Protons (H +) accumulate in the thylakoid space during electron transport between photosystems I and II. The excess of protons in the thylakoid space enters the photorespiration pathway. converts NADP to NADPH and generates ATP in the process. is small enough to diffuse back out through the lipid bilayer. raises the pH of the space until the processes stop. moves from the thylakoid space to the stroma through an ATP synthase complex channel that generates ATP.

During electron transfer (generated during photosynthesis) protons (H + ions) accumulate in the inner space of the tilacoid. This buildup is used to generate a proton motive force across the thylakoid membrane.

Protons are not able to directly cross the lipid layer of the thylakoid membrane, but pass through a membrane molecule called ATP synthase. This molecule is responsible for the formation of ATP from ADP (adenosine diphosphate) + Pi (inorganic phosphorus). In other words, protons move from the tilacoid space to the stroma through a complex ATP synthase channel that generates ATP