3.5 Photosynthesis
5 min read•december 28, 2022
Caroline Koffke
Haseung Jun
Caroline Koffke
Haseung Jun
is a chemical process with the following equation: H2O + CO2 → + .
Both plants and photosynthetic bacteria are capable of this complex conversion process. The overall reaction is spurred by the energy from a striking a pigment in the . It is thought that first evolved in .
is broken down into two major steps which are dependent on one another: and (). Both of these processes occur in the of a photosynthetic organism.
Image courtesy of WikiMedia Commons.
Chloroplast
occur in the thylakoid membranes of the . These are the “pancakes” of the , as they look like a stack of flattened disks. The possess important pigments called . This pigment has electrons in it that are excited when energy is input by a . There are many pigments, but for , we'll focus more on , the main one.
Image courtesy of WikiMedia Commons.
When light strikes the , an electron from a molecule of is excited and travels through the . In the process, a concentration gradient of hydrogen ions is formed. This will be used later to produce ATP through . The electron lost from is replaced by an electron from water. This creates more hydrogen ions and the production of oxygen, which is released from the plant.
Light-Dependent Reactions (Electron Transport Chain)
When light hits the pigments, it'll hit first, which is embedded in the internal membrane of the and excites electrons. This causes H+ ions to move into the thylakoid space and to replenish electrons, the light splits water, called photolysis, into two H+ ions and 1/2 of and electrons, which replaces the missing electrons in . Why are the electrons missing then? Well, it's because the electrons continue to jump down the thylakoid membrane, bumping into , and thus leaving . With the electrons going down the thylakoid membrane, hydrogen ions continue to be pumped into the membrane.
Because there a lot of hydrogen ions inside the thylakoid space, it's natural for the H+ ions to want to leave the thylakoid space. But the only way for these ions to leave is to go through a transport protein called ATP (adenosine triphosphate) synthase, where ADP (adenosine diphosphate) is phosphorylated (add another phosphate) when H+ goes through it.
Other electrons from bind to an electron carrier, such as . Electron carriers transport electrons in the form of a hydrogen ion. These electrons can then be used in other processes. In this case, the electrons will be used to form bonds in the .
Image courtesy of Giphy.
The ATP and electron carriers produced during the are essential to the production of in the . The production of oxygen is toxic to the plants but provides the rest of the world with the opportunity to breathe.
Light-Independent Reactions (Calvin Cycle)
The are named due to the fact that they do not require light in order to proceed. This set of reactions is also referred to as the . These reactions take place in the of the , or the gooey space in between the thylakoid pancakes. With the help of ATP and , CO2 is turned into sugar.
In the , carbon dioxide is converted into an organic carbon source, most often modeled by . The first step of this reaction involves the enzyme ribulose bisphosphate carboxylase, abbreviated as rubisco. This enzyme is responsible for , taking carbon dioxide from the air and converting it into an organic, usable form.
After carbon dioxide has been fixed, the process begins to convert it into . This involves the creation of a lot of bonds. In order to make bonds, electrons and energy are required. This is where the electron carriers and ATP from the come into play.
By using the energy from ATP and the electrons from the electron carriers, a number of enzymes are able to convert organic carbon into glyceraldehyde-3-phosphate, or G3P. G3P is a precursor for a number of carbohydrates such as , , and . The cell can use this to create a number of important energy and structural components.
Image courtesy of WikiMedia Commons.
Also important, the ATP that is used is broken down into ADP and a phosphate group which can be recycled and rebonded in the . Similarly, the electron carrier becomes NADP+ after dropping off the hydrogen. This can then be refilled with an electron in the .
Summary
is hard to understand and visualize, but it's an important part of the AP curriculum. Study tips include trying to draw out the process yourself and explain it to a friend or yourself.
Image Courtesy of Slide Player
Understanding the can be the most challenging, so really make sure you understand what causes what. Remember, the sole purpose of is creating sugar. Also, represents a "loaded dumptruck" with electrons.
| Stage | Location | Input | Output |
| Light-Dependent | Thylakoid membrane, , | Excited electrons, H2O | , ATP, |
| Light-Independent | 3 CO2, 9 ATP, 6 | sugar |
Key Terms to Review (29)
ADP (adenosine diphosphate)
: ADP is an organic compound that plays a crucial role in metabolism. It's converted to ATP for storage of energy during cell metabolism.ATP (Adenosine Triphosphate)
: ATP is a high-energy molecule that stores and provides energy for many biochemical reactions in the cell.ATP synthase
: ATP synthase is an enzyme that creates the energy storage molecule adenosine triphosphate (ATP). It uses a proton gradient to power this process.C6H12O6
: C6H12O6 represents a molecule of glucose, which is a simple sugar that organisms use as an energy source.Calvin Cycle
: The Calvin Cycle is a set of chemical reactions that take place in chloroplasts during photosynthesis. It uses the energy from light to convert carbon dioxide into glucose.Carbon Fixation
: Carbon fixation is the process by which inorganic carbon (usually in the form of carbon dioxide) is converted to organic compounds by living organisms, primarily through photosynthesis in plants.Cellulose
: Cellulose is a complex carbohydrate, or polysaccharide, that is composed of glucose units and forms the main component of plant cell walls.Chlorophyll
: Chlorophyll is a green pigment found in plants, algae, and cyanobacteria that absorbs light energy (specifically blue and red wavelengths) to carry out photosynthesis.Chloroplast
: Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in the energy-storage molecules ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate) while freeing oxygen from water.CO2 (Carbon Dioxide)
: Carbon dioxide is a colorless, odorless gas produced by burning carbon and organic compounds and by respiration. It's absorbed by plants in photosynthesis.Electron Transport Chain
: The electron transport chain is a series of protein complexes and electron carrier molecules within the inner mitochondrial membrane that harvest energy from electrons to create ATP.Glucose
: Glucose is a simple sugar (monosaccharide) that serves as the main source of energy for cells in living organisms.Glyceraldehyde-3-phosphate, or G3P
: G3P is a three-carbon sugar molecule that is an important intermediate in both glycolysis and the Calvin cycle. It's essentially what gets produced when glucose breaks down for energy.H2O (Water)
: H2O, or water, is a molecule composed of two hydrogen atoms bonded to one oxygen atom. It's essential for all known forms of life and plays a critical role in various biological processes.Hydrogen ions concentration gradient
: This refers to the difference in concentration between two areas separated by a membrane. In biological systems, this often involves hydrogen ions (protons) moving across a membrane, such as the inner mitochondrial membrane or thylakoid membrane in chloroplasts.Light-Dependent Reactions
: Light-dependent reactions are the first stage of photosynthesis where light energy is converted into chemical energy, resulting in the production of ATP (energy currency of cells) and NADPH (an electron carrier).Light-independent reactions
: These are the second stage of photosynthesis (also known as the Calvin Cycle), where ATP and NADPH produced in the light-dependent reactions are used to convert carbon dioxide into glucose.NADPH
: NADPH is a coenzyme used in anabolic reactions, which build large molecules from small molecules. It provides the high-energy electrons needed to make carbon-carbon bonds during photosynthesis.O2
: O2 or Oxygen gas is a colorless, odorless reactive gas that forms about 21% of the earth's atmosphere. It supports combustion and respiration in most living organisms.Photon of light
: A photon of light is a particle representing a quantum of light or other electromagnetic radiation. It carries energy proportional to the radiation frequency but has zero rest mass.Photosynthesis
: Photosynthesis is the process by which green plants, algae, and some bacteria use sunlight to synthesize foods with the help of chlorophyll pigments. They convert carbon dioxide and water into glucose (a type of sugar) and oxygen.Photosystem I
: Photosystem I is a protein complex involved in photosynthesis that uses light energy to transfer electrons from plastocyanin to ferredoxin, leading to the production of NADPH.Photosystem II
: Photosystem II is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It captures photons and uses the energy to extract electrons from water molecules.Prokaryotic Cells
: Prokaryotic cells are simple, small cells that lack a nucleus or other membrane-bound organelles. They are typically found in bacteria and archaea.Rubisco (ribulose bisphosphate carboxylase)
: Rubisco is an enzyme involved in the first major step of carbon fixation; it catalyzes the conversion of carbon dioxide and ribulose bisphosphate into an unstable 6-carbon intermediate that immediately splits into two molecules of 3-phosphoglycerate.Starch
: Starch is a polysaccharide produced by most green plants as energy storage. It's composed of glucose units connected by glycosidic bonds.Stroma
: The stroma is the fluid-filled space surrounding the grana (stacks of thylakoids) within the chloroplast where the "dark" reactions of photosynthesis (Calvin cycle) occur.Thylakoid Membranes
: These are internal membranes of a chloroplast where light-dependent reactions occur during photosynthesis. They contain pigments such as chlorophyll which absorb light energy.Water photolysis
: Water photolysis is the process by which light energy splits water molecules into hydrogen ions, electrons, and oxygen gas during photosynthesis.3.5 Photosynthesis
5 min read•december 28, 2022
Caroline Koffke
Haseung Jun
Caroline Koffke
Haseung Jun
is a chemical process with the following equation: H2O + CO2 → + .
Both plants and photosynthetic bacteria are capable of this complex conversion process. The overall reaction is spurred by the energy from a striking a pigment in the . It is thought that first evolved in .
is broken down into two major steps which are dependent on one another: and (). Both of these processes occur in the of a photosynthetic organism.
Image courtesy of WikiMedia Commons.
Chloroplast
occur in the thylakoid membranes of the . These are the “pancakes” of the , as they look like a stack of flattened disks. The possess important pigments called . This pigment has electrons in it that are excited when energy is input by a . There are many pigments, but for , we'll focus more on , the main one.
Image courtesy of WikiMedia Commons.
When light strikes the , an electron from a molecule of is excited and travels through the . In the process, a concentration gradient of hydrogen ions is formed. This will be used later to produce ATP through . The electron lost from is replaced by an electron from water. This creates more hydrogen ions and the production of oxygen, which is released from the plant.
Light-Dependent Reactions (Electron Transport Chain)
When light hits the pigments, it'll hit first, which is embedded in the internal membrane of the and excites electrons. This causes H+ ions to move into the thylakoid space and to replenish electrons, the light splits water, called photolysis, into two H+ ions and 1/2 of and electrons, which replaces the missing electrons in . Why are the electrons missing then? Well, it's because the electrons continue to jump down the thylakoid membrane, bumping into , and thus leaving . With the electrons going down the thylakoid membrane, hydrogen ions continue to be pumped into the membrane.
Because there a lot of hydrogen ions inside the thylakoid space, it's natural for the H+ ions to want to leave the thylakoid space. But the only way for these ions to leave is to go through a transport protein called ATP (adenosine triphosphate) synthase, where ADP (adenosine diphosphate) is phosphorylated (add another phosphate) when H+ goes through it.
Other electrons from bind to an electron carrier, such as . Electron carriers transport electrons in the form of a hydrogen ion. These electrons can then be used in other processes. In this case, the electrons will be used to form bonds in the .
Image courtesy of Giphy.
The ATP and electron carriers produced during the are essential to the production of in the . The production of oxygen is toxic to the plants but provides the rest of the world with the opportunity to breathe.
Light-Independent Reactions (Calvin Cycle)
The are named due to the fact that they do not require light in order to proceed. This set of reactions is also referred to as the . These reactions take place in the of the , or the gooey space in between the thylakoid pancakes. With the help of ATP and , CO2 is turned into sugar.
In the , carbon dioxide is converted into an organic carbon source, most often modeled by . The first step of this reaction involves the enzyme ribulose bisphosphate carboxylase, abbreviated as rubisco. This enzyme is responsible for , taking carbon dioxide from the air and converting it into an organic, usable form.
After carbon dioxide has been fixed, the process begins to convert it into . This involves the creation of a lot of bonds. In order to make bonds, electrons and energy are required. This is where the electron carriers and ATP from the come into play.
By using the energy from ATP and the electrons from the electron carriers, a number of enzymes are able to convert organic carbon into glyceraldehyde-3-phosphate, or G3P. G3P is a precursor for a number of carbohydrates such as , , and . The cell can use this to create a number of important energy and structural components.
Image courtesy of WikiMedia Commons.
Also important, the ATP that is used is broken down into ADP and a phosphate group which can be recycled and rebonded in the . Similarly, the electron carrier becomes NADP+ after dropping off the hydrogen. This can then be refilled with an electron in the .
Summary
is hard to understand and visualize, but it's an important part of the AP curriculum. Study tips include trying to draw out the process yourself and explain it to a friend or yourself.
Image Courtesy of Slide Player
Understanding the can be the most challenging, so really make sure you understand what causes what. Remember, the sole purpose of is creating sugar. Also, represents a "loaded dumptruck" with electrons.
| Stage | Location | Input | Output |
| Light-Dependent | Thylakoid membrane, , | Excited electrons, H2O | , ATP, |
| Light-Independent | 3 CO2, 9 ATP, 6 | sugar |
Key Terms to Review (29)
ADP (adenosine diphosphate)
: ADP is an organic compound that plays a crucial role in metabolism. It's converted to ATP for storage of energy during cell metabolism.ATP (Adenosine Triphosphate)
: ATP is a high-energy molecule that stores and provides energy for many biochemical reactions in the cell.ATP synthase
: ATP synthase is an enzyme that creates the energy storage molecule adenosine triphosphate (ATP). It uses a proton gradient to power this process.C6H12O6
: C6H12O6 represents a molecule of glucose, which is a simple sugar that organisms use as an energy source.Calvin Cycle
: The Calvin Cycle is a set of chemical reactions that take place in chloroplasts during photosynthesis. It uses the energy from light to convert carbon dioxide into glucose.Carbon Fixation
: Carbon fixation is the process by which inorganic carbon (usually in the form of carbon dioxide) is converted to organic compounds by living organisms, primarily through photosynthesis in plants.Cellulose
: Cellulose is a complex carbohydrate, or polysaccharide, that is composed of glucose units and forms the main component of plant cell walls.Chlorophyll
: Chlorophyll is a green pigment found in plants, algae, and cyanobacteria that absorbs light energy (specifically blue and red wavelengths) to carry out photosynthesis.Chloroplast
: Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in the energy-storage molecules ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate) while freeing oxygen from water.CO2 (Carbon Dioxide)
: Carbon dioxide is a colorless, odorless gas produced by burning carbon and organic compounds and by respiration. It's absorbed by plants in photosynthesis.Electron Transport Chain
: The electron transport chain is a series of protein complexes and electron carrier molecules within the inner mitochondrial membrane that harvest energy from electrons to create ATP.Glucose
: Glucose is a simple sugar (monosaccharide) that serves as the main source of energy for cells in living organisms.Glyceraldehyde-3-phosphate, or G3P
: G3P is a three-carbon sugar molecule that is an important intermediate in both glycolysis and the Calvin cycle. It's essentially what gets produced when glucose breaks down for energy.H2O (Water)
: H2O, or water, is a molecule composed of two hydrogen atoms bonded to one oxygen atom. It's essential for all known forms of life and plays a critical role in various biological processes.Hydrogen ions concentration gradient
: This refers to the difference in concentration between two areas separated by a membrane. In biological systems, this often involves hydrogen ions (protons) moving across a membrane, such as the inner mitochondrial membrane or thylakoid membrane in chloroplasts.Light-Dependent Reactions
: Light-dependent reactions are the first stage of photosynthesis where light energy is converted into chemical energy, resulting in the production of ATP (energy currency of cells) and NADPH (an electron carrier).Light-independent reactions
: These are the second stage of photosynthesis (also known as the Calvin Cycle), where ATP and NADPH produced in the light-dependent reactions are used to convert carbon dioxide into glucose.NADPH
: NADPH is a coenzyme used in anabolic reactions, which build large molecules from small molecules. It provides the high-energy electrons needed to make carbon-carbon bonds during photosynthesis.O2
: O2 or Oxygen gas is a colorless, odorless reactive gas that forms about 21% of the earth's atmosphere. It supports combustion and respiration in most living organisms.Photon of light
: A photon of light is a particle representing a quantum of light or other electromagnetic radiation. It carries energy proportional to the radiation frequency but has zero rest mass.Photosynthesis
: Photosynthesis is the process by which green plants, algae, and some bacteria use sunlight to synthesize foods with the help of chlorophyll pigments. They convert carbon dioxide and water into glucose (a type of sugar) and oxygen.Photosystem I
: Photosystem I is a protein complex involved in photosynthesis that uses light energy to transfer electrons from plastocyanin to ferredoxin, leading to the production of NADPH.Photosystem II
: Photosystem II is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It captures photons and uses the energy to extract electrons from water molecules.Prokaryotic Cells
: Prokaryotic cells are simple, small cells that lack a nucleus or other membrane-bound organelles. They are typically found in bacteria and archaea.Rubisco (ribulose bisphosphate carboxylase)
: Rubisco is an enzyme involved in the first major step of carbon fixation; it catalyzes the conversion of carbon dioxide and ribulose bisphosphate into an unstable 6-carbon intermediate that immediately splits into two molecules of 3-phosphoglycerate.Starch
: Starch is a polysaccharide produced by most green plants as energy storage. It's composed of glucose units connected by glycosidic bonds.Stroma
: The stroma is the fluid-filled space surrounding the grana (stacks of thylakoids) within the chloroplast where the "dark" reactions of photosynthesis (Calvin cycle) occur.Thylakoid Membranes
: These are internal membranes of a chloroplast where light-dependent reactions occur during photosynthesis. They contain pigments such as chlorophyll which absorb light energy.Water photolysis
: Water photolysis is the process by which light energy splits water molecules into hydrogen ions, electrons, and oxygen gas during photosynthesis.
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