Biology – 8.1 Transport in plants | e-Consult

Method: Potted plants of the same species and size are required. The light intensity can be varied by placing the plants at different distances from a light source (e.g., lamps with varying wattage). Temperature and humidity should be kept constant. Plants should be watered regularly. Transpiration rate can be measured as described above (weight change or potometer). It is important to ensure that the light source provides consistent light quality (e.g., using lamps with a similar spectrum).

Variables:

• Independent Variable: Light intensity (e.g., low, medium, high – measured in lux or similar units).
• Dependent Variable: Transpiration rate (measured as change in mass or water uptake by potometer).
• Controlled Variables:

  • Plant species and size
  • Temperature
  • Humidity
  • Soil type
  • Pot size
  • Watering regime

Explanation: Light intensity affects transpiration rate because light stimulates the opening of stomata. When stomata are open, water vapour can escape from the leaf. Higher light intensity generally leads to a greater rate of stomatal opening and therefore a higher transpiration rate. However, very high light intensities can sometimes lead to stomatal closure due to water stress, which would then reduce transpiration.