Heterotrophic nutrition is shown in non-chlorophyllous organisms. Complex nutrients prepared by other organisms are used by heterotrophs.
This form of nutrition differs depending on the type and availability of food material as well as how it is obtained by the organisms.
(1) Food source is stationary such as grass used by a cow.
(2) Food source is mobile such as deer used by a lion.
There is a range of strategies by which the food is taken in and used by the organisms.
(1) Some organisms breakdown the complex food material outside the body and then absorb it. e.g., fungi like bread moulds, yeast and mushrooms.
(2) Some organisms take in complex material and break it down inside their bodies.
The materials can be taken in and broken down depends on the body design and functioning.
(i) Herbivorous animals use only plant materials, e.g., cow, deer. (ii) Carnivorous use other animals, e.g., tiger, lion. (iii) Omnivorous animals use other animals and their products, plants and their products as their food e.g., cockroach, man, etc.
(3) Some other organisms derive nutrition from plants or animals without killing them. This parasitic nutritive strategy is used by a wide variety of organisms. e.g., cuscuta (amar-bel), ticks lice, leech, tapeworms, etc.