Respiration and Germination Practical (Copy)

Respiration and Germination Practicals – Expanded Section (O Level & IGCSE Biology Alternate to Practical)

Part A: Respiration Practical

1. Key Concepts

• Respiration: Process of releasing energy from glucose.
  • Aerobic: With oxygen → Glucose + O₂ → CO₂ + H₂O + energy
  • Anaerobic: Without oxygen → In animals: glucose → lactic acid
  • In yeast: glucose → ethanol + CO₂

2. Detecting Carbon Dioxide Production

Limewater Test

• Reagent: Limewater (Ca(OH)₂)
• Positive Result: Limewater turns cloudy/milky in presence of CO₂

Setup:

• Germinating seeds in a flask
• Delivery tube to test tube with limewater

Observation:

• Bubbles = CO₂
• Limewater becomes cloudy → respiration occurring

3. Respirometer Practical (O₂ Uptake Measurement)

Purpose: Measure oxygen consumption by living organisms (e.g., germinating seeds or insects)

Apparatus:

• Respirometer (sealed tube)
• Soda lime or potassium hydroxide (absorbs CO₂)
• Capillary tube or manometer
• Ruler/scale to measure movement

Procedure:

1. Place germinating seeds in the respirometer.
2. Add soda lime to absorb any CO₂ produced.
3. Use a capillary tube with liquid to detect pressure change.
4. As O₂ is consumed, the liquid in the tube moves.
5. Measure distance moved over time.

Control: Use boiled seeds or dead insects to show that no O₂ is used without respiration.

4. Temperature Effect on Respiration

Setup:

• Germinating seeds placed in test tubes at different temperatures
• Limewater or hydrogen carbonate indicator to detect CO₂
• Observe rate of color change or bubbling

Hydrogencarbonate indicator:

• Orange → Yellow (more CO₂)
• Orange → Purple (less CO₂, more O₂ absorption)

5. Common Observations

Part B: Germination Practical

1. Key Conditions for Germination

• Water – activates enzymes
• Oxygen – for aerobic respiration
• Warmth – for enzyme activity
• (Light is NOT essential)

2. Common Germination Setup

Experiment:

Set up 4 test tubes or petri dishes with seeds in different conditions:

3. Interpreting Results

• Germination only occurs when all three conditions are present.
• Seeds may swell but not grow without oxygen.
• Cold conditions slow enzyme activity → delayed germination

4. Practical Notes

• Use cotton wool or filter paper to hold seeds
• Use oil layer or boiled water for anaerobic conditions
• Seal flasks with rubber bungs or cling film to block oxygen

Common Errors to Avoid

• Forgetting to include a control (e.g., boiled seeds or no water)
• Mixing up respiration and photosynthesis
• Not sealing anaerobic setups properly
• Assuming light is required for germination

Marking Points for Respiration & Germination Practicals