It is obtained by digesting organic compounds. Animals, fungi, and protoctists are unable to synthesize organic compounds to use as food. They are known as heterotrophs.
All heterotrophs (except blood and gut parasites) have to convert solid food into soluble compounds capable of being absorbed (digestion). When the soluble products of digestion aof the organism where complex materials (assimilation) are broken down for the release of energy (respiration). All heterotrophs depend on autotrophs for their nutrition. Heterotrophic plants have only 4 types
The three main types of heterotrophic nutrition are:
- Holozoic nutrition: the word holozoic is made from two words- holo= whole and zoikos= animals and literally means animals which eat their food whole. Complex food is taken into a specialist digestive system and broken down into small pieces to be absorbed. This consists of 5 stages, ingestion, digestion, absorption, assimilation and egestion. E.g.: human
- Saprobiontic/saprotrophic nutrition: Organisms feed on dead organic remains of other organisms.E.g.: decomposers
- Parasitic nutrition: Organisms obtain food from other living organisms (the host), with the host receiving no benefit from the parasite.When a parasite is present inside the body of the host, it is known as an endoparasite. Generally endoparasites attack and live in an intestine of an organism whereas parasites such as mites and leeches attach themselves to the outside of the hosts body. They are known as ectoparasites.They suck and feed on the blood of the host. E.g.: tapeworms
- Symbiotic nutrition: Certain plants live in close association with other plants for long periods and share and shelter. E.g.: fungi and algae,rizobium and leguminous plants plants