HOW MANY POUNDS OF OXYGEN DO WE "EAT" EACH DAY?
Engelberg, Joseph.
Illuminations Column, Department of Physiology, University of Kentucky
College of Medicine, Lexington, KY 40536-0084
APStracts 2:0015S, 1995.
ABSTRACT
In teaching the energetics of food we often find that students can manipulate
equations to convert grams to calories and so on, but fail to grasp the "big
picture" concepts of energy exchange. It might help if students were able to
conceptualize that oxygen is "food" ever bit as much as any meat or vegetable.
An approach that should facilitate this is to calculate (or have students
calculate) the number of pounds (by dry weight) of oxygen we consume each day
in relation to the weight of the food we eat. The answer is a surprising
attention grabber. Each day we consume about the same number of pounds of
oxygen as we consume of food. Let's check this by calculation. 1. A moderately
active person expends about 3000 kilocalories a day. To produce this energy on
an average diet they consume 1.4 pounds (dry weight) of food along with 500
liters of oxygen. 2. To convert the 500 liters of oxygen to grams, recall that
at normal temperature and pressure (NTP) one gram molecular weight of an ideal
gas occupies 22.4 liters. Thus, 500 liters of oxygen gas contains 500/22.4 =
22 moles of molecular oxygen (O 2 ). 3. The molar weight of O 2 is 32 grams
per mole (2X16, the molar weight of elemental oxygen). Therefore, it follows
that the moderately active person consumes: 22 moles O 2 X 32 gO 2 /mole = 700
g O 2 , or O.7 kg O 2 per day. 4. 0.7 kg O 2 X 2.14 pounds/kg = 1.5 pounds of
oxygen per day , a figure very close to the 1.4 pounds of food we eat per day.
Received 19 August 1996; accepted in final form 19 August 1996.
APS Manuscript Number S027-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996