Mike Renfroe, age 15, of Winston Salem, North Carolina, for his question:
How much oxygen does a person consume in a year?
Oxygen, of course, is the vital fuel for the chemical processes of the living cells and the body varies its intake of this vital gas with its daily activities. Physical exercise requires an extra supply and a minimum is required during restful sleep. However, with a bit of figuring, we can estimate the average yearly requirement for an average man. Let's measure the oxygen gas in quart milk bottles. The oxygen used by the average citizen equals the amount of milk used daily by a healthy community of about 250,000 persons.
On a small laboratory scale we can figure how much oxygen the body uses to produce a precise amount of fuel energy in terms of Calories. However, when it comes to actual breathing, the lungs are very wasteful. We use only about one fourth of the oxygen we breathe in and, of course, oxygen accounts for only about 21 per cent of every breath of fresh air. In one year, a fairly active man needs to consume almost a quarter of a million quarts of oxygen. But to get it, he must breathe a moderate ¬sized ocean of fresh air.
Let's start to figure from a small scale laboratory unit. A quart equals 1.1 liters. The body uses one liter of oxygen gas to consume 1.25 grams of basic glucose. Each gram of glucose yields four Calories. To consume five Calories of food, then, we need about one quart of oxygen which is slightly more than the lab liter. An average man requires a daily diet of about 3,000 Calories to live an active life. To consume this much food, he must make use of about 600 quarts of oxygen. Based on our small scale lab unit, his yearly supply of oxygen can be estimated as 232,000 quarts.
From a more practical point of view, we must figure two other factors. When our man inhales, his lungs absorb only about a quarter of the oxygen available in the air. The rest is returned outside when he exhales. To get his yearly supply, his rather wasteful lungs need to take in about 928,000 quarts of oxygen. But oxygen makes up only 20.96 per cent of the air he breathes. This means that during a year, he inhales and exhales about five million quarts of air just to get the 232,000 quarts of oxygen that his body actually uses.
The lungs may be rather .wasteful, but the body has precise mechanisms to adjust its breathing in step with its activities. When resting, an average person uses up about 1 1/2 quarts of oxygen per minute. When walking, this is stepped up to about 4 1/2 quarts and when running, the oxygen requirement is about 10 quarts per minute. Our yearly figure is based on average periods of rest and assorted activities and estimated on a daily diet of 3,000 Calories.