Generation of proton gradients across membranes occurs during

Respiration and photosynthesis

Explanation:

The proton gradient is formed by the electron transport chain and this is across the inner mitochondria membrane that enables ATP synthesis through chemiosmosis.

Oxygen is needed in the cell for oxidative phosphorylation and it is of 2 component this include the electron transport chain and chemiosmiosis.

Electron transport chain- Electron are transport from one molecule to another.

Chemiosmosis- The energy is stored and then used to make ATP.

thinking it would be physical characteristics