5.2—Photophosphorylation, ATP and energy supply

Photophosphorylation uses light-driven electron energy to add inorganic phosphate to ADP and make ATP. ATP hydrolysis then releases a small, usable energy supply for processes such as active transport, synthesis and movement.

ATP is an energy-transfer molecule rather than a long-term store: ADP + Pi can be regenerated to ATP during respiration or photosynthesis, then ATPase-catalysed hydrolysis returns ADP + Pi.

During photosynthesis, ATP made on the thylakoid membrane supplies energy for Calvin-cycle reactions in the stroma. The ATP is not consumed as the carbon skeleton; it powers the chemical steps.

ATP hydrolysis releases usable energy, not “energy from a phosphate bond” in isolation. Photophosphorylation and oxidative phosphorylation are different ways of making ATP.