Elodea Photosynthesis Lab
Question:
What gases do plants use and produce in the process of photosynthesis?
Predictions:
Fill in the table below with your ideas. Don’t worry about being right or wrong, this is just to see
what you already know about the reaction.
What do plants need/use/consume?
(reactants)
What do plants give off? (products)
Using what you wrote in the boxes, try to write an equation for the photosynthesis reaction.
Reactants go on the left side of the arrow and products go on the right.
Example: Cake mix + Egg + Oil  Cake
______________________________________________________________________________
Materials:
Test Tubes
Water
Straw
Bromothymol Blue
Foil
Elodea
Safety:
• Keep safety goggles on at all times
• Do not drink the liquid or suck up the liquid in the straw
• Do not touch materials until instructed
Procedure:
1. Obtain 2 test tubes containing bromothymol blue and water.
2. Use tape to label both test tubes with your names, homeroom, and CO 2 or no CO2.
Name
Homeroom
CO2
Name
Homeroom
No CO2
3. GENTLY start blowing through the straw into the liquid in the test tube labeled CO 2.
Blow until you see a color change. This may take several breaths.
a) When you blow into the test tube what gas are you putting into the liquid?
4. Record the color of both test tubes in the data table.
5. Add a sprig of Elodea to both test tubes and cover with foil.
6. Place the test tubes in the test tube rack by the light and let them sit overnight.
Data Table:
Bromothymol Blue = blue when no CO2 is in the liquid
Bromothymol Blue = yellow when CO2 is in the liquid
Color of Test Tube on Day 1
Color of Test Tube on Day 2
Test Tube with CO2
Test Tube without CO2
IVCDV Chart
Independent Variable
Constants
Dependent Variable
Hypothesis: If _____________________________________________________________, then
_____________________________________________________________________________.
Using colored markers or pencils, draw what the two test tubes look like after adding CO2 to
one test tube and Elodea to both test tubes.
Day 1:
CO2
No CO2
Day 2:
Using colored markers or pencils, draw what the two test tubes look like after 24 hours and
record the color of each test tube in the data table on page 2.
Analysis Questions:
1. Explain why the color of the test tube containing bromothymol blue changed colors
when you blew into it with the straw.
2. What color did the test tube containing bromothymol blue, CO2, and Elodea change
overnight?
3. Why do you think there are bubbles in the test tube? What could this gas be?
4. Did the color change overnight in the test tube without CO2?
5. Using these results, which gas do you think is used by plants during photosynthesis?
Which gas do you think is produced? Explain your answer using complete sentences.
6. Using 1-2 complete sentences, summarize what you learned about photosynthesis
during this experiment.