Investigating the effect of environmental factors

• Environmental factors in water uptake:

  • Air movement, humidity, temperature and light intensity all have an effect on the rate at which transpiration occurs.
  • The table below explains how these four factors affect the rate of transpiration when they are all high; the opposite effect would be observed if they were low.
• Transpiration Rate Factors Table:

  
• Investigating the effect of environmental factors on the rate of transpiration (part 1):

  • We can investigate the effect of different environmental conditions (such as temperature, humidity, light intensity and wind movement) on the rate of transpiration using a piece of apparatus called a potometer.
• Investigating the effect of environmental factors on the rate of transpiration (part 2):

  • There are 2 types of potometer:
  • A mass potometer measures a change in mass of a plant as a measure of the amount of water that has evaporated from the leaves and stem.
  • A bubble potometer measures the uptake of water by a stem as a measure of the amount of water that is being lost by evaporation consequently pulling water up through the stem to replace it.
• Method (part 1):

  • Cut a shoot underwater.
  • To prevent air entering the xylem and place in tube.
  • Set up the apparatus as shown in the diagram and make sure it is airtight, using Vaseline to seal any gaps.
  • Dry the leaves of the shoot.
  • Wet leaves will affect the results.
  • Remove the capillary tube from the beaker of water to allow a single air bubble to form and place the tube back into the water.
  • Set up a lamp 10 cm from the leaf.
  • Allow the plant to adapt to the new environment for 5 minutes.
  • Record the starting location of the air bubble.
• Method (part 2):

  • Leave for 30 minutes.
  • Record the end location of the air bubble.
  • Change the light intensity.
  • Reset the bubble by opening the tap below the reservoir.
  • Repeat the experiment.
  • Calculate the rate of transpiration by dividing the distance the bubble travelled by the time period.
  • The further the bubble travels in the same time period, the greater the rate of transpiration.
• What is the equation for calculating the rate of transpiration?(bubble potometer)

  Here it is, but in a picture.

  
• Results:

  • As light intensity increases, the rate of transpiration increases.
  • This is shown by the bubble moving a greater distance in the 30 minute time period when the lamp was placed closer to the leaf.
  • Transpiration rate increases with light intensity because more stomata tend to be open in bright light in order to maximise photosynthesis.
  • The more stomata that are open, the more water can be lost by evaporation and diffusion through the stomatal pores.
• Limitations:

  • The potometer equipment has a leak.
  • The plant cutting has a blockage.
  • The potometer has shown no change during the experiment.