It is called photosynthesis the process by which some organisms use the solar radiation energy for synthesize organic molecules which they can later use as fuel for their cellular metabolism.
In this way, thanks to photosynthesis, these organisms are able to make their own food with the help of light, which is why they are classified as living organisms. photoautotrophs.
There are two main types of photosynthesis: oxygenic photosynthesis and the anoxygenic photosynthesis.
All floorsalong with most of algae and cyanobacteriaperform oxygenic photosynthesis. This type of photosynthesis uses light energy to combine water (HtwoO) and carbon dioxide (COtwo) and form glucose.
in this reaction water acts as an electron donor (reducing agent) and molecular oxygen (O) is producedtwo) as a waste productor, and so it is called oxygenic photosynthesis.
The global reaction of oxygenic photosynthesis responds to the following equation:
6COtwo + 12HtwoO + Light → C6H12EITHER6 + 6Otwo + 6HtwoEITHER
The anoxygenic photosynthesis is another type of photosynthesis in which no oxygen is released and that they only do certain groups of bacteria. Instead of water intervenes another inorganic molecule as electron donorfor example hydrogen sulfide (HtwoS):
COtwo + 2HtwoS + Light → [CH2O] + 2S + HtwoEITHER
anoxygenic photosynthetic bacteria
Among eukaryotic organisms, only plants and algae are capable of photosynthesis, and in both cases they perform oxygenic photosynthesis.
In the case of prokaryotic organisms, we find bacteria that carry out oxygenic photosynthesis (the cyanobacteria) and bacteria that carry out anoxygenic photosynthesis.
Among the anoxygenic photosynthetic bacteria there is a great variety, both in their phylogenetics and in the composition of the photosynthetic apparatus, while the organisms that carry out oxygenic photosynthesis (plants, algae and cyanobacteria) share a common mechanism.
In fact, the chloroplasts of plants and algae are believed to come from ancient cyanobacteria that entered into symbiosis with primitive plants and algae, which is why they would share the same common mechanism of photosynthesis.
None of the anoxygenic photosynthetic bacteria is capable of using water as an electron donor, in other words, they are not able to oxidize water. Instead they use sulfur compounds, hydrogen or organic substrates that donate electrons to reduce CO moleculestwo and transform it into organic carbon.
The most studied anoxygenic photosynthetic bacteria are purple sulfur bacteriawhich could be related to our mitochondria, but there are other groups:
- purple sulfur bacteria: family Chromatiaceaefamily Ectothiorhodospiraceae. They are anaerobic or microaerophilic. They use hydrogen sulfide (HtwoS, in solution called hydrogen sulfide) and produce gaseous sulfur (Stwo). They do not tolerate the presence of oxygen, so they usually live in stagnant waters or sulphurous hydrothermal sources.
- green sulfur bacteria: family Chlorobiaceae. They use hydrogen sulfide (HtwoS) or sulfur (S) as electron donor.
- acid bacteria: as electron donor can use various compounds. For example, iron bacteria use ferrous oxide, which, by giving up electrons, oxidizes and forms insoluble ferric oxide that gives the typical brown color of the waters where these bacteria live.
- heliobacteria: the photosynthetic pigment bacteriochlorophyll g is unique to this type of bacteria. Exclusively anaerobic. They are considered photoheterotrophs, since they obtain energy from light or chemical products, but do not use CO2 as a carbon source (their carbon source is exclusively organic compounds).
- anoxygenic filamentous bacteria: previously known as green and purple non-sulfur bacteria, but later it was discovered that some use sulfur compounds. They can be photoautotrophs, chemoorganotrophs, or photoheterotrophs.
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