Question: How are the amounts of oxygen and carbon dioxide related to each other? Observe: Put two Elodea sprigs into a test tube. Put the O2/CO2 probe into the tube with the Elodea. Click Play. As the Gizmo runs, Pause () it a few times.

A.
How do the oxygen (O2) and carbon dioxide (CO2) levels change over time?

B.
What is always true about the total amount of O2 and CO2 in the test tube?

C.
What happens when the CO2 reaches zero?

Revise and repeat: Click Reset. Remove the plants. Repeat the experiment with two snails.

A.
How do the gas levels change?
O2

CO2

B.
What is the total of O2 and CO2?

Challenge: In the process of photosynthesis, plants use carbon dioxide (CO2), water (H2O), and light energy to produce a sugar (C6H12O6) and oxygen (O2). In the process of aerobic respiration, animals and plants release energy from sugar and oxygen and produce carbon dioxide and water. The chemical equations that describe these reactions look like this:

6CO2 + 6H2O + light C6H12O6 + 6O2 C6H12O6 + 6O2 6CO2 + 6H2O + energy

How do these equations explain why the total amount of O2 and CO2 remains the same?