Which cellular process can replenish ATP from ADP?

The process of replenishing ATP from ADP can occur through both photosynthesis and respiration, making this answer the most comprehensive.

In photosynthesis, particularly during the light-dependent reactions, sunlight energy is captured and used to produce ATP from ADP. This process involves the electron transport chain, which generates a proton gradient across the thylakoid membrane. The ATP synthase enzyme then uses this gradient to convert ADP back into ATP, effectively replenishing the energy currency of the cell.

Similarly, during cellular respiration, ATP is regenerated from ADP through the activities of both glycolysis and the citric acid cycle, followed by the electron transport chain. In this process, glucose is oxidized, and the energy released is utilized to drive the synthesis of ATP from ADP, predominantly during oxidative phosphorylation.

Therefore, since both processes contribute to ATP synthesis, selecting both photosynthesis and respiration accurately reflects the broader mechanisms through which cells maintain their energy needs.