General equation of photosynthesis. The meaning of photosynthesis, its scale
Photosynthesis is the conversion of light energy into energy chemical bonds organic compounds.
Photosynthesis is characteristic of plants, including all algae, a number of prokaryotes, including cyanobacteria, and some unicellular eukaryotes.
In most cases, photosynthesis produces oxygen (O2) as a by-product. However, this is not always the case as there are several different pathways for photosynthesis. In the case of oxygen release, its source is water, from which hydrogen atoms are split off for the needs of photosynthesis.
Photosynthesis consists of many reactions in which various pigments, enzymes, coenzymes, etc. participate. The main pigments are chlorophylls, in addition to them, carotenoids and phycobilins.
In nature, two ways of plant photosynthesis are common: C 3 and C 4. Other organisms have their own specific reactions. What unites these different processes under the term “photosynthesis” is that in all of them, in total, the conversion of photon energy into a chemical bond occurs. For comparison: during chemosynthesis, the energy of the chemical bond of some compounds (inorganic) is converted into others - organic.
There are two phases of photosynthesis - light and dark. The first depends on the light radiation (hν), which is necessary for the reactions to proceed. The dark phase is light independent.
In plants, photosynthesis takes place in chloroplasts. As a result of all reactions, primary organic substances are formed, from which carbohydrates, amino acids, fatty acids, etc. are then synthesized. Usually, the total reaction of photosynthesis is written in relation to glucose - the most common product of photosynthesis:
6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2
The oxygen atoms included in the O 2 molecule are not taken from carbon dioxide, but from the water. Carbon dioxide is a source of carbon which is more important. Due to its binding, plants have the opportunity to synthesize organic matter.
Presented above chemical reaction There is generalized and total. It is far from the essence of the process. So glucose is not formed from six individual molecules of carbon dioxide. The binding of CO 2 occurs in one molecule, which first attaches to an already existing five-carbon sugar.
Prokaryotes have their own characteristics of photosynthesis. So in bacteria, the main pigment is bacteriochlorophyll, and oxygen is not released, since hydrogen is not taken from water, but often from hydrogen sulfide or other substances. In blue-green algae, the main pigment is chlorophyll, and oxygen is released during photosynthesis.
Light phase of photosynthesis
In the light phase of photosynthesis, ATP and NADP·H 2 are synthesized due to radiant energy. It happens on the thylakoids of chloroplasts, where pigments and enzymes form complex complexes for the functioning of electrochemical circuits, through which electrons and partly hydrogen protons are transferred.
The electrons end up at the coenzyme NADP, which, being negatively charged, attracts some of the protons and turns into NADP H 2 . Also, the accumulation of protons on one side of the thylakoid membrane and electrons on the other creates an electrochemical gradient, the potential of which is used by the ATP synthetase enzyme to synthesize ATP from ADP and phosphoric acid.
The main pigments of photosynthesis are various chlorophylls. Their molecules capture the radiation of certain, partly different spectra of light. In this case, some electrons of chlorophyll molecules move to a higher energy level. This is an unstable state, and, in theory, electrons, by means of the same radiation, should give the energy received from outside into space and return to the previous level. However, in photosynthetic cells, excited electrons are captured by acceptors and, with a gradual decrease in their energy, are transferred along the chain of carriers.
On thylakoid membranes, there are two types of photosystems that emit electrons when exposed to light. Photosystems are a complex complex of mostly chlorophyll pigments with a reaction center from which electrons are torn off. In a photosystem, sunlight catches a lot of molecules, but all the energy is collected in the reaction center.
The electrons of photosystem I, having passed through the chain of carriers, restore NADP.
The energy of the electrons detached from photosystem II is used to synthesize ATP. And the electrons of photosystem II fill the electron holes of photosystem I.
The holes of the second photosystem are filled with electrons formed as a result of water photolysis. Photolysis also occurs with the participation of light and consists in the decomposition of H 2 O into protons, electrons and oxygen. It is as a result of the photolysis of water that free oxygen is formed. Protons are involved in the creation electrochemical gradient and restoration of NADP. Electrons are received by the chlorophyll of photosystem II.
Approximate summary equation of the light phase of photosynthesis:
H 2 O + NADP + 2ADP + 2P → ½O 2 + NADP H 2 + 2ATP
Cyclic electron transport
The so-called non-cyclic light phase of photosynthesis. Is there some more cyclic electron transport when NADP reduction does not occur. In this case, electrons from photosystem I go to the carrier chain, where ATP is synthesized. That is, this electron transport chain receives electrons from photosystem I, not II. The first photosystem, as it were, implements a cycle: the emitted electrons return to it. On the way, they spend part of their energy on the synthesis of ATP.
Photophosphorylation and oxidative phosphorylation
The light phase of photosynthesis can be compared to the stage cellular respiration- oxidative phosphorylation, which occurs on the cristae of mitochondria. There, too, ATP synthesis occurs due to the transfer of electrons and protons along the carrier chain. However, in the case of photosynthesis, energy is stored in ATP not for the needs of the cell, but mainly for the needs of the dark phase of photosynthesis. And if during respiration organic substances serve as the initial source of energy, then during photosynthesis it is sunlight. The synthesis of ATP during photosynthesis is called photophosphorylation rather than oxidative phosphorylation.
Dark phase of photosynthesis
For the first time the dark phase of photosynthesis was studied in detail by Calvin, Benson, Bassem. The cycle of reactions discovered by them was later called the Calvin cycle, or C 3 -photosynthesis. In certain groups of plants, a modified photosynthesis pathway is observed - C 4, also called the Hatch-Slack cycle.
In the dark reactions of photosynthesis, CO 2 is fixed. The dark phase takes place in the stroma of the chloroplast.
Recovery of CO 2 occurs due to the energy of ATP and the reducing power of NADP·H 2 formed in light reactions. Without them, carbon fixation does not occur. Therefore, although the dark phase does not directly depend on light, it usually also proceeds in light.
Calvin cycle
The first reaction of the dark phase is the addition of CO 2 ( carboxylatione) to 1,5-ribulose biphosphate ( ribulose 1,5-diphosphate) – RiBF. The latter is a doubly phosphorylated ribose. This reaction is catalyzed by the enzyme ribulose-1,5-diphosphate carboxylase, also called rubisco.
As a result of carboxylation, an unstable six-carbon compound is formed, which, as a result of hydrolysis, decomposes into two three-carbon molecules phosphoglyceric acid (PGA) is the first product of photosynthesis. FHA is also called phosphoglycerate.
RiBP + CO 2 + H 2 O → 2FGK
FHA contains three carbon atoms, one of which is part of the acidic carboxyl group (-COOH):
FHA is converted into a three-carbon sugar (glyceraldehyde phosphate) triose phosphate (TF), which already includes an aldehyde group (-CHO):
FHA (3-acid) → TF (3-sugar)
This reaction consumes the energy of ATP and the reducing power of NADP · H 2 . TF is the first carbohydrate of photosynthesis.
Thereafter most of triose phosphate is used to regenerate ribulose bisphosphate (RiBP), which is again used to bind CO 2 . Regeneration involves a series of ATP-consuming reactions involving sugar phosphates with 3 to 7 carbon atoms.
It is in this cycle of RiBF that the Calvin cycle is concluded.
A smaller part of the TF formed in it leaves the Calvin cycle. In terms of 6 bound molecules of carbon dioxide, the yield is 2 molecules of triose phosphate. The total reaction of the cycle with input and output products:
6CO 2 + 6H 2 O → 2TF
At the same time, 6 RiBP molecules participate in the binding and 12 FHA molecules are formed, which are converted into 12 TF, of which 10 molecules remain in the cycle and are converted into 6 RiBP molecules. Since TF is a three-carbon sugar, and RiBP is a five-carbon one, in relation to carbon atoms we have: 10 * 3 = 6 * 5. The number of carbon atoms that provide the cycle does not change, all the necessary RiBP is regenerated. And six molecules of carbon dioxide included in the cycle are spent on the formation of two molecules of triose phosphate leaving the cycle.
The Calvin cycle, based on 6 bound CO 2 molecules, takes 18 ATP molecules and 12 NADP · H 2 molecules, which were synthesized in reactions of the light phase of photosynthesis.
The calculation is carried out for two triose phosphate molecules leaving the cycle, since the glucose molecule formed later includes 6 carbon atoms.
Triose phosphate (TF) is the end product of the Calvin cycle, but it can hardly be called the end product of photosynthesis, since it almost does not accumulate, but, reacting with other substances, turns into glucose, sucrose, starch, fats, fatty acids, amino acids. Except TF important role plays FGK. However, such reactions occur not only in photosynthetic organisms. In this sense, the dark phase of photosynthesis is the same as the Calvin cycle.
PHA is converted into a six-carbon sugar by stepwise enzymatic catalysis. fructose-6-phosphate, which turns into glucose. In plants, glucose can be polymerized into starch and cellulose. The synthesis of carbohydrates is similar to the reverse process of glycolysis.
photorespiration
Oxygen inhibits photosynthesis. The more O 2 in environment, the less efficient is the CO 2 binding process. The fact is that the enzyme ribulose bisphosphate carboxylase (rubisco) can react not only with carbon dioxide, but also with oxygen. In this case, the dark reactions are somewhat different.
Phosphoglycolate is phosphoglycolic acid. The phosphate group is immediately cleaved from it, and it turns into glycolic acid (glycolate). For its "utilization" oxygen is needed again. Therefore, the more oxygen in the atmosphere, the more it will stimulate photorespiration and the more oxygen the plant will need to get rid of the reaction products.
Photorespiration is the light-dependent consumption of oxygen and the release of carbon dioxide. That is, the exchange of gases occurs as during respiration, but takes place in chloroplasts and depends on light radiation. Photorespiration depends on light only because ribulose biphosphate is formed only during photosynthesis.
During photorespiration, carbon atoms are returned from glycolate to the Calvin cycle in the form of phosphoglyceric acid (phosphoglycerate).
2 Glycolate (C 2) → 2 Glyoxylate (C 2) → 2 Glycine (C 2) - CO 2 → Serine (C 3) → Hydroxypyruvate (C 3) → Glycerate (C 3) → FGK (C 3)
As you can see, the return is not complete, since one carbon atom is lost when two molecules of glycine are converted into one molecule of the amino acid serine, while carbon dioxide is released.
Oxygen is needed at the stages of conversion of glycolate to glyoxylate and glycine to serine.
The conversion of glycolate to glyoxylate and then to glycine occurs in peroxisomes, and serine is synthesized in mitochondria. Serine again enters the peroxisomes, where it first produces hydroxypyruvate, and then glycerate. Glycerate already enters the chloroplasts, where FHA is synthesized from it.
Photorespiration is typical mainly for plants with C3-type photosynthesis. It can be considered harmful, since energy is wasted on the conversion of glycolate into FHA. Apparently, photorespiration arose due to the fact that ancient plants were not ready for a large amount of oxygen in the atmosphere. Initially, their evolution took place in an atmosphere rich in carbon dioxide, and it was he who mainly captured the reaction center of the rubisco enzyme.
C 4 -photosynthesis, or the Hatch-Slack cycle
If in C 3 photosynthesis the first product of the dark phase is phosphoglyceric acid, which includes three carbon atoms, then in the C 4 pathway, the first products are acids containing four carbon atoms: malic, oxaloacetic, aspartic.
C 4 -photosynthesis is observed in many tropical plants, for example, sugar cane, corn.
C 4 -plants absorb carbon monoxide more efficiently, they have almost no photorespiration.
Plants in which the dark phase of photosynthesis proceeds along the C 4 pathway have a special leaf structure. In it, the conducting bundles are surrounded by a double layer of cells. The inner layer is the lining of the conducting beam. The outer layer is mesophyll cells. Chloroplast cell layers differ from each other.
Mesophilic chloroplasts are characterized by large grains, high activity of photosystems, absence of the enzyme RiBP carboxylase (rubisco) and starch. That is, the chloroplasts of these cells are adapted mainly for the light phase of photosynthesis.
In the chloroplasts of the cells of the conducting bundle, the grana are almost not developed, but the concentration of RiBP carboxylase is high. These chloroplasts are adapted for the dark phase of photosynthesis.
Carbon dioxide first enters the mesophyll cells, binds with organic acids, is transported in this form to the sheath cells, is released, and then binds in the same way as in C3 plants. That is, the C 4 -path complements rather than replaces C 3 .
In the mesophyll, CO 2 is added to phosphoenolpyruvate (PEP) to form oxaloacetate (acid), which includes four carbon atoms:
The reaction takes place with the participation of the PEP-carboxylase enzyme, which has a higher affinity for CO 2 than rubisco. In addition, PEP-carboxylase does not interact with oxygen, and therefore is not spent on photorespiration. Thus, the advantage of C4 photosynthesis is more efficient fixation of carbon dioxide, an increase in its concentration in the sheath cells, and, consequently, more efficient operation of RiBP carboxylase, which is almost not consumed for photorespiration.
Oxaloacetate is converted into a 4-carbon dicarboxylic acid (malate or aspartate), which is transported to the chloroplasts of the cells lining the vascular bundles. Here, the acid is decarboxylated (removal of CO2), oxidized (removal of hydrogen) and converted to pyruvate. Hydrogen restores NADP. Pyruvate returns to the mesophyll, where PEP is regenerated from it with the consumption of ATP.
The torn off CO 2 in the chloroplasts of the lining cells goes to the usual C 3 path of the dark phase of photosynthesis, i.e., to the Calvin cycle.
Photosynthesis along the Hatch-Slack pathway requires more energy.
The C 4 pathway is thought to have evolved later than the C 3 pathway and is largely an adaptation against photorespiration.
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Tasks: To form knowledge about the reactions of plastic and energy exchanges and their relationship; recall the structural features of chloroplasts. Describe the light and dark phases of photosynthesis. Show the importance of photosynthesis as a process that provides the synthesis of organic substances, the absorption of carbon dioxide and the release of oxygen into the atmosphere.
Lesson type: lecture.
Equipment:
- Visual aids: tables by general biology;
- TCO: computer; multimedia projector.
Lecture plan:
- History of the study of the process.
- Photosynthesis experiments.
- Photosynthesis as an anabolic process.
- Chlorophyll and its properties.
- Photosystems.
- The light phase of photosynthesis.
- Dark phase of photosynthesis.
- Limiting factors of photosynthesis.
Lecture progress
History of the study of photosynthesis
1630 year of the beginning of the study of photosynthesis . Van Helmont proved that plants form organic substances, and do not receive them from the soil. Weighing the pot with earth and willow, and separately the tree itself, he showed that after 5 years the mass of the tree increased by 74 kg, while the soil lost only 57 g. He decided that the tree receives food from water. We now know that carbon dioxide is being used.
AT 1804 Saussure found that water plays an important role in the process of photosynthesis.
AT 1887 chemosynthetic bacteria discovered.
AT 1905 Blackman established that photosynthesis consists of two phases: fast - light and a series of successive slow reactions of the dark phase.
Photosynthesis experiments
1 experience proves the value sunlight(Fig. 1.) | 2 experience proves the importance of carbon dioxide for photosynthesis (Fig. 2.) |
3 experience proves the importance of photosynthesis (Fig. 3.) |
|
Photosynthesis as an anabolic process
- Every year, as a result of photosynthesis, 150 billion tons of organic matter and 200 billion tons of free oxygen are formed.
- Cycle of oxygen, carbon and other elements involved in photosynthesis. Maintains the modern composition of the atmosphere necessary for existence modern forms life.
- Photosynthesis prevents an increase in the concentration of carbon dioxide, preventing the Earth from overheating due to the greenhouse effect.
- Photosynthesis is the basis of all food chains on Earth.
- The energy stored in products is the main source of energy for mankind.
The essence of photosynthesis consists in the conversion of the light energy of the sun's beam into chemical energy in the form of ATP and NADP·H 2.
The overall photosynthesis equation is:
6CO 2 + 6H 2 O→C 6 H 12 O 6 + 6O 2
There are two main types of photosynthesis:
Chlorophyll and its properties
Types of chlorophyll
Chlorophyll has modifications a, b, c, d. They differ in structural structure and light absorption spectrum. For example: chlorophyll b contains one oxygen atom more and two hydrogen atoms less than chlorophyll a.
All plants and oxyphotobacteria have yellow-green chlorophyll a as their main pigment, and chlorophyll b as an additional pigment.
Other plant pigments
Some other pigments are able to absorb solar energy and transfer it to chlorophyll, thereby involving it in photosynthesis.
Most plants have a dark orange pigment - carotene, which in the animal body turns into vitamin A and a yellow pigment - xanthophyll.
Phycocyanin and phycoerythrin- contain red and blue-green algae. In red algae, these pigments are more actively involved in the process of photosynthesis than chlorophyll.
Chlorophyll minimally absorbs light in the blue-green part of the spectrum. Chlorophyll a, b - in the violet region of the spectrum, where the wavelength is 440 nm. The unique function of chlorophyll consists in the fact that it intensively absorbs solar energy and transfers it to other molecules.
Pigments absorb a certain wavelength, unabsorbed parts of the solar spectrum are reflected, which provides the color of the pigment. Green light is not absorbed, so chlorophyll is green.
Pigments- this is chemical compounds, which absorb visible light, causing the electrons to become excited. The shorter the wavelength, the greater the energy of light and the greater its ability to transfer electrons to an excited state. This state is unstable and soon the whole molecule returns to its usual low-energy state, losing excitation energy. This energy can be used for fluorescence.
Photosystems
Plant pigments involved in photosynthesis are "packed" into chloroplast thylakoids in the form of functional photosynthetic units - photosynthetic systems: photosystem I and photosystem II.
Each system consists of a set of auxiliary pigments (from 250 to 400 molecules) that transfer energy to one molecule of the main pigment and it is called reaction center. It uses solar energy for photochemical reactions.
The light phase goes necessarily with the participation of light, the dark phase both in the light and in the dark. The light process occurs in the thylakoids of chloroplasts, the dark process occurs in the stroma, i.e. these processes are spatially separated.
Light phase of photosynthesis
AT 1958 Arnon and his collaborators studied the light phase of photosynthesis. They found that light is the source of energy during photosynthesis, and since in the light in chlorophyll synthesis from ADP + F.c. → ATP, then this process is called phosphorylation. It is associated with the transfer of electrons in membranes.
The role of light reactions: 1. ATP synthesis - phosphorylation. 2. Synthesis of NADP.H 2 .
The electron transport path is called Z-scheme.
Z-scheme. Acyclic and cyclic photophosphorylation(Fig. 6.)
In the course of cyclic electron transport, there is no formation of NADP.H 2 and photodecomposition of H 2 O, hence the release of O 2. This path is used when there is an excess of NADP.H 2 in the cell, but additional ATP is required.
All these processes belong to the light phase of photosynthesis. In the future, the energy of ATP and NADP.H 2 is used to synthesize glucose. This process does not require light. These are reactions of the dark phase of photosynthesis.
Dark phase of photosynthesis or Calvin cycle
The synthesis of glucose occurs during a cyclic process, which was named after the scientist Melvin Calvin, who discovered it, and was awarded the Nobel Prize.
Rice. 8. Calvin cycle
Each reaction of the Calvin cycle is carried out by its own enzyme. For the formation of glucose are used: CO 2 , protons and electrons from NADP.H 2 , the energy of ATP and NADP.H 2 . The process takes place in the stroma of the chloroplast. The initial and final compound of the Calvin cycle, to which, with the help of an enzyme ribulose diphosphate carboxylase CO2 joins, is a five-carbon sugar - ribulose bisphosphate containing two phosphate groups. As a result, a six-carbon compound is formed, which immediately decomposes into two three-carbon molecules. phosphoglyceric acid, which are then restored to phosphoglyceraldehyde. At the same time, part of the resulting phosphoglyceraldehyde is used to regenerate ribulose biphosphate, and thus the cycle is renewed again (5C 3 → 3C 5), and part is used to synthesize glucose and other organic compounds (2C 3 → C 6 → C 6 H 12 O 6).
For the formation of one glucose molecule, 6 cycle revolutions are required and 12NADP.H 2 and 18 ATP are required. From the overall reaction equation it turns out:
6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2
It can be seen from the above equation that C and O atoms entered glucose from CO 2, and hydrogen atoms from H 2 O. Glucose can later be used both for the synthesis of complex carbohydrates (cellulose, starch) and for the formation of proteins and lipids.
(C 4 - photosynthesis. In 1965, it was proved that in sugar cane, the first products of photosynthesis are acids containing four carbon atoms (malic, oxaloacetic, aspartic). Corn, sorghum, millet belong to C 4 plants).
Limiting factors of photosynthesis
The rate of photosynthesis is the most important factor influencing the yield of agricultural crops. So, for the dark phases of photosynthesis, NADP.H 2 and ATP are needed, and therefore the rate of dark reactions depends on light reactions. In low light, the rate of formation of organic matter will be low. So light is the limiting factor.
Of all the factors simultaneously affecting the process of photosynthesis limiting will be the one that is closer to the minimum level. It installed Blackman in 1905. Different factors can be limiting, but one of them is the main one.
Space role of plants(described K. A. Timiryazev) lies in the fact that plants are the only organisms that absorb solar energy and accumulate it in the form of potential chemical energy of organic compounds. The released O 2 supports the vital activity of all aerobic organisms. From oxygen, ozone is formed, which protects all living things from ultraviolet rays. Plants used a huge amount of CO 2 from the atmosphere, the excess of which created a "greenhouse effect", and the temperature of the planet dropped to its current values.
Photosynthesis Photosynthesis is a processtransformation
absorbed by the body
light energy in
chemical energy
organic
(inorganic)
connections.
The main role is the recovery of CO2 to
carbohydrate levels with
energy use
Sveta.
Development of the doctrine of photosynthesis
Kliment Arkadyevich Timiryazev(May 22 (June 3), 1843, Petersburg - 28
April 1920, Moscow) Scientific works
Timiryazev are devoted to the issue of
decomposition of atmospheric carbon dioxide
green plants under the influence
solar energy. The study of the composition and
optical properties of green pigment
plants (chlorophyll), its genesis,
physical and chemical conditions
decomposition of carbon dioxide, definition
constituent parts of a sunbeam,
participating in this event
quantitative relationship study
between the absorbed energy and
work done. Joseph Priestley (March 13
1733 - February 6, 1804) -
British clergyman, dissenter, naturalist,
philosopher, public figure.
Made history first
as an eminent chemist,
discovered oxygen and
carbon dioxide Pierre Joseph Peltier - (March 22, 1788 - July 19
1842) - French chemist and pharmacist, one of
founders of alkaloid chemistry.
In 1817, together with Joseph Bieneme Cavantou, he
isolated a green pigment from the leaves of plants, which
they called it chlorophyll. Alexey Nikolaevich Bakh
(5 (17) March 1857 - May 13,
1946) - Soviet biochemist and
plant physiologist. expressed
the idea that CO2 assimilation
during photosynthesis is
coupled redox process,
occurring due to hydrogen and
hydroxyl of water, and oxygen
released from the water through
intermediate peroxides
connections.
General photosynthesis equation
6 CO2 + 12 H2OC6H12O6 + 6 O2 + 6 H2O In higher plants, photosynthesis takes place in
specialized cells of leaf organelles
chloroplasts.
Chloroplasts are round or disc-shaped
bodies 1-10 microns long, up to 3 microns thick. Content
there are from 20 to 100 of them in cells.
Chemical composition (% by dry weight):
Protein - 35-55
Lipids - 20-30
Carbohydrates - 10
RNA - 2-3
DNA - up to 0.5
Chlorophyll - 9
Carotenoids - 4.5
Chloroplast structure
10. Origin of chloroplasts
Types of chloroplast formation:Division
budding
nuclear path
darkness
nucleus
initial
particle
light
prolamillary
body
proplastida
chloroplast
nuclear pathway diagram
11. Ontogeny of chloroplasts
12.
Chloroplasts are green plastids thatfound in plant cells and algae.
Chloroplast ultrastructure:
1. outer membrane
2. intermembrane
space
3. inner membrane
(1+2+3: shell)
4. stroma (fluid)
5. thylakoid with lumen
6. thylakoid membrane
7. grana (stack of thylakoids)
8. thylakoid (lamella)
9. starch grain
10. ribosome
11. plastid DNA
12. plstoglobula (drop of fat)
13. Pigments of photosynthetic plants
chlorophyllsphycobilins
Phycobilins
carotenoids
flavonoid
pigments
14. Chlorophyll
Chlorophyll -green pigment,
conditioning
coloration of chloroplasts
plants in green
color. Chemical
structure
chlorophylls -
magnesium complexes
various
tetrapyrroles.
Chlorophyll have
porphyrin
structure.
15.
chlorophyllsChlorophyll "a"
(blue-green
bacteria)
Chlorophyll "c"
(brown algae)
Chlorophyll "b"
(higher plants,
green, char
seaweed)
Chlorophyll "d"
(red algae)
16. Phycobilins
Phycobilins arepigments,
representing
auxiliary
photosynthetic
pigments that can
transmit energy
absorbed quanta
light on chlorophyll,
expanding the spectrum of action
photosynthesis.
open tetrapyrrole
structures.
Found in algae.
17. Carotenoids
Structural formula18.
Carotenoids arefat-soluble
yellow pigments,
red and orange
colors. attached
coloring to most
orange vegetables and
fruits.
19. Groups of carotenoids:
Carotenes are a yellow-orange pigmentunsaturated hydrocarbon
from the group of carotenoids.
Formula C40H56. Insoluble
in water but soluble in
organic solvents.
Found in the leaves of all plants, as well as in
carrot root, rose hips, etc. Is
provitamin vitamin A.
2.
Xanthophylls are plant pigments
crystallizes in prismatic crystals
yellow color.
1.
20. Flavonoid pigments
Flavonoids are a groupwater-soluble natural
phenolic compounds.
Represent
heterocyclic
oxygen-containing
compounds predominantly
yellow, orange, red
colors. They belong to
compounds C6-C3-C6 series -
their molecules have two
benzene rings connected
with each other three-carbon
fragment.
Structure of flavones
21. Flavonoid pigments:
Anthocyanins are natural substances that color plants;belong to glycosides.
Flavones and flavonols. They act as absorbers of UV rays, thereby protecting chlorophyll and cytoplasm
from destruction.
22. Stages of photosynthesis
lightImplemented in
grana of chloroplasts.
Leaks when available
light fast< 10 (-5)
sec
dark
Implemented in
colorless protein stroma
chloroplasts.
For flowing light
not required
Slow ~ 10 (-2) sec
23.
24.
25. Light stage of photosynthesis
During the light stage of photosynthesis,high-energy products: ATP serving in
cell as a source of energy, and NADPH, which is used
as a restorer. As a by-product
oxygen is released.
General Equation:
ADP + H3PO4 + H2O + NADP
ATP + NADPH + 1/2O2
26.
Absorption spectraPAR: 380 - 710 nm
Carotenoids: 400550 nm main
maximum: 480 nm
Chlorophylls:
in the red region of the spectrum
640-700 nm
in blue - 400-450 nm
27. Chlorophyll arousal levels
1 level. Associated with the transition to a higherenergy level of electrons in the system
conjugation of two bonds
2nd level. Associated with the excitation of unpaired electrons
four nitrogen and oxygen atoms in a porphyrin
ring.
28. Pigment systems
Photosystem IConsists of 200 molecules
chlorophyll "a",50
caroinoid molecules and 1
pigment molecules
(P700)
Photosystem II
Consists of 200 molecules
chlorophyll "a670", 200
chlorophyll "b" molecules and
one molecule of pigment
(P680)
29. Localization of electron and proton transport reactions in the thylakoid membrane
30. Non-cyclic photosynthetic phosphorylation (Z - scheme, or Govindzhi scheme)
xe
Фg e
FF e
NADP
Px
e
FeS
e
ADP
Cyt b6
e
II FS
NADPH
ATP
e
I FS
cit f
e
e
Pts
e
R680
hV
O2
e
H2 O
R700
hV
FF - feofetin
Px - plastoquinone
FeS - iron-sulfur protein
Cyt b6 - cytochrome
Pc - plastocyanin
Fg - ferodoxin
x - unknown nature.
compound
31. Photosynthetic phosphorylation
Photosynthetic phosphorylation is the processenergy formation of ATP and NADPH during photosynthesis with
using light quanta.
Kinds:
non-cyclic (Z-scheme). Two
pigment systems.
cyclic. Photosystem I is involved.
pseudocyclic. It follows the type of non-cyclic, but not
visible release of oxygen.
32. Cyclic photosynthetic phosphorylation
eADP
Фg
e
ATP
Cytb6
e
e
Quote f
e
P700
hV
e
ADP
ATP
Cyt b6 - cytochrome
Fg - ferodoxin
33. Cyclic and non-cyclic transport of electrons in chloroplasts
34.
The chemistry of photosynthesisPhotosynthesis
carried out
through
sequential alternation of two phases:
light,
flowing
With
big
speed and temperature-independent;
dark, so named because for
reactions occurring in this phase
light energy is not required.
35. Dark stage of photosynthesis
In the dark stage with the participation of ATP and NADPHCO2 is reduced to glucose (C6H12O6).
Although light is not required for this
process, he participates in its regulation.
36. C3 photosynthesis, Calvin cycle
Calvin cycle or recoveryThe pentose phosphate cycle consists of three stages:
Carboxylation of RDF.
Recovery. 3-FHA is reduced to
3-FGA.
Regeneration of the RDF acceptor. Carried out in a series
reactions of interconversions of phosphorylated sugars with
different number of carbon atoms (triosis, tetrose,
pentose, hexose, etc.)
37. General equation of the Calvin cycle
H2CO (P)C=O
HO-C-H + * CO2
H-C-OH
H2CO (P)
RDF
H2*CO (P)
2 NSON
UNSD
3-FGK
H2*CO (P)
2НSON
SOO (R)
1,3-FGK
H2*CO (P)
2НSON
C=O
H
3-FGA
H2*CO (P)
2C=O
NSON
3-FDA
condensation, or
polymerization
H
H2CO (P)
H2CO (P)
C=O
C=O
C=O
NSON
NOCH
NOCH
NOCH
H*SON
NSON
H*SON
NSON
NSON
NSON
H2CO (P)
H2SON
H2CO (P)
1,6-diphosphate-fructose-6glucose-6fructose
phosphate
phosphate
H
C=O
NSON
NOCH
H*SON
NSON
H2SON
glucose
38. C4 photosynthesis (Hatch-Slack-Karpilov path)
Occurs in plants with two types of chloroplast.In addition to RDF, the CO2 acceptor can be three
carbon compound - phosphoenol PVC (FEP)
C4 - the path was first discovered
in tropical grasses. In works
Yu.S. Karpilov, M. Hatch, K. Slack with
labeled carbon
it was shown that the first
the products of photosynthesis in these
plants are organic
acids.
39.
40. Crassula type photosynthesis
characteristic of plantssucculents. At night
fix carbon in
organic acids by
advantage in apple. it
takes place under the influence
enzymes
pyruvatecarboxylase. it
allows during the day
keep the stomata closed and
thus reduce
transpiration. This type
called SAM photosynthesis.
41. CAM photosynthesis
CAM photosynthesis separatesCO2 assimilation and the Calvin cycle are not in
space as in C4, but in time. At night in
vacuoles of cells in a similar way
the above mechanism with open
stomata accumulate malate, during the day
closed stomata is the Calvin cycle. This
mechanism allows you to save as much as possible
water, however, is inferior in efficiency to both C4 and
C3.
42.
43.
photorespiration44. Influence of internal and external factors on photosynthesis
Photosynthesismuch
changes due to
influence on him
complex often
interacting
external and internal
factors.
45. Factors affecting photosynthesis
1.ontogenetic
plant condition.
Maximum
intensity
photosynthesis observed
during the transition
plants from vegetation to
reproductive phase. At
aging leaves
intensity
photosynthesis significantly
falls.
46. Factors affecting photosynthesis
2. Light. Photosynthesis does not occur in the dark becausecarbon dioxide formed during respiration is released from
leaves; with increasing light intensity,
compensation point at which absorption
carbon dioxide during photosynthesis and its release during
breath balance each other.
47. Factors affecting photosynthesis
3. Spectralthe composition of the world.
Spectral
solar composition
experiencing light
some
changes in
during the day and
throughout the year.
48. Factors affecting photosynthesis
4. CO2.Is the main
substrate for photosynthesis and
its content depends
the intensity of this process.
The atmosphere contains
0.03% by volume; increase
volume of carbon dioxide from 0.1
up to 0.4% increases
photosynthesis rate up to
certain limit, and
then changes
saturation with carbon dioxide.
49. Factors affecting photosynthesis
5.Temperature.In plants of moderate
zone optimal
temperature for
photosynthesis
is 20-25; at
tropical - 2035.
50. Factors affecting photosynthesis
6. Water content.Reducing tissue dehydration by more than 20%
leads to a decrease in the rate of photosynthesis and to
its further termination, if the loss of water will
more than 50%.
51. Factors affecting photosynthesis
7. Trace elements.Fe deficiency
causes chlorosis and
affects activity.
enzymes. Mn
necessary for
release
oxygen and for
absorption of carbon dioxide
gas. Lack of Cu and
Zn reduces photosynthesis
by 30%
52. Factors affecting photosynthesis
8.Pollutingsubstances and
chemical
drugs.
Cause
decline
photosynthesis.
Most
dangerous
substances: NO2,
SO2, suspended
particles.
53. Daily course of photosynthesis
At moderate daytime temperatures and sufficienthumidity daily course of photosynthesis approximately
corresponds to a change in the intensity of the solar
insolation. Photosynthesis starting in the morning at sunrise
sun, reaches its maximum at noon,
gradually decreases in the evening and stops with sunset
sun. At higher temperatures and lower
humidity, the photosynthesis maximum shifts to the early
watch.
54. Conclusion
Thus, photosynthesis is the only process onEarth, walking on a grand scale, associated with
converting sunlight energy into chemical energy
connections. This energy stored by green plants
forms the basis for the life of all other
heterotrophic organisms on Earth from bacteria to humans.
The chemical equation of the photosynthesis process can be generally represented as follows:
6CO 2 + 6H 2 O + Qlight → C 6 H 12 O 6 + 6O 2.
Photosynthesis is a process in which the electromagnetic energy of the sun is absorbed by chlorophyll and auxiliary pigments and converted into chemical energy, the absorption of carbon dioxide from the atmosphere, its reduction into organic compounds and the return of oxygen to the atmosphere.
During photosynthesis from simple inorganic compounds(CO 2 , H 2 O) various organic compounds are built. As a result, chemical bonds are rearranged: instead of C - O and H - O bonds, C - C and C - H bonds arise, in which electrons occupy a higher energy level. Thus, energy-rich organic substances that animals and humans feed on and receive energy from (during respiration) are initially created in a green leaf. We can say that almost all living matter on Earth is the result of photosynthetic activity.
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. AT further work A number of scientists (Y. Ingengauz, J. Senebier, T. Saussure, J. B. Bussengo) found that green plants absorb CO 2 from the air, from which, with the participation of water, organic matter is formed in the light. It was this process that in 1877 the German scientist W. Pfeffer called photosynthesis. Great importance to reveal the essence of photosynthesis, he had 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.
Photosynthesis involves both light and dark reactions. A number of experiments were carried out proving that in the process of photosynthesis, not only reactions that take place with the use of light energy, but also dark reactions that do not require the direct participation of light energy take place. We can cite the following evidence for the existence of dark reactions in the process of photosynthesis:
1) photosynthesis accelerates with increasing temperature. It directly follows from this that some stages of this process are not directly related to the use of light energy. The dependence of photosynthesis on temperature is especially pronounced at high light intensities. Apparently, in this case, the rate of photosynthesis is limited precisely by dark reactions;
2) the efficiency of the use of light energy in the process of photosynthesis turned out to be higher with intermittent illumination. At the same time, for more efficient use of light energy, the duration of dark intervals should significantly exceed the duration of light intervals.
photosynthesis pigments
In order for light to have an effect on the plant organism and, in particular, to be used in the process of photosynthesis, it must be absorbed by photoreceptor pigments. Pigments are colored substances. Pigments absorb light of a certain wavelength. Unabsorbed parts of the solar spectrum are reflected, which determines the color of the pigments. Thus, the green pigment chlorophyll absorbs red and blue rays, while green rays are mainly reflected. The visible part of the solar spectrum includes wavelengths from 400 to 700 nm. Substances that absorb the entire visible spectrum appear black.
Pigments concentrated in plastids can be divided into three groups: chlorophylls, carotenoids, phycobilins.
To the group chlorophylls include organic compounds that contain 4 pyrrole rings connected by magnesium atoms and have a green color.
Currently, about ten chlorophylls are known. They differ in chemical structure, color, distribution among living organisms. All higher plants contain chlorophylls a and b. Chlorophyll c is found in diatoms, chlorophyll d is found in red algae.
The main pigments without which photosynthesis does not proceed are chlorophyll a for green plants and bacteriochlorophylls for bacteria. For the first time, an accurate idea of the pigments of the green leaf of higher plants was obtained thanks to the work of the largest Russian botanist M.S. Colors (1872-1919). He developed a new chromatographic method for separating substances and isolated leaf pigments in their pure form.
The chromatographic method for separating substances is based on their different adsorption capacities. This method has been widely used. M.S. The color passed the extract from the leaf through a glass tube filled with powder - chalk or sucrose (chromatographic column). The individual components of the pigment mixture differed in the degree of adsorption and moved at different speeds, as a result of which they were concentrated in different zones of the column. By dividing the column into separate parts (zones) and using the appropriate solvent system, it was possible to isolate each pigment. It turned out that the leaves of higher plants contain chlorophyll a and chlorophyll b, as well as carotenoids (carotene, xanthophyll, etc.). Chlorophylls, like carotenoids, are insoluble in water, but readily soluble in organic solvents. Chlorophyll a and b differ in color: chlorophyll a is blue-green, and chlorophyll b is yellow-green. The content of chlorophyll a in the leaf is about three times greater than that of chlorophyll b.
Carotenoids are yellow and orange pigments of aliphatic structure, derivatives of isoprene. Carotenoids are found in all higher plants and in many microorganisms. These are the most common pigments with a variety of functions. Carotenoids containing oxygen are called xanthophylls. The main representatives of carotenoids in higher plants are two pigments - carotene (orange) and xanthophyll (yellow). Unlike chlorophylls, carotenoids do not absorb red rays, and also do not have the ability to fluoresce. Like chlorophyll, carotenoids in chloroplasts and chromatophores are in the form of water-insoluble complexes with proteins. Carotenoids, absorbing certain parts of the solar spectrum, transfer the energy of these rays to chlorophyll molecules. Thus, they contribute to the use of rays that are not absorbed by chlorophyll.
Phycobilins- red and blue pigments found in cyanobacteria and some algae. Studies have shown that red algae and cyanobacteria contain phycobilins along with chlorophyll a. The chemical structure of phycobilins is based on four pyrrole groups.
Phycobilins are represented by pigments: phycocyanin, phycoerythrin and allophycocyanin. Phycoerythrin is an oxidized phycocyanin. Phycobilins form strong compounds with proteins (phycobilin proteins). The connection between phycobilins and proteins is destroyed only by acid.
Phycobilins absorb rays in the green and yellow parts of the solar spectrum. This is the part of the spectrum that lies between the two main absorption lines of chlorophyll. Phycoerythrin absorbs rays with a wavelength of 495-565 nm, and phycocyanin - 550-615 nm. Comparison of the absorption spectra of phycobilins with the spectral composition of light in which photosynthesis takes place in cyanobacteria and red algae shows that they are very close. This suggests that phycobilins absorb light energy and, like carotenoids, transfer it to the chlorophyll molecule, after which it is used in the process of photosynthesis. The presence of phycobilins in algae is an example of the adaptation of organisms in the process of evolution to the use of parts of the solar spectrum that penetrate the sea water column (chromatic adaptation). As is known, red rays corresponding to the main absorption line of chlorophyll are absorbed when passing through the water column. The green rays penetrate most deeply, which are absorbed not by chlorophyll, but by phycobilins.
Properties of chlorophyll
All chlorophylls are magnesium salts of pyrrole. In the center of the chlorophyll molecule are magnesium and four pyrrole rings connected to each other by methane bridges.
According to the chemical structure, chlorophylls are esters of a dicarboxylic organic acid - chlorophyllin and two alcohol residues - phytol and methyl.
The most important part of the chlorophyll molecule is the central nucleus. It consists of four pyrrole five-membered rings connected by carbon bridges and forming a large porphyrin core with nitrogen atoms in the middle, associated with a magnesium atom. The chlorophyll molecule has an additional cyclopentanone ring, which contains carbonyl and carboxyl groups linked by an ether bond with methyl alcohol. The presence in the porphyrin core of a circularly conjugated system of ten double bonds and magnesium are responsible for the characteristic green color of chlorophyll.
Chlorophyll c differs from chlorophyll a only in that instead of a methyl group in the second pyrrole ring it has an aldehyde COH group. Chlorophyll is blue-green, while chlorophyll b is light green. They are adsorbed in different layers of the chromatogram, which indicates different chemical and physical properties. By modern ideas, the biosynthesis of chlorophyll B goes through chlorophyll a.
Fluorescence is a property of many bodies under the influence of incident light, in turn, to emit light: the wavelength of the emitted light is usually greater than the wavelength of the exciting light. One of the most important properties chlorophylls is their brightest pronounced ability to fluorescence, which is intense in solution and suppressed in chlorophyll contained in leaf tissues, in plastids. If you look at a solution of chlorophyll in the rays of light passing through it, then it seems emerald green, but if you look at it in the rays of reflected light, then it becomes red - this is the phenomenon of fluorescence.
Chlorophylls differ in absorption spectra, while in chlorophyll b, compared to chlorophyll a, the absorption band in the red region of the spectrum is somewhat shifted towards short-wavelength rays, and in the blue-violet region, the absorption maximum is shifted towards long-wavelength (red) rays.
Photosynthesis is the process of synthesizing organic substances from inorganic substances using light energy. In the vast majority of cases, photosynthesis is carried out by plants using cell organelles such as chloroplasts containing green pigment chlorophyll.
If plants were not capable of synthesizing organic matter, then almost all other organisms on Earth would have nothing to eat, since animals, fungi and many bacteria cannot synthesize organic substances from inorganic ones. They only absorb ready-made ones, split them into simpler ones, from which they again assemble complex ones, but already characteristic of their body.
This is the case if we talk about photosynthesis and its role very briefly. To understand photosynthesis, you need to say more: what specific inorganic substances are used, how does synthesis occur?
Photosynthesis requires two inorganic matter- carbon dioxide (CO 2) and water (H 2 O). The first is absorbed from the air by the aerial parts of plants mainly through the stomata. Water - from the soil, from where it is delivered to the photosynthetic cells by the conducting system of plants. Photosynthesis also requires the energy of photons (hν), but they cannot be attributed to matter.
In total, as a result of photosynthesis, organic matter and oxygen (O 2) are formed. Usually, under organic matter, glucose (C 6 H 12 O 6) is most often meant.
organic compounds mostly composed of carbon, hydrogen and oxygen atoms. They are found in carbon dioxide and water. However, photosynthesis releases oxygen. Its atoms come from water.
Briefly and generally, the equation for the reaction of photosynthesis is usually written as follows:
6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2
But this equation does not reflect the essence of photosynthesis, does not make it understandable. Look, although the equation is balanced, it has a total of 12 atoms in free oxygen. But we said that they come from water, and there are only 6 of them.
In fact, photosynthesis occurs in two phases. The first is called light, second - dark. Such names are due to the fact that light is needed only for the light phase, the dark phase is independent of its presence, but this does not mean that it goes in the dark. The light phase flows on the membranes of the thylakoids of the chloroplast, the dark phase - in the stroma of the chloroplast.
In the light phase, CO 2 binding does not occur. There is only the capture of solar energy by chlorophyll complexes, its storage in ATP, the use of energy for the reduction of NADP to NADP * H 2. The flow of energy from chlorophyll excited by light is provided by electrons transmitted through the electron transport chain of enzymes built into thylakoid membranes.
Hydrogen for NADP is taken from water, which, under the action of sunlight, decomposes into oxygen atoms, hydrogen protons and electrons. This process is called photolysis. Oxygen from water is not needed for photosynthesis. The oxygen atoms from two water molecules combine to form molecular oxygen. The reaction equation for the light phase of photosynthesis briefly looks like this:
H 2 O + (ADP + F) + NADP → ATP + NADP * H 2 + ½O 2
Thus, the release of oxygen occurs in the light phase of photosynthesis. The number of ATP molecules synthesized from ADP and phosphoric acid per photolysis of one water molecule can be different: one or two.
So, ATP and NADP * H 2 enter the dark phase from the light phase. Here, the energy of the first and the restorative force of the second are spent on the binding of carbon dioxide. This step of photosynthesis cannot be explained simply and briefly, because it does not proceed in such a way that six CO 2 molecules combine with hydrogen released from NADP * H 2 molecules and glucose is formed:
6CO 2 + 6NADP * H 2 → C 6 H 12 O 6 + 6NADP
(the reaction takes place with the expenditure of energy from ATP, which breaks down into ADP and phosphoric acid).
The above reaction is just a simplification for ease of understanding. In fact, carbon dioxide molecules bind one at a time, joining the already prepared five-carbon organic matter. An unstable six-carbon organic substance is formed, which breaks down into three-carbon carbohydrate molecules. Some of these molecules are used for the resynthesis of the initial five-carbon substance for CO 2 binding. This resynthesis is provided Calvin cycle. Smaller part a carbohydrate molecule containing three carbon atoms exits the cycle. Already from them and other substances, all other organic substances (carbohydrates, fats, proteins) are synthesized.
That is, in fact, three-carbon sugars come out of the dark phase of photosynthesis, and not glucose.