AIIMS 2019 Biology ATP Synthesis MCQ Question

ATP formation occurs through various mechanisms, including photophosphorylation, oxidative phosphorylation, and substrate-level phosphorylation, making option D correct. Photophosphorylation occurs in chloroplasts during photosynthesis, where light energy is converted into chemical energy, while oxidative phosphorylation takes place in mitochondria, utilizing the electron transport chain and chemiosmosis to generate ATP from ADP and inorganic phosphate (Pi). Substrate-level phosphorylation directly synthesizes ATP during glycolysis and the Krebs cycle through the transfer of a phosphate group from a substrate molecule to ADP. Each of these processes plays a crucial role in cellular energy metabolism, highlighting the versatility of ATP production in living organisms.