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IBDP Biology- Measuring Rate of Transpiration

Topic 9- Potometer

· IBDP BIOLOGY,IB,Transpiration

Measuring the rate of Transpiration  

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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 

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  • 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!

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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)

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