Photosynthesis and Cellular Respiration Lab
Question:
What is the relationship between the processes of photosynthesis and respiration?
Background Information: Copy the paragraph below and fill in the blanks.
Green plants use ___ light to make ___ (food for plant and other organisms). To do so, the plant must use
____ and ____ in a process called _____. To release the energy contained in ____ it must be converted to
chemical energy called ____. This process is called _____. It also produces _____ and ____, which are the
reactants for the process of _____.
WORD BANK:
1. cellular respiration
2. photosynthesis
3. sugar (C6H12O6)
4. carbon dioxide (CO2)
5. water (H2O)
6. oxygen (O2)
7. sun
8. ATP
In the presence of CO2, bromothymol blue solution will turn yellow. Using this information, formulate a
hypothesis for testing the effectiveness of photosynthesis in the light versus the dark.
Materials (group of 4)
 2 test tubes
 2 Elodea


light source
drinking straw
Procedure
1. Measure out .75 pipette full of bromothymol blue solution and 4mL of water for each of the two
flasks. Caution: Bromothymol blue is a dye and can stain your hands and clothing.
2. Insert one end of a drinking straw into the test tube. Gently blow through the straw. Keep blowing
until there is a change in the appearance of the bromothymol blue solution. Repeat this procedure
with the other flask. Answer the questions below.
a. What was the color of the bromothymol blue solution before you exhaled into it?
b. What gas did you exhale into the water? (evidence)
c. What color did the bromothymol blue change to? (evidence)
d. PREDICT, Why did it change color? Why did we use bromothymol blue in this experiment?
3. Place a sprig of Elodea into each tube. Cover each tube.
4. Place one tube in the dark for 24 hours. Place the other tube under the light for the same amount of
time.
a. Identify the Control Group and Independent Group
Observations/Data
Day 1
color of solution before ________ (TT 1) color of solution after exhalation ________ (TT 1)
color of solution before ________ (TT 2) color of solution after exhalation ________ (TT 2)
Day 2
5. After 24 hours, examine each flask.
a. What differences did you observe
TT 2
between the Elodea in the light and TT 1
color
day
2__
Color day 2___
the Elodea in the dark? (evidence)
b. EXPLAIN why you think a change
happened. (claim)
Analysis/Conclusion
CLAIM – A conclusion that answers the original question
EVIDENCE – Scientific data that supports the claim. The data needs to be appropriate and sufficient
to support the claim.
REASONING – A justification that links the claim to the evidence. It shows why the data counts as
evidence by using appropriate and sufficient scientific principles.
TITLE
CLAIM
DRAWING
EVIDENCE
DRAWING
REASONING
DRAWING