A<unk>  (also spelled as<unk>  or microbe is an organism that is microscopic (too small to be seen by the human eye). The study of<unk> s is called microbiology.<unk> s include bacteria, fungi, archaea or protists, but not viruses and prions, which are generally classified as non-living. Most<unk> s are single-celled, or unicellular, but some are microscopic, and some unicellular protists are visible to the average human.<unk> s live almost everywhere on Earth where there is liquid water, including hot springs, on the ocean floor, and deep inside rocks within Earth's crust.<unk> s are critical to nutrient recycling in ecosystems as they act as decomposers. As some<unk> s can also fix nitrogen, they are an important part of the nitrogen cycle. However, pathogenic microbes can invade other organisms and cause diseases that kill millions of people every year.
Microorganism
Biomolecule
Chemical substance
Biological pigment
Organic compound
Parasitic worm
Metal
Vector 