22 Feb. Science 8 Transpiration; Blocking sunlight and starch; Interpreting results

Meet at study site to collect leaves/data. Return to lab. Follow safety guidelines.

Today we will go and gather the results from the leaf experiments set up during last class.

First, carefully remove the plastic bag that was covering the leaf. Do not spill any water. Very carefully measure the water in ml. (Read the cylinder carefully. You might want to empty the bag into a beaker and then pour the water from the beaker into the cylinder. If your bag did not collect any water, the most likely reason is that the bag was not sufficiently closed. Transpiration involves evaporation at the leaf surface. You might imagine it is a complicated process for water to move into the roots and up the plant into the leaves. Some of the water is used for photosynthesis. The water in the plant also gives it turgor and dissolves various molecules that are transported in the plant. There is no pump for this circulation (like a heart in animals) but rather a complex interaction of physical processes “managed” by the plant. To get a “taste” of the coordination of processes, browse the article/link below:

Lay the leaf that was in the bag flat on some 1 cm x 1 cm graph paper. Trace the outline. Estimate the surface area. (Both partners estimate and then compare. You should be close to each other.)

Enter the data in this spreadsheet. Let me know when you want to enter the data and I will add you to the list of those who can edit. When all data has been entered, you will be notified. You should then make a scatter plot with volume of transpired water on the vertical (y-) axis and surface area of leaf on the horizontal (x-) axis. Be sure to title graph, label axis with variable and unit, choose convenient, consistent scales that includes all the data and covers 1/2 the graph paper.


Next remove the leaves that were covered with black paper. We will return to the room and de-color the leaves.

Use eye protection. Take care with the hot ethanol and hot water. Avoid inhaling the fumes (we will have the exhaust fans on.) Avoid contact with skin. No flame. Pour the used ethanol in the designated container.

Procedure explained and demonstrated in class.

  • Collect covered leaves. Remember which leaf was cover with which design.
  • Remove paper cover on leaves.
  • Place leaves in hot water for 5 minutes.
  • Place boiled leaf in a container of ethanol and place the container in a boiling water bath for 10 minutes.






  • Place a de-colored leaf in a container and add iodine as a starch indicator.
  • How do you interpret the results?
  • Describe and take pictures of your leaf. Do this very soon after adding the iodine as the leaves will eventually dry out and curl and you may not get a clear picture.
  • See these notebook entries from former Science 8 students:
  • 20kbardos.5.Feb.StarchExperiment
  • 20mkataoka.Starch.Feb5

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