Fungi include such things as mushrooms, athlete's foot, apple-scab, corn smut, wheat rust, wood rots, and so forth. The most famous mold is the genus Penicillium , from which we get the antibiotic penicillin. The name Penicillium comes from the Latin word for brush because under the microscope, the mold has a brush-like appearance. Molds are composed of long strands of cells, resembling spaghetti, which are collectively called mycelium . Molds carry their stomachs on the outside, unlike people who digest food on the inside.
Molds digest food by producing enzymes outside of their cells.
The enzymes break down foods in their environment into small molecules, and then the mold brings back the molecules into its cells for continued digestion and energy. This is the opposite of what people do - we eat foods from outside of our bodies, and the enzymes to break the food down are inside of our stomach. Cheeses which are made with molds, such as Brie, Camebert, or true blue cheese, will grow out their molds when left in a warm, moist environment that has fresh air. Wet paper products, such as cardboard, or materials high in cellulose, such as wet hay or grass also will grow molds well. Molds must have a moist environment to grow, with lots of fresh air.