July 21, 2021
Measuring the rate of Transpiration
A Potometer can be used to measure the rate of water uptake
Method:
- Fresh shoot is cut under water and is transferred to the apparatus under water to aviod air bubbles
- Air bubble moves along tube as water is absorbed by shoot
- A resrvior is set up that allows water to flow into the capilliary tube, pushing the air bubble back to the start of the tube
- As the plant transpires it draws water out of the capilliary tube to replace the losses
- The capilliary tube is narrow so the losses of water from the plant gives mesurable movements of the air bubble
- Repeat measurements of the distance moved in one minute to ensure the data gained is reliable
Factors to consider when setting up a Potometer
- Use plants that have shoots with thin waxy cuticles
- Shoots must be cut under water - prevent air from entering xylem vessels which will block water flow. Thouroughly seal the contact point
- Leaves that are going to be used must be dry
- Use a mass potometer (plant with complete root system is immersed in container)
Temperature and Transpiration
- Higher temperature increases evaporation and therefore transpiration
- Increased rate of diffusion through air spaces and humidity of outside air is lowered
- In very high temperatures stomata may close
Wind Speed and Transpiration
- Wind moves evaporated water molecules away from leaf
- The facter the air movement the quicker the water will be moved - this keeps a high concentration gradient of water between the inside and outside of leaf. Transpiration rate increases
- Very high wind speed causes the stomata to close which lowers the overall transpiration rate
Humidity and Transpiration and Comparison
- The more humid the air the more water is inside it
- This reduces the concentration gradient between the air spaces inside the leaf and the air outside
- Water molecules will diffuse out more slowly therefore decreasing the transpiration rate
Conclusion
Warmer temperature increases the transpiration rate
Transpiration rate is higher on a Windy Day
Transpiration rate is higher when the air is less humid
That's all for this experiment!
References:
- https://www.google.com/url?sa=i&url=http%3A%2F%2Fwww.passmyexams.co.uk%2FGCSE%2Fbiology%2Fmeasuring-transpiration.html&psig=AOvVaw14_vcuOyTV0pGtfWxMX-uC&ust=1626974810720000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCJiq7c_X9PECFQAAAAAdAAAAABAO
- https://www.google.com/url?sa=i&url=https%3A%2F%2Fen.wikibooks.org%2Fwiki%2FSchool_Science%2FPotometer&psig=AOvVaw14_vcuOyTV0pGtfWxMX-uC&ust=1626974810720000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCJiq7c_X9PECFQAAAAAdAAAAABAZ
Drafted by Venetia (Biology)