In living organisms, complex chemical activities do what to substances

A. builds them up and breaks them down

B. only builds them up

C. nothing

D. only breaks them down

Builds them up and breaks them down

Explanation:

Metabolism is the breakdown or build up of substances to maintain the vital processes of the cells and the organism. The chemical reactions of metabolism are organized into metabolic pathways. Metabolism can be divided into two categories:

Catabolism - the breakdown of complex substances to obtain energy

Anabolism - the synthesis of compounds using energy from simple molecules