The largest group of fungi are multicellular organisms, but there are also single-cell fungi, such as yeast.

A characteristic feature of fungi is their cell wall made of chitin. A fungal cell may be mononucleate, binucleate, or multinucleate - a multinucleated cell is called a cellulose.

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