CIE IGCSE Biology: 复习笔记：11.1.4 Differences in Inspired & Expired Air

• Air that is breathed in and air that is breathed out has different amounts of gases in it due to exchanges that take place in the alveoli
• Atmospheric air contains around 20 – 21% oxygen, of which we only absorb around 4 – 5%, breathing out air containing around 16% oxygen
• Normal carbon dioxide content of air is around 0.04% and, as carbon dioxide diffuses into the alveoli from the blood, we breathe out air containing around 4% carbon dioxide
• The air we breathe out contains more water vapour than when we breathe it in, and the temperature of exhaled air is higher than inhaled air

Composition of Air Table

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