LAB – Photosynthesis vs Respiration

Background

1. The equation for photosynthesis is:

chlorophyll

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

elodea

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.

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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: __________