Kai has a see-through glass tank with air, plants, and animals that eat those plants. He sealed the tank so no material can get into or out of it,
but light can get in when the tank is not covered.
The light for the tank has been on all day, and Kai measured the carbon
in the air and found that it is decreasing. How is carbon moving between
the air and the living things in the tank? What is happening to the amount
of carbon in living things?