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Photosynthesis OAT 2
| Question | Answer |
|---|---|
| What is photosynthesis? | The process by which light energy from the sun is used to synthesize glucose. |
| What is the overall reaction for photosynthesis? | 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂ |
| Which pigments absorb energy from sunlight? | Chlorophyll A, Chlorophyll B, and carotenoids. |
| What happens when photons hit chlorophyll? | Photons excite electrons; excited electrons are unstable and re-emit energy. |
| Which chlorophyll molecules absorb the excited electron energy, and what are their designations? | Chlorophyll A molecules — P₆₈₀ (associated with PSII) and P₇₀₀ (associated with PSI). |
| What is the structure of Chlorophyll A? | It has a porphyrin ring with an Mg²⁺ atom inside. |
| What organelle does photosynthesis occur in, and what type of organelle is it? | The chloroplast — a double-membraned organelle in plant cells. |
| What are the 9 anatomical parts of a chloroplast? | 1) Outer membrane, 2) Granum (stacks of thylakoids), 3) Thylakoid, 4) Thylakoid membrane, 5) Thylakoid lumen, 6) Intermembrane space, 7) Inner membrane, 8) Stroma lamellae, 9) Stroma. |
| Where does the ETC (non-cyclic photophosphorylation) occur in the chloroplast? | The thylakoid membrane. |
| Where does photolysis occur, and what accumulates there as a result of the ETC? | The thylakoid lumen; H⁺ ions accumulate there. |
| Where does cyclic photophosphorylation occur? | The stroma lamellae. |
| Where does the Calvin cycle occur? | The stroma. |
| What happens to electrons in the light reaction at PSII? | Electrons trapped by PSII are energized by light, 2 excited electrons are passed to a primary electron acceptor, and they move through the ETC, losing energy that forms approximately 1.5 ATP. |
| What happens at the end of the ETC (at PSI)? | Electrons are re-energized and passed to a different primary electron acceptor, where they can proceed via either the cyclic or non-cyclic pathway. |
| What happens in cyclic photophosphorylation? | 2 electrons from PSI go back through the first ETC, generating 1 ATP; the electrons are recycled into PSI and can repeat the cycle. |
| What happens in non-cyclic photophosphorylation? | 2 electrons go through an ETC and combine with NADP⁺ and H⁺ to form NADPH, which is then used in the Calvin cycle to create glucose. |
| What is photolysis? | The splitting of H₂O into 2H⁺, 2e⁻, and ½O₂ at PSII. |
| What are the three products of photolysis and what happens to each? | 2H⁺ → used for NADPH formation; 2e⁻ → replenish the electrons lost in PSII; ½O₂ → released as gas. |
| How does chemiosmosis work in photosynthesis? | H⁺ accumulates in the thylakoid lumen (via photolysis and cytochromes pumping H⁺ from the stroma between PSII and PSI), creating a pH and electrical gradient; ATP synthase uses this gradient to convert ADP into ATP. |
| Where does chemiosmosis occur in the chloroplast? | Across the thylakoid membrane. |
| What is the ATP produced by chemiosmosis used for? | The Calvin cycle to create glucose. |
| What is the action spectrum of chlorophyll? | Chloroplasts are highly effective at absorbing red and blue light; green wavelengths are reflected, making green light the least effective for photosynthesis. |
| What is the purpose of the Calvin cycle (dark reaction)? | To fix CO₂ into glucose (specifically 2 G3P). |
| Is the Calvin cycle light-dependent? | No — it is light independent, but it requires NADPH and ATP produced by the light reactions. |
| What are the 4 steps of the Calvin cycle in order? | 1) Carboxylation, 2) Reduction, 3) Regeneration, 4) Carbohydrate Synthesis. |
| Describe the Carboxylation step of the Calvin cycle. | 6CO₂ + 6RuBP → 12 PGA; catalyzed by the enzyme RuBisCo. |
| Describe the Reduction step of the Calvin cycle. | 12 ATP + 12 NADPH convert 12 PGA into 12 G3P (PGAL); the byproducts NADP⁺ and ADP go into non-cyclic photophosphorylation. |
| Describe the Regeneration step of the Calvin cycle. | 6 ATP convert 10 G3P back into 6 RuBP (to continue the cycle). |
| Describe the Carbohydrate Synthesis step of the Calvin cycle. | The remaining 2 G3P are used to form glucose. |
| What enzyme catalyzes the carboxylation step of the Calvin cycle? | RuBisCo. |
| What is C4 photosynthesis and why is it used? | It alters the location of photosynthesis — CO₂ is moved to bundle sheath cells to minimize photorespiration and water loss; it produces an intermediary 4-carbon compound and uses 1 extra ATP. |
| What is CAM photosynthesis and why is it used? | It alters the timing of photosynthesis — CO₂ is fixed at night instead of during the day to minimize photorespiration and water loss. |
| What is the key difference between C4 and CAM photosynthesis? | C4 changes the location of CO₂ fixation (bundle sheath cells); CAM changes the timing of CO₂ fixation (nighttime). |
| What do cytochromes do in the light reaction? | Between PSII and PSI, cytochromes pump H⁺ from the stroma into the thylakoid lumen, contributing to the pH and electrical gradient used for chemiosmosis. |
Created by:
smurtab