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| Types of Heterotrophic Nutrition |
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| Heterotrophic nutrition is broadly classified as holozoic, saprotrophic and parasitic. |
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| Holozoic nutrition |
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| This type of nutrition involves the taking in of solid particles as food (there are exceptions which are called fluid feeders) which have to be further broken down into simpler particles inside the organism. These particles may be big or small. For e.g. Animals like the earthworm and mussels are called microphagous feeders as they take in food which is in very small particles. Hydra and sea anemone are called macrophagous feeders as they take in large pieces of food. Holozoic nutrition involves ingestion of food, its digestion, absorption and assimilation. Hence digestion is intra cellular. |
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| Saprotrophic |
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| 'sapros' refers to rotten and 'trophic' refers to food. Saprotrophic nutrition is the process by which the organisms feed on dead and decaying matter. The food is digested outside the cells or even outside the body of the organism - extracellular digestion. The organism secretes digestive juices, which contain enzymes, directly on to the food. The digestive juices makes the food soluble and it is then absorbed by the organism through the body surface. |
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| Plants that are saprotrophic are called saprophytes and animals that are saprotrophic are called saprozoic animals. |
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| Examples of saprozoic animals are Mastigamoeba and Chilomonas. The digestive juices are secreted by the cell membranes, which means the general body surface, as they are single-celled protozoans. |
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| Examples of saprophytes - numerous bacteria and fungi. |
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| Saprotrophs are different from detritus feeders. Like saprotrophs detritus feeders also feed on dead plants and animals. However, they are different from saprotrophic forms, as digestion takes place inside the body. |
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| Parasitic |
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| In ancient Greece, the person getting free meals for entertaining others by his amusing conversations was called a parasite - 'para' refers to beside and 'sitos' refers to grains. Thus, parasitism is defined as an association between individuals of two different species in which one is benefited and the other is harmed. |
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Parasitic roots of Cuscuta |
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| The benefiting partner is called the parasite and the other partner is called the host. The parasite is dependent on the host for food or shelter or both. |
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| Parasites may be ectoparasites, that which live on the outer surface of the host (E.g: - ticks, mites, leeches) or may be endoparasites, that which live inside the body of the host (E.g: - tapeworm, liver fluke). |
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| Endoparasites are generally disease causing. The disease causing parasites are called pathogens. |
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| Note: |
| There are some other interesting forms of nutrition like the coprophagy which refers to feeding on faeces and carrion feeders which feed on decomposing animal bodies. |
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