David Chase, age 10, of Mundelein, Illinois, for his question:

How do plants breathe?

We breathe in oxygen and breathe out carbon dioxide. Plants, we are told, take in carbon dioxide and return oxygen to the air. But they do this to make their food and it has nothing to do with how they breathe. Their busy cells use up oxygen and create waste carbon dioxide, just as ours do. In anirials this is called breathing. But in plants it is called respiration.

Plants cannot inhale and exhale as we do because they have no lungs and no noses. Instead they have countless pores in their leaves and stems. Molecules of air keep seeping through these tiny doorways. When they get inside, they seep from cell to cell. As they pass by, the cells trade their waste carbon dioxide for fresh oxygen. In time, the airy gases inside find a tiny pore and seep outside again. Now they carry less oxygen and more carbon dioxide. Plant respiration is slow and lazy, but like breathing it goes on day and night. In the daytime their food making operation takes carbon dioxide and returns oxygen.