Question

Determine the mass of oxygen absorbed by the body in one breating cycle

Answer 1

An ordinary breath for a 70-kg adult is about 500ml of air. We call this the tidal volume. Since oxygen is 21% by volume of air, then the volume of oxygen inhaled is about 105ml.

The density of pure oxygen at sea level is 1.43kg per cubic metre. So 105ml of air has a mass of about 150mg, or 0.15g.

The forced vital capacity is the volume you can voluntarily breathe, from the lowest possible volume in your lungs to the highest possible volume in your lungs. The figure is about 3.5 litres for a 70-kg adult male.

However, it's very inefficient to breathe like this, even during exercise. Athletes will increase their tidal volume, but also their respiratory rate, in response to exercise. The minute volume is the product you get when you multiply tidal volume by respiratory rate, and is a much more helpful way to look at breathing than the vital capacity.

Answer 2

a ordinary breath for a 70 kg weight absorbs 500 ml oxygen in that's 21% by volume