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Human energy consumption can be measured indirectly by measuring oxygen use, since the digestive process is basically one of oxidizing food. About how much energy is produced for each liter of oxygen consumed, independent of the type of food?
AAbout 2 kJ per liter
BAbout 20 kJ per liter
CAbout 200 kJ per liter
DAbout 2000 kJ per liter
Answer & Solution
Correct answer: B. About 20 kJ per liter
1. Because digestion is essentially the oxidation of food, the rate of oxygen consumption tracks the rate of energy release closely.
2. Approximately 20 kJ of energy are produced for each liter of oxygen consumed, regardless of whether the food is fat, protein, or carbohydrate.
3. This fixed conversion factor is what allows tables of oxygen consumption during activities to be converted directly into power output in watts.
4. 2 kJ and 200 kJ per liter are each off from the stated factor by a full order of magnitude, and 2000 kJ per liter is off by two orders of magnitude.
_Source: OpenStax College Physics (CC BY 4.0), Ch 7 "Work, Energy, and Energy Resources", section 7.8 Work, Energy, and Power in Humans_
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