An organism is heterotroph when the organic matter you need is obtained from external sources. Subsequently, this organic matter is used in the different metabolic routes and transformed into the different components of the organism, but the primary source of organic matter is substances synthesized by other organisms. This is how animals feed, for example.

organisms autotrophson the contrary, they can synthesize their own organic matter from inorganic substances. For example, plants are autotrophic organisms that synthesize organic matter from COtwo, water and energy from solar radiation. These organisms are said to ‘fix’ inorganic carbon and transform it into organic carbon which can then be used by heterotrophic organisms.

How do fungi eat?

Fungi are eukaryotic organisms that form their own biological kingdom, the fungi kingdomand that they feed heterotrophically but with a big difference with animals: they do not ingest organic matter but digest it in the external environment and absorb it directly from there.

Fungi can grow on the ground or on organic matter, for example on a log. There are also unicellular free-living aquatic fungi and there are also fungi that can grow on living organic matter, either symbiotically or causing infections, for example, the dermatomycosis.

In any case, the fungus secretes lytic enzymes to the outside that digest organic matter in the environment, such as polysaccharides, lipids and proteins, and transform it into simpler substances that can be absorbed by the cells of the fungus. Absorption is by osmotic absorption, hence this type of feeding is known as osmotrophy.

Yeast fungi, yeasts, are unicellular fungi that secrete enzymes and absorb nutrients through their cell membrane, but multicellular fungi grow mostly with a structure of hyphae.

Hyphae are filaments made up of elongated, tubular cells surrounded by a wall of chitin. The group of hyphae of a fungus form a threadlike network known as mycelium. Being a filamentous network, the mycelium has a high ratio of surface area to volume and provides a large absorption surface.

As autotrophic organisms, fungi are completely dependent on organic matter synthesized by other organisms. This organic matter can be obtained from dead organic matter or from living organic matter, either in a parasitic way or in a mutualistic way. Thus, fungi can be:

  1. saprophytes: they feed on dead organic matter found in the environment and play a prominent role as primary decomposers and therefore in the biogeochemical cycles.
  2. parasites: they are fungi that feed on living organic matter provided by a host to which they cause damage, that is, they cause infections in the host, sometimes even causing death.
  3. Mutualists: they obtain organic matter from a living host but do not harm it, rather the host receives benefits from the relationship with the fungus. One of the best known mutualistic relationships in fungi is the mycorrhizae, formed by the association of a fungus and the roots of a plant; the fungus obtains organic matter from the plant and in return increases the absorption of water and minerals from the soil. Another outstanding example of mutualism are the lichensorganisms formed by the association between a fungus and an algae, sometimes also with the participation of cyanobacteria.