Which macromolecule is usually oxidized to release energy during...

Photosynthesis, of course, takes place within the chloroplasts (in the eukaryotes), whereas the breakdown of complex molecules to yield energy takes place in the cytoplasm and in the mitochondria (also only in eukaryotes). The breaking of the C-C bonds of complex compounds through oxidation within the cells, leading to release of a considerable amount of energy is called respiration. The compounds that are oxidized during this process are known as respiratory substrates. Usually carbohydrates are oxidized to release energy, but proteins, fats and even organic acids can be used as respiratory substances in some plants, under certain conditions.