What two processes does metabolism consist of?

Metabolism is broadly defined as the set of life-sustaining chemical reactions that occur in living organisms. It is divided into two fundamental processes: anabolism and catabolism.

Anabolism refers to the constructive phase of metabolism where small molecules are built up into larger and more complex molecules. This process requires energy, which is typically supplied by the breakdown of ATP (adenosine triphosphate). Anabolic pathways are vital for growth, repair, and the synthesis of new cellular components.

Catabolism, on the other hand, involves the breakdown of larger molecules into smaller ones, releasing energy in the process. This energy can then be used for various cellular functions, such as movement, growth, and reproduction. Catabolic processes are essential for providing the energy necessary to fuel all of life's activities.

The other options mentioned, while related to biological processes, do not encapsulate the entirety of metabolism in the way that anabolism and catabolism do. Digestion and absorption are specifically part of the food processing phase prior to metabolism, whereas respiration and circulation pertain to systems that support life but do not specifically define metabolic pathways. Thus, the correct components of metabolism are the processes of anabolism and catabolism.