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Biology Cellular Respiration and Photosynthesis Flashcards

7 cards from real CLEP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. What is the role of ubiquinone (Coenzyme Q) in the electron transport chain?

    Answer: It accepts electrons from Complexes I and II and shuttles them to Complex III

    Ubiquinone is a mobile, lipid-soluble electron carrier that collects electrons from both Complex I and Complex II and delivers them to Complex III.

  2. How many ATP molecules are produced per NADH oxidized by the mitochondrial electron transport chain (using the P/O ratio of ~2.5)?

    Answer: 2.5 ATP

    Modern measurements of the P/O ratio indicate that approximately 2.5 ATP molecules are synthesized per NADH oxidized, replacing the older estimate of 3 ATP.

  3. Photorespiration in C3 plants occurs when Rubisco fixes oxygen instead of CO2. What is the net effect on the plant?

    Answer: It consumes ATP and releases CO2, reducing photosynthetic efficiency

    When Rubisco reacts with O2 (oxygenase activity), the products enter the photorespiratory pathway, which consumes ATP and NADPH and releases CO2 without producing sugar.

  4. In non-cyclic electron flow (the Z-scheme), what is the ultimate electron donor and acceptor?

    Answer: H2O is the donor; NADP+ is the acceptor

    Water (H2O) donates electrons (via the OEC to PSII), and NADP+ is the final electron acceptor, being reduced to NADPH by ferredoxin-NADP+ reductase at PSI.

  5. Which of the following best explains why the inner mitochondrial membrane must be impermeable to protons (H+)?

    Answer: To maintain the proton gradient necessary for ATP synthesis by ATP synthase

    The impermeability of the inner membrane to H+ is essential because the proton gradient (proton-motive force) is the driving force for ATP synthase; any leak would dissipate the gradient and uncouple oxidative phosphorylation.

  6. During cyclic electron flow in photosynthesis, which of the following is produced?

    Answer: ATP only

    In cyclic electron flow, electrons cycle from PSI through ferredoxin and the cytochrome b6f complex back to plastocyanin and PSI, generating only ATP (via proton pumping) without producing NADPH or O2.

  7. Which metabolic pathway is shared by both aerobic respiration and fermentation?

    Answer: Glycolysis

    Glycolysis occurs in the cytoplasm of all cells and is the common first stage of both aerobic respiration and fermentation, converting glucose to pyruvate.