Cynthia Kaiaec, age 10, of Cleveland, Ohio, for her question:
Where do plants get their oxygen?
We all know that the plants provide us with constant supplies of breathable oxygen. But we tend to forget that the plants themselves need oxygen. Since the czygen they produce is used by us and the animal world, it is natural to wonder who or what supplies the oxygen the plants needs.
Plants need a day and night supply of oxygen, just as we do. However, every green leaf is a natural oxygen manufacturing factory. The work goes on during the daylight hours and the oxygen, you might say, is produced by accident. The greenery is busy using sunlight to convert molecules of water and carbon dioxide into simple sugar, the basic food of all plant life. The process, of course, is photosynthesis the sunbeam recipe. ,
Scientists are beginning to understand some of the complicated processes of photosynthesis and someday we hope to copy nature's sunshine recipe. The energy of sunlight is used to rearrange simple atoms and molecules into other molecules. It is a complicated chemical process. And as the sugar molecules are assembled, a number of oxygen molecules' are left over. To the plant, they become a waste product and they are returned to the air. On a sunny day, a green forest pours countless tons of this by product oxygen into the sir.
There is enough to supply all the people and every breathing animal upon the earth. There also is enough for the plants themselves. For they too need oxygen to carry on the' chemical activities of their living cells. A plant, however, has no nose and no lungs to carry on our kind of breathing. The ordinary gases of the air enter through surface pores called "stomata" and seep out again through the same small doorways.
Once inside the plant, the air seeps leisurely from cell to cell. Each cell grabs from the mirture a molecule or two of the gas it happens to need at the moment. About one fifth of normal air is oxygen and each living plant cell takes oxygen molecules day and night. The chemical process that uses the oxygen produces carbon dioxide as a waste gas, just as we do. These waste molecules circulate around until they eventually reach the surface stomata. They ooze through the pores and mingle with the air outdoors.
Plants add small amounts of carbon dioxide to the in the process of respiration. They add tons and tons of oxygen as a by product of their photosynthesis. They do not put out enough carbon dioxide to supply their photosynthesis aciivity. But they do put out enough fresh, breathable oxygen to sipply our needs and the needs of the animals and plenty more to supply their own needs.
The waste gas we breathe out supplies the plant world with extra carbon dioxide. This waste gas from the human, animal and plant world adds less than one per cent to the gaseous mixture of the air. The generous plant world contributes the 21 per cent of oxygen present in the airy mixture. They use as much of it as they need and leave the rest. A plant gives out carbon dioxide day and night and surplus oxygen during the day. For this reason, a thoughtful nurse removes green plants from a sick room after dark. Without light, plants compete with us for the oxygen in the air.