The study of human breathing
shows that compared to the inspired air (which enters the lungs), the
exhaled air (rejected by the lungs):
- Contains more carbon dioxide.
- Contains less dioxygen.
- Contains as much nitrous.
comparison between inhaled air and exhaled air shows that breathing:
- Produces some carbon dioxide.
- Uses dioxygen.
- Requires no nitrous.
Dioxygen is therefore necessary for life.
proportions of dioxygen and carbon dioxide in the air remain stable
because during the day plants use carbon dioxide and produce dioxygen.
This phenomenon is called photosynthesis and leads to a balance that
maintains stable proportions of dioxygen and carbon dioxide.