CAPF AC 2023 Q22: Science & Technology – Biology
- (a) upon substrate concentration, temperature and pH.
- (b) only on substrate concentration and pH, but not on temperature.
- (c) only on pH and temperature, but not on substrate concentration.
- (d) only on temperature, but not on pH and substrate concentration.
Answer: (a) upon substrate concentration, temperature and pH.
Explanation
What controls the speed of an enzyme
How to think: enzymes are proteins.
A protein's shape, and so its activity, changes with temperature and pH.
The amount of substrate also matters until the enzyme is fully busy.
So all three count.
| Factor | Effect on the rate |
|---|---|
| Substrate concentration | Rate rises, then levels off at a maximum when all enzyme molecules are occupied |
| Temperature | Rate is highest at the optimum temperature; high heat denatures the enzyme |
| pH | Each enzyme has an optimum pH; pepsin works at about 2, trypsin at about 8 |
Also: inhibitors and the amount of enzyme change the rate.
Answer: (a).
Why each option is right or wrong
- (a) CORRECT. The rate depends on substrate concentration, temperature and pH.
- (b) Incorrect. Temperature strongly affects enzymes; heat can denature them.
- (c) Incorrect. Substrate concentration also affects the rate.
- (d) Incorrect. pH and substrate concentration matter as well as temperature.
Key point
Enzyme activity depends on temperature, pH, substrate concentration and inhibitors. Human enzymes: optimum about 37 °C. Pepsin: acidic pH. Salivary amylase: about neutral. High temperature denatures; low temperature only inactivates.
Remember
Enzymes: temperature, pH and substrate all matter.
Common mistakes
- Thinking enzymes work the same at any temperature.
- Forgetting that the rate stops rising once the enzyme is saturated.
- Believing all enzymes prefer a neutral pH.
Exam tip
Educated guess: three options contain the word only and deny one factor each. The option that includes everything is the safe textbook statement.
Sources
- NCERT Class XI Biology — Biomolecules (factors affecting enzyme activity)
- NCERT Class X Science — Life Processes (enzymes in digestion)