Cambridge IGCSE Enzymes

What is a catalyst?

• A substance that changes its structure during a reaction

• A substance that is not involved in any reaction

• A substance that increases the rate of a chemical reaction

• A substance that decreases the rate of a chemical reaction

What is the role of enzymes in metabolic reactions?

• To speed up the reactions

• To change the reactions

• To stop the reactions

• To slow down the reactions

What is the active site of an enzyme responsible for?

• Combining with the substrate

• Changing the enzyme's shape

• Releasing the product

• Stopping the reaction

How does temperature affect enzyme activity?

• Stops enzyme activity

• Increases enzyme activity

• Has no effect on enzyme activity

• Decreases enzyme activity

What happens to enzymes at temperatures above 50 degrees?

• They become inactive

• They speed up reactions

• They are denatured and stop functioning correctly

• They become more efficient

At what pH level does pepsin, a protein-digesting enzyme, work best?

• pH 10

• pH 7

• pH 5

• pH 2

What is formed when an enzyme binds with a substrate?

• Enzyme-substrate complex

• Enzyme complex

• Substrate complex

• Product complex

Why does enzyme activity rise with temperature?

• Enzyme and substrate molecules stop moving

• Enzyme and substrate molecules gain more kinetic energy

• Enzyme and substrate molecules lose kinetic energy

• Enzyme and substrate molecules change shape

What happens to enzyme activity when pH increases or drops too much?

• It becomes more efficient

• It slows and eventually stops

• It increases

• It remains constant

What is the purpose of enzymes in cells?

• To control reactions and ensure they occur quickly enough

• To prevent reactions

• To stop all reactions

• To slow down reactions