Harvey Dalzell, age 12, of Selkirk, Manitoba, for his question:

What is the carbon dioxide cycle?

A good housekeeper runs things by an orderly system of routines and the best of all housekeepers is nature. The laws of nature work in orderly routines to keep our planetary home running smoothly. Many of nature's routines work in schedules that repeat in neverending cycles.

In nature, a cycle is a series of events with no end or beginning. Each event leads to the next and no one can say with which event the series ends and the next series begins. Such a cycle is economical because the same substance can be used and reused in a never ending schedule of duties. One of life's vital substances is carbon dioxide and the carbon dioxide cycle is. nature's method of keeping it circulating through its endless chores.

Day and night, we take in vital oxygen and return waste carbon dioxide to the air. So do all the animals and the plants. Tons of carbon dioxide are added to the atmosphere every hour and if this were the end of the story, life on our planet soon would suffocate. But it is merely one event in a series of events that dovetail together in an endless repeating cycle.

There is only one atom of difference between the two gases involved in the cycle. Oxygen gas occurs in molecules, each composed of two atoms of oxygen. A molecule of carbon dioxide is a package of one oxygen molecule plus an atom of carbon. When the carbon atom is removed, waste carbon dioxide is converted into life giving oxygen. This chemical conversion is done automatically by the green plant world on a grand. scale.

Plants manufacture their basic food from water and carbon dioxide. With the help of sunlight, the green chlorophyll in the foliage converts these raw materials into sugar. The elaborate chemical conversion is called photosynthesis. In the process, molecules of raw materials are broken down and remade into sugar molecules  and oxygen is a by product. Every daylight hour, the green plant world uses tons of carbon dioxide and pours out tons of fresh oxygen. It blends with the air and breezes blow it around the globe. We take our quota of the life giving gas and return carbon dioxide to the air  so do the plants and animals. And the two vital gases continue on in their cycle of changes.

In the normal process of respiration, the plant world gives off carbon dioxide  but not enough to supply the needs of photosynthesis. The thriving greenery also needs the carbon dioxide from animal respiration. In return for this gift from the animal world, the plant world pours out constant supplies of fresh oxygen for all the living things upon our teeming earth.

We can call this global interchanging of gases the carbon dioxide cycle or the oxygen cycle or perhaps the oxygen carbon dioxide cycle. The quiet give and take goes on between plants and animals of the sea, just as it does on the land. Without surplus carbon dioxide from animals, plant survival would be feeble. But without a thriving plant world, the animals would not survive at all and neither would we. We depend upon plants for our vital oxygen and directly or indirectly .for all of our life giving food.