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.