“Heterotroph is an organism that is unable to synthesize its own food, and therefore, has to rely on other sources, specifically plant and animal matter.”
All animals and non-photosynthetic plants are classified as heterotrophs since they are unable to prepare food. So these organisms resort to other various forms of nutrition. Hence, from an ecological perspective, heterotrophs are always secondary or tertiary consumers in a food chain.
Humans and other vertebrates rely on converting organic, solid or liquid food into energy. Other organisms such as fungi rely on converting dead organic matter into nutrients. In essence, heterotrophs break down complex food into its readily usable constituents.
Types of Heterotrophic Nutrition
In nature, organisms exhibit various types of heterotrophic nutrition. They are as follows:
- Holozoic Nutrition
- Saprophytic Nutrition
- Parasitic Nutrition
Holozoic Nutrition
Holozoic nutrition involves the ingestion and internal processing of solid and liquid food in an organism. 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, the unwanted and undigested particles are excreted out.
Examples of animals that exhibit holozoic nutrition include all vertebrates. Even some unicellular organisms such as amoeba also exhibit holozoic nutrition
Holozoic Nutrition in Amoeba
Amoeba exhibits holozoic nutrition. The process takes place in the following steps:
- The amoeba projects its pseudopodia and encircles the food. It then engulfs the food by the process of phagocytosis.
- The food vacuoles of amoeba are rich in digestive enzymes, which help break the food into simpler substances. This process is known as digestion.
- The digested food is absorbed into the cytoplasm leaving behind the undigested materials. This absorbed food is utilised to produce energy for the growth and development of the cell.
- The undigested food material is ejected out by the rupturing of the cell membrane.
Further Reading: Nutrition in amoeba
An amoeba exhibiting heterotrophic nutrition
Types of Holozoic Organisms
Holozoic organisms can be divided into three types:
- Herbivores- These organisms depend upon plants for their food. Cows, buffaloes, deer, elephants are herbivores.
- Carnivores- These animals feed on other animals for their food. Lions, tigers and leopards are carnivores.
- Omnivores- These animals can survive on either plants or animals for their food. Cockroach, pig, chimpanzees, raccoons and ant are some examples of omnivores.
Saprophytic Nutrition
Saprophytes (animals which follow saprophytic nutrition) feed on dead and decayed organisms for energy. They are an important part of the ecosystem as they help to keep our environment clean and recycle nutrient back into the ecosystem.
Some examples of saprophytes are fungi and certain types of bacteria. These are also responsible for the staling of bread and other similar food products.
Saprophytes release certain enzymes to act on the complex organic matter. It works by breaking it down into its constituents, which can be easily consumed by them.
Explore more: Saprophytes
Parasitic Nutrition
Organisms that live in or on other organisms and acquire food at the expense of its host are called parasites. Most parasites are harmful to the hosts’ health; sometimes, they even kill the host. Both animals and plants may serve as a host. Unlike commensalism, the parasite causes some harm to its host. A few examples of parasites are louse on a human head, Cuscuta plant and tapeworms.
Cymothoa exigua is an unusual parasite. It is also known as the tongue-eating louse and is aptly named so as it is found in the mouth of the marine fish Lithognathus. It essentially severs the fish’s tongue, cutting off the blood supply and causing the tongue to fall off. The louse then attaches itself to the remains of the tongue and essentially acts as the fish’s new tongue.
To know more about what is holozoic nutrition, saprophytic nutrition, parasitic nutrition and other concepts related to heterotrophic nutrition, register at BYJU’S website, or download the BYJU’S app for further reference.
Frequently Asked Questions
1. What do you understand by heterotrophic mode of nutrition?
Heterotrophic nutrition is the mode of nutrition where the organism is unable to prepare its food and hence, depends upon plants or other organisms for nutrition.
2. What are the different types of heterotrophic nutrition?
Heterotrophic nutrition can be one of three types – holozoic, saprophytic or parasitic. Holozoic nutrition can be seen in most vertebrates and some unicellular organisms like the amoeba. Saprophytic nutrition is where the organisms feed on dead and decaying matter. Examples include bacteria and fungi. Parasitic nutrition is where an organism lives in or on its host and acquires nutrition at the expense of its host. Examples include lice and tapeworms.
3. What are the different types of heterotrophs?
There are four different types of heterotrophs which include herbivores, carnivores, omnivores and decomposers. Herbivores, carnivores and omnivores exhibit the holozoic type of heterotrophic nutrition.
4. What is holozoic nutrition?
Holozoic nutrition involves the consumption of solid and liquid food materials by the organisms. Steps include ingestion, digestion, absorption, assimilation and excretion. It is exhibited by certain unicellular organisms such as amoeba. Most vertebrates exhibit holozoic nutrition such as humans, cows and dogs.
5. What do you mean by chemosynthetic heterotrophs?
Chemosynthetic heterotrophs obtain energy by chemical reactions, i.e., oxidation of organic compounds. For eg., the organisms that obtain energy by the oxidation of glucose during the process of respiration are chemosynthetic heterotrophs.
6. How is heterotrophic nutrition different from autotrophic nutrition?
In autotrophic nutrition, the organisms prepare their own food. This type of nutrition is seen in plants where they prepare their food by the process of photosynthesis. On the contrary, heterotrophic nutrition is observed in organisms that depend upon other organisms for food. This can be seen in cows, dogs, tigers, elephants and humans.
7. What is nutrition?
Nutrition is the process of obtaining food required to obtain energy to carry out life processes. There are two major modes of nutrition- autotrophic nutrition and heterotrophic nutrition.
8. Give a few examples of heterotrophs.
Bacteria, fungi, yeast, cows, dogs, humans are all heterotrophs. They all depend on plants and other animals for their food.
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List out some organisams for each mode of nutrition mentioned in the heterotrophs
Holozoic – Amoeba, most free-living animals, humans
Saprotrophic – Fungi
Parasitic – Pathogenic bacteria, various disease-causing protozoan such as Plasmodium, worms, etc.
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