Difference between Phototrophs and Chemotrophs

Different organisms have different mechanisms to produce their food. Some organisms are able to produce their food while some are not able to produce their food and are depended on the food produced by other organisms. Accordingly, they are categorized into Phototrophs and Chemotrophs. Let us see how Phototrophs differ from Chemotrophs!

Phototrophs:

Phototrophs refer to those organisms which use sunlight as their main source of energy to produce their food. They capture light energy and convert it into chemical energy inside their cells, e.g. green plants convert light energy into chemical energy by photosynthesis or they are able to fix carbon from the carbon dioxide into organic compounds. Phototrophs are further classified into two main groups: Photoautotrophs and photoheterotrophs.

1) Photoautotroph: These organisms carry out photosynthesis to produce their food using light, water and carbon dioxide. In the presence of sunlight, carbon dioxide and water are converted into organic compounds like carbohydrates, fats and proteins which are used in cellular functions like biosynthesis and respiration. Some common examples of photoautotroph include green plants and photosynthetic bacteria.

2) Photoheterotrophs: These organisms can use sunlight as their source of energy but cannot use carbon dioxide as their only carbon source. They use organic compounds from their environment as the source of carbon, e.g. purple non-sulfur bacteria and green non-sulfur bacteria.

Chemotrophs

Chemotrophs are the organisms which get their energy from the oxidation or breakdown of carbon dioxide or inorganic chemical compounds by chemosynthesis, the main production metabolism in Chemotrophs. During this process, simple molecules with carbon like carbon dioxide and methane are converted into organic compounds by oxidizing hydrogen gas, hydrogen sulphide, sulphur etc. Some common examples of Chemotrophs include sulphur oxidizing proteobacteria, neutrophilic iron-oxidizing bacteria etc. Chemotrophs are further classified into chemoautotrophs and chemoheterotrophs.

1) Chemoautotrophs: They are able to make their own food through chemosynthesis. They derive energy from chemical reactions and synthesize the required organic compounds from carbon dioxide. They use carbon dioxide as a carbon source and utilize or oxidize inorganic compounds like hydrogen sulfide, sulphur, ammonia for energy and to synthesize organic compounds e.g. sulphur and iron bacteria. They are usually found in hostile habitats such as deep sea vents.

2) Chemoheterotrophs: They are not able to fix carbon to form their own organic compounds (food). They depend on organic compounds for the energy and carbon source. In other words, they ingest food produced by other organisms like lipids, proteins and carbohydrates. E.g. fungi, bacteria and some sulphur bacteria, etc.

Based on the above information, some of the key differences between Phototrophs and Chemotrophs are as follows:

Phototrophs	Chemotrophs
They use light energy in order to produce energy or carry out cellular functions.	They obtain energy by oxidizing electron donors or chemical compounds.
Source of energy is sunlight.	Source of energy is the oxidation of chemical compounds (organic or inorganic).
They generally perform photosynthesis.	They generally perform chemosynthesis.
Types include Photoautotrophs and Photoheterotrophs	Types include chemoautotrophs and chemoheterotrophs
They can use sunlight.	They cannot use sunlight.
Common examples include green plants, algae, cyanobacteria, purple non-sulphur bacteria, heliobacteria etc.	Common examples include nitrosomonas, Acidithiobacillus ferrooxidans.