Bioenergetics This term is composed of two parts, ‘bio’ and ‘energetics’, which are examined in succession.

Bio is derived from the Greek word ‘bios’ meaning life. To define life, one can start by explaining what living organisms are. Living organisms are distinguished from inert matter by their structure and function. They possess an organization which has a hierarchical structure observed not only within a single cell (single-celled organisms) but also in groups of cells themselves organized in interdependent organs (multicellular organisms). This organization bestows on living organisms their capacity for assimilation and reproduction. Assimilation is a prerequisite for reproduction, therefore assimilation is the key characteristic of living organisms. This can be defined as the capacity of the organism to make its own substance, not only from inorganic matter (autotrophy) but also from organic matter (heterotrophy). When assimilation finally ceases, the death of the organism ensues. Thus, for the biologist, life is the state of an organism during active assimilation.