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What is heterotrophic nutrition?

The term ‘heterotrophic nutrition refers to the mode of nutrition where organisms depend on other organisms for nutrients in order to stay alive. All animals as well as non-green plants are heterotrophic. Heterotrophic organisms have to get, and absorb, the organic substances that they need to survive.

Almost all heterotrophs need to convert solid food into soluble compounds that are capable of being absorbed (The technical term for this is digestion). After this, these soluble products are being broken down so that energy is released. This is called respiration. All heterotrophs rely on autotrophs for their nutrition.

There are four types of heterotrophic nutrition:

  • ‘Holozoic Nutrition’ refers to animals which eat their food whole. Complex food consumed and is taken into a specialist digestive system. There it is broken down into tiny pieces to be absorbed. This process of five stages: ingestion, digestion, absorption, assimilation and egestion.
  • ‘Saprobiotic/Saprophytic Nutrition’ refers organisms which feed on dead organic remains of other organisms.
  • ‘Parasitic Nutrition’ refers to organisms that obtain food from other living organisms (the host). This host does not receive any benefit from the parasite. When a parasite is in the body of the host, it is referred to as an endoparasite. These parasites consume the blood of the host. An example of a parasite is a tapeworm.
  • ‘Symbiotic Nutrition’ refers to when two organisms live in close association in order to benefit each other. Alternatively, one of the two benefits the other while suffers neither loss but nor gain. Examples of organisms which function in a symbiotic relations are fungi and algae and rhizobium in the roots of leguminous plants.

What are examples of heterotrophs?

There are two types of heterotrophic organisms:

  • Photoheterotrophic Organisms

This type of organisms makes use of light for energy and nutrition purposes. However, they don’t use carbon dioxide for their carbon source. Thus, they must rely on compounds such as carbohydrates, fatty acids, and alcohol in the form of non-sulphuric bacteria.

  • Chemoheterotrophic Organisms

Chemoheterotrophic organisms get their energy by oxidising pre-formed organic compounds. For their nutrition, they consume other living or dead organisms such as animals, fungi, bacteria as well as nearly all pathogens. In a nutshell, photoheterotroph get their energy through light and chemoheterotroph makes use of chemical energy.

Here is a list of examples of heterotrophic organisms:

  • Herbivores, omnivores and carnivores
  • Fungi and protozoa
  • Non-sulphur bacteria:
  • Heliobacteria:
  • Manganese-oxidising bacteria

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What are autotrophs?

An autotroph, or a primary producer, is an organism which is responsible for producing complex organic compounds such as carbohydrates, fats as well as proteins which humans can get their daily nutritional requirements from. These organisms produce these compounds from simple substances that are present in its surroundings and generally make use of energy from light (photosynthesis) or inorganic chemical reactions (chemosynthesis) to make this happen.

Autotrophs constitute producers in a food chain. Examples of these organisms are plants on land or, alternatively, algae in water. Autotrophic organisms do not require a living source of energy or organic carbon. They can reduce carbon dioxide in order to make organic compounds for biosynthesis and create a bank of chemical energy.

Most autotrophs utilise water as the reducing agent, however some can make use of other hydrogen compounds such as hydrogen sulphide. A few autotrophs, such as green plants and algae, are phototrophs. This means that they convert electromagnetic energy from sunlight into chemical energy in the format of reduced carbon.

What are examples of autotrophic organisms?

Scientists classify autotrophic organisms according to how they get their energy. Types of autotrophs include photoautotrophs as well as chemoautotrophs:

  • Photoautotrophs

Photoautotrophs are organisms which get the energy to make organic materials from sunlight. Photoautotrophs consist of all plants, green algae, and bacteria which perform photosynthesis. Photoautotrophic organisms make fuel and organic compounds heterotrophs, such as human beings, to get their nutritional needs.

  • Chemoautotrophs

Chemoautotrophs are organisms which get energy from inorganic chemical processes. Today, chemoautotrophs are generally found in deep-water environments which receive no sunlight. Many of these organisms need to live around deep sea volcanic vents, which produce sufficient heat to allow metabolism in chemoautotrophs to occur at a high rate.

Chemoautotrophs use chemicals which are volatile – such as molecular hydrogen, hydrogen sulphide, elemental sulphur, ferrous iron and ammonia – as their energy sources. This makes them well-suited to living in places that would otherwise be toxic to many other organisms. Chemoautotrophs are also well suited to living  in places without sunlight. Chemoautotrophs are usually bacteria or archaebacteria, as their metabolisms are usually not efficient enough to support multicellularity.

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