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bacteria :
Microscopic, one-celled organisms that live almost everywhere on Earth including in and on the human body. There are thousands of different kinds of bacteria. Under a microscope, some are round, others are rod-like, and still others look like spirals. Some kinds of bacteria cause diseases and infections. Other kinds break down and help in the decay of dead animal and plant materials and thus enrich the soil. Within our bodies, bacteria help in the digestion of food. They also are used to produce dairy products such as cheese and yogurt. [Bacteria comes from a Greek word meaning “little rods.”]
