Final answer:
During chemiosmosis, ATP is synthesized from ADP and inorganic phosphate using the energy from a proton gradient across the mitochondrial membrane or the thylakoid membrane in photosynthetic organisms.
Step-by-step explanation:
During the process of chemiosmosis, energy stored in a proton gradient is used to synthesize ATP from ADP (adenosine diphosphate) and inorganic phosphate (Pi or P₁).
Chemiosmosis involves the movement of protons (H+) through a protein complex called ATP synthase, which acts both as a channel and an enzyme. As protons flow down their electrochemical gradient, components within ATP synthase turn, catalyzing the transformation of ADP and Pi into ATP through a process called oxidative phosphorylation. This is similar to how the flow of water through a turbine generates electricity in a hydroelectric dam.
In eukaryotic cells, this process occurs in the mitochondria during cellular respiration and is a crucial step for producing more than 100 ATP molecules in the presence of oxygen. In photosynthetic organisms, chemiosmosis is also used during the light reactions of photosynthesis to create ATP, contributing to the energy conversion process of photophosphorylation.