ATP (adenosine triphosphate) is required for endothermic processes but can be re-synthesised when coupled to exothermic processes:

ATP is synthesised across the inner membranes of the mitochondria and chloroplasts so they are adapted to give max. surface area. Energy for ATP synthesis is supplied by ATP-ase enzymes that are powered by a proton gradient

NADH (NADPH in photosynthesis) and FADH₂ are reduced coenzymes that are used to carry electrons to a different part of the organelle