You cannot see a microorganism without using a microscope. You also cannot taste or smell microorganisms such as bacteria in contaminated food. However, you can smell the odor of bacteria metabolizing sweat. Toenail fungal infections also produce an odor.
While all the bacteria and archaea are microorganisms, only some fungi and algae are. Some animals, such as rotifers and almost all protozoa, are microscopic. The tiny organisms live in soil, the atmosphere, on the ocean floor and deep inside rocks. Microorganisms aid decomposition in the recycling of nutrients in ecosystems. Airborne microorganisms may influence precipitation and weather. Others are active in the nitrogen cycle.