Lactase is essential for digesting lactose in milk. This enzyme is specific for this sugar. Why?Molecules and active sites vary in size; only properly sized molecules can fit.There is a precise compatibility between the active site and the lactose molecule.Specificity refers to the action of the enzyme, such as hydrolysis, and relatively few molecules can be hydrolyzed.Reaction-specific enzymes assume a fit by folding around the most numerous substrate molecules.