Explain how the shape of an enzyme allows it to catalyse a reaction, and describe what happens to enzyme activity when the temperature is increased well above the optimum.

An enzyme has a specific active site that is shaped to fit its substrate.
The substrate is complementary to the active site, so it binds to form an enzyme‑substrate complex.
This binding lowers the activation energy and the reaction proceeds.
When the temperature rises well above the optimum, the active site changes shape or the enzyme becomes denatured.
The substrate can no longer fit, so the reaction rate falls or stops.