Which of the following statements is correct?

Question

BlackTom AI · Accepted Answer

Let’s break down each option and test it against fundamental cellular biology concepts.
Option 1: 'Electrons move from the thylakoid space to the stroma through the ATP synthase to produce ATP.' In chloroplasts, the main flow is electron transport across the thylakoid membrane with protons pumped into the thylakoid lumen, creating a gradient used by ATP synthase. However, the direction described for electrons moving through ATP synthase is incorrect; ATP synthase uses the proton gradient to synthesize ATP as protons flow back across the membrane, not as electrons move through ATP synthase. So this statement mischaracterizes the electron flow and the role of ATP synthase.
Option 2: 'O2 provides the electron for the electron transport in both mitochondria and chloroplasts.' Oxygen does act as the final electron acceptor in mitochondrial respiration, but it does not 'provide' electrons; electrons come from NADH and FADH2. In chloroplasts, the electron donor is water, and O2 is a product, not a donor. Therefore, this blanket claim is inaccurate for both organelles.
Option 3: 'The dark reactions (Calvin cycle) of photosynthesis occur in the matrix of the mitochondrion.' This is factually wrong: the Calvin cycle occurs in the stroma of the chloroplast, not in the mitochondrial matrix. Hence, this option confuses organelles and processes.
Option 4: 'The inner membrane of the mitochondrion and the thylakoid membrane of a thylakoid are the sites of chemiosmotic ATP synthesis.' This statement correctly identifies the critical membranes where chemiosmosis drives ATP synthesis: the inner mitochondrial membrane and the thylakoid membrane in chloroplasts. Here, a proton motive force across these membranes powers ATP synthase to produce ATP, aligning with the chemiosmotic model.
In summary, the first three options contain inaccuracies about the direction of electron flow, the sources of electrons, or the location of specific photosynthetic reactions, while the fourth option accurately describes the sites of chemiosmotic ATP synthesis across the two organelle membranes involved.

Bio 93 Section CDE 2025 Midterm 2- Section E

Which of the following statements is correct?

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