In biology, the word matrix is used for the material between animal or plant cells, or generally the material (or "tissue") in which more specialized structures are embedded, and also specifically for one part of the mitochondrion. The internal structure of connective tissues is a extracellular matrix.

The term matrix is also used for the "medium" in which bacteria are grown (or "cultured"), so a Petri dish of agar may be the matrix for culturing a sample swabbed from someone's sore throat.

Mitochondrial matrix

In the mitochondrion, the matrix contains soluble enzymes that catalyze the oxidation of pyruvate and other small organic molecules.