Name the two elements that are the most abundant in the human body. What are their percentage weights?

Oxygen at 65% is the most abundant and carbon is next at 18.5%.

96.2% of the body weight of a human comes from ‘organic elements’ present in many different forms. DNA, RNA proteins, lipids and sugars are all composed primarily of O, C, H and N. These elements are also present in water (H 2 O) and carbon dioxide (CO 2) as well as in other small molecules. Their percentage weights are as follows:

Oxygen –– 65.0%

Carbon –– 18.5%

Hydrogen –– 9.5%

Nitrogen –– 3.2%

Apart from this, 3.9% of the body weight comes from elements present in the form of salts. They are very important for the maintenance of homeostasis (meaning ‘well balanced organism’). Calcium is a major component of bones and teeth. Iron is necessary for oxygen transport by red blood cells. Sulphur is present in most proteins and potassium keeps the heart beating smoothly and regularly. The percentage weights of these elements are given below:

Calcium –– 1.5%

Phosphorus –– 1.0%

Potassium –– 0.4%

Sulphur –– 0.3%

Sodium –– 0.2%

Chlorine –– 0.2%

Magnesium –– 0.1%

Iodine –– 0.1%

Iron –– 0.1%

The trace elements compose less than 0.5% of the total body weight but then again, they are essential for homeostasis. Some of these elements are cofactors of critical enzymes in the body (meaning that without them, the enzyme cannot work at all and that even low concentrations of the relevant element can make the enzyme work very well.)