What term is used to describe the sum of all chemical reactions in an organism?

The term that describes the sum of all chemical reactions in an organism is metabolism. Metabolism encompasses all the biochemical processes that occur within living organisms, including those that build up or break down substances (anabolism and catabolism, respectively). This includes various activities like breaking down food for energy, synthesizing necessary molecules, and the regulation of various physiological functions.

Homeostasis refers to the maintenance of a stable internal environment within an organism, which is not solely focused on chemical reactions. Digestion specifically pertains to the breakdown of food into simpler molecules that can be absorbed and utilized by cells, which is just one portion of metabolic processes. Respiration typically relates to the cellular processes that convert food into energy, specifically involving oxygen and carbon dioxide, but it is also only one component of the broader metabolic processes taking place. Therefore, metabolism is the most comprehensive and correct term that encompasses all these chemical reactions.