A fungus is any member of the group of eukaryotic organisms that includes yeasts, molds and mushrooms, classified in the biological kingdom Fungi. The cited article says a characteristic placing fungi in a different kingdom from plants, bacteria and some protists is having chitin in their cell walls, that fungi, like animals, are heterotrophs that acquire their nutrition by absorbing dissolved organic molecules, typically by secreting digestive enzymes into their environment, and that a fungus does not perform photosynthesis. Pests and diseases recorded in the atlas as caused by fungi are grouped under this concept.