Answer:
The biological activity of an enzyme depends mostly on its tertiary structure.
Step-by-step explanation:
Enzymes are proteins, specifically, globular proteins, this means that they have a ball-like shape. Every enzyme has an active site that ensembles with its substrate. The union of the substrate to the enzyme depends on this active site. If this union didn't occur, the enzyme wouldn't have biological activity. The active site is formed by the folding of the protein or what is called "tertiary structure". Therefore, the biological activity of an enzyme mostly depends on its tertiary structure.