Science Buddies: "Ask an Expert"

I am working with a partner attempting to simulate the atmosphere of the Paleozoic era using sealed containers with increased oxygen levels with butterflies and meal worms. The issue we are dealing with is that our teacher does not trust us to use oxygen tanks. Is there a way to catalyze a reaction inside the chamber that would give us a manageable increase in oxygen?

The first idea that came to me is simply adding more plant life to your environment. As long as you can accurately measure the oxygen concentration inside, you could maybe titrate the plant density to reach the approximate levels you are looking for?