Biology – 8.1 Transport in plants | e-Consult

Method: Similar to the temperature investigation, potted plants of the same species and size should be used. The key difference is controlling the humidity around the leaves. This can be achieved by placing the plants in chambers with varying humidity levels (e.g., 60%, 70%, 80%, 90%). Temperature and light intensity should be kept constant across all chambers. Plants should be watered regularly. Transpiration rate can be measured as described above (weight change or potometer).

Variables:

• Independent Variable: Humidity (e.g., 60%, 70%, 80%, 90%).
• Dependent Variable: Transpiration rate (measured as change in mass or water uptake by potometer).
• Controlled Variables:

  • Plant species and size
  • Temperature
  • Light intensity
  • Soil type
  • Pot size
  • Watering regime

Explanation: Transpiration rate is affected by humidity because the water potential gradient between the leaf and the atmosphere is reduced when humidity is high. A smaller water potential gradient means that the rate of water evaporation from the leaf surface is slower. Therefore, transpiration rate decreases with increasing humidity.