Biology Flashcards: Interpret Photosynthesis Energy Flow Models

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This deck focuses on Interpret Photosynthesis Energy Flow Models, giving you a quick way to review the definitions, rules, and examples that matter most for Biology.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: What process directly produces $O_2$ during the light reactions?

Answer: Photolysis (splitting) of $H_2O$. Water splitting releases oxygen as a byproduct.

Flashcard 2: What is the carbon input molecule for the Calvin cycle?

Answer: $CO_2$. Source of carbon atoms for sugar synthesis.

Flashcard 3: What molecules return from the Calvin cycle to the light reactions after energy is used?

Answer: ADP + P$_i$ and NADP$^+$. Depleted energy carriers return for regeneration.

Flashcard 4: In energy-flow models, what does ATP primarily provide to the Calvin cycle?

Answer: Energy to drive endergonic reactions. Powers thermodynamically unfavorable carbon fixation steps.

Flashcard 5: What is photophosphorylation?

Answer: ATP production powered by light-driven electron transport. Light energy drives phosphate addition to ADP.

Flashcard 6: Which molecule is the source of the oxygen gas released during photosynthesis?

Answer: Water ($H_2O$). Water molecules are split to provide electrons and protons.

Flashcard 7: Which molecule is the immediate product of light reactions that directly powers carbon fixation steps?

Answer: ATP. Provides phosphate bond energy for biosynthetic reactions.

Flashcard 8: What is photophosphorylation?

Answer: ATP production powered by light-driven electron transport. Light energy drives phosphate addition to ADP.

Flashcard 9: Identify the correct source of electrons that ultimately reduce NADP$^+$ in photosynthesis.

Answer: $H_2O$ provides the electrons. Water is the ultimate electron donor in photosynthesis.

Flashcard 10: Which outcome indicates cyclic electron flow is operating in a model?

Answer: ATP produced but no NADPH and no $O_2$. Circular flow generates only ATP without oxygen release.

Flashcard 11: What is the role of the electron transport chain between PSII and PSI in energy flow?

Answer: Converts electron energy into a proton gradient. Energy released pumps protons across the membrane.

Flashcard 12: Which molecule is oxidized during the Calvin cycle to regenerate NADP$^+$ for light reactions?

Answer: NADPH is oxidized to NADP$^+$. Loses electrons to regenerate the oxidized form.

Flashcard 13: What form of energy enters a photosynthetic system from the environment?

Answer: Light energy (photons). Electromagnetic radiation provides the initial energy for photosynthesis.

Flashcard 14: Identify the correct interpretation of NADPH in a model: energy carrier or structural carbohydrate?

Answer: Energy and electron carrier. NADPH stores and transfers both energy and electrons.

Flashcard 15: What form of energy enters a photosynthetic system from the environment?

Answer: Light energy (photons). Electromagnetic radiation provides the initial energy for photosynthesis.

Flashcard 16: Identify the correct location for ATP synthase in chloroplasts in energy-flow models.

Answer: Embedded in the thylakoid membrane. Enzyme spans the membrane to access proton gradient.

Flashcard 17: Which chloroplast region is the site of the Calvin cycle (light-independent reactions)?

Answer: Stroma. Fluid-filled space where carbon fixation occurs.

Flashcard 18: Which enzyme uses the proton gradient to synthesize ATP in photosynthesis?

Answer: ATP synthase. Uses proton flow to drive phosphorylation of ADP.

Flashcard 19: In energy-flow models, what does NADPH primarily provide to the Calvin cycle?

Answer: High-energy electrons (reducing power). Supplies electrons needed for carbon reduction reactions.

Flashcard 20: Which enzyme uses the proton gradient to synthesize ATP in photosynthesis?

Answer: ATP synthase. Uses proton flow to drive phosphorylation of ADP.

Flashcard 21: Which electron flow pathway produces oxygen: cyclic or noncyclic?

Answer: Noncyclic electron flow. Linear pathway includes water splitting and oxygen release.

Flashcard 22: In the Z-scheme, what happens to electron energy immediately after photon absorption?

Answer: Electron energy increases (excitation). Light photons boost electrons to higher energy levels.

Flashcard 23: Which photosystem (II or I) acts first in the typical Z-scheme of electron flow?

Answer: Photosystem II. Initial photosystem in the linear electron flow sequence.

Flashcard 24: Which molecule is oxidized during the Calvin cycle to regenerate NADP$^+$ for light reactions?

Answer: NADPH is oxidized to NADP$^+$. Loses electrons to regenerate the oxidized form.

Flashcard 25: What molecule is reduced to store high-energy electrons during the light reactions?

Answer: NADP$^+$ is reduced to NADPH. Gains electrons and hydrogen to become the reduced form.

Flashcard 26: What is the role of the electron transport chain between PSII and PSI in energy flow?

Answer: Converts electron energy into a proton gradient. Energy released pumps protons across the membrane.

Flashcard 27: Which outcome indicates cyclic electron flow is operating in a model?

Answer: ATP produced but no NADPH and no $O_2$. Circular flow generates only ATP without oxygen release.

Flashcard 28: What is the carbon input molecule for the Calvin cycle?

Answer: $CO_2$. Source of carbon atoms for sugar synthesis.

Flashcard 29: What are the main products that leave the Calvin cycle to contribute to sugar synthesis?

Answer: G3P (a 3-carbon sugar). Three-carbon precursor for glucose and other sugars.

Flashcard 30: Which organelle is the main site of photosynthesis in plants and algae?

Answer: Chloroplast. Double-membrane organelle specialized for photosynthetic reactions.

Flashcard 31: What is the key difference between cyclic and noncyclic electron flow?

Answer: Cyclic makes ATP only; noncyclic makes ATP, NADPH, and $O_2$. Different pathways produce different energy carriers.

Flashcard 32: Which molecule is the final electron acceptor in the light-dependent reactions?

Answer: NADP$^+$. Accepts electrons at the end of the electron transport chain.

Flashcard 33: Which photosystem (II or I) acts first in the typical Z-scheme of electron flow?

Answer: Photosystem II. Initial photosystem in the linear electron flow sequence.

Flashcard 34: Which molecule is the immediate product of light reactions that directly powers carbon fixation steps?

Answer: ATP. Provides phosphate bond energy for biosynthetic reactions.

Flashcard 35: What is the correct matter-flow statement for carbon in photosynthesis models?

Answer: Carbon atoms move from $CO_2$ into sugars. Carbon fixation transfers inorganic carbon to organic compounds.

Flashcard 36: What molecules return from the Calvin cycle to the light reactions after energy is used?

Answer: ADP + P$_i$ and NADP$^+$. Depleted energy carriers return for regeneration.

Flashcard 37: What are the reactant inputs to the Calvin cycle that represent energy and reducing power?

Answer: ATP and NADPH. Chemical energy and reducing power for carbon fixation.

Flashcard 38: Which molecule carries high-energy electrons from light reactions to the Calvin cycle?

Answer: NADPH. Transfers electrons from light reactions to carbon fixation.

Flashcard 39: What process directly produces $O_2$ during the light reactions?

Answer: Photolysis (splitting) of $H_2O$. Water splitting releases oxygen as a byproduct.

Flashcard 40: What is the immediate energy currency produced by the light reactions for use in the Calvin cycle?

Answer: ATP and NADPH. High-energy molecules that power carbon fixation reactions.

Flashcard 41: In the Z-scheme, what happens to electron energy as electrons move down the ETC?

Answer: Electron energy decreases stepwise. Energy is released as electrons move between carriers.

Flashcard 42: Which organelle is the main site of photosynthesis in plants and algae?

Answer: Chloroplast. Double-membrane organelle specialized for photosynthetic reactions.

Flashcard 43: In the Z-scheme, what happens to electron energy immediately after photon absorption?

Answer: Electron energy increases (excitation). Light photons boost electrons to higher energy levels.

Flashcard 44: Identify the correct interpretation: increased proton gradient causes ATP to increase or decrease?

Answer: ATP production increases. Stronger gradient drives more ATP synthesis.

Flashcard 45: What is the correct matter-flow statement for carbon in photosynthesis models?

Answer: Carbon atoms move from $CO_2$ into sugars. Carbon fixation transfers inorganic carbon to organic compounds.

Flashcard 46: What is the name of the model describing electron energy changes from PSII to PSI?

Answer: Z-scheme (electron transport chain model). Shows electron energy changes through both photosystems.

Flashcard 47: Which side of the thylakoid membrane has higher $H^+$ concentration during light reactions?

Answer: Thylakoid lumen. Interior space accumulates protons from water splitting.

Flashcard 48: Find the correct pairing in a model: PSII with water splitting or PSI with water splitting?

Answer: PSII is linked to water splitting. PSII receives electrons from water oxidation.

Flashcard 49: What is the immediate energy currency produced by the light reactions for use in the Calvin cycle?

Answer: ATP and NADPH. High-energy molecules that power carbon fixation reactions.

Flashcard 50: What is the primary purpose of cyclic electron flow in energy balance models?

Answer: To produce extra ATP without making NADPH. Adjusts ATP/NADPH ratio for Calvin cycle needs.

Flashcard 51: Which process directly builds the proton gradient: Calvin cycle or ETC activity in thylakoids?

Answer: Electron transport chain activity in thylakoids. ETC pumps protons to create the driving force.

Flashcard 52: Which molecule carries high-energy electrons from light reactions to the Calvin cycle?

Answer: NADPH. Transfers electrons from light reactions to carbon fixation.

Flashcard 53: Which chloroplast membrane hosts the light-dependent reactions?

Answer: Thylakoid membrane. Contains photosystems and electron transport chains.

Flashcard 54: Which step is endergonic and requires energy input: making ATP or hydrolyzing ATP?

Answer: Making ATP from ADP + P$_i$ is endergonic. Requires energy input to form high-energy bonds.

Flashcard 55: What are the main products that leave the Calvin cycle to contribute to sugar synthesis?

Answer: G3P (a 3-carbon sugar). Three-carbon precursor for glucose and other sugars.

Flashcard 56: What molecule is reduced to store high-energy electrons during the light reactions?

Answer: NADP$^+$ is reduced to NADPH. Gains electrons and hydrogen to become the reduced form.

Flashcard 57: Choose the correct description of the Calvin cycle: produces ATP or consumes ATP?

Answer: Consumes ATP (and NADPH). Calvin cycle uses ATP rather than producing it.

Flashcard 58: Choose the correct statement about $O_2$ in photosynthesis: from $CO_2$ or from $H_2O$?

Answer: $O_2$ comes from $H_2O$, not from $CO_2$. Oxygen originates from water splitting, not carbon fixation.

Flashcard 59: Which statement best describes energy flow: energy cycles or matter cycles in photosynthesis?

Answer: Matter cycles; energy flows through and is not recycled. Energy flows one-way while matter is recycled.

Flashcard 60: Choose the correct description of the Calvin cycle: produces ATP or consumes ATP?

Answer: Consumes ATP (and NADPH). Calvin cycle uses ATP rather than producing it.

Flashcard 61: Identify the correct interpretation of NADPH in a model: energy carrier or structural carbohydrate?

Answer: Energy and electron carrier. NADPH stores and transfers both energy and electrons.

Flashcard 62: Choose the correct statement about $O_2$ in photosynthesis: from $CO_2$ or from $H_2O$?

Answer: $O_2$ comes from $H_2O$, not from $CO_2$. Oxygen originates from water splitting, not carbon fixation.

Flashcard 63: Which chloroplast membrane hosts the light-dependent reactions?

Answer: Thylakoid membrane. Contains photosystems and electron transport chains.

Flashcard 64: Which electron flow pathway returns electrons to PSI: cyclic or noncyclic?

Answer: Cyclic electron flow. Circular pathway recycles electrons back to origin.

Flashcard 65: What is the key difference between cyclic and noncyclic electron flow?

Answer: Cyclic makes ATP only; noncyclic makes ATP, NADPH, and $O_2$. Different pathways produce different energy carriers.

Flashcard 66: Which outcome indicates noncyclic electron flow is operating in a model?

Answer: Production of NADPH and release of $O_2$. Linear flow produces both reducing power and oxygen.

Flashcard 67: Which photosystem (II or I) is primarily responsible for reducing NADP$^+$ to NADPH?

Answer: Photosystem I. Final photosystem that provides electrons for NADPH formation.

Flashcard 68: Identify the correct source of electrons that ultimately reduce NADP$^+$ in photosynthesis.

Answer: $H_2O$ provides the electrons. Water is the ultimate electron donor in photosynthesis.

Flashcard 69: What are the reactant inputs to the Calvin cycle that represent energy and reducing power?

Answer: ATP and NADPH. Chemical energy and reducing power for carbon fixation.

Flashcard 70: Which outcome indicates noncyclic electron flow is operating in a model?

Answer: Production of NADPH and release of $O_2$. Linear flow produces both reducing power and oxygen.

Flashcard 71: What is the name of the electrochemical gradient used to power ATP synthesis in chloroplasts?

Answer: Proton motive force (H$^+$ gradient). Concentration and electrical gradient drives ATP synthesis.

Flashcard 72: Which step is endergonic and requires energy input: making ATP or hydrolyzing ATP?

Answer: Making ATP from ADP + P$_i$ is endergonic. Requires energy input to form high-energy bonds.

Flashcard 73: Which chloroplast region is the site of the Calvin cycle (light-independent reactions)?

Answer: Stroma. Fluid-filled space where carbon fixation occurs.

Flashcard 74: Which statement best describes energy flow: energy cycles or matter cycles in photosynthesis?

Answer: Matter cycles; energy flows through and is not recycled. Energy flows one-way while matter is recycled.

Flashcard 75: Which enzyme catalyzes carbon fixation by adding $CO_2$ to RuBP?

Answer: Rubisco. Key enzyme that incorporates inorganic carbon into organic molecules.

Flashcard 76: What is the primary purpose of cyclic electron flow in energy balance models?

Answer: To produce extra ATP without making NADPH. Adjusts ATP/NADPH ratio for Calvin cycle needs.

Flashcard 77: In energy-flow models, what does NADPH primarily provide to the Calvin cycle?

Answer: High-energy electrons (reducing power). Supplies electrons needed for carbon reduction reactions.

Flashcard 78: Which molecule is the source of the oxygen gas released during photosynthesis?

Answer: Water ($H_2O$). Water molecules are split to provide electrons and protons.

Flashcard 79: Which photosystem (II or I) is primarily responsible for reducing NADP$^+$ to NADPH?

Answer: Photosystem I. Final photosystem that provides electrons for NADPH formation.

Flashcard 80: Which electron flow pathway returns electrons to PSI: cyclic or noncyclic?

Answer: Cyclic electron flow. Circular pathway recycles electrons back to origin.

Flashcard 81: In energy-flow models, what does ATP primarily provide to the Calvin cycle?

Answer: Energy to drive endergonic reactions. Powers thermodynamically unfavorable carbon fixation steps.

Flashcard 82: What is the name of the electrochemical gradient used to power ATP synthesis in chloroplasts?

Answer: Proton motive force (H$^+$ gradient). Concentration and electrical gradient drives ATP synthesis.

Flashcard 83: In the Z-scheme, what happens to electron energy as electrons move down the ETC?

Answer: Electron energy decreases stepwise. Energy is released as electrons move between carriers.

Flashcard 84: Which enzyme catalyzes carbon fixation by adding $CO_2$ to RuBP?

Answer: Rubisco. Key enzyme that incorporates inorganic carbon into organic molecules.

Flashcard 85: Which molecule is the final electron acceptor in the light-dependent reactions?

Answer: NADP$^+$. Accepts electrons at the end of the electron transport chain.

Flashcard 86: Identify the correct location for ATP synthase in chloroplasts in energy-flow models.

Answer: Embedded in the thylakoid membrane. Enzyme spans the membrane to access proton gradient.

Flashcard 87: Find the correct pairing in a model: PSII with water splitting or PSI with water splitting?

Answer: PSII is linked to water splitting. PSII receives electrons from water oxidation.

Flashcard 88: Identify the correct interpretation: increased proton gradient causes ATP to increase or decrease?

Answer: ATP production increases. Stronger gradient drives more ATP synthesis.

Flashcard 89: What is the name of the model describing electron energy changes from PSII to PSI?

Answer: Z-scheme (electron transport chain model). Shows electron energy changes through both photosystems.

Flashcard 90: Which electron flow pathway produces oxygen: cyclic or noncyclic?

Answer: Noncyclic electron flow. Linear pathway includes water splitting and oxygen release.

Flashcard 91: Which side of the thylakoid membrane has higher $H^+$ concentration during light reactions?

Answer: Thylakoid lumen. Interior space accumulates protons from water splitting.