Around 70,000 known species belong to the Fungus kingdom. They include yeast, which are unicellular, and moulds and mushrooms, which are multicellular.
All the cells found in fungi have a cell wall which is external to the plasma membrane and formed out of a substance called chitin.
They are all heterotrophic, but depending on where they get the organic matter from, they can be: saprophytes, parasites and symbiotic.
A saprophyte fungus feeds on the remains of other living things.
A parasite fungus feeds from living organisms, causing diseases.
A symbiotic fungus takes nutrients from other organisms, and in return, provides some kind of benefit. For example, lichens maintain a symbiotic relationship between a multicellular fungus and photosynthetic organisms, for example, green algae. The fungus protects the photosynthetic organism from drying out.