Enzyme Experiments (Copy)

Enzyme Experiments – Expanded Section (O Level & IGCSE Biology Alternate to Practical)

1. Key Enzyme Concepts

• Enzymes: Biological catalysts that speed up chemical reactions.
• Made of proteins and are specific to their substrates.
• Work best at an optimum temperature and pH.
• Become denatured if conditions are too extreme (shape of active site changes permanently).

2. Common Enzyme Practical Questions

You may be asked to:

• Investigate how temperature, pH, or concentration affects enzyme activity.
• Measure time taken for a substrate to be broken down.
• Identify control variables.
• Describe and interpret color changes, bubbling, or clear zones as signs of reaction.

3. Key Enzyme Experiments

A. Starch Breakdown by Amylase

• Substrate: Starch
• Enzyme: Amylase
• Product: Maltose

Procedure:

1. Add equal volumes of starch solution and amylase into a test tube.
2. Place in water bath at different temperatures (e.g., 20°C, 30°C, 40°C, 50°C, 60°C).
3. Every 30 seconds, take a sample and place on a tile with iodine.
4. Record the time taken for the iodine to stop turning blue-black.
5. The shorter the time, the faster the enzyme is working.

Control: Boiled amylase or starch alone (no enzyme) to prove no reaction occurs without enzyme.

Expected Results:

• Fastest reaction at ~37°C
• Slower at low temperatures
• No reaction or enzyme denatured at 60°C+

B. Catalase Breaking Down Hydrogen Peroxide

• Substrate: Hydrogen peroxide (H₂O₂)
• Enzyme: Catalase (from potato or liver)
• Product: Water + Oxygen

Procedure:

1. Add catalase source (e.g., mashed potato) into a test tube.
2. Add a set volume of H₂O₂.
3. Collect the gas released using a delivery tube into a measuring cylinder or use a gas syringe.
4. Measure volume of oxygen released in a fixed time.
5. Repeat at different temperatures or pH levels.

Observation: More bubbles or gas collected = faster reaction.

Control: Use boiled potato (no active catalase).

4. Variables to Consider

5. Data Recording Table Example

6. Explaining Results Scientifically

• “At higher temperatures, enzymes have more kinetic energy, causing more frequent collisions with substrate.”
• “At very high temperatures, the enzyme’s active site is denatured and can no longer bind to substrate.”
• “Optimum pH ensures active site maintains the correct shape for binding.”

7. Calculating Rate of Enzyme Activity

• Rate = 1 / time
  • If time taken to digest starch is 30 sec → rate = 1/30 = 0.033 s⁻¹
• For catalase: Rate = volume of O₂ / time

8. Common Exam Instructions

• “Describe how you would investigate the effect of temperature on enzyme activity.”
• “Explain why boiled enzyme was used as a control.”
• “Explain why the iodine changed color more slowly at lower temperatures.”

Marking Points for Enzyme Practical Questions

Common Mistakes to Avoid

• Forgetting to include a control
• Not timing or measuring accurately
• Overheating enzymes during preparation
• Using general terms like “it broke the food” instead of “substrate converted to product”
• Confusing temperature effect with pH effect