2.58B: Practical: Investigate the Role of Environmental Factors in Determining the Rate of Transpiration from a Leafy Shoot

TRANSPIRATION: Loss of Water vapour from stems and leaves of plants - inevitable consequence of gas exchange

POTOMETER: Device Used to Measure the Volume of Water Absorbed by the Plant

INVESTIGATING FACTORS THAT AFFECT TRANSPIRATION

Diagram showing Use of Potometer to Measure the Effect of Factors on Transpiration

METHOD: Cut shoot underwater to prevent air from entering Xylem and place through hole fo stopper provided with potometer Fill potometer with Water and fit the stopper holding the leafy shoot to apparatus Use vaseline to seal apparatus to ensure equipment is airtight Trap air bubble in capillary tube by: Dip end of capillary tube into beaker of Water Close tap of reservoir and remove beaker of Water to allow plant to transpire for a few minutes Re-immerse capillary tube into beaker of Water Measure and record the starting distance of air bubble Change environmental factor being investigated Allow shoot to adapt to new environment for a fixed period of time Measure and record the final distance of air bubble to calculate the total volume of Water absorbed by plant Change intensity of environmental factor and repeat process

RESULTS The greater the distance moved by air bubble during the fixed period of time, the larger the volume of Water absorbed by the plant, and hence an increase in transpiration rate

ENVIRONMENTAL FACTORS: Temperature : Heaters or submerging shoot in heated Water baths Humidity : Encasing plant in plastic bag with variable levels of vapour Wind : Placing fan at variable distance from plant Light Intensity : Placing lamp at variable distance from plant