Question

what statement describes metabolism?
metabolism refers only to reactions that harvest energy by breaking down molecules.
metabolism refers to the sum of all chemical reactions that occur within an organism.
metabolism refers to the effects of ph, temperature, and allosteric substances on enzymes.
metabolism refers only to reactions that expend energy to build molecules.

Explanation:

Metabolism encompasses all chemical reactions in an organism, including both catabolic (breaking - down) and anabolic (building - up) processes. The first and fourth options are too narrow as they focus only on energy - harvesting or energy - expending reactions respectively. The third option is about factors affecting enzymes, not the definition of metabolism.

Answer:

Metabolism refers to the sum of all chemical reactions that occur within an organism.