Keith Murray, age 11, of Newport News, Virginia, for his question:

Is it true that plants breathe?

By breathing we mean absorbing oxygen gas as a fuel for the chemical processes of living cells. We breathe in oxygen and breathe out waste carbon dioxide from this slow burning process. We learn that plants absorb our waste carbon dioxide and return supplies of breathable oxygen to the atmosphere. This seems to contradict the notion that plants also use oxygen fuel more or less as we do. Nevertheless, this is a true fact.

Day and night, plants absorb oxygen through their pores and their cells use it as fuel to carry on their life activities. Waste carbon dioxide from these processes is returned to the air. However, during the daylight hours the plant world absorbs carbon dioxide to carry on photosynthesis. This very different process creates sugary plant food    and returns waste oxygen to the air. In the daytime, plants give off much more oxygen than they need. But photosynthesis stops when daylight ends. At night the plants take in oxygen and return only carbon dioxide to the air.