Autotrophic and Heterotrophic organisms

All organisms are not the same in many ways. Primitive organisms like algae and plants encompass organelles that can synthesize their food while humans and animals cannot. Though humans are the supreme power in the universe, we cannot prepare food on our own.  When a plant and an animal expose themselves to sunshine, the plant can prepare food while the animal cannot. The word sunshine is more precisely used because the sun is the primary source from which we all derive food. Based on whether the organisms contribute to photosynthesis( preparing food)or not, all organisms are classified into autotrophs and heterotrophs. Majority of the plants are self-reliant (except some carnivorous plants) as they do not depend on other organisms for their energy.   Conversely, heterotrophs obtain their nutritional requirements from complex organic substances prepared by others.

Autotrophs

The word autotroph was coined by a German botanist, Albert Bernhard Frank in 1892. The English term auto refers to self while the Greek term τροφή (trophy) means "nourishment" or "food", implying that autotrophs can nourish by self. The first autotrophic organism appeared 2 billion years ago. An autotroph is distinguished by its ability to directly interact with solar energy to produce food in the form of complex organic compounds: carbohydrates, fats, and proteins. They make use of raw materials like water, minerals, and carbon to synthesize these compounds. Autotrophs such as plants along with Algae, Seaweeds and some Phytoplankton fit to the bottom of the food chain.

Types of autotrophs

Autotrophs are classified into photoautotrophs and chemoautotrophs. Organisms like green plants and algae convert the electromagnetic energy from sunlight into chemical energy are called photoautotrophs. On the other hand, chemoautotrophs such as Cyanobacteria make use of some organic or inorganic chemical compounds to synthesize their food. Most chemoautotrophs are lithotrophs. Lithotrophs make use of inorganic electron donors as reducing agents for their photosynthesis. Some of them include ammonium, elemental sulfur, hydrogen sulfide, hydrogen gas, and ferrous oxide.

Heterotrophs

The word heterotroph was obtained from the Ancient Greek origin,( ἕτερος) héteros meaning  "other" while trophe refers to "nutrition". It was used for the first time in the year 1946 while conducting an experiment in a microbiology lab. Based on what a heterotroph eats, it can be categorized as primary consumer, secondary consumer or a tertiary consumer in a food chain. Some common heterotrophic organisms include all animals,  fungi, parasites, most of the bacteria and protists. All heterotrophs are placed above the autotrophs and are further classified into chemotrophs and photoheterotrophs. Chemotrophs obtain energy by the oxidation of electron donors from their environment and are commonly found in the ocean floors where there is minimal to no sunlight. Due to the scarcity of sunlight in the deep oceans, they are accustomed to the chemotrophic nutrition. On the other hand, photoheterotrophs obtain light energy to convert to chemical energy in the cells while they get their required carbon from other organisms (organic sources). Some examples include green non-sulfur bacteria, purple non-sulfur bacteria, and heliobacteria.

 

Differences between the autotrophs and heterotrophs

Criteria

Heterotrophs

Autotrophs

Meaning

Heterotrophs cannot prepare food on their own but they obtain it from autotrophs.

Autotrophs can synthesize food on their own

Example

All animals and fungi, some bacteria and protists, and many parasitic plants.

Almost all green plants, algae, some bacteria etc.

Mostly belong to Most Heterotrophs belong to the animal kingdom Most Autotrophs belong to the plant kingdom
Anatomical difference They lack chlorophyll They contain  chlorophyll

Types

2  main categories:  Photoheterotrophs and Chemoheterotrophs.

2 main categories:Photoautotroph sand Chemoautotrophs.

Source of energy

Heterotrophs rely on other organisms to get their energy.

Autotrophs rely on sunlight to convert it into energy.

Position in the food chain

They are fit into 3 levels in a food chain: primary consumers( level 2 ), secondary consumers ( level 3 ) or tertiary consumers ( level 4 ).

Autotrophs are at the bottom of the food chain

Role

They act as consumers.

They act as producers.

Movement

Heterotrophs can move from one place to another in search of food.

Most autotrophs are stationary.

Saprotrophs

Saprotrophs are commercially used in saprotrophic nutrition. They obtain nutrients from the dead matter of other plants and animals. They are mostly seen as mushroom-like creatures grown on the wooden plant`s roots during the rainy season.  Some of the most common saprotrophs are Rhizopus (bread mould), mucor (pin mould), Yeast, and Agaricus (a mushroom). For information go to Saprotrophs.

Heterotrophic plants 

Heterotrophic plants, also called carnivorous plants or parasitic plants, cannot synthesize food due to the absence of the green pigment- chlorophyll. Such plants trap some insects for their food. They have pitcher, a pouch-like structure at the apex of their leaves. The pitcher can quickly grasp the insect and shut its opening. Some parasitic plants like dodder have no leaves but they are distinguished by their weak, cylindrical stem that coils around the host to form suckers. Suckers help to attack the host`s stem to reach the vascular bundles. The invading plant absorbs water and nutrients from these bundles. Parasitic plants are classified into holoparasites and hemiparasites. A  holoparasite is a total parasite as it is entirely dependent on its host while hemiparasite is partly dependent on the host. 

 

Read more 

  1. Introduction to plant nutrition   

  2. Coordination in plants

  3. Plant breeding techniques

  4. Sexual reproduction in plants

  5. Respiration in plants

 

Questions

  1. Distinguish between photoautotrophs and photoheterotrophs.

  2. What are chemoheterotrophs?

  3. Explain about heterotrophic plants.

  4. Distinguish between autotrophs and heterotrophs.

 

 



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