APS Box — Different Questions, Different Units

Different biological questions often highlight different explanatory units.

Biological Question	Primary Explanatory Focus
Heredity	Gene
Metabolism and cellular organisation	Cell
Integrated behaviour and regulation	Organism
Evolutionary continuity	Species or lineage
Ecological interaction	Ecosystem

This does not mean that each question belongs exclusively to a single unit. Rather, different biological entities become especially informative for different kinds of explanation. The search for one universally fundamental unit becomes difficult because life itself is organised through multiple interacting forms of continuity.