Response to stimulus" refers to processing events in the brain. the reaction of an organism to a signal. the five senses (sight, hearing, touch, smell and taste). the behavior of an organism in a particular situation. (This is easy peasy I'm just seeing if you guys know it )​

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.