Heterotrophic nutrition is the obtaining of food by eating or absorbing nutrients from the external environment, and using these for internal processes. This is the opposite of autotrophic nutrition, in which an organism generates its own food from an energy source, such as the sun with photosynthetic plants. Organisms which are heterotrophic are refered to as heterotrophs.

Heterotrophic nutrition is divided up into four main types:

Holozoic: The form of nutrition common in larger animals such as ourselves, involving internal digestion of food in a specialised digestive tract.

Saprobiontic: Digestion of dead organic material outside of the body for later reabsorbtion. Rhizopus is the favoured example, commonly known as Pin Mould. Rhizopus grows a large mesh of hyphae over the surface of the food substrate (often bread or pasta), and releases enzymes into the substrate which break down the food for reabsorbtion.

Mutualistic: Nutrition involving two or more organisms from separate species, where both or all organisms benefit nutritionally. The methanogenic bacteria in the stomachs of Ruminant herbivores such as cows are a good example of this - the bacteria gain a supply of food and urea from the herbivore, while the Ruminant gains fatty acids from the bacteria which is uses as a respiratory substrate, as well as a supply of protein.

Parasitic: One organism living on or inside another organism and absorbing nutrients from it, keeping it alive but not offering any benefit to its host. Tape worm (taenia) attaches itself to the inside wall of the small intestine of human beings, and absorbs broken down nutrients which the host has digested over its large surface area.

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