Photoautotrophs are that can utilize light energy from sunlight and chemical element (such as carbon) from inorganic compounds to produce needed to sustain their own metabolism (i.e. autotrophy). Such biological activities are known as photosynthesis, and examples of such organisms include , algae and cyanobacteria.
Eukaryotic photoautotrophs absorb photonic energy through the photopigment chlorophyll (a porphyrin derivative) in their endosymbiont , while prokaryotic photoautotrophs use chlorophylls and bacteriochlorophylls present in free-floating . Plants, algae, and cyanobacteria perform oxygenic photosynthesis that produces oxygen as a byproduct, while some bacteria perform anoxygenic photosynthesis.
Origin and the Great Oxidation Event
Chemical and geological evidence indicate that photosynthetic
cyanobacteria 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 free oxygen and led to the Great Oxidation Event roughly 2.4 to 2.1 billion years ago during the
Neoarchean-
Paleoproterozoic boundary.
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 enabled more energetic metabolism of organic molecules, leading to
symbiogenesis and the
evolution of
, and allowing the diversification of
complex life on Earth.
Prokaryotic photoautotrophs
Prokaryotic photoautotrophs include
Cyanobacteria,
Pseudomonadota,
Chloroflexota,
Acidobacteriota, Chlorobiota,
Bacillota,
Gemmatimonadota, and Eremiobacterota.
Cyanobacteria is the only prokaryotic group that performs oxygenic photosynthesis. Anoxygenic photosynthetic bacteria use Photosystem I- and Photosystem II-like , which are pigment protein complexes for capturing light.
Eukaryotic photoautotrophs
Eukaryotic photoautotrophs include
red algae,
,
,
Cryptomonad,
Chlorophyta, and
Embryophyte.
These organisms perform
photosynthesis through organelles called
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
Endosymbiont with
cyanobacteria 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
(
Gigantoproductus) and
(
Tridacna) also evolved photoautotrophy.
