BackThe Chemistry of Life: Elements, Compounds, and Atomic Structure
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The Chemistry of Life
Introduction
The study of biology begins with understanding the chemical basis of life. All living organisms are composed of matter, which is made up of elements and compounds. The unique properties of life arise from the interactions of these chemical components.
Elements and Compounds
Definitions and Properties
Matter: Anything that takes up space and has mass.
Element: A substance that cannot be broken down into other substances by chemical reactions. Each element is defined by its unique number of protons.
Compound: A substance consisting of two or more elements combined in a fixed ratio. Compounds have characteristics different from those of their constituent elements.
Example: Water (H2O) is a compound made from hydrogen and oxygen. Its properties are distinct from those of hydrogen gas and oxygen gas.
The Elements of Life
Major and Trace Elements in the Human Body
Living organisms require a variety of elements, but only a few are present in large amounts. These elements are essential for life and are involved in biological processes.
Element | Symbol | Percentage of Body Mass (including water) |
|---|---|---|
Oxygen | O | 65.0% |
Carbon | C | 18.5% |
Hydrogen | H | 9.5% |
Nitrogen | N | 3.3% |
Calcium | Ca | 1.5% |
Phosphorus | P | 1.0% |
Potassium | K | 0.4% |
Sulfur | S | 0.3% |
Sodium | Na | 0.2% |
Chlorine | Cl | 0.2% |
Magnesium | Mg | 0.1% |
Major elements (O, C, H, N) make up about 96% of the human body.
Minor elements (Ca, P, K, S, Na, Cl, Mg) account for most of the remaining mass.
Trace elements (e.g., Fe, Zn, I) are required in very small amounts but are essential for health.
Example: Iron (Fe) is a trace element necessary for oxygen transport in blood.
