• In this lab, we will investigate the process of photosynthesis.
• We will learn how the amount of light affects photosynthesis.
• To do this, we will use:
– An Elodea plant,
– The chemical Bromothymol Blue
• Bromothymol Blue acts as an indicator to show if photosynthesis is occurring. Bromothymol Blue works because it is able to detect the presence of CO2 (needed for photosynthesis) and O2 (released during photosynthesis) in solution.
– Bromothymol blue + CO
2
– Bromothymol blue + O
2
= green color
= blue color

1) Write the equation for photosynthesis .
2) Write a hypothesis in an
“If_____then____” format.
– You will need to relate this to what happens to water that has CO
2 in it and what could happen when a plant is added.
3) Now read the class set of instructions.

Class set of Elodea & Bromothymol Blue Lab
DEMO Instructions…read
1. Pour 75 mL of water into a plastic cup.
2. Add 2 mL of bromothymol blue to the water. It should be a blue solution.
3. GENTLY blow into the solution causing it to bubble for approximately 1 minute. Use a straw. The solution should turn green.
4. Label 3 clear containers marked: 1, 2, & 3
• Container 1 will be the control (no Elodea)
• Container 2 will be the Elodea in the dark
• Container 3 will be the Elodea in the light
5. Pour 25 mL of the solution into each of the three containers.
6. Cover container 1 with plastic wrap (there is no Elodea in container 1), cover completely with tin foil and place it in a safe location near a light source.
7. Add a 7 cm piece of Elodea to container 2. Using the straw, GENTLY push the
Elodea to the bottom of the test tube. Then cover container 2 with plastic wrap and then cover the whole container with tinfoil and place it in a safe location that is completely dark.
8. Add a 7 cm piece of Elodea to container 3. Using your straw, GENTLY push the Elodea to the bottom of the test tube. Cover the container with plastic wrap. Then place it in a safe location near a light source.

• Predict what color container 1 will be after the experiment.
__________________
• Predict what color container 2 will be after the experiment.
__________________
• Predict what color container 3 will be after the experiment.
__________________

Sample
Color before experiment
Color after experiment
No Elodea covered with tinfoil (control)
Elodea + light and covered with tinfoil
Elodea + light