Temperature: Higher temperatures increase the kinetic energy of water molecules, accelerating evaporation and diffusion rates.
Humidity: High humidity reduces the concentration gradient between the leaf interior and the atmosphere, significantly slowing down transpiration.
Air Movement (Wind): Wind sweeps away the 'boundary layer' of saturated air near the leaf surface, maintaining a steep concentration gradient and increasing the rate.
Light Intensity: Increased light causes guard cells to become turgid and open the stomata to allow in for photosynthesis, which simultaneously increases water loss.
Potometer Analysis: When using a potometer, remember it measures water uptake, not directly transpiration. While they are usually equal, some water is used for photosynthesis or turgidity.
Limiting Factors: In exam questions, identify which factor is 'limiting' the rate. For example, if light intensity is high but humidity is 100%, the rate will remain low regardless of light.
Data Interpretation: Look for 'plateaus' in graphs. If the rate stops increasing as light intensity rises, the stomata are likely fully open, and another factor (like temperature) has become limiting.
Common Units: Ensure you check units for transpiration rates, often expressed as volume per unit time per unit leaf area (e.g., ).
