Carol Vincent, age 11, of Indianapolis, Ind., for her question:

 Do plants breathe?

Plants breathe all the time, day and night. Like us, they breathe in oxygen and breathe out carbon dioxide. Oxygen enters the plants through tiny pores. It seeps through with the air and once inside the tissues it is used as needed. Carbon dioxide is produced in the process and it seeps through the same pores to join the air outside.

If this is so, how do the plants fill the air with oxygen? This happens because of another process called photosynthesis. Photosynthesis goes on during the daylight hours. It is the process by which plants make food and it happens in the green leaves and stems.

This process uses carbon dioxide from the air and returns oxygen as waste. For this job, plants need more carbon dioxide than they produce. They use this waste gas breathed out by animals. In return, they replenish the air with fresh oxygen ‑ some of which they need to breathe themselves.