Which two major reactions are involved in energy metabolism?

Energy metabolism primarily involves two major reactions: anabolism and catabolism.

Anabolism refers to the metabolic pathways that construct molecules from smaller units. These processes require energy, as they are involved in building complex substances like proteins, nucleic acids, and lipids, which are essential for growth, repair, and maintenance of cells. Examples of anabolic processes include protein synthesis and the synthesis of glycogen from glucose.

On the other hand, catabolism encompasses the metabolic pathways that break down molecules into smaller units. These processes release energy by breaking down complex molecules like carbohydrates, fats, and proteins into simpler ones, ultimately converting them into ATP (adenosine triphosphate), which is the energy currency of the cell. An example is glycolysis, where glucose is broken down to provide energy.

Together, these two processes are crucial for maintaining the body's energy balance. While digestion and absorption, contraction and relaxation, and respiration and fermentation relate to various aspects of biological function and energy utilization, they do not specifically encompass the primary reactions of energy metabolism in terms of the synthesis and breakdown of biomolecules. Thus, anabolism and catabolism are directly linked to the fundamental processes of energy production and consumption in the body.