Mark Fink, age 12, of Huntsville, Alabama, for his question:

Do all plants give off gases?

Living plants need oxygen, just as we do, to carry on the life processes in their busy cells. The oxygen fuel is converted by slow combustion into carbon dioxide, the same waste gas exhaled in our breathing process. Plants, however, have no lungs or nose. Air containing vital oxygen enters through tiny pores and circulates directly among the living cells. Carbon dioxide exits through the same pores. The process is called respiration.

With the exception of certain tiny_micro orgmisns, all living.ilants carry 6n''fheir vital respiration day and night. They take oxygen from the air around them and return carbon dioxide, just as sae do. But during the daylight hours, green plants carry on an added exchange of gases with the air. This process is photosynthesis, the recipe used by green chlorophyll to manufacture basic plant food from air, water and sunlight. The gas used in photosynthesis is carbon dioxide and the waste gas of the process is oxygen. All plants continuously give off carbon dioxide in respiration. Through the daylight hours, green plants also give off oxygen.