Light Intensity: Increased light causes stomata to open wider to facilitate intake for photosynthesis, which simultaneously increases the pathway for water vapor to escape.
Temperature: Higher temperatures increase the kinetic energy of water molecules, accelerating evaporation from mesophyll surfaces and increasing the capacity of air to hold moisture.
Humidity: High external humidity reduces the concentration gradient between the leaf and the air, significantly slowing the rate of diffusion.
Air Movement: Wind sweeps away the 'boundary layer' of saturated air near the leaf surface, maintaining a steep concentration gradient and increasing transpiration.
A potometer is a device used to estimate the rate of transpiration by measuring the rate of water uptake by a leafy shoot.
It operates on the assumption that water uptake is approximately equal to water lost through transpiration, though a small fraction of water is used for photosynthesis and turgidity.
Methodological Precision: The shoot must be cut underwater to prevent air bubbles from entering the xylem, which would break the cohesive water column (embolism).
The movement of an air bubble along a capillary tube over a set time allows for the calculation of the rate: .
Identify Variables: In experiments, always distinguish between the independent variable (e.g., wind speed) and the dependent variable (distance moved by the bubble).
Control Factors: When testing one factor (like light), ensure others (like temperature) are kept constant using heat shields or water baths.
Sanity Check: If a question asks why the bubble stopped moving, check for leaks in the potometer seal or if the plant has wilted (stomata closed).
Units Matter: Ensure transpiration rates are expressed clearly, such as of leaf area.
