Photosynthesis vs Chemosynthesis: Definition, Differences and Examples

All living organism needs energy to perform their different normal metabolic functions. Food is the source of energy of the living body. Photosynthesis is the process by which the chlorophyll-containing green plant and algae synthesizes glucose (carbohydrates) and evolves oxygen using CO2 of the air and water in the presence of sunlight. During the photosynthesis, light energy is converted into chemical energy and is stored as the carbohydrates.

More chlorophyll-containing plants carry out the photosynthesis efficiently. There are two categories of photosynthesis: oxygenic photosynthesis and anoxygenic photosynthesis. In plants, cyanobacteria, and algae, oxygenic photosynthesis occurs but in green sulfur bacteria and purple sulfur bacteria, anoxygenic photosynthesis occurs. In oxygenic photosynthesis, water releases electron and forms carbon dioxide. In this case, water is oxidized and carbon dioxide is reduced to produce glucose. Besides these, O2 is also produced as a by-product whereas, in anoxygenic photosynthesis, oxygen does not produce as a by-product.​​​​

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Equation of Oxygenic Photosynthesis:

image of Equation of Oxygenic Photosynthesis

Equation of Anoxygenic Photosynthesis:

image of Equation of Anoxygenic Photosynthesis

Organisms produce their food through the process of two primary production mechanisms: chemosynthesis and photosynthesis. In both the processes, glucose is produced. In the chemosynthesis process, glucose is produced in the organism`s cell from chemical reactions by synthesizing the organic compounds in the absence of direct sunlight but in the process of photosynthesis, glucose is produced by synthesizing the organic compounds in the presence of direct sunlight.

Chemosynthesis is the process where glucose is made as an energy source in the organism`s cell from the chemical reaction. Generally, this process occurs in organisms such as crab, shrimp, big tube worms and fish, which live in the darkest regions (hydrothermal vents) of the ocean where sunlight is unable to reach. For survival, over 300 species of marine organisms near hydrothermal vents mainly depend on chemosynthesis. In this case, chemosynthetic bacteria which reside in these organisms, that help to oxidize hydrogen sulfide to get energy.

Chemical Reaction of Chemosynthesis:​​​​

image of Equation of Chemosynthesis

The chemosynthetic organisms are also known as chemotrophs. There are two types of chemotrophs: chemoorganotrophs and chemolithotrophs. Chemoorganotrophs are such type of organisms which obtain their energy source by oxidizing the chemical bonds in organic compounds while Chemolithotrophs obtain energy by using electrons from inorganic chemical sources like ammonium ions, hydrogen sulfide, elemental sulfur, and ferrous ions.

Some notable examples of chemolithotrophs are Acidithiobacillus ferrooxidans (Iron bacteria), Nitrosomonas, Nitrobactor (nitrosifying bacteria), proteobacteria (sulfur-oxidizing bacteria), aquificaeles and methanogenic archaea, etc. Chemosynthesis is mostly occurred by microbes, which live on the seafloor and form microbial mats where grazers like scale worms, limpets, and snails eat on the mat.

Difference between Chemosynthesis and Photosynthesis

Important Points



Sources of Energy

Organisms use chemical energy such as H2S

Sunlight is the main source for photosynthetic organisms.


Sulfur compounds are produced as byproducts

Oxygen releases as a byproduct.


Chemosynthetic organisms are known as chemotrophs

Photosynthetic organisms are known as phototrophs.


In this case, no pigments are involved.

In this case, different types of pigments such as chlorophyll, carotenoids, and phycobilins are involved


Chemosynthetic organisms are collectively known as chemotrophs. These are of two types:

 Chemoorganotrophs and chemolithotrophs.

Photosynthetic organisms are collectively known as phototrophs. These are of two types:

Photoautotrophs and photoheterotrophs.

Energy conversion

In this case, inorganic compounds are converted into organic compounds.

Light energy is converted into chemical energy.


Chemosynthesis occurs in Acidithiobacillus ferrooxidans, Nitrobacter, Nitrosomonas, sulfur-oxidizing proteobacteria, aquificaeles and archaea like methanogenic archaea, etc.

Photosynthesis occurs in green plants, cyanobacteria, algae and Rhodobacter, etc.  

Concluding Remarks

All living organisms can grow, move, metabolize, reproduce, and they respond to stimuli and can adapt to the environment. The body of the living things contains millions of cells which perform various functions. The different chemical process also takes place in the cells such as metabolism. To carry out the many functions, organisms must need energy and use it to sustain life.

The major source of energy for organisms especially green plants, cyanobacteria, and algae is the sun. They produce energy by the process of photosynthesis. But many animals inhabit in hydrothermal vents or darkness regions in the deep sea, where the sunlight does not reach at all. In this area, most of the animals get energy through the process of chemosynthesis.

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