ELECTRON TRANSPORT, CHEMIOSMOSIS, AND PHOSPHORYLATION
In aerobic respiration, glucose is oxidized, and its electrons are passed to the electron transport chain in the inner mitochondrial membrane. In photosynthesis, chlorophyll a is oxidized by light (photo-oxidized), and its electrons are passed to the electron transport chain in the thylakoid membrane.

In both cases, the energy released by the electrons as they pass through the electron transport chain is used to actively transport (pump) hydrogen ions across a membrane—across the inner mitochondrial membrane into the intermembrane space in mitochondria, and across the thylakoid membrane into the thylakoid lumen in chloroplasts.

Both the inner mitochondrial membrane and the thylakoid membrane are impermeable to hydrogen ions. Diffusion occurs only via specific transport proteins. This diffusion is called chemiosmosis. In both aerobic respiration and photosynthesis, the transport protein is an enzyme called ATP synthase. As the hydrogen ions (protons) diffuse through ATP synthase, they cause the central structure of the enzyme to rotate. This rotation somehow enables the synthesis of ATP from ADP and inorganic phosphate.