A fungus can't move around or make its own food. Fungi absorb food from decaying organisms and wastes in the environment. A fungus can be one celled or many celled. Some fungi contain chemicals that fight diseases. Others keep our environment clean. A fungus turns cheeses sharp and tangy. Yeast, another fungus, puts bubbles in bread. Certain fungi produce problems. Athlete's foot, an itchy disease, is another fungus. Others that grow in damp places like basements cause flu-like symptoms.