Essential Concept of Metabolism

Metabolism is the sum of all chemical processes in a living organism. It consists of anabolism, reactions that require energy to synthesize complex molecules from simpler ones, and catabolism, reactions that release energy by breaking complex molecules into simpler ones.

Autotroph, which use carbon dioxide to synthesize organic molecules, include photoautotrophs (which carry on photosynthesis) and chemoautotrophs.
Heterotrophs, which use organic molecules made by other organisms, include chemoheterotrophs, and photohetrotrophs (obtain chemical energy from light).
For growth, movement, and other activities, metabolic pathways use energy captured in the catabolic pathways.

ENZYMES
Properties of Enzymes
Enzymes are proteins that catalyze chemical reactions in living organisms by lowering the activation energy needed for a reaction to occur.
Enzymes have an active site, the binding site to which the substrate (the substance on which the enzymes act) attaches to form an enzyme-substrate complex. Enzymes typically exhibit a high degree of specificity in the reactions they catalyze.