A student placed a living green plant in an airtight, transparent container filled with air from the room. The container was exposed to sunlight for one week. At the end of the week the student was to determine which gases had increased in concentration. Assuming enough water and carbon dioxide were available for the proper growth of the plant, which gas would you expect to be present in increased concentration?

The questions have been asked in several important state and regional science exams in the United States. For example: TAKS-Texas Assessment of Knowledge and Skills, New York State Educational Department Regents exams, California Standards Test, etc.