“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.

Also Read:

• Autotrophic Nutrition
• Nutrition In Living Organisms & Modes Of Nutrition