As heterotrophs, fungi absorb food through specialized organs rather than ingesting it through a mouth. Three categories exist that specify the exact absorption methods used to feed. Saprophytes digest dead organic material, parasites absorb nutrients from a living host in a way that is harmful to the host and mutualistic symbionts absorb nutrients from a living host but also provide some sort of benefit to the host.
Different fungi take different forms and are found in different contexts, but they are all united by the fact that they absorb nutrients. Fungi differ from plants in that they do not have chlorophyll or other means of manufacturing nutrients for themselves. Because they must have some sort of host from which to feed, fungi are dependent on other organic beings for survival. The fungi that digest dead organic matter serve an important function by assisting with the decomposition of things like fallen trees and leaves, and this keeps the life cycles of forested areas running smoothly.