8.6 Photosynthesis
3 min read•june 18, 2024
is a complex process that turns sunlight into energy for plants. It involves various pigments that capture light and two main reaction types. These reactions work together to produce glucose, the plant's food source.
The process starts with light-capturing pigments like . Then, make and . Finally, light-independent reactions use these products to fix carbon and make glucose. This glucose fuels plant growth and life.
Photosynthetic Pigments and Light Capture
Distribution of photosynthetic pigments
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- Chlorophylls serve as primary photosynthetic pigments
- found in all photosynthetic organisms (plants, algae, cyanobacteria)
- found in plants and green algae (Chlorophyta)
- Absorb red and blue light wavelengths, reflect green light giving plants their characteristic color
- Accessory pigments enhance light capture and provide photoprotection
- (carotenes and xanthophylls) absorb light energy and transfer it to chlorophylls
- Protect cells from photodamage by dissipating excess light energy
- Found in plants, algae, and some bacteria (carrots, tomatoes)
- (phycoerythrin and phycocyanin) absorb green and yellow light
- Found in red algae (Rhodophyta) and cyanobacteria
- Enable in deeper water by capturing wavelengths that penetrate further
- (carotenes and xanthophylls) absorb light energy and transfer it to chlorophylls
- organize pigments for efficient energy transfer
- Contain chlorophylls and accessory pigments
- Funnel captured light energy to reaction centers
Photosynthetic Reactions and Products
Outputs of photosynthesis reactions
- Light-dependent reactions () occur in membranes
- Capture light energy using photosynthetic pigments (chlorophylls, carotenoids)
- Generate ATP through process
- Produce NADPH (reduced nicotinamide adenine dinucleotide phosphate) as electron carrier
- Split water molecules, releasing oxygen as a byproduct (source of atmospheric oxygen)
- Light-independent reactions occur in the
- Also known as the or dark reactions (can occur in absence of light)
- Use ATP and NADPH from light-dependent reactions to power
- Fix atmospheric CO2 () into organic compounds (glucose, other carbohydrates)
- Produce glucose and other carbohydrates for energy storage and biosynthesis
Glucose production in photosynthesis
- Carbon fixation initiates glucose synthesis
- carboxylase/oxygenase () enzyme catalyzes the addition of CO2 to
- Produces two molecules of () as initial stable products
- Reduction phase converts 3-PGA to simple sugars
- ATP and NADPH from light-dependent reactions are used to convert 3-PGA to (G3P)
- G3P is a simple sugar that serves as building block for glucose and other carbohydrates
- Regeneration phase ensures continuity of the Calvin cycle
- Some G3P is used to regenerate RuBP, allowing the Calvin cycle to continue
- Maintains a constant supply of RuBP for carbon fixation
- Glucose synthesis occurs through condensation reactions
- Remaining G3P molecules are combined to form glucose and other carbohydrates (starch, cellulose)
- Glucose is used for energy storage or transported to other parts of the plant
Cyclic vs noncyclic photophosphorylation
- involves both photosystems
- Electron flow from PSII to PSI via generates a proton gradient
- Produces both ATP (via ATP synthase) and NADPH (via )
- Oxygen is released as a byproduct of water splitting at PSII
- involves only PSI
- Electrons cycle back from ferredoxin to cytochrome b6f complex and then to PSI
- Generates a proton gradient for ATP production via ATP synthase
- Does not produce NADPH, as electrons do not reach ferredoxin-NADP+ reductase
- No oxygen is released, as water is not split during this process
Electron Transport and Energy Conversion
- facilitates energy transfer in light reactions
- Consists of protein complexes embedded in
- Transfers electrons from water to NADP+, generating NADPH
- Creates a proton gradient used for ATP synthesis
Key Terms to Review (66)
3-PGA: 3-Phosphoglycerate (3-PGA) is a three-carbon molecule formed in the Calvin cycle during photosynthesis. It is the first stable product of carbon fixation in the C3 pathway.
3-phosphoglycerate: 3-phosphoglycerate (3-PGA) is a 3-carbon molecule formed during the Calvin cycle of photosynthesis. It is an intermediate that plays a crucial role in the synthesis of glucose.
Anderson: Anderson is a reference to the Anderson cascade impactor, a device used to measure particle size distribution in aerosols. In microbiology, it can be applied to study the dispersion of photosynthetic microorganisms in various environments.
Anoxygenic photosynthesis: Anoxygenic photosynthesis is a form of photosynthesis used by certain bacteria that does not produce oxygen as a byproduct. Instead, it utilizes molecules other than water as electron donors.
ATP: ATP (Adenosine Triphosphate) is the primary energy carrier in cells. It stores and provides energy necessary for various cellular processes.
ATP (Adenosine Triphosphate): ATP, or adenosine triphosphate, is the primary energy currency of the cell. It is a high-energy molecule that stores and transports chemical energy within living organisms, powering a wide range of cellular processes. ATP is central to the fundamental mechanisms of life, as it is involved in various metabolic pathways, including carbohydrate metabolism, cellular respiration, and photosynthesis.
Bacteriochlorophyll: Bacteriochlorophyll is a type of chlorophyll found in photosynthetic bacteria that helps capture light energy for photosynthesis. It plays a crucial role in converting light energy into chemical energy.
Calvin Cycle: The Calvin cycle, also known as the dark reactions or the light-independent reactions, is a series of biochemical reactions that occur in the stroma of chloroplasts in photosynthetic organisms. It is the second stage of photosynthesis, where the energy and reducing power generated during the light-dependent reactions (the first stage) are used to produce organic compounds, primarily glucose, from carbon dioxide.
Calvin-Benson cycle: The Calvin-Benson cycle, also known as the Calvin cycle, is a series of biochemical reactions that take place in the stroma of chloroplasts during photosynthesis. It is responsible for converting carbon dioxide and other compounds into glucose.
Carbon Dioxide: Carbon dioxide is a colorless, odorless gas that is produced as a byproduct of various metabolic and combustion processes. It is a vital component in the natural carbon cycle and plays a crucial role in the processes of fermentation and photosynthesis.
Carbon Fixation: Carbon fixation is the process by which inorganic carbon, such as carbon dioxide (CO2), is converted into organic compounds, typically carbohydrates, through the use of energy. This process is a fundamental aspect of photosynthesis and is crucial for the sustenance of life on Earth.
Carotenoid: Carotenoids are pigments found in microorganisms that play a crucial role in photosynthesis by absorbing light energy. They also protect against oxidative damage caused by excess light.
Carotenoids: Carotenoids are a group of naturally occurring pigments that are responsible for the vibrant colors seen in many plants, algae, and some bacteria. They are lipid-soluble molecules that play crucial roles in various biological processes, including photosynthesis, photoprotection, and as antioxidants.
Cellular respiration: Cellular respiration is a metabolic process that converts glucose into ATP (adenosine triphosphate) through glycolysis, the Krebs cycle, and oxidative phosphorylation. It is essential for providing energy to cells.
Chlorophyll: Chlorophyll is a green pigment found in the chloroplasts of plants, algae, and cyanobacteria. It plays a crucial role in photosynthesis by absorbing light energy, primarily from the blue and red parts of the electromagnetic spectrum.
Chlorophyll: Chlorophyll is a green pigment found in plants, algae, and cyanobacteria that is essential for photosynthesis. It absorbs sunlight, particularly red and blue wavelengths, and uses the energy to convert carbon dioxide and water into glucose and oxygen.
Chlorophyll a: Chlorophyll a is the primary photosynthetic pigment found in the chloroplasts of plants, algae, and certain bacteria. It is responsible for the green color of most photosynthetic organisms and plays a crucial role in the process of photosynthesis by absorbing light energy from the sun, which is then used to drive the conversion of carbon dioxide and water into glucose and oxygen.
Chlorophyll b: Chlorophyll b is a type of chlorophyll, a green pigment found in the chloroplasts of plants and some algae. It is essential for the process of photosynthesis, which is the conversion of light energy from the sun into chemical energy that can be used by the plant.
Chloroplast: Chloroplasts are organelles found in plant cells and certain algae that conduct photosynthesis. They convert light energy into chemical energy stored in glucose.
Cyclic photophosphorylation: Cyclic photophosphorylation is a process in photosynthesis where electrons are recycled back to the photosystem, generating ATP without producing NADPH. This pathway helps balance the ATP/NADPH ratio during light-dependent reactions.
Cytochrome b6f Complex: The cytochrome b6f complex is a large, multi-subunit protein complex that acts as an essential component of the electron transport chain in the light-dependent reactions of photosynthesis. It plays a crucial role in the transfer of electrons between photosystem II and photosystem I, ultimately driving the production of ATP.
Electrochemical gradient: An electrochemical gradient is a difference in the concentration of ions across a membrane, coupled with a difference in electric charge. It is essential for processes like ATP synthesis during photosynthesis.
Electron Transport Chain: The electron transport chain is a series of protein complexes and electron carriers embedded in the inner membrane of mitochondria or the thylakoid membrane of chloroplasts. It is a crucial component of cellular respiration and photosynthesis, responsible for the final stages of energy production in living organisms.
Electron transport system: The electron transport system (ETS) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions. This process generates a proton gradient across the membrane, ultimately producing ATP through chemiosmosis.
ETS: The Electron Transport System (ETS) is a series of protein complexes and other molecules that transfer electrons through a membrane to create a proton gradient. This process ultimately generates ATP through chemiosmosis.
Ferredoxin-NADP+ Reductase: Ferredoxin-NADP+ reductase is an enzyme that catalyzes the transfer of electrons from the iron-sulfur protein ferredoxin to the cofactor NADP+, converting it to the reduced form NADPH. This enzyme plays a crucial role in the light-dependent reactions of photosynthesis, where it helps generate the reducing power necessary for the Calvin cycle.
Glyceraldehyde 3-Phosphate: Glyceraldehyde 3-phosphate (G3P or GAP) is a crucial intermediate in the metabolic pathways of photosynthesis and glycolysis. It is a triose phosphate, meaning it is a three-carbon sugar phosphate that serves as a key building block for the synthesis of larger carbohydrate molecules.
Granum: A granum is a stack of thylakoid membranes found within the chloroplasts of plant cells. It plays a critical role in the light-dependent reactions of photosynthesis, where light energy is converted into chemical energy.
Light Reactions: The light reactions, also known as the light-dependent reactions, are the first stage of photosynthesis where energy from sunlight is captured and converted into chemical energy in the form of ATP and NADPH. This process takes place in the thylakoid membranes of the chloroplasts within plant cells.
Light-dependent reaction: The light-dependent reaction is the first phase of photosynthesis where solar energy is converted into chemical energy in the form of ATP and NADPH. It occurs in the thylakoid membranes of chloroplasts.
Light-Dependent Reactions: Light-dependent reactions are the first stage of photosynthesis, where energy from sunlight is captured and used to produce energy-rich molecules that power the subsequent light-independent reactions. These light-driven processes take place in the thylakoid membranes of the chloroplasts within plant cells.
Light-harvesting complex: A light-harvesting complex (LHC) is a group of proteins and pigments in photosynthetic organisms that capture and transfer light energy to the reaction center during photosynthesis. It plays a crucial role in maximizing the efficiency of light absorption.
Light-Harvesting Complexes: Light-harvesting complexes are specialized pigment-protein structures found in the photosynthetic membranes of plants, algae, and certain bacteria. These complexes are responsible for efficiently capturing and funneling light energy to the reaction centers, where the initial steps of photosynthesis take place.
Light-independent reaction: Light-independent reactions, also known as the Calvin cycle, occur in the stroma of chloroplasts where ATP and NADPH from light-dependent reactions are used to produce glucose. These reactions do not require light directly but rely on the products of light-dependent reactions.
NADH: NADH is a coenzyme that plays a crucial role in energy production within cells by transporting electrons during cellular respiration. It is the reduced form of NAD+ (nicotinamide adenine dinucleotide).
NADPH: NADPH (Nicotinamide Adenine Dinucleotide Phosphate) is a coenzyme that plays a crucial role in anabolic reactions and photosynthesis. It acts as a reducing agent, donating electrons and hydrogen to various biochemical reactions.
Noncyclic photophosphorylation: Noncyclic photophosphorylation is the process in photosynthesis where electrons flow from water to NADP+, producing ATP and NADPH. This occurs in the thylakoid membrane of chloroplasts and involves both Photosystem I and Photosystem II.
Oxidative phosphorylation: Oxidative phosphorylation is the process by which cells generate ATP through the electron transport chain and chemiosmosis in the mitochondria. It is the final stage of cellular respiration, involving oxygen as the final electron acceptor.
Oxygenic photosynthesis: Oxygenic photosynthesis is the process by which certain organisms convert light energy into chemical energy, producing oxygen as a byproduct. This process mainly occurs in plants, algae, and cyanobacteria.
Photooxidation: Photooxidation is a chemical process in which molecules are oxidized by the energy of light, leading to the formation of reactive oxygen species that can cause damage to cellular components. This process is particularly relevant in the context of photosynthesis, where it plays a crucial role in the conversion of light energy into chemical energy.
Photophosphorylation: Photophosphorylation is the process of converting light energy into chemical energy in the form of ATP during photosynthesis. It occurs in the thylakoid membranes of chloroplasts and involves electron transport chains.
Photophosphorylation: Photophosphorylation is the process by which ATP is generated in the chloroplasts of photosynthetic organisms, using the energy from the absorption of light. It is a crucial step in the light-dependent reactions of photosynthesis, where the energy from sunlight is converted into the chemical energy of ATP.
Photosynthesis: Photosynthesis is a biochemical process by which phototrophic organisms convert light energy into chemical energy, storing it in the bonds of glucose molecules. This process primarily occurs in chlorophyll-containing cells and involves both light-dependent and light-independent reactions.
Photosynthesis: Photosynthesis is the process by which certain organisms, such as plants and some bacteria, use the energy from sunlight to convert carbon dioxide and water into glucose and oxygen. This process is essential for the survival of many life forms on Earth, as it provides the primary source of energy and food for a vast array of organisms.
Photosynthesis is a crucial topic in the context of 4.3 Nonproteobacteria Gram-Negative Bacteria and Phototrophic Bacteria, 5.4 Algae, 8.6 Photosynthesis, and 9.5 Other Environmental Conditions that Affect Growth, as it is the fundamental process that powers the growth and development of these organisms.
Photosynthetic Membranes: Photosynthetic membranes are specialized cellular structures that house the chloroplasts and other organelles responsible for the process of photosynthesis. These membranes provide the necessary environment and machinery for the conversion of light energy into chemical energy in the form of ATP and NADPH, which are then used to power various cellular processes.
Photosynthetic pigment: Photosynthetic pigments are molecules that absorb light energy and convert it into chemical energy during photosynthesis. They play a crucial role in capturing light at different wavelengths to drive the process of photosynthesis.
Photosystem: A photosystem is a protein complex in chloroplasts and cyanobacteria that absorbs light during photosynthesis, initiating the conversion of light energy into chemical energy. It consists of a reaction center surrounded by light-harvesting complexes.
Photosystem: A photosystem is a complex of proteins and pigments found in the thylakoid membranes of chloroplasts in plants and cyanobacteria. It is the site where the initial light-dependent reactions of photosynthesis occur, capturing and converting light energy into chemical energy.
Photosystem I: Photosystem I is a key component of the photosynthetic electron transport chain found in the thylakoid membranes of cyanobacteria, algae, and plants. It is responsible for the light-driven transfer of electrons from the primary electron donor to the final electron acceptor, ultimately powering the production of ATP and reducing power in the form of NADPH for the Calvin cycle.
Photosystem I (PSI): Photosystem I (PSI) is a protein complex in the thylakoid membrane that plays a crucial role in the light-dependent reactions of photosynthesis. It is responsible for the final stage of electron transport, ultimately producing NADPH.
Photosystem II: Photosystem II is a large protein complex found in the thylakoid membranes of photosynthetic organisms, such as cyanobacteria, algae, and plants. It is a crucial component of the light-dependent reactions of photosynthesis, responsible for the initial steps of the process that ultimately lead to the production of energy-rich molecules like ATP and NADPH.
Photosystem II (PSII): Photosystem II (PSII) is a protein complex in the thylakoid membrane of chloroplasts involved in the light-dependent reactions of photosynthesis. It uses light energy to extract electrons from water, generating oxygen and protons.
Phototrophic eukaryotes: Phototrophic eukaryotes are organisms that possess chloroplasts to perform photosynthesis, converting light energy into chemical energy. They include various algae, plants, and some protists.
Phycobilins: Phycobilins are a group of light-harvesting pigments found in the photosynthetic apparatus of certain cyanobacteria and red algae. These pigments play a crucial role in the photosynthetic process by absorbing specific wavelengths of light and transferring the energy to chlorophyll molecules, enhancing the efficiency of light capture.
Phycocyanins: Phycocyanins are pigment-proteins from the phycobiliprotein family, found in cyanobacteria and certain algae. They play a crucial role in capturing light energy for photosynthesis.
Phycoerythrins: Phycoerythrins are a group of red and pink pigments found in cyanobacteria and red algae, which play a crucial role in capturing light energy for photosynthesis. These pigments absorb blue-green to yellow-green light, enhancing the efficiency of photosynthesis in deep water or low-light environments.
Reaction center: The reaction center is a complex of proteins and pigments that plays a central role in the initial steps of photosynthesis by converting light energy into chemical energy. It is the site where photon absorption leads to the transfer of electrons.
Ribulose Bisphosphate: Ribulose bisphosphate, also known as RuBP, is a key intermediate in the Calvin cycle of photosynthesis. It is a 5-carbon sugar that acts as the initial substrate for carbon dioxide fixation, a crucial step in the conversion of light energy into chemical energy during the light-independent reactions of photosynthesis.
Ribulose bisphosphate (RuBP): Ribulose bisphosphate (RuBP) is a five-carbon sugar involved in the Calvin cycle of photosynthesis. It acts as a substrate for the enzyme RuBisCO to fix carbon dioxide into organic molecules.
Ribulose bisphosphate carboxylase (RuBisCO): Ribulose bisphosphate carboxylase (RuBisCO) is an enzyme involved in the first major step of carbon fixation in the Calvin cycle of photosynthesis. It catalyzes the reaction between ribulose-1,5-bisphosphate (RuBP) and carbon dioxide to form two molecules of 3-phosphoglycerate.
RuBisCO: RuBisCO, or Ribulose-1,5-bisphosphate carboxylase/oxygenase, is a critical enzyme involved in the Calvin cycle of photosynthesis. It catalyzes the first major step in carbon fixation, where it captures atmospheric carbon dioxide and incorporates it into organic compounds that can be used by the plant for energy and growth.
Stroma: The stroma is the fluid-filled matrix of a chloroplast, where the Calvin cycle reactions of photosynthesis occur. It contains enzymes, DNA, ribosomes, and is integral to the conversion of carbon dioxide into glucose.
Stroma: The stroma is the fluid-filled space between the thylakoid membranes within the chloroplasts of plant cells. It is the site where the light-independent reactions of photosynthesis, also known as the Calvin cycle or dark reactions, take place.
Thylakoid: A thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria where the light-dependent reactions of photosynthesis occur. It contains chlorophyll and other pigments that capture light energy.
Thylakoid: The thylakoid is a flattened, membrane-bound structure found within the chloroplasts of photosynthetic organisms, such as plants and cyanobacteria. It is the site where the light-dependent reactions of photosynthesis occur, providing the energy and reducing power necessary for the subsequent carbon fixation reactions.
Z-scheme: A Z-scheme is a diagrammatic representation of the electron transport chain in photosynthesis. It illustrates the flow of electrons through photosystem II and photosystem I, highlighting energy changes.