What is the complex process by which food is used by a living organism?

The process by which food is utilized by a living organism is known as metabolism. Metabolism encompasses all the chemical reactions that occur within cells to convert food into energy. This includes breaking down food substances during digestion, absorbing the nutrients into the bloodstream, and using those nutrients to fuel bodily functions, build and repair tissues, and produce energy.

Metabolism can be categorized into two main processes: catabolism, which involves the breakdown of molecules to release energy, and anabolism, which focuses on the synthesis of compounds needed by cells. This holistic approach highlights how organisms not only break down food but also transform those nutrients into the various biomolecules necessary for life.

In contrast, digestion specifically refers to the mechanical and chemical processes that break down food into smaller components, while absorption pertains to the uptake of nutrients from the digestive tract into the bloodstream. Circulation, on the other hand, is the system that distributes these absorbed nutrients throughout the body. Therefore, while digestion, absorption, and circulation are integral components of how food is processed, metabolism encompasses the entire spectrum of utilizing that food at a cellular level.