Part of Lesson Plan: Investigating Photosynthesis- A Color Story
Activity Overview / Details
Using the attached labels label five test tubes per group. Next, have the students removed the leaves one at a time and place them into the corresponding test tube. It’s important to keep track which leaves are which, therefore the labels come in handy.
Before you test the leaves for starch, the chlorophyll must be removed from the leaves. To remove the chlorophyll from the leaves, I fill the test tubes with rubbing alcohol and heat them in hot water for 5-7 minutes. The heating process must occur outside on hot plates because of the toxic fumes that are released from heating the rubbing alcohol. I set up at table just outside of my classroom and take one group outside at a time. In the mean time, the other students are working on the attached photosynthesis worksheet. After the color has disappeared from each leaf, I use the tweezers to swirl each leaf in a beaker of water. I then have the students place the leaves in the labeled Petri dishes filled with Iodine (print another set of labels). The iodine is for the starch test. Iodine turns black/deep purple in the presences of starch. Therefore, the more black/deep purple color the more starch has been accumulating, which means the more sugar has been produced because of photosynthesis. I use just enough iodine to cover each leaf. After one minute, the students use the tweezers to gently swirl the leaf in a clean beaker of worker and then lay the leaf on the labeled piece of paper (see attached). It will be very clear which leaves produced the most amount of starch. The leaf covered in blue cellophane and the control leaves tend to have the most amount starch accumulated.