If a student tested the bubbles collected in the test tube what would they find they are made of and how do you know?

Hello. This question is incomplete. The full question is:

A student prepared two beakers with identical sprigs of a water plant as shown below. She placed Beaker A in the shade and the Beaker B beside a fluorescent lamp. She then systematically changed the distance from the beaker to the lamp. She counted the bubbles given off by the plants in each beaker.  

If the student later tested the bubbles collected in the test tube, What would she find they are made of?

oxygen

Explanation:

The bubbles are oxygen and we can say that because this is the gas that plants release through photosynthesis. In this case, we can also confirm that the plant that was exposed to fluorescent light, showed more bubbles than the other plant, since the light allowed the photosynthetic rate of this plant to be higher, releasing more oxygen to the environment.