Questions: The pH of the inner thylakoid space and of the stroma have been measured. Which, if any, relationship would you expect to find? There is no consistent relationship. The pH within the inner thylakoid space is the same as that of the stroma. The pH within the inner thylakoid space is greater than that of the stroma. The pH within the inner thylakoid space is less than that of the stroma.

The answer is the last one: The pH within the inner thylakoid space is less than that of the stroma.

Explanation for each option:

1. There is no consistent relationship.

   • This option is incorrect because there is a well-established relationship between the pH of the inner thylakoid space and the stroma due to the processes of photosynthesis.

2. The pH within the inner thylakoid space is the same as that of the stroma.

   • This option is incorrect because the pH levels are not the same. The processes occurring in the thylakoid space and the stroma lead to different pH levels.

3. The pH within the inner thylakoid space is greater than that of the stroma.

   • This option is incorrect because the pH within the inner thylakoid space is actually lower (more acidic) than that of the stroma.

4. The pH within the inner thylakoid space is less than that of the stroma.

   • This option is correct. During the light reactions of photosynthesis, protons (H⁺ ions) are pumped into the thylakoid space, leading to a higher concentration of H⁺ ions and thus a lower pH (more acidic) compared to the stroma.

Summary: The pH within the inner thylakoid space is less than that of the stroma due to the accumulation of protons (H⁺ ions) in the thylakoid space during the light-dependent reactions of photosynthesis.