Photosynthesis and Chemosynthesis in Biology

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).