Heterotrophic nutrition is nutrition obtained by digesting organic compounds prepared by other plants or animal tissues. All animals and non-green plants cannot make their own food; hence they depend on others directly or indirectly for their food supply. They are called heterotrophs. They break down the complex compounds into simpler forms. Simply put, heterotrophs have to depend on other sources for their survival. They lack chlorophyll and thus cannot perform photosynthesis. Essentially heterotrophic mode of nutrition is further subdivided into three groups called as: Holozoic, Saprophytic and Parasitic nutrition. A brief description of these divisions is mentioned below.
Types Of Heterotrophic Nutrition
1. Holozoic Nutrition:
The name of this nutrition originated from Greece where ‘holos’ means complete and ‘zoon’ stands for animal. This type of nutrition involves consumption of food portion through mouth (opening) .This process is called ingestion. Once consumed, the food particles are broken down into simpler forms and the process is termed as digestion. Finally, the vital nutrients are absorbed by the body and the unwanted and undigested portions are eliminated. The process of expelling the waste material from the digestive tract via anus is defined as egestion. Holozoic nutrition involves all the processes including ingestion, digestion and egestion.
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2. Saprophytic Nutrition:
Again ‘Saprophytic’ is a Greek term in which ‘sapro’ means rotten while ‘phyto’ is plants. This kind of nutrition involves processing or decomposing the rotten foliage and dead or decaying organic matter of organisms. Saprophytes have a tendency to gorge on dead products like wood, rotten plants, stored food to name a few. Some organisms that follow saprophytic nutrition are a host of fungi like mushrooms, yeasts and moulds. In this mode of nutrition, secretion of certain enzymes are released which break down the complex food into simpler forms. The processed leftover is then reabsorbed by the saprophytes. This process of extracellular digestion is an integral part of saprophytic nutrition. It can be best observed on Neurospora, a common bread mould or even pin mould.
3. Parasitic Nutrition:
Parasitic is derived from the root word Parasite. ‘Para’ is a Greek term for feeding and ‘site’ denotes grains. Parasitic nutrition is a mode of heterotrophic nutrition where an organism (known as a parasite) lives on the body surface or inside the body of another type of organism (known as a host).
For instance, a hook-worm lives in the intestine of humans and feeds on it without going through the process of ingestion or egestion. This nutrition is viable for those organisms that do not possess properly developed organs and depend on their host’s body for deriving the nourishment. Some most common examples of organisms following this nutrition are cuscuta, tapeworms, leeches, plasmodium, and so on. Ideally, parasitic nutrition involves dwelling of the parasites within the host’s body and feeding on their blood and intestines as their nutrition. However, sometimes the organisms position itself on the surface of the host’s body, probably the skin and derive the nutrition, such types are called ectoparasites. Mosquitoes and leeches are the perfect examples of parasitic nutrition in which they suck out blood as nutrition from the host’s body surface.
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On the basis of heterotrophic nutrition, animals and plants have been classified under the above mentioned groups; however these organisms can be further classified as herbivores, carnivores, omnivores and scavengers. Heterotrophic nutrition essentially differs from autotrophic nutrition. Organisms following heterotrophic nutrition are ideally known as consumers of the ecosystem. Unlike autotrophs, heterotrophs are dependent on others for their survival and require ready-made complex food for nutrition, sourced to them by similar organisms in the form of other animals and plants.
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