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Some prokaryotes are pathogenic, causing disease and even death in plants and animals. [5] Marine prokaryotes are responsible for significant levels of the photosynthesis that occurs in the ocean, as well as significant cycling of carbon and other nutrients. [6] Prokaryotes live throughout the biosphere.
Cyanobacteria is the only prokaryotic group that performs oxygenic photosynthesis. Anoxygenic photosynthetic bacteria use PSI- and PSII-like photosystems, which are pigment protein complexes for capturing light. [5] Both of these photosystems use bacteriochlorophyll. There are multiple hypotheses for how oxygenic photosynthesis evolved.
Chloroplasts (from the Greek chloros for green, and plastes for "the one who forms" [31]) are organelles that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in the energy-storage molecules while freeing oxygen from water in plant and algal cells.
Some dinoflagellates are known to be photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey (phagotrophy). [76] Some species are endosymbionts of marine animals and other protists, and play an important part in the biology of coral reefs .
Some examples are bacteriorhodopsin and bacteriophytochromes in some bacteria. See also: phytochrome and phototropism. Most prokaryotes (bacteria and archaea) are unable to sense the direction of light, because at such a small scale it is very difficult to make a detector that can distinguish a single light direction.
Prokaryotes evolved before eukaryotes, and lack nuclei, mitochondria, and most of the other distinct organelles that characterize the eukaryotic cell. Some unicellular prokaryotes, such as cyanobacteria, form colonies held together by biofilms, and large colonies can create multilayered microbial mats.
Cyanobacteria, which are prokaryotic organisms which carry out oxygenic photosynthesis, occupy many environmental conditions, including fresh water, seas, soil, and lichen. Cyanobacteria carry out plant-like photosynthesis because the organelle in plants that carries out photosynthesis is derived from an [ 4 ] endosymbiotic cyanobacterium. [ 5 ]
They have many features that allow them to survive in these oligotrophic (low-nutrient) and low-light regions, such as the use several nitrogen sources, including nitrate, ammonium, and urea. [6] Their small size and large surface area allows for efficient nutrient acquisition, incident light absorption, and organism growth. [ 7 ]