The mechanism for ATP synthesis is chemiosmosis in:

Explanation

Chemiosmosis is the process that produces ATP by using a proton gradient across a membrane, and it takes place in both photosynthesis and respiration, which makes option C correct. In photosynthesis, light energy drives the movement of electrons through the thylakoid membranes, creating a proton gradient that powers ATP formation. In respiration, electrons from the breakdown of glucose move through the mitochondrial membrane, generating a similar gradient used to produce ATP. Fermentation does not involve chemiosmosis because it makes ATP directly through substrate-level phosphorylation without using proton gradients.