s9 Bioenergetics and metabolism The generation of metabolic energy is a major activity of all cells, and two cytoplasmic organelles are specifically devoted to energy metabolism and the production of ATP. Mitochondria are responsible for generating most of the useful energy from the breakdown of lipids and carbohydrates, and chloroplasts use energy captured from sunlight to synthesize carbohydrates from CO2 and H2O. The peroxisome contains enzymes involved in a variety of different metabolic pathways, including the breakdown of fatty acids and: the metabolism of a by-product of photosynthesis§9 Bioenergetics and metabolism The generation of metabolic energy is a major activity of all cells, and two cytoplasmic organelles are specifically devoted to energy metabolism and the production of ATP. Mitochondria are responsible for generating most of the useful energy from the breakdown of lipids and carbohydrates, and chloroplasts use energy captured from sunlight to synthesize carbohydrates from CO2 and H2O. The peroxisome contains enzymes involved in a variety of different metabolic pathways, including the breakdown of fatty acids and the metabolism of a by-product of photosynthesis