Multicellular organisms are the most numerous group among fungi, but there are also single-celled fungi, like yeast.

A distinctive feature of fungi is the cell walls built of chitin. The fungus cell can be mononuclear, two-nuclear, or multinuclear - a multinuclear cell is called multinucleate.

Fungi can breathe aerobically or anaerobically (yeast). Anaerobic respiration is called fermentation. As a result, ethyl alcohol and CO2 are produced.