| Element |
% of Humans by Weight |
Functions in Life |
| Potassium |
0.3 |
Important for nerve function, muscle contraction, and water-ion balance in body fluids |
| Sulfur |
0.2 |
Structural component of some proteins |
| Sodium |
0.1 |
Primary ion in body fluids; essential for nerve function |
| Chlorine |
0.1 |
Major ion in body fluids |
| Magnesium |
Trace |
Cofactor for enzymes; important to muscle contraction and nerve transmission |
| Iron |
Trace |
Basic component of hemoglobin |
Most living organisms are aerobic; that is, they require oxygen to complete the total breakdown of glucose for the production of adenosine triphosphate (ATP), the energy for life. Many people think that humans need oxygen to breathe, but actually people need oxygen to recycle the spent electrons and hydrogen ions (H ) produced as byproducts of aerobic respiration.
