Bright Light, Small Leaf Lab

By Judy Klassen, Abigail Navarro, and Sara Fehr


Will a leaf's transpiration rate increase due to an intensity of light during water transpiration?


If we change the intenseness of light on a leaf during water transpiration for a 10 minute time period, then the leaf's transpiration rate will increase because of the increase of energy being added to the leaf.

Manipulated Variable:

The manipulated variable in this lab is a really bright light.


The range to be used is 0-10 minutes.

Three Constant Factors:

  • Amount of water

  • 1 Leaf

  • Temperature


  • potometer

  • pipette

  • water

  • 1 leaf

  • lamp w/ light bulb

  • syringe
  • 1 timer
  • graph paper
  • petroleum jelly
  • 1 clamp
  • razor blade


Calculate the area of the leaf on graph paper. Watch to see whether the changing intensity of the light has any effect on the transpiration rate of water through a leaf for a 10 minute time period. Record the results of mL decease of water with each minute that passes on the timer.


We observed that the water level didn’t drop dramatically as expected during the experiment. During the 9 minute mark, however, there was a slight change in the elevation of water. The lamp didn’t add much of an effect on the leaf and the water transpiration that was occurring.


Big image
Big image


Area of leaf: 3,780 mm²

Transpiration Rate: 5.291005291e-6 ml/mm²/min

The transpiration rate was slow, but there was a recorded change between the time the ten minutes started to the end of the first minute that led us to get the transpiration rate that we did.


While we did not see a significant change in the amount of water left, there were very slight ones in the beginning and near the end of the experiment. If we had not put the petroleum jelly around the end of the leaf like we had, the transpiration rate probably would have been faster than it was. While our experiment resulted in only a slight transpiration rate, this shows that the brightness of the light did have a small effect on the leaf.