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?
A) The pH within the thylakoid is less than that of the stroma.
B) The pH of the stroma is lower than that of the other two measurements.
C) The pH of the stroma is higher than that of the thylakoid space but lower than that of the cytosol.
D) The pH of the thylakoid space is higher than anywhere else in the cell.
E) There is no consistent relationship.

Question

Quizplus · Accepted Answer

The pH within the thylakoid is expected to be lower (more acidic) than that of the stroma and the cytosol. This is because during the light reactions of photosynthesis, protons (H+) are pumped from the stroma into the thylakoid space, creating an electrochemical gradient. This gradient is used to drive the production of ATP by ATP synthase as protons flow back into the stroma. Since protons are being actively transported into the thylakoid space, it is expected that the pH within the thylakoid would be more acidic than the stroma and cytosol.

The PH of the Inner Thylakoid Space Has Been Measured