8.3 Using Light Energy to Make Organic Molecules
3 min read•june 14, 2024
is the powerhouse of life on Earth. It converts sunlight into chemical energy, driving ecosystems and fueling the food chain. The , , and work together to transform inorganic carbon into organic compounds.
This process is the foundation of energy flow in ecosystems. capture light energy, which then moves through food webs. While some energy is lost as heat, the remaining energy supports diverse ecological communities and keeps our planet's ecosystems thriving.
Photosynthesis and Energy Flow
Steps of Calvin cycle
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- Carbon fixation ()
- Enzyme catalyzes addition of CO2 to (RuBP)
- Forms two molecules of (3-PGA)
- Reduction
- and from convert 3-PGA to (G3P)
- G3P simple sugar used to make and other organic compounds (, )
- Regeneration
- Some G3P molecules regenerate RuBP, allowing cycle to continue
- Remaining G3P molecules synthesize glucose and other organic compounds (, )
Carbon fixation in energy conversion
- Carbon fixation converts inorganic carbon (CO2) into organic compounds
- Occurs during Calvin cycle of photosynthesis
- Catalyzed by enzyme RuBisCO
- CO2 added to ribulose bisphosphate (RuBP) to form 3-phosphoglycerate (3-PGA)
- Light energy captured during light-dependent reactions powers carbon fixation
- ATP and NADPH generated in light-dependent reactions reduce 3-PGA to glyceraldehyde 3-phosphate (G3P)
- G3P simple sugar used to synthesize glucose and other organic compounds (starch, )
- Carbon fixation converts light energy into chemical energy stored in organic molecules
- Glucose and other organic compounds store energy in chemical bonds
- Energy released through cellular respiration powers cellular processes (growth, reproduction)
- can occur when RuBisCO fixes oxygen instead of carbon dioxide, reducing photosynthetic efficiency
Photosynthesis in ecosystem energy flow
- Photosynthetic organisms (primary producers) capture light energy and convert into chemical energy
- Light energy powers synthesis of organic compounds from inorganic materials (CO2 and H2O)
- Organic compounds store chemical energy in bonds
- Primary producers form base of most food chains and food webs
- (primary consumers) obtain energy by consuming primary producers (plants, algae)
- (secondary and tertiary consumers) obtain energy by consuming herbivores and other carnivores (predators)
- Energy transferred from one to next through consumption
- Only fraction of energy (typically 10%) transferred to next trophic level
- Remaining energy lost as heat or used for metabolic processes (respiration, excretion)
- break down dead organisms and return nutrients to ecosystem
- Decomposition releases energy as heat and recycles nutrients, making available for primary producers (bacteria, fungi)
- Photosynthesis primary source of energy input in most ecosystems
- Drives flow of energy from primary producers to consumers and
- Supports growth and maintenance of diverse ecological communities (coral reefs, rainforests)
Light-dependent reactions and energy capture
- captures photons and transfers energy to reaction centers
- generates ATP through chemiosmosis driven by
- NADPH produced as electrons are transferred from water to NADP+
Key Terms to Review (36)
3-phosphoglycerate: 3-phosphoglycerate (3-PGA) is a three-carbon molecule that plays a crucial role as an intermediate in both glycolysis and the Calvin cycle. It forms during the conversion of glucose to pyruvate in glycolysis and is also produced during the fixation of carbon dioxide in photosynthesis, where it serves as a precursor for glucose synthesis. This dual role makes 3-PGA essential for energy production and organic molecule formation in living organisms.
Amino acids: Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid contains an amino group, a carboxyl group, and a unique side chain (R-group).
Amino Acids: Amino acids are organic compounds that serve as the building blocks of proteins, consisting of an amino group, a carboxyl group, and a unique side chain. They play critical roles in various biological processes, including protein synthesis, metabolism, and the regulation of cellular functions.
ATP: Adenosine triphosphate (ATP) is a high-energy molecule that serves as the primary energy currency of the cell, driving various biological processes. It plays a critical role in energy transfer within cells, linking energy-releasing reactions to energy-requiring processes, making it essential for cellular functions and metabolism.
Calvin cycle: The Calvin cycle is a series of biochemical reactions that occur in the stroma of chloroplasts, where carbon dioxide is fixed into organic molecules using energy derived from ATP and NADPH, produced during the light-dependent reactions of photosynthesis. This cycle plays a crucial role in converting light energy into chemical energy in the form of glucose, which is essential for the survival and growth of plants and other photosynthetic organisms.
Carbon assimilation: Carbon assimilation is the process by which autotrophic organisms, such as plants, convert inorganic carbon dioxide (CO₂) from the atmosphere into organic compounds like glucose using light energy. This process is a crucial part of photosynthesis and enables the transformation of light energy into chemical energy, supporting life by providing the organic matter necessary for growth and metabolism.
Carbon fixation: Carbon fixation is the process by which inorganic carbon dioxide (CO₂) is converted into organic compounds by living organisms, primarily during photosynthesis. This process is crucial because it forms the foundation for the production of carbohydrates, which serve as energy sources for plants and other organisms. In plants, carbon fixation occurs during the Calvin cycle, where CO₂ is incorporated into organic molecules, leading to the synthesis of sugars and other vital compounds.
Carnivores: Carnivores are organisms that primarily consume other animals for energy and nutrients. They play a crucial role in ecosystems as predators, helping to control prey populations and maintain ecological balance. By utilizing energy stored in the bodies of other organisms, carnivores contribute to the flow of energy through food webs and impact the structure and dynamics of various habitats.
Cellulose: Cellulose is a complex carbohydrate and a key structural component of plant cell walls. It is composed of linear chains of glucose molecules linked by β-1,4-glycosidic bonds.
Cellulose: Cellulose is a complex carbohydrate, specifically a polysaccharide made up of long chains of glucose molecules linked together by β(1→4) glycosidic bonds. It serves as a key structural component in the cell walls of plants, providing rigidity and strength while playing an essential role in the synthesis of biological macromolecules and cellular interactions.
Chloroplast: Chloroplasts are organelles found in plant cells and algae responsible for photosynthesis. They convert light energy into chemical energy stored in glucose molecules.
Chloroplast: Chloroplasts are membrane-bound organelles found in plant cells and some algae that are responsible for photosynthesis, the process of converting light energy into chemical energy. They contain chlorophyll, the green pigment that captures sunlight, allowing the plant to produce glucose and oxygen from carbon dioxide and water.
Decomposers: Decomposers are organisms that break down dead or decaying organic matter, recycling nutrients back into the ecosystem. In prokaryotes, this role is often filled by certain bacteria and archaea.
Decomposers: Decomposers are organisms, primarily bacteria and fungi, that break down dead organic matter, recycling nutrients back into the ecosystem. They play a crucial role in energy flow by converting complex organic substances into simpler compounds, making nutrients available for primary producers like plants to use. This process is essential for maintaining healthy ecosystems and supporting the growth of new life.
Electron transport chain: The electron transport chain (ETC) is a series of protein complexes and other molecules located in the inner mitochondrial membrane that transfer electrons from electron donors to electron acceptors via redox reactions, ultimately generating adenosine triphosphate (ATP) through oxidative phosphorylation. It plays a critical role in energy metabolism and cellular respiration, connecting various metabolic processes.
Fatty acids: Fatty acids are long-chain hydrocarbons with a carboxyl group (-COOH) at one end, playing a vital role as building blocks of lipids. They are essential components of various biological macromolecules and serve as a primary energy source in living organisms, connecting to various processes such as metabolism, energy storage, and cell membrane structure.
Glucose: Glucose is a simple sugar and a vital carbohydrate that serves as a primary energy source for living organisms. This monosaccharide is crucial for various biological processes, including cellular respiration, energy production, and as a building block for larger carbohydrates.
Glucose-sparing effect: Glucose-sparing effect is a metabolic process where the body prioritizes the use of fats and proteins for energy to conserve glucose for the brain. This mechanism is crucial during fasting or intense exercise when glucose levels are low.
Glyceraldehyde 3-phosphate: Glyceraldehyde 3-phosphate (G3P) is a three-carbon sugar molecule that plays a crucial role in cellular metabolism, particularly in the process of photosynthesis and glycolysis. It is an intermediate compound formed during the Calvin cycle, where carbon dioxide is fixed and converted into organic molecules using light energy. G3P is essential for synthesizing glucose and other carbohydrates, making it a key player in the conversion of light energy into stored chemical energy.
Herbivores: Herbivores are organisms that primarily consume plant material for energy and nutrients. This group of animals plays a crucial role in ecosystems, as they contribute to the cycling of nutrients and energy flow within food webs by feeding on producers, like plants, which convert light energy into chemical energy through photosynthesis.
Light-dependent reactions: The light-dependent reactions are the first stage of photosynthesis where light energy is converted into chemical energy in the form of ATP and NADPH. These reactions take place within the thylakoid membranes of the chloroplasts.
Light-dependent reactions: Light-dependent reactions are the initial stage of photosynthesis where light energy is captured and converted into chemical energy in the form of ATP and NADPH. These reactions take place in the thylakoid membranes of chloroplasts and are crucial for providing the energy needed for the subsequent stages of photosynthesis, including the formation of organic molecules.
Light-harvesting complex: A light-harvesting complex is a group of proteins and pigments that capture and transfer light energy to the reaction center in photosynthetic organisms. This complex is crucial for converting solar energy into chemical energy during photosynthesis, as it facilitates the absorption of light, particularly in chlorophyll molecules, and channels that energy for use in the synthesis of organic molecules.
NADPH: NADPH (nicotinamide adenine dinucleotide phosphate) is a crucial coenzyme involved in various metabolic processes, primarily acting as a reducing agent in anabolic reactions. It plays a significant role in photosynthesis by providing the necessary reducing power for converting carbon dioxide into glucose, linking energy conversion and biosynthesis.
Photophosphorylation: Photophosphorylation is the process of converting light energy into chemical energy in the form of ATP (adenosine triphosphate) during photosynthesis. This process occurs in the thylakoid membranes of chloroplasts, where light energy is captured by chlorophyll and used to add a phosphate group to ADP (adenosine diphosphate), ultimately producing ATP. It is a crucial step in harnessing solar energy and plays a vital role in fueling the synthesis of organic molecules from carbon dioxide and water.
Photorespiration: Photorespiration is a metabolic process in plants that occurs when the enzyme RuBisCO oxygenates RuBP, leading to the consumption of energy and the release of CO2 instead of producing glucose during photosynthesis. This process typically happens under conditions of high oxygen levels and low carbon dioxide concentrations, causing inefficiency in the plant's ability to fix carbon and produce organic molecules using light energy.
Photosynthesis: Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in glucose, using carbon dioxide and water while releasing oxygen as a byproduct. This process is fundamental to life on Earth as it provides the primary energy source for nearly all living organisms and contributes to the cycling of carbon and oxygen in ecosystems.
Photosystem: A photosystem is a protein complex found in the thylakoid membranes of plants, algae, and cyanobacteria that plays a critical role in the light-dependent reactions of photosynthesis. It captures photons and utilizes the energy to drive electron transport chains.
Photosystem: A photosystem is a complex of proteins and pigments in the thylakoid membranes of chloroplasts that plays a crucial role in capturing light energy during photosynthesis. It consists of a light-harvesting complex, which contains chlorophyll and accessory pigments, and a reaction center where the conversion of light energy into chemical energy occurs. The two types of photosystems, Photosystem I and Photosystem II, work together in the light-dependent reactions to produce ATP and NADPH for subsequent use in synthesizing organic molecules.
Primary producers: Primary producers are organisms, primarily plants and certain microorganisms, that can create their own food through the process of photosynthesis or chemosynthesis. They form the base of the food web by converting light energy or chemical energy into organic matter, which serves as a food source for other organisms in the ecosystem.
Ribulose bisphosphate: Ribulose bisphosphate (RuBP) is a five-carbon sugar phosphate that plays a crucial role in the process of photosynthesis, specifically in the Calvin cycle where carbon fixation occurs. It serves as the primary carbon dioxide acceptor, facilitating the conversion of inorganic carbon into organic molecules during light-dependent reactions. RuBP is essential for synthesizing glucose and other carbohydrates that plants use for energy and growth.
RuBisCO: RuBisCO, or ribulose-1,5-bisphosphate carboxylase/oxygenase, is an enzyme that plays a critical role in the process of photosynthesis by catalyzing the first major step of carbon fixation. This enzyme facilitates the reaction between carbon dioxide and ribulose bisphosphate, leading to the production of 3-phosphoglycerate, which is a key intermediate in the synthesis of organic molecules. RuBisCO is essential for converting inorganic carbon into a usable form for plants and is considered one of the most abundant proteins on Earth.
Starch: Starch is a carbohydrate composed of long chains of glucose molecules, serving as a primary energy storage form in plants. This polysaccharide is synthesized through the process of photosynthesis and is broken down into glucose when energy is needed, making it a crucial component in both plant metabolism and human nutrition.
Thylakoid: A thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria, playing a crucial role in the process of photosynthesis. These structures are organized into stacks called grana and contain chlorophyll and other pigments that capture light energy, which is essential for converting sunlight into chemical energy during the light-dependent reactions.
Thylakoid lumen: The thylakoid lumen is the inner space enclosed by the thylakoid membrane within chloroplasts. It plays a critical role in the light-dependent reactions of photosynthesis.
Trophic level: A trophic level refers to the position an organism occupies in a food chain, which is based on its feeding relationships and energy transfer within an ecosystem. These levels help illustrate how energy flows from one organism to another, starting from primary producers like plants that convert light energy into organic matter, to various levels of consumers, including herbivores and carnivores. Understanding trophic levels is essential for grasping how ecosystems function and maintain balance.