Every non-autotrophic organism which depends on others for their food is called heterotrophs. Heterotrophs include every animal and non-photosynthetic plant which are unable to prepare organic molecules on their own. Heterotrophic nutrition can be classified into three types, based on the ways in which organisms obtain their food:
Saprophytes (animals which follow saprophytic nutrition) feed on dead and decayed organisms for energy. They consume dead and decayed remains of animals and plants. In this way, they help clean the environment. Some examples of saprophytes are fungi and certain types of bacteria. These are also responsible for the staling of bread, cakes etc.Saprophytes release certain enzymes to act on the complex organic matter and break it into simpler substances which can be easily consumed by them.
Organisms which feed on other organisms by deriving out nutrients from other animals (hosts) are called parasites. Parasites extract the nutrients from the host and are harmful to their health, sometimes they even kill the host. Both animals and plants may serve as host.
In the case of a parasite, the host is never in benefit. Few examples of parasites are louse on a human head, Cuscuta plant, and tapeworms.
Human follows the holozoic mode of nutrition. Holozoic nutrition means the feeding of solid and liquid food by animals. This involves the steps of ingestion, digestion, absorption, assimilation, and excretion. Ingestion is the intake of food, which is broken down into simpler organic matters by a process called digestion. After extraction of useful components, every other unwanted and indigested particle is excreted out. Other holozoic organisms are animals like cat, deer, dog etc. and also amoeba.
Based on feeding habits heterotrophs are classified as herbivores, carnivores, and omnivores.
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