Your answer is microbe, but also known as microorganism.
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.
