For information on a specific unit, click on the first letter of its name: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z. Answers to the three most frequently asked questions:
Microorganisms were the first living creatures on earth. It is estimated there are a total of 5 nonillion microorganisms on earth (5x1020). You will find nearly 10 million a millilitre of ocean water and 40 million in a gram of soil. They are also ubiquitous on the human body.
A cluster of Escherichia coli bacteria magnified 10,000 times. A microorganism or microbe is a microscopic organism, which may be single-celled or multicellular. The study of microorganisms is called microbiology, a subject that began with the discovery of microorganisms in the 1670s by Antonie van Leeuwenhoek. Robert Hooke coined the term cell after viewing plant cells under his microscope.