Home > Encyclopedia of Science > Bacteria

• Characteristics of bacteria
• Words to Know
• Bacterial growth
• Harmless, beneficial, and harmful bacteria
• Hardy survivors

Bacteria are very small organisms, usually consisting of one cell, that lack chlorophyll (a green pigment found in plants that allows for the production of food). Except for viruses, they are the smallest living things on Earth. Many bacteria are so small that a million of them, laid end-to-end, would measure no more than about five centimeters (two inches). The term bacteria is the plural form of the word bacterium, which represents a single organism.

Bacteria are found everywhere, in the air, soil, water, and inside your body and on your skin. They tend to multiply very rapidly under...