Enzymes: explain question

A researcher is investigating an enzyme that catalyses the hydrolysis of a specific disaccharide. The enzyme's active site appears to have a rigid, pre-formed shape that exactly matches the shape of its substrate. However, when the substrate binds, the active site undergoes a slight conformational change. This observation appears to support one of the two main hypotheses of enzyme-substrate binding.

Explain the difference between the lock-and-key hypothesis and the induced-fit hypothesis of enzyme action, referring to the observations above.