The H⁺ (protons) accumulate in the thylakoid space during electron transport between photosystems I and II. The excess of protons in the thylakoid space

A) enters the photorespiration pathway.
B) raises the pH of the space until the processes stop.
C) is small enough to diffuse back out through the lipid bilayer.
D) converts NADP⁺ to NADPH and generates ATP in the process.
E) moves from the thylakoid space to the stroma through the ATP synthase complex.

The excess of protons in the thylakoid space moves from the thylakoid space to the stroma through the ATP synthase complex, generating ATP in the process. This process is known as chemiosmosis and is a key mechanism for the production of ATP in photosynthesis. Option A is incorrect because the photorespiration pathway is not related to the excess of protons in the thylakoid space. Option B is incorrect because the excess of protons does not raise the pH indefinitely, as this would ultimately result in the cessation of photosynthesis. Option C is incorrect because the excess of protons is not small enough to diffuse back out through the lipid bilayer. Option D is incorrect because the conversion of NADP+ to NADPH is part of the light-independent reactions of photosynthesis and is not directly related to the excess of protons in the thylakoid space.