Effect of Temperature on Sugar Production

Research Question:

• How does temperature affect sugar transport within a plant?
• How does impaired sugar transport affect the levels of sugar and starch within a leaf? What does this say about where sugar is synthesized and where it might be transported to?

Materials:

• One houseplant with medium-size leaves
• Benedict’s solution (available from a scientific supply house or online)
• Eyedropper
• Iodine
• Ice cubes
• Medium-size test tube
• Small saucepan (alternatively, you can use a ring stand, beaker and Bunsen burner)
• Measuring spoons
• Kitchen tongs to hold the test tube.

Experimental Procedure

1. Practice using Benedict’s solution to measure sugar. Put 1/8 teaspoon of sugar in the test tube and add enough water to fill the test tube half way. Shake well. Add 20 drops of Benedict’s solution. Heat the water in the saucepan or set up a water bath using a beaker, ringstand and Bunsen burner. Suspend the test tube in the water bath with kitchen tongs or a clamp. As the solution heats, the color of the solution should change from blue to green, to yellow to orange, depending upon the amount of sugar. Experiment with lesser amounts of sugar and more Benedict’s solution. Once you are comfortable with this and have a good sense as to the sensitivity of the Benedict’s solution, clean your equipment and begin the experiment.
2. Place your plant in direct sunlight. Identify two leaves on the plant that are approximately the same size. One of these leaves will be your control. Without damaging the leaves or removing them from the plant, hold ice cubes to one of petioles for twenty minutes.
3. Remove both leaves from the plant, making sure you don’t confuse your chilled leaf with your control. Cut each evenly in half, down the central vein. One half of the leaf will be used for sugar testing, and the other half will be used for starch testing. Set one half of each leaf aside.
4. Test for sugar as you did in step 1. However, unlike step 1, put one half of the unchilled leaf in the test tube, instead of the sugar. Take a picture of the leaf after the color has changed and make a note of how dramatically the color changed.
5. Repeat step 5, using one half of with the chilled leaf, repeating exactly what you did in step 4. Make notes about how the color change differed.
6. Using an eyedropper, add iodine to the each leaf half that you set aside in step 3. Write down whether the color changed.

Terms/Concepts: Benedict’s solution, testing for sugar, testing for starch, sugar transport, photosynthesis

References:

• USDA Agricultural Research Service: Understanding Sugar Transport in Plants
• Missouri State University: Transport in Plants