Photoautotrophs are organisms that use light energy and inorganic carbon to produce organic materials. Eukaryotic photoautotrophs absorb energy through the

chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to a ...

molecules in their

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

s while prokaryotic photoautotrophs use chlorophylls and bacteriochlorophylls present in their cytoplasm. All known photoautotrophs perform photosynthesis. Examples include plants,

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

, and

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

Origin and the Great Oxidation Event

Chemical and geological evidence indicate that photosynthetic

existed about 2.6 billion years ago and anoxygenic photosynthesis had been taking place since a billion years before that. Oxygenic photosynthesis was the primary source of

oxygenation Oxygenation may refer to: * Oxygenation (environmental), a measurement of dissolved oxygen concentration in soil or water * Oxygen saturation (medicine), the process by which concentrations of oxygen increase within a tissue * Water oxygenation, t ...

and led to the Great Oxidation Event (the Oxygen Catastrophe) roughly 2.4 to 2.1 billion years ago. Although the end of the Great Oxidation Event was marked by a significant decrease in gross primary productivity that eclipsed extinction events, the development of

aerobic respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

enabled energy extraction from organic molecules, allowing multi-cellular growth and diversification of life on Earth.

Prokaryotic photoautotrophs

Prokaryotic photoautotrophs include

Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

Pseudomonadota Pseudomonadota (synonym Proteobacteria) is a major phylum of Gram-negative bacteria. The renaming of phyla in 2021 remains controversial among microbiologists, many of whom continue to use the earlier names of long standing in the literature. The ...

Chloroflexota The Chloroflexota are a phylum of bacteria containing isolates with a diversity of phenotypes, including members that are aerobic thermophiles, which use oxygen and grow well in high temperatures; anoxygenic phototrophs, which use light for photo ...

Acidobacteriota Acidobacteriota is a phylum of Gram-negative bacteria. Its members are physiologically diverse and ubiquitous, especially in soils, but are under-represented in culture. Description Members of this phylum are physiologically diverse, and can be ...

Chlorobiota The green sulfur bacteria are a phylum of obligately anaerobic photoautotrophic bacteria that metabolize sulfur. Green sulfur bacteria are nonmotile (except ''Chloroherpeton thalassium'', which may glide) and capable of anoxygenic photosynthes ...

, Bacillota, Gemmatimonadota, and Eremiobacterota. Cyanobacteria is the only prokaryotic group that performs oxygenic photosynthesis. Anoxygenic photosynthetic bacteria use

PSI Psi, PSI or Ψ may refer to: Alphabetic letters * Psi (Greek) (Ψ, ψ), the 23rd letter of the Greek alphabet * Psi (Cyrillic) (Ѱ, ѱ), letter of the early Cyrillic alphabet, adopted from Greek Arts and entertainment * "Psi" as an abbreviation ...

- and PSII-like

photosystem Photosystems are functional and structural units of protein complexes involved in photosynthesis. Together they carry out the primary photochemistry of photosynthesis: the absorption of light and the transfer of energy and electrons. Photosystems ...

s, which are pigment protein complexes for capturing light. Both of these photosystems use bacteriochlorophyll. There are multiple hypotheses for how oxygenic photosynthesis evolved. The loss hypothesis states that PSI and PSII were present in anoxygenic ancestor cyanobacteria from which the different branches of anoxygenic bacteria evolved. The fusion hypothesis states that the photosystems merged later through horizontal gene transfer. The most recent hypothesis suggests that PSI and PSII diverged from an unknown common ancestor with a protein complex that was coded by one gene. These photosystems then specialized into the ones that are found today.

Eukaryotic photoautotrophs

Eukaryotic photoautotrophs include

red algae Red algae, or Rhodophyta (, ; ), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority ...

, haptophytes, stramenopiles, cryptophytes, chlorophytes, and

land plants The Embryophyta (), or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophytes () have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of green algae as siste ...

. These organisms perform photosynthesis through organelles called

s and are believed to have originated about 2 billion years ago. Comparing the genes of chloroplast and cyanobacteria strongly suggests that chloroplasts evolved as a result of endosymbiosis with

that gradually lost the genes required to be free-living. However, it is difficult to determine whether all chloroplasts originated from a single, primary endosymbiotic event, or multiple independent events. Some brachiopods (''

Gigantoproductus ''Gigantoproductus'' is a genus of extinct brachiopods in the order Productida and the family Monticuliferidae. The species were the largest of the carboniferous brachiopods, with the largest known species reaching in shell width. Such huge ...

'') and

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

s ('' Tridacna'') also evolved photoautotrophy.

References

{{Reflist Trophic ecology Biology terminology Photosynthesis