Final answer:
The key element in catabolic reactions is carbon. Catabolic reactions break down larger molecules into smaller parts, releasing energy. Carbohydrates contain carbon and oxygen.
Step-by-step explanation:
The key element in catabolic reactions is carbon.
Catabolic reactions break down larger molecules, such as carbohydrates, lipids, and proteins from ingested food, into their constituent smaller parts. They also include the breakdown of ATP, which releases the energy needed for metabolic processes in all cells throughout the body.
Carbohydrates contain carbon and oxygen.