Name: ________________________________


Date: ____________



LAB Photosynthesis vs Respiration




1. The equation for photosynthesis is:



CO2 + H2O + light ------------------> C6H12O6 + O2



2. We use bromothymol blue (BTB) to see if water is acid or not.


light blue = neutral

light yellow = acid


You respiration creates CO2 . When you blow into water, your CO2 in the water does this:


CO2 + H2O --------------> H2CO3 (acid)


Elodea, like all plants uses CO2 in photosynthesis and will change the color of the water from yellow to blue.





1. Add deionized water to 2 test tubes until 4 cm from top.

2. Add enough drops of BTB to each tube to turn water pale blue.

3. Use straw to gently blow CO2 into water in each tube until it turns pale yellow

4. Get Elodea from Mr. Wigger and put into one tube.

5. Get your group #.

6. Record time you put your tubes in rack in front of light. (back of this paper)

7. Record time your tube with the Elodea changes to light blue.


Watch carefully for the exact time the change happens!!!






Group: ________

Distance from light: __________




Start time

End time

Total minutes and seconds

tube with Elodea




tube without Elodea