Space Adventure

What is a microbe?

A microbe is any living organism that spends its life at a size too tiny to be seen with the naked eye. Microbes include bacteria and archaebacteria, protists, some fungi and even some very tiny animals that are too small to be seen without the aid of a microscope. Viruses and the recently discovered prions are also considered microbes.

The term microbe is short for microorganism, which means small organism. To help people understand the different types of microbes, they are grouped or classified in various ways. Microbes are extremely diverse and represent all the great kingdoms of life, including the animals, plants, fungi, protists and bacteria (see the tree below). In fact, in terms of numbers, most of the diversity of life on Earth is represented by microbes.

Here is an outline of the major groups of organisms:

At the most basic level, all living things can be divided into two major groups of organisms depending on the type of cells they have. Those organisms which contain more complex cells and which have nuclei are called eukaryotes ("true kernal or nucleus"). These organisms include animals, plants, fungi and protists. The other group of organisms are less complex and lack nuclei and are called prokaryotes ("before nucleus"). The prokaryotes are also known as bacteria or as monerans. An amazing recent discovery has shown that the bacteria can be divided into two groups, one of which, the archaebacteria, is more closely related to humans than is the other group of bacteria, the eubacteria, which are discussed below.

All microbes are related to one another and to humans. To see how all forms of life are related, check out the Tree of Life World Wide Web site.