Key Differences Between Photosynthesis and Chemosynthesis
In biochemistry, chemosynthesis is the biological conversion of one or more carbon-containing molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic compounds (e.g., hydrogen gas, hydrogen sulphide) or ferrous ions as a source of energy, rather than sunlight, as in photosynthesis. Chemoautotrophs, organisms that obtain carbon from carbon dioxide through chemosynthesis, are phylogenetically diverse.
Groups that include conspicuous or biogeochemical-important taxa include the sulphur-oxidising Gammaproteobacteria, the Campylobacterota, the Aquificota, the methanogenic archaea, and the neutrophilic iron-oxidising bacteria.
What is Photosynthesis?
Photosynthesis is a biological process in which light energy is used to synthesise organic compounds. Most green plants and some bacteria use this type of autotroph. These organisms are called photoautotrophs. In the presence of sunlight and chlorophyll, the body converts carbon dioxide and water into carbohydrates. Oxygen is also released as a by-product. This process plays an important role in maintaining the level of oxygen on earth.
Examples of Chemosynthesis
The yellow sulphur granules are visible in the cytoplasm of bacteria that perform the reaction. Another example of chemosynthesis was discovered in 2013 when bacteria were found living in basalt below the sediment of the ocean floor. These bacteria were not associated with a hydrothermal vent.
What is Chemosynthetic Bacteria?
In simple words, these bacteria capture energy and make it available for everyone in the ecosystem thriving at the ocean floor. The bacteria essentially derive energy from chemical nutrients (inorganic compounds) through oxidation. Also referred to as autotrophs, the bacteria get energy from breaking chemical bonds during a chemical reaction. The energy released is then used by them to manufacture glucose (food).
Chemosynthetic Bacteria Examples
Nitrifying Bacteria
Nitrifying bacteria initiate oxidation of ammonium to nitrite, which is later oxidised to nitrates to obtain energy. Nitrates act as nutrients for plants and promote their growth. Nitrifying bacteria commonly occur in aquatic environments (freshwater, marine water, potable water). Their other habitats include sewage and soil.
Sulphur Bacteria
These bacteria reside at great depths below the surface of the sea, near the hydrothermal vents. Hydrogen sulphide seeps from these vents, which is oxidised by the bacteria to derive energy. Due to these bacteria, diverse ecosystems having innumerable species of marine animals flourish near hydrothermal vents. Thiobacillus and Beggiatoa are the two common species of sulphur bacteria.
Iron Bacteria
These bacteria thrive in iron-rich environments. They are found in abundance in wells, as there is adequate iron and other minerals such as manganese there. The bacteria are also present in streams, shallow aquifers, and soil. These microorganisms obtain energy by converting ferrous iron to the ferrous state. It is a part of their metabolism, which enables them to derive energy and make food. Ferrobacillus and Gallionella are the most common species of iron bacteria.
Which Plants Produce Their Food by Chemosynthesis?
Some rare autotrophs produce food through a process called chemosynthesis rather than photosynthesis. Autotrophs involved in Chemosynthesis do solar energy to produce food. Instead, they often cook their food using the energy of a chemical reaction that combines hydrogen sulphide or methane with oxygen.
Difference Between Photosynthesis and Chemosynthesis
Interesting Facts
Chemosynthesis was first identified in 1977 when a team of scientists on an ocean research expedition near the Galápagos Islands off the coast of Ecuador found hot vents on the ocean floor spewing a chemical soup of hot fluid.
Photosynthesis requires carbon dioxide and water to make sugar and oxygen. Cellular respiration uses oxygen and sugar to release energy, carbon dioxide, and water. Plants and other photosynthetic organisms perform both sets of reactions.
Important Questions
Q1. How many types of chemosynthetic bacteria are there?
Ans. Below are some types of chemosynthesis bacteria:
Metal Ion Bacteria
The most well-known type of bacteria that use metal ions for chemosynthesis are iron bacteria. Iron bacteria can actually pose a problem for water systems in iron-rich environments. This is because they consume dissolved metal ions in soil and water – and produce insoluble clumps of rust-like ferric iron, which can stain plumbing fixtures and even clog them up.
Nitrogen Bacteria
Nitrogen bacteria are any bacteria that use nitrogen compounds in their metabolic process. While all of these bacteria use electrons from nitrogen compounds to create organic compounds, they can have very different effects on their ecosystem depending on what compounds they use.
Q2. What are the two types of photosynthesis?
Ans. There are two different types of photosynthesis:
Oxygenic photosynthesis
Anoxygenic photosynthesis
Oxygenic Photosynthesis
Oxygenic photosynthesis is more common in plants, algae and cyanobacteria. During this process, electrons are transferred from water to carbon dioxide by light energy, to produce energy. During this transfer of electrons, carbon dioxide is reduced while water is oxidised, and oxygen is produced along with carbohydrates. During this process, plants take in carbon dioxide and expel oxygen into the atmosphere.
Anoxygenic Photosynthesis
This type of photosynthesis is usually seen in certain bacteria, such as green sulphur bacteria and purple bacteria which dwell in various aquatic habitats. Oxygen is not produced during the process.
Conclusion
Photosynthetic cells contain chlorophyll and other light-sensitive pigments that capture solar energy. In the presence of carbon dioxide, cells can convert this solar energy into energy-rich organic molecules such as glucose. In chemical synthesis, bacteria living on the seafloor or in animals use the energy stored in the chemical bond between hydrogen sulphide and methane to produce glucose from water and carbon dioxide (dissolved in seawater).
FAQs on Photosynthesis and Chemosynthesis: Concepts, Differences & Examples
1. What is the main difference between photosynthesis and chemosynthesis?
The primary difference lies in the energy source used to produce food. Photosynthesis uses light energy, typically from the sun, to convert carbon dioxide and water into glucose (sugar). In contrast, chemosynthesis uses chemical energy derived from the oxidation of inorganic molecules, such as hydrogen sulfide or methane, to synthesise organic compounds. This allows chemosynthetic organisms to thrive in environments without sunlight.
2. What is the fundamental importance of photosynthesis for most life on Earth?
The importance of photosynthesis is immense as it forms the foundation of nearly all terrestrial and aquatic food chains. Its key contributions include:
- Energy Conversion: It converts solar energy into chemical energy (glucose), which is the primary fuel for most living organisms.
- Oxygen Production: As a byproduct, it releases oxygen into the atmosphere, which is essential for the aerobic respiration of animals, plants, and other organisms.
- Carbon Cycle Regulation: It plays a crucial role in the global carbon cycle by capturing atmospheric carbon dioxide and converting it into organic matter.
3. Where does chemosynthesis typically occur, and what are some examples of chemosynthetic organisms?
Chemosynthesis predominantly occurs in extreme environments where sunlight is absent. Key locations include:
- Deep-sea hydrothermal vents: Here, bacteria and archaea use compounds like hydrogen sulfide released from the Earth's crust.
- Cold seeps: Methane and hydrocarbon-rich fluids seeping from the ocean floor provide the necessary chemicals.
- Subterranean caves: Certain bacteria can derive energy from minerals in the rock and water.
4. What are the general chemical equations for photosynthesis and chemosynthesis?
The general, balanced equation for photosynthesis is:
6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂
(Carbon Dioxide + Water + Light → Glucose + Oxygen)
For chemosynthesis, the equation varies depending on the chemical being oxidized. A common example using hydrogen sulfide is:
CO₂ + 4H₂S + O₂ → CH₂O + 4S + 3H₂O
(Carbon Dioxide + Hydrogen Sulfide + Oxygen → Formaldehyde (a simple sugar) + Sulfur + Water)
5. How are photosynthesis and chemosynthesis similar in their overall goal?
Despite using different energy sources, photosynthesis and chemosynthesis are fundamentally similar because both are processes of autotrophic nutrition. Their shared goal is to convert inorganic carbon (usually from carbon dioxide) into organic compounds (food/sugars). In doing so, both processes form the producer level of their respective ecosystems, creating the energy base upon which other organisms, or heterotrophs, depend for survival.
6. If photosynthesis uses light, what exactly powers the process of chemosynthesis?
Chemosynthesis is powered by the energy released from specific exergonic chemical reactions, specifically the oxidation of inorganic substances. Instead of capturing photons, chemosynthetic organisms act as catalysts for these reactions. The energy released from breaking the chemical bonds of compounds like hydrogen sulfide (H₂S), ammonia (NH₃), or ferrous iron (Fe²⁺) is harnessed to drive the synthesis of glucose from carbon dioxide. This chemical energy effectively replaces the light energy used in photosynthesis.
7. Is chemosynthesis considered a type of autotrophic nutrition? Explain the relationship.
Yes, chemosynthesis is a specific type of autotrophic nutrition. An autotroph is any organism that can produce its own food from inorganic sources. Autotrophic nutrition is categorised based on the energy source used:
- Photoautotrophs: Organisms that use light energy to create food via photosynthesis. This includes plants, algae, and cyanobacteria.
- Chemoautotrophs: Organisms that use energy from chemical reactions to create food via chemosynthesis. This includes certain bacteria and archaea.
8. Which process is believed to have evolved first on Earth: chemosynthesis or photosynthesis?
Scientific evidence strongly suggests that chemosynthesis evolved first. Early Earth's atmosphere was anoxic (lacked free oxygen) and the planet lacked a protective ozone layer, making the surface inhospitable due to high levels of UV radiation. However, the early oceans were rich in dissolved inorganic chemicals from intense volcanic and hydrothermal activity. These conditions were ideal for chemoautotrophs to thrive in protected environments like deep-sea vents. Photosynthesis, especially the oxygenic version we see in plants today, evolved much later after the Earth's conditions became more stable.
