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.
Any organism too small to see with the unaided eye is classified as a microorganism. These include bacteria, viruses, protozoa (such as the paramecium and ameba), various type â¦ of plankton, and many other things. microorganism is a small, typically single-celled organism, such  as a bacterium, virus, fungus, or algae, that is small enough to  require a microscope to observe it.