Enzymes Quiz
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5 questions, one answer each
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1. Which statement best defines an enzyme?
- A. A biological catalyst that speeds up chemical reactions without being permanently changed
- B. A protein that stores energy for use in metabolic reactions
- C. A substance that slows down chemical reactions to prevent damage to cells
- D. An inorganic molecule that provides the energy needed for reactions to occur
2. According to the lock and key model of enzyme action, what is the relationship between the active site and the substrate?
- A. The active site is larger than the substrate to allow flexibility
- B. The active site is complementary in shape to the substrate, allowing them to fit together
- C. The active site changes shape to fit any substrate molecule
- D. The active site and substrate have opposite electrical charges that attract
3. What happens to an enzyme when it is permanently denatured?
- A. It temporarily loses activity but regains function when conditions return to normal
- B. The shape of its active site is permanently altered, preventing substrate binding
- C. It becomes a different enzyme with new catalytic properties
- D. It bonds covalently to the substrate and cannot be reused
4. An enzyme has an optimum pH of 7.0. What would happen if the pH were changed to 10.0?
- A. The enzyme activity would increase because it is operating above the optimum
- B. The enzyme would be denatured, causing a permanent loss of active site shape and activity
- C. The enzyme activity would decrease temporarily but return to normal when pH is restored
- D. The substrate concentration would increase, allowing more enzyme–substrate complexes to form
5. In an investigation of catalase enzyme activity, the rate of reaction initially increases with substrate concentration, but then plateaus. What does this plateau indicate? (HT)
- A. The enzyme has become denatured and can no longer catalyse the reaction
- B. All enzyme molecules are saturated with substrate—further increases in substrate concentration cannot increase the reaction rate
- C. The pH of the solution has become unfavourable for enzyme activity
- D. The temperature has dropped, slowing down enzyme–substrate collisions