9. A class wanted to test the effect of increasing CO2 concentration on the amount of oxygen produced by photosynthesis. They placed elodea plants in 4 test tubes containing water at 25°C. They filled each tube with fresh
water. Test tube 1 received 0.6g of baking soda to supply CO2. Test tube 2 received 0.4g of baking soda Test tube
3 received 0.2g of baking soda. Test tube 4 received 0.0g of baking soda. A collection tube was placed over each
test tube to collect the oxygen gas. The light source was placed 30 cm away from the test tube.
a. What is the independent variable?
b. What is the dependent variable?
c. What is the control?
d. What are 2 constants?
e. If photosynthesis is occurring, should the amount of oxygen be increasing or decreasing? Explain.
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