LABORATORY REVIEW
CELL RESPIRATION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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The pH within the thylakoid is lower than that of the stroma.
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The pH of the thylakoid space is higher than anywhere else in the cell.
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The pH of the stroma is higher than that of the thylakoid space, but lower than that of the cytoplasm.
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The pH of the stroma is higher than that of the cytoplasm.
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Detailed explanation-1: -The pH of the inner thylakoid space has been measured, as have the pH of the stroma and of the cytosol of a particular plant cell. Which, if any, relationship would you expect to find? The pH within the thylakoid is less than that of the stroma.
Detailed explanation-2: -pumped out of the stroma and into the thylakoid space creating a difference of 3.0-3.5 pH units. This gradient generates a proton motive force to drive ATP synthesis, similar to mitochondria. However, in chloroplasts, nearly all of it is contributed by a pH gradient rather than a membrane potential.
Detailed explanation-3: -Note that a high concentration of protons = an acidic pH, so the thylakoid lumen has a much more acidic (lower) pH than the stroma. This whole process is quite analogous to the process that occurs during cellular respiration in the mitochondria.
Detailed explanation-4: -During photosynthesis, the lumen becomes acidic, as low as pH 4, compared to pH 8 in the stroma.