Photosynthesis - a unique system of processes for the creation of organic substances from inorganic substances using chlorophyll and light energy and the release of oxygen into the atmosphere, implemented on a huge scale on land and in water.
All processes of the dark phase of photosynthesis proceed without direct consumption of light, but high-energy substances (ATP and NADPH), which are formed with the participation of light energy during the light phase of photosynthesis, play an important role in them. During the dark phase, the energy of ATP macroenergy bonds is converted into the chemical energy of organic compounds of carbohydrate molecules. This means that the energy of sunlight is, as it were, conserved in chemical bonds between the atoms of organic substances, which is of great importance in the energetics of the biosphere and specifically for the life of the entire living population of our planet.
Photosynthesis occurs in the chloroplasts of the cell and is the synthesis of carbohydrates in chlorophyll-bearing cells, which takes place with the consumption of energy from sunlight. Distinguish between light and tempo phases of photosynthesis. The light phase, with the direct consumption of light quanta, provides the synthesis process with the necessary energy in the form of NADH and ATP. The dark phase - without the participation of light, but through a numerous series of chemical reactions (Calvin cycle) provides the formation of carbohydrates, mainly glucose. The importance of photosynthesis in the biosphere is enormous.
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Photosynthesis light and dark phases abstract
Dark Phase Photosynthesis Test Solve
Light phase and dark processes
Report on the dark phase of photosynthesis
Light reactions of photosynthesis take place in
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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 themselves produce 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 the. This stored chemical energy comes from the conversion of inorganic carbon (carbon dioxide) to organic carbon. The breathing process releases stored chemical energy.
In addition to the foods 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 in protein production). 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 as well as insect-eating plants 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.
Determination of photosynthesis
Photosynthesis is the chemical process by which plants, some and 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 thanks to it oxygen is released, on which all life depends.
Why do plants need glucose (food)?
Like humans and other living things, plants also need food to keep them alive. The value of glucose for plants is as follows:
- Glucose from 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, which are needed for 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 need sunlight. In light-dependent reactions, the energy of sunlight is absorbed by chlorophyll and converted into stored chemical energy in the form of an electron carrier molecule NADPH (nicotinamide adenine dinucleotide phosphate) and an 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 the dark phases do not use light as a reagent (and as a result, can occur day or night), they need the products of light-dependent reactions to function. Light independent molecules depend on energy carrier molecules - ATP and NADPH - to create new carbohydrate molecules. After the transfer of energy, the molecules of the energy carriers return to the light phases to obtain more energetic electrons. In addition, several dark phase enzymes are activated by light.
Photosynthesis phase diagram
The note: This means that the dark phases will not continue if the plants are deprived of light for too long, as they are using light phase products.
Plant leaf structure
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 features of plants is their large leaf surface area. Most green plants have wide, flat, and open leaves that can capture as much solar energy (sunlight) as needed for photosynthesis.
- Central vein and petiole
The central vein and petiole are joined 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 plate, 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 web of veins in the leaves carries water from the stems to the leaves. The released glucose is also directed to other parts of the plant from the leaves through the veins. In addition, these portions of the sheet support and keep the sheet metal plate flat to capture more sunlight. The location of the veins (venation) depends on the type of plant.
- The base of the sheet
The base of the leaf is its lowest part, which is articulated with the stem. Often, a paired number of stipules is located at the base of the leaf.
- Edge of the sheet
Depending on the type of plant, the leaf edge can have a different shape, including: whole-edged, toothed, serrate, notched, crenate, etc.
- Top of the leaf
Like the leaf edge, the tip comes in a variety of shapes, including: sharp, rounded, obtuse, elongated, drawn, etc.
Internal structure of leaves
Below is a similar diagram of the internal structure of leaf tissues:
- Cuticle
The cuticle acts as the main protective layer on the surface of the plant. It is usually thicker at the top of the sheet. The cuticle is covered with a wax-like substance that protects the plant from water.
- Epidermis
The epidermis is the layer of cells that is the integumentary tissue of the leaf. Its main function is to protect the inner 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 plant tissue. This is where the process of photosynthesis takes place. In most plants, the mesophyll is divided into two layers: the upper one is palisade and the lower one is spongy.
- Protective cells
Defense cells are specialized cells in the leaf epidermis that are used to control gas exchange. They have a protective function for the stomata. The stomatal pores become large when water is freely available; otherwise, the defense cells become flaccid.
- 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 byproduct of photosynthesis, leaves the plant through the stomata. When the stomata are open, water is lost by evaporation and must be replenished through the transpiration stream with water absorbed by the roots. Plants are forced to balance the amount of absorbed CO2 from the air and the loss of water through the stomatal pores.
Conditions for photosynthesis
Below 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 designation CO2. It is formed when carbon and organic compounds are burned, and also occurs during respiration.
- Water... A clear liquid chemical, odorless and tasteless (under normal conditions).
- Light. While artificial light is also suitable for plants, natural sunlight tends to create the best conditions for photosynthesis because it contains natural UV radiation that has a positive effect on plants.
- Chlorophyll. It is a green pigment found in the leaves of plants.
- Nutrients and Minerals. Chemicals and organic compounds that plant roots absorb from the soil.
What is formed as a result of photosynthesis?
- Glucose;
- Oxygen.
(Light energy is shown in parentheses as it is not matter)
The note: Plants get 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 a store of energy.
If factors promoting photosynthesis are absent or present in enough, this can negatively affect the plant. For example, less light creates favorable conditions for insects that eat the leaves of the plant, and lack of water slows down.
Where does photosynthesis take place?
Photosynthesis takes place inside plant cells, in small plastids called chloroplasts. Chloroplasts (mostly found in the mesophyll layer) contain a green substance called chlorophyll. Below are the other parts of the cell that work with the chloroplast to carry out photosynthesis.
Plant cell structure
Functions of plant cell parts
- : provides structural and mechanical support, protects cells from, fixes and defines the shape of the cell, controls the rate and direction of growth, and gives shape to plants.
- : provides a platform for most of the 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 during photosynthesis.
- : a cavity within the cellular cytoplasm that stores water.
- : contains a genetic mark (DNA) that controls cell activity.
Chlorophyll absorbs light energy required for photosynthesis. It is important to note that not all color wavelengths of light are absorbed. Plants primarily absorb red and blue waves - they do not absorb light in the green range.
Carbon dioxide from photosynthesis
Plants get carbon dioxide from the air through their leaves. Carbon dioxide seeps through a small hole at the bottom of the leaf called the stomata.
The lower part of the leaf has loosely spaced cells to allow carbon dioxide to reach other cells in the leaves. It also allows the oxygen produced during photosynthesis to easily leave the leaf.
Carbon dioxide is present in the air we breathe at very low concentrations and is a necessary factor in the dark phase of photosynthesis.
Light in the process of photosynthesis
The sheet usually has a large surface area, so it can absorb a lot of light. Its upper surface is protected from water loss, disease and weather by a wax layer (cuticle). The top of the leaf is where the light falls. This mesophyll layer is called palisade. It is adapted to absorb a large amount of light, because it contains many chloroplasts.
In light phases, the process of photosynthesis increases with more light. More chlorophyll molecules are ionized and more ATP and NADPH are generated if the light photons are focused on the green leaf. Although light is extremely important in light phases, it should be noted that excessive amounts of it can damage chlorophyll and reduce photosynthesis.
Light phases are not very dependent on temperature, water or carbon dioxide, although all of them are needed to complete the photosynthesis process.
Water in the process of photosynthesis
Plants get the water they need for photosynthesis through their roots. They have root hairs that grow in the soil. The roots have a large surface area and thin walls that allow water to pass through easily.
The image shows plants and their cells with enough water (left) and lack of water (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 withers. Without water, the plant will not be able to photosynthesize fast enough and may even die.
How important is water for plants?
- Provides dissolved minerals that support plant health;
- Is a medium for transportation;
- Supports stability and uprightness;
- Cools and moisturizes;
- It 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 the building blocks in plants for tissue growth. Thus, photosynthesis is the way in which roots, stems, leaves, flowers and fruits are formed. Without the process of photosynthesis, plants cannot grow or reproduce.
- Producers
Because of their photosynthetic ability, plants are known to be producers and form the backbone of nearly every food chain on earth. (Algae are the equivalent of plants in). All food we eat comes from organisms that are photosynthetic. We eat these plants directly or eat animals such as cows or pigs that consume plant foods.
- The backbone of the food chain
Within aquatic systems, plants and algae also form the backbone of the food chain. Algae serve as food for, which, in turn, act as a food source for larger organisms. Without photosynthesis in the aquatic environment, life would be impossible.
- Removal of carbon dioxide
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 levels of carbon dioxide are rising at an alarming rate, any process that removes carbon dioxide from the atmosphere is environmentally important.
- Nutrient Cycle
Plants and other photosynthetic organisms play a vital role in the nutrient cycle. Nitrogen in the air is fixed in plant tissues and becomes available for making proteins. Trace elements found in soil can also be incorporated into plant tissue and made available to herbivores further down the food chain.
- Photosynthetic addiction
Photosynthesis depends on the intensity and quality of light. At the equator, where sunlight is abundant throughout the year and water is not a limiting factor, plants grow at high rates and can get quite large. Conversely, photosynthesis in the deeper parts of the ocean is less common because light does not penetrate these layers, and as a result, this ecosystem is more sterile.
Thylakoid membranes contain a large number of proteins and low molecular weight pigments, both free and combined with proteins, which are combined into two complex complexes called photosystem I and photosystem I I. The nucleus of each of these photosystems is a protein containing green pigment chlorophyll capable of absorbing light in the red region of the spectrum. Various pigments that make up photosynthetic complexes are capable of capturing even very weak light and transferring its energy to chlorophyll; therefore, photosynthesis can proceed even under low light (for example, in the shade of trees or in cloudy weather).
The absorption of a quantum of light by the chlorophyll molecule of photosystem II leads to its excitation, namely, one of the electrons is transferred to a higher energy level. This electron is transferred to the chain of electron carriers, or rather, to pigments and cytochrome proteins dissolved in the thylakoid membrane, somewhat reminiscent of the cytochromes of the inner mitochondrial membrane (see figure). By analogy with the mitochondrial electron transport chain, there is a decrease in the energy of an electron during its transfer from carrier to carrier. Part of its energy is spent on the transfer of protons across the membrane from the chloroplast stroma into the thylakoid. Thus, on the thylakoid membrane appears proton concentration gradient ... This gradient can be used with a special enzyme. ATP synthetase for the synthesis of ATP from ADP and H 3 PO 4 (F n). Those. in chloroplasts the same so-called “dam” principle is realized, which was considered earlier on the example of mitochondria. ATP synthesis during the light phase of photosynthesis is called photophosphorylation ... This name is due to the fact that it uses the energy of sunlight. A distinctive feature of oxidative phosphorylation in mitochondria is that the energy for the synthesis of ATP is generated during the oxidation of organic substrates (see section ““).
The reduction of oxidized chlorophyll, which has "lost" an electron, of photosystem II occurs as a result of the activity of a special enzyme that decomposes a water molecule, taking electrons from it (molecules):
H 2 O -> 2e - + 2H + + 1 / 2O 2
The above process is named photolysis of water , and it flows on the inner side of the thylakoid membrane. This process leads to an even greater increase in the concentration gradient of protons on the membrane, and, consequently, to additional synthesis of ATP.
That is, we can say that water is a "supplier" of electrons for chlorophyll. A by-product of this reaction is molecular oxygen, which, due to diffusion, leaves the chloroplasts and is released into the atmosphere through the stomata.
Let's try to trace further the "fate" of electrons detached from chlorophyll of photosystem II. They pass through the carrier chain and enter the reaction center of photosystem I, which also contains a chlorophyll molecule. This chlorophyll molecule also absorbs a quantum of light and transfers its energy to one of the electrons, thus raising it to a higher energy level. An electron, passing through a chain of special carrier proteins, is transferred to the NADP + molecule. This NADP + molecule receives one more electron in the next cycle, captures a proton from the chloroplast stroma and is reduced to NADPH.
So, electrons that have been “torn off” from the water molecule receive high energy due to the absorption of light quanta by chlorophylls of photosystems II and I, then, passing along the carrier chain, they reduce NADP +. Part of the energy of these electrons is spent on transferring protons across the thylakoid membrane and creating a concentration gradient. Then the energy of the proton gradient will be used to synthesize ATP by the enzyme ATP synthase.
Photosynthesis Is a set of processes for the synthesis of organic compounds from inorganic ones due to the conversion of light energy into the energy of chemical bonds. Phototrophic organisms include green plants, some prokaryotes - cyanobacteria, purple and green sulfur bacteria, plant flagellates.
Research into the process of photosynthesis began in the second half of the 18th century. An important discovery was made by the outstanding Russian scientist K.A.Timiryazev, who substantiated the doctrine of the cosmic role of green plants. Plants absorb sunlight and convert light energy into the energy of chemical bonds of organic compounds synthesized by them. Thus, they ensure the preservation and development of life on Earth. The scientist also theoretically substantiated and experimentally proved the role of chlorophyll in the absorption of light during photosynthesis.
Chlorophylls are the main photosynthetic pigment. In structure, they are similar to hemoglobin heme, but instead of iron they contain magnesium. The iron content is necessary to ensure the synthesis of chlorophyll molecules. There are several chlorophylls that differ in their chemical structure. Mandatory for all phototrophs is chlorophyll a . Chlorophyllb found in green plants, chlorophyll c - in diatoms and brown algae. Chlorophyll d characteristic of red algae.
Green and purple photosynthetic bacteria have special bacteriochlorophylls ... Bacterial photosynthesis has much in common with plant photosynthesis. It differs in that hydrogen sulphide is the donor of hydrogen in bacteria, and water in plants. Green and purple bacteria lack photosystem II. Bacterial photosynthesis is not accompanied by the release of oxygen. The overall equation of bacterial photosynthesis:
6С0 2 + 12H 2 S → C 6 H 12 O 6 + 12S + 6Н 2 0.
Photosynthesis is based on the redox process. It is associated with the transfer of electrons from compounds that provide donor electrons to compounds that accept them - acceptors. Light energy is converted into the energy of synthesized organic compounds (carbohydrates).
Chloroplast membranes have special structures - reaction centers that contain chlorophyll. In green plants and cyanobacteria, two are distinguished photo systems – first (I) and second (II) , which have different reaction centers and are interconnected through the electron transport system.
Two phases of photosynthesis
The process of photosynthesis consists of two phases: light and dark.
It occurs only when there is light on the inner membranes of mitochondria in the membranes of special structures - thylakoids ... Photosynthetic pigments capture light quanta (photons). This leads to the "excitation" of one of the electrons of the chlorophyll molecule. With the help of carrier molecules, the electron moves to the outer surface of the thylakoid membrane, acquiring a certain potential energy.
This electron in photosystem I can return to its energy level and restore it. NADP (nicotinamide adenine dinucleotide phosphate) can also be transferred. Interacting with hydrogen ions, electrons reduce this compound. Reduced NADP (NADPH) supplies hydrogen to reduce atmospheric CO2 to glucose.
Similar processes take place in photosystem II ... Excited electrons can be transferred to photosystem I and restored. The restoration of photosystem II occurs at the expense of electrons supplied by water molecules. Water molecules break down (photolysis of water) into hydrogen protons and molecular oxygen, which is released into the atmosphere. Electrons are used to restore photosystem II. Water photolysis equation:
2H 2 0 → 4H + + 0 2 + 2e.
When electrons return from the outer surface of the thylakoid membrane to the previous energy level, energy is released. It is stored in the form of chemical bonds of ATP molecules, which are synthesized during reactions in both photosystems. The synthesis of ATP with ADP and phosphoric acid is called photophosphorylation ... Some of the energy is used to evaporate water.
During the light phase of photosynthesis, energy-rich compounds are formed: ATP and NADPH. During the decay (photolysis) of a water molecule, molecular oxygen is released into the atmosphere.
The reactions take place in the internal environment of chloroplasts. They can occur with or without light. Organic substances are synthesized (CO2 is reduced to glucose) using the energy that is formed in the light phase.
The carbon dioxide recovery process is cyclical and is called Calvin cycle ... Named after the American researcher M. Calvin, who discovered this cyclical process.
The cycle begins with the reaction of atmospheric carbon dioxide with ribulezobiphosphate. Enzyme catalyzes the process carboxylase ... Ribule biphosphate is a five-carbon sugar combined with two phosphoric acid residues. A number of chemical transformations take place, each of which catalyzes its own specific enzyme. How final product photosynthesis is formed glucose , and also ribulezobiphosphate is restored.
The overall equation of the photosynthesis process:
6C0 2 + 6H 2 0 → C 6 H 12 O 6 + 60 2
Thanks to the process of photosynthesis, the light energy of the Sun is absorbed and is converted into the energy of chemical bonds of synthesized carbohydrates. Energy is transferred to heterotrophic organisms through food chains. In the process of photosynthesis, carbon dioxide is absorbed and oxygen is released. All atmospheric oxygen is of photosynthetic origin. Over 200 billion tons of free oxygen are released annually. Oxygen protects life on Earth from ultraviolet radiation by creating an ozone shield in the atmosphere.
The process of photosynthesis is ineffective, since only 1-2% of solar energy is transferred to the synthesized organic matter. This is due to the fact that plants do not absorb light enough, part of it is absorbed by the atmosphere, etc. Most of the sunlight is reflected from the Earth's surface back into space.
Photosynthesis is a rather complex process and includes two phases: light, which always occurs exclusively in light, and dark. All processes take place inside chloroplasts on special small organs - thylakoids. During the light phase, a quantum of light is absorbed by chlorophyll, resulting in the formation of ATP and NADPH molecules. In this case, water breaks down, forming hydrogen ions and giving off an oxygen molecule. The question arises, what are these incomprehensible mysterious substances: ATP and NADH?
ATP is a special organic molecule found in all living organisms and is often referred to as "energy" currency. It is these molecules that contain high-energy bonds and are the source of energy for any organic synthesis and chemical processes in the body. Well, NADPH is actually a source of hydrogen, it is used directly in the synthesis of high molecular weight organic substances - carbohydrates, which occurs in the second, dark phase of photosynthesis using carbon dioxide. But let's start in order.
Light phase of photosynthesis
Chloroplasts contain a lot of chlorophyll molecules, and they all absorb sunlight. At the same time, light is absorbed by other pigments, but they do not know how to carry out photosynthesis. The process itself occurs only in some chlorophyll molecules, of which there are very few. Other molecules of chlorophyll, carotenoids and other substances form special antenna, as well as light-harvesting complexes (SSC). They, like antennas, absorb light quanta and transmit excitation to special reaction centers or traps. These centers are located in photosystems, of which plants have two: photosystem II and photosystem I. They contain special chlorophyll molecules: respectively, in photosystem II - P680, and in photosystem I - P700. They absorb light of exactly this wavelength (680 and 700 nm).
The diagram makes it clearer how everything looks and happens during the light phase of photosynthesis.
In the figure, we see two photosystems with chlorophylls P680 and P700. The figure also shows the carriers through which the transport of electrons occurs.
So: both chlorophyll molecules of the two photosystems absorb a quantum of light and are excited. Electron e- (red in the figure) goes to a higher energy level.
Excited electrons have a very high energy, they break off and enter a special carrier chain, which is located in the membranes of thylakoids - the internal structures of chloroplasts. The figure shows that from photosystem II from chlorophyll P680 an electron passes to plastoquinone, and from photosystem I from chlorophyll P700 to ferredoxin. In the chlorophyll molecules themselves, in place of the electrons after their detachment, blue holes with a positive charge are formed. What to do?
To make up for the lack of an electron, the chlorophyll P680 molecule of photosystem II receives electrons from water, while hydrogen ions are formed. In addition, it is due to the decomposition of water that oxygen released into the atmosphere is formed. And the chlorophyll P700 molecule, as can be seen from the figure, makes up for the lack of electrons through the carrier system from photosystem II.
In general, no matter how difficult it is, this is how the light phase of photosynthesis proceeds, its main essence lies in the transfer of electrons. It can also be seen from the figure that, parallel to the transport of electrons, hydrogen ions H + move across the membrane, and they accumulate inside the thylakoid. Since there are a lot of them there, they move outward with the help of a special coupling factor, which is orange in the figure, shown on the right and looks like a mushroom.
In conclusion, we see the final stage of electron transport, the result of which is the formation of the above-mentioned NADH compound. And due to the transfer of H + ions, an energy currency is synthesized - ATP (seen in the figure on the right).
So, the light phase of photosynthesis is completed, oxygen was released into the atmosphere, ATP and NADH were formed. What's next? Where is the promised organic? And then comes the dark stage, which consists mainly of chemical processes.
Dark phase of photosynthesis
For the dark phase of photosynthesis, a mandatory component is carbon dioxide - CO2. Therefore, the plant must constantly absorb it from the atmosphere. For this purpose, there are special structures on the surface of the leaf - stomata. When they open, CO2 enters the inside of the leaf, dissolves in water and enters into the reaction of the light phase of photosynthesis.
During the light phase, in most plants, CO2 binds to a five-carbon organic compound (which is a chain of five carbon molecules), resulting in two molecules of a three-carbon compound (3-phosphoglyceric acid). Because the primary result is precisely these three-carbon compounds; plants with this type of photosynthesis are called C3 plants.
Further synthesis in chloroplasts is rather complicated. Ultimately, a six-carbon compound is formed, from which glucose, sucrose or starch can then be synthesized. It is in the form of these organic substances that the plant accumulates energy. Only a small part of them remains in the sheet and is used for its needs. The rest of the carbohydrates travel throughout the plant and go exactly where energy is most needed, for example, to growth points.