by The Old Scott
Take a breath, and let it out. Now, think of yourself doing this minute after minute, hour after hour, year after year. Every breath you inhale contains approximately 21 percent oxygen. Every stale breath you exhale contains only 16 percent oxygen. You use up a lot of precious oxygen—you and the billions of other people on this earth, and all the billions of air-breathing animals. In fact, someone estimated that all of the animal life on Earth consumes about 10,000 tons of oxygen with every tick of the second hand on your watch!
This has been going on for thousands of years, yet still there is sufficient oxygen. How can that be? Why aren't we gasping for every breath, straining after an increasingly short supply of oxygen?
Defer that question for a moment, and think about this poser: Every exhalation adds carbon dioxide to our atmosphere, for carbon dioxide is a by-product of the living process. Why hasn't our atmosphere overloaded with carbon dioxide—and put another huge strain on our breathing?
And still another question: Why hasn't the world run out of food long ago? We know that all animal life ultimately depends on plant life for food–but what do plants eat? We see plants constantly growing, but what is their food?
All these questions are related, and there is one answer to them all: The world's supply of oxygen is renewed, and the surplus of carbon dioxide is removed, and abundant plant growth is provided by one amazingly intricate process, called "photosynthesis."
Photosynthesis is the process by which all green plants convert energy from sunlight into food energy. The raw materials for this process are carbon dioxide, water, and sunlight. Working with these, in the presence of chlorophyll (which gives plants their green color), the plants produce oxygen and food.
Let it sink in: We have not run out of oxygen, because photosynthesis produces oxygen in plants. We have not smothered in too much carbon dioxide, because photosynthesis takes it back out of the air. We have not starved, because plants continuously produce food (for themselves, and in turn for us) from sunlight, water, and carbon dioxide. This wonderful process is an endlessly repeating cycle–and we may well ask: What would we do without it?
If we examined a single cell in a green leaf, we would discover tiny granules called "mitochondria." These tiny bits of matter are actually busy factories, which turn glucose (a basic food) and oxygen into energy for the plant, with a by-product of carbon dioxide. This is very similar to our own production of energy–but this is only the consuming half of the plant's living cycle.
The creative half of each plant's cycle centers on miniature factories called "chloroplasts," where carbon dioxide, water, and energy are converted into food and free oxygen. Fortunately for us, plants produce far more oxygen than they consume.
Scientists and scholars have been probing the secrets of photosynthesis for centuries, but they are only beginning to comprehend all that goes on inside a leaf. They have learned that chlorophyll is a tremendously complicated substance, containing many different enzymes (facilitators) which initiate or speed up the many chemical changes involved in photosynthesis. The more closely the process is examined, the more complex it is revealed to be.
And here, perhaps, is the greatest wonder of all: This hugely complex process, which humans are still laboring to understand, had to be in place and fully functioning from the very beginning of life–or so soon after as to make no real difference. It takes a stiff neck indeed not to see what God hath wrought! Truly, the life-balancing, world-balancing photosynthesis cycle is a mark of the Master!
Photosynthesis, by Isaac Asimov, Basic Books, Inc., 1968.
"Photosynthesis," by R. Govindjee, in Encyclopedia of Science and Technology, Vol. 10, pp. 200-210, McGraw-Hill, 1977.