Chapter 6: Enzymes covers the role of enzymes in biological reactions. This post includes Class 9 Biology Chapter 6 MCQs with answers and explanations to help students understand enzyme structure, function, factors affecting enzyme activity, and their importance in metabolism.
1. What are enzymes?
- A. Hormones
- B. Biological catalysts ✅
- C. Vitamins
- D. Nucleic acids
Explanation: Enzymes are proteins that speed up chemical reactions in living organisms without being used up.
2. What happens to an enzyme at high temperature?
- A. It becomes more active
- B. It denatures and loses function ✅
- C. It replicates
- D. It produces hormones
Explanation: High temperatures can break the structure of enzymes, rendering them inactive.
3. Which of the following best describes an enzyme’s specificity?
- A. Enzymes act randomly
- B. Each enzyme works on a specific substrate ✅
- C. Enzymes act on all substances
- D. Enzymes are not selective
Explanation: Enzymes have specific active sites that only bind to particular substrates.
4. What is the optimum temperature for most human enzymes?
- A. 10°C
- B. 50°C
- C. 37°C ✅
- D. 70°C
Explanation: 37°C is the normal body temperature, which is ideal for most enzymes to function efficiently.
5. What does the term “active site” refer to?
- A. The location of digestion
- B. The specific region where substrate binds ✅
- C. The center of the cell
- D. The product of the reaction
Explanation: The active site is the part of an enzyme where the substrate fits and the reaction occurs.
6. Which of the following factors affects enzyme activity?
- A. Substrate color
- B. pH and temperature ✅
- C. Wind and light
- D. Enzyme size only
Explanation: Enzyme activity is influenced by factors such as pH and temperature.
7. Which enzyme breaks down starch?
- A. Amylase ✅
- B. Lipase
- C. Protease
- D. Catalase
Explanation: Amylase is an enzyme that breaks down starch into simple sugars.
8. What is the function of catalase?
- A. Breaks down proteins
- B. Breaks down hydrogen peroxide ✅
- C. Synthesizes glucose
- D. Forms DNA
Explanation: Catalase breaks hydrogen peroxide into water and oxygen, protecting cells from damage.
9. How do enzymes increase the rate of reactions?
- A. By increasing temperature
- B. By raising activation energy
- C. By lowering activation energy ✅
- D. By adding more molecules
Explanation: Enzymes lower the energy needed to start a reaction, making it occur faster.
10. What is the result if the enzyme shape changes?
- A. It becomes faster
- B. It may not bind the substrate ✅
- C. It becomes a hormone
- D. It doubles in size
Explanation: Changes in enzyme shape can prevent it from binding to its substrate, making it ineffective.
11. Which enzyme works best in acidic pH?
- A. Amylase
- B. Pepsin ✅
- C. Trypsin
- D. Lipase
Explanation: Pepsin is active in the acidic environment of the stomach and digests proteins.
12. What is the substrate of lipase?
- A. Lipids ✅
- B. Proteins
- C. Starch
- D. DNA
Explanation: Lipase is an enzyme that breaks down lipids (fats) into fatty acids and glycerol.
13. Which property of enzymes allows them to be reused?
- A. They are non-living
- B. They are not consumed in reactions ✅
- C. They are inorganic
- D. They are destroyed after use
Explanation: Enzymes remain unchanged after the reaction and can be used again for similar reactions.
14. What happens when enzyme concentration increases?
- A. Rate of reaction decreases
- B. Rate of reaction increases (up to a point) ✅
- C. Enzymes stop working
- D. Temperature increases
Explanation: More enzymes mean more active sites are available, speeding up reactions until substrate becomes limiting.
15. Which statement best describes the lock and key model?
- A. Enzyme fits perfectly with its substrate ✅
- B. Enzyme opens cell membranes
- C. Substrate breaks enzyme shape
- D. Enzyme locks nutrients
Explanation: The lock and key model explains how the enzyme’s active site fits exactly with its specific substrate.