.

1 - chloroplast stroma; 2 - grana thylakoid.

Dark phase

This phase occurs in the stroma of the chloroplast. Its reactions do not require light energy, so they occur not only in the light, but also in the dark. Dark phase reactions are a chain of successive transformations of carbon dioxide (coming from the air), leading to the formation of glucose and other organic substances.

The first reaction in this chain is the fixation of carbon dioxide; The carbon dioxide acceptor is a five-carbon sugar. ribulose biphosphate(RiBF); enzyme catalyzes the reaction Ribulose biphosphate carboxylase(RiBP carboxylase). As a result of carboxylation of ribulose bisphosphate, an unstable six-carbon compound is formed, which immediately breaks down into two molecules phosphoglyceric acid(FGK). A cycle of reactions then occurs in which phosphoglyceric acid is converted through a series of intermediates to glucose. These reactions use the energy of ATP and NADPH 2 formed in the light phase; The cycle of these reactions is called the “Calvin cycle”:

6CO 2 + 24H + + ATP → C 6 H 12 O 6 + 6H 2 O.

In addition to glucose, other monomers of complex organic compounds are formed during photosynthesis - amino acids, glycerol and fatty acids, nucleotides. Currently, there are two types of photosynthesis: C 3 - and C 4 photosynthesis.

C 3-photosynthesis

This is a type of photosynthesis in which the first product is three-carbon (C3) compounds. C 3 photosynthesis was discovered before C 4 photosynthesis (M. Calvin). It is C 3 photosynthesis that is described above, under the heading “Dark phase”. Characteristic features of C 3 photosynthesis: 1) the carbon dioxide acceptor is RiBP, 2) the carboxylation reaction of RiBP is catalyzed by RiBP carboxylase, 3) as a result of carboxylation of RiBP, a six-carbon compound is formed, which decomposes into two PGAs. FGK is restored to triose phosphates(TF). Some of the TF is used for the regeneration of RiBP, and some is converted into glucose.

1 - chloroplast; 2 - peroxisome; 3 - mitochondria.

This is a light-dependent absorption of oxygen and release of carbon dioxide. At the beginning of the last century, it was established that oxygen suppresses photosynthesis. As it turned out, for RiBP carboxylase the substrate can be not only carbon dioxide, but also oxygen:

O 2 + RiBP → phosphoglycolate (2C) + PGA (3C).

The enzyme is called RiBP oxygenase. Oxygen is a competitive inhibitor of carbon dioxide fixation. The phosphate group is split off and the phosphoglycolate becomes glycolate, which the plant must utilize. It enters peroxisomes, where it is oxidized to glycine. Glycine enters the mitochondria, where it is oxidized to serine, with the loss of already fixed carbon in the form of CO 2. As a result, two glycolate molecules (2C + 2C) are converted into one PGA (3C) and CO 2. Photorespiration leads to a decrease in the yield of C3 plants by 30-40% ( With 3 plants- plants characterized by C 3 photosynthesis).

C 4 photosynthesis is photosynthesis in which the first product is four-carbon (C 4) compounds. In 1965, it was found that in some plants (sugar cane, corn, sorghum, millet) the first products of photosynthesis are four-carbon acids. These plants were called With 4 plants. In 1966, Australian scientists Hatch and Slack showed that C4 plants have virtually no photorespiration and absorb carbon dioxide much more efficiently. The pathway of carbon transformations in C 4 plants began to be called by Hatch-Slack.

C 4 plants are characterized by a special anatomical structure of the leaf. All vascular bundles are surrounded by a double layer of cells: the outer layer is mesophyll cells, the inner layer is sheath cells. Carbon dioxide is fixed in the cytoplasm of mesophyll cells, the acceptor is phosphoenolpyruvate(PEP, 3C), as a result of carboxylation of PEP, oxaloacetate (4C) is formed. The process is catalyzed PEP carboxylase. Unlike RiBP carboxylase, PEP carboxylase has a greater affinity for CO 2 and, most importantly, does not interact with O 2 . Mesophyll chloroplasts have many grains where light phase reactions actively occur. Dark phase reactions occur in the chloroplasts of the sheath cells.

Oxaloacetate (4C) is converted to malate, which is transported through plasmodesmata into the sheath cells. Here it is decarboxylated and dehydrogenated to form pyruvate, CO 2 and NADPH 2 .

Pyruvate returns to the mesophyll cells and is regenerated using the energy of ATP in PEP. CO 2 is again fixed by RiBP carboxylase to form PGA. PEP regeneration requires ATP energy, so it requires almost twice as much energy as C 3 photosynthesis.

The meaning of photosynthesis

Thanks to photosynthesis, billions of tons of carbon dioxide are absorbed from the atmosphere every year and billions of tons of oxygen are released; photosynthesis is the main source of the formation of organic substances. Oxygen forms the ozone layer, which protects living organisms from short-wave ultraviolet radiation.

During photosynthesis, a green leaf uses only about 1% of the solar energy falling on it; productivity is about 1 g of organic matter per 1 m2 of surface per hour.

Chemosynthesis

The synthesis of organic compounds from carbon dioxide and water, carried out not due to the energy of light, but due to the energy of oxidation of inorganic substances, is called chemosynthesis. Chemosynthetic organisms include some types of bacteria.

Nitrifying bacteria ammonia is oxidized to nitrous and then to nitric acid (NH 3 → HNO 2 → HNO 3).

Iron bacteria convert ferrous iron into oxide iron (Fe 2+ → Fe 3+).

Sulfur bacteria oxidize hydrogen sulfide to sulfur or sulfuric acid (H 2 S + ½O 2 → S + H 2 O, H 2 S + 2O 2 → H 2 SO 4).

As a result of oxidation reactions of inorganic substances, energy is released, which is stored by bacteria in the form of high-energy ATP bonds. ATP is used for the synthesis of organic substances, which proceeds similarly to the reactions of the dark phase of photosynthesis.

Chemosynthetic bacteria contribute to the accumulation of minerals in the soil, improve soil fertility, promote wastewater treatment, etc.

Go to lectures No. 11“The concept of metabolism. Biosynthesis of proteins"

Go to lectures No. 13“Methods of division of eukaryotic cells: mitosis, meiosis, amitosis”