Main Difference – Chemosynthesis vs Photosynthesis
Chemosynthesis and photosynthesis are the two primary production mechanisms where organisms produce their own food. Both processes are involved in the production of simple sugars like glucose starting from carbon dioxide and water. The main difference between chemosynthesis and photosynthesis is that chemosynthesis is the process which synthesizes the organic compounds in the cell by the energy generated from chemical reactions whereas photosynthesis is the process which synthesizes organic compounds by the energy obtained from the sunlight.
This article looks at,
1. What is Chemosynthesis
– Definition, Characteristics, Process
2. What is Photosynthesis
– Definition, Characteristics, Process
3. What is the difference between Chemosynthesis and Photosynthesis
What is Chemosynthesis
Chemosynthesis is the synthesis of organic compounds with the use of energy obtained by oxidizing inorganic compounds. Chemosynthesis occurs in the absence of sunlight, in places like hydrothermal vents in the deep ocean. Organisms living in hydrothermal vents utilize inorganic compounds coming out from the seafloor as their source of energy for the production of food. Thus, hydrothermal vents consist of high biomass including sparse distribution of animals, who depend on the food dropping down by chemosynthesis. Chemosynthesis is mostly done by microbes, which are found on the seafloor, forming microbial mats. Scaleworms, limpets, and snails like grazers can be found on the mat eating it. Predators come and eat these grazers as well. Animals like tube worms are found living as symbionts with chemosynthetic bacteria. Giant tube worms next to a hydrothermal vent are shown in figure 1.
Figure 1: Giant tube worms next to a hydrothermal vent
During chemosynthesis, bacteria use the energy stored in chemical bonds of either hydrogen sulfide or hydrogen gas in order to produce glucose from dissolved carbon dioxide and water. The chemical reaction for the utilization of hydrogen sulfide in chemosynthesis is shown below.
12H2S + 6CO2 → C6H12O6 (Glucose) + 6H2O + 12S
The organisms which perform chemosynthesis are called chemotrophs. Chemoorganotrophs and chemolithotrophs are the two categories of chemotrophs. Chemolithotrophs use electrons from inorganic chemical sources like hydrogen sulfide, ammonium ions, ferrous ions and elemental sulfur. Acidithiobacillus ferrooxidans which is an iron bacteria, Nitrosomonas which is a nitrosifying bacteria, Nitrobactor which is a nitrifying bacteria, sulfur oxidizing proteobacteria, aquificaeles and methanogenic archaea are the examples chemolithotrophs.
What is Photosynthesis
Photosynthesis is the process in which the green plants and algae synthesize glucose form carbon dioxide and water by using sunlight as the source of energy. The pigment chlorophyll is involved in this process. In plants, photosynthesis occurs in specialized plastids called chloroplasts. Higher plants consist of leaves, containing more chlorophyll in order to carry out the photosynthesis efficiently.
Figure 2: Photosynthesizing leaves
Two categories of photosynthesis are found: oxygenic photosynthesis and anoxygenic photosynthesis. Oxygenic photosynthesis occurs in cyanobacteria, algae, and plants, whereas anoxygenic photosynthesis occurs in purple sulfur bacteria and green sulfur bacteria. During oxygenic photosynthesis, the electrons are transferred from water to carbon dioxide. Thereby, water is oxidized and carbon dioxide is reduced, producing glucose. Hence, the electron donor in oxygenic photosynthesis is water. Oxygen gas is a by-product of oxygenic photosynthesis. In contrast, anoxygenic photosynthesis does not produce oxygen as a by-product. The electron donor is variable and it can be hydrogen sulfide. The chemical reactions of both oxygenic and anoxygenic photosynthesis are shown below.
Oxygenic photosynthesis:
6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2 + 6H2O
Anoxygenic photosynthesis:
CO2 + 2H2S + Light Energy → [CH2O] + 2S + H2O
The organisms which perform photosynthesis are called phototrophs. Photoautotrophs and photoheterotrophs are the two categories of phototrophs. The carbon source of photoautotrophs is carbon dioxide whereas the carbon source of photoheterotrophs is organic carbon. Green plants, cyanobacteria, and algae are examples of photoautotrophs and some bacteria like Rhodobactor are examples for photoheterotrophs.
Difference Between Chemosynthesis and Photosynthesis
Energy Source
Chemosynthesis: Energy source of chemosynthesis is the chemical energy stored in inorganic chemicals like hydrogen sulfide.
Photosynthesis: Energy source of photosynthesis is sunlight.
Energy Conversion
Chemosynthesis: Chemical energy stored in inorganic compounds are stored in organic compounds during chemosynthesis.
Photosynthesis: The light energy is converted into chemical energy during photosynthesis.
Organisms
Chemosynthesis: Chemosynthetic organisms are collectively called chemotrophs.
Photosynthesis: Photosynthetic organisms are collectively called phototrophs.
Pigments Involved
Chemosynthesis: No pigments are involved in the chemosynthesis.
Photosynthesis: Chlorophyll, carotenoids, and phycobilins are the pigments involved in photosynthesis.
Plastids Involved
Chemosynthesis: Plastids are not involved in chemosynthesis.
Photosynthesis: Chloroplasts are the plastids found in plants; the reactions of photosynthesis are concentrated in the cell.
Oxygen as a By-product
Chemosynthesis: Oxygen gas is not released as a by-product.
Photosynthesis: Oxygen is released as the by-product during photosynthesis.
Contribution to Total Biospheric Energy
Chemosynthesis: Chemosynthesis has a lower contribution to the total biospheric energy.
Photosynthesis: Photosynthesis has a higher contribution to the total biospheric energy.
Categories
Chemosynthesis: Chemoorganotrophs and chemolithotrophs are the two categories of chemotrophs.
Photosynthesis: Photoautotrophs and photoheterotrophs are the two categories of phototrophs.
Presence
Chemosynthesis: Chemosynthesis is found in bacteria like Acidithiobacillus ferrooxidans, Nitrosomonas, Nitrobacter, sulfur-oxidizing proteobacteria, aquificaeles and archaea like methanogenic archaea.
Photosynthesis: Photosynthesis is found in green plants, cyanobacteria, algae and Rhodobactor like bacteria.
Conclusion
Chemosynthesis and photosynthesis are two types of primary productions found among organisms. Chemosynthesis and photosynthesis fuel all the life forms on the earth. Both most chemosynthetic and photosynthetic organisms utilize carbon dioxide and water in order to produce organic compounds as food. Chemosynthesis uses the chemical energy stored in inorganic compounds in order to produce simple sugars like glucose. It is the primary energy source of most of the animals found in hydrothermal vents in the deep sea, where the sunlight is unable to reach. In contrast, photosynthesis uses the light energy of the sun in order to produce glucose. Chemosynthesis is mostly found in bacteria, which can either live independently on the seafloor or symbionts living inside animals like tube worms by replacing their guts. Land plants are the primary producers of most food chains on earth. However, the main difference between chemosynthesis and photosynthesis is their energy source.
Reference:
1. National Research Council (US) Committee on Research Opportunities in Biology. “Ecology and Ecosystems.” Opportunities in Biology. U.S. National Library of Medicine, 01 Jan. 1989. Web. 03 Apr. 2017.
2. National Research Council (US) Ocean Studies Board. “Achievements in Biological Oceanography.” 50 Years of Ocean Discovery: National Science Foundation 1950-2000. U.S. National Library of Medicine, 01 Jan. 1970. Web. 03 Apr. 2017.
3. Cooper, Geoffrey M. “Photosynthesis.” The Cell: A Molecular Approach. 2nd edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 03 Apr. 2017.
Image Courtesy:
1. “Giant tube worms next to vent” By Nasa – (Public Domain) via Commons Wikimedia
2. “318743” (Public Domain) via Pixabay
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