Required Practical: Investigating Factors Affecting Transpiration

🧪 Required Practical: Investigating Factors Affecting Transpiration

Aim

To investigate how environmental factors affect the rate of transpiration using a potometer.

Variables

• Independent: Factor being tested (e.g., wind speed, temperature, humidity, light)
• Dependent: Rate of water uptake (bubble movement)
• Control: All other factors, plant type, leaf area, time of day

Method for Testing Wind Speed

1. Set up potometer with shoot in standard conditions
2. Allow 10 minutes equilibration
3. Measure bubble movement over 5 minutes (no wind)
4. Position fan at set distance (e.g., 30cm)
5. Turn on fan at low speed
6. Allow 5 minutes equilibration
7. Measure bubble movement over 5 minutes
8. Repeat with medium and high fan speeds
9. Calculate rates and plot graph

Expected Results

• Wind: Linear increase with wind speed
• Temperature: Exponential increase with temperature
• Light: Rapid increase then plateau
• Humidity: Inverse relationship

Sources of Error

• Air bubbles in xylem
• Leaks in apparatus
• Changes in stomatal opening over time
• Temperature changes from fan motor
• Shoot stress from cutting

Improvements

• Use multiple shoots and average results
• Control temperature with water bath
• Use humidity chamber for humidity tests
• Allow longer equilibration time
• Use data logger for continuous measurement