Phototroph

 ( Photosynthesis ) 

Phototrophs () are that carry out photon capture to acquire energy. They use the energy from light to carry out various cellular metabolic processes. It is a common misconception that phototrophs are obligatorily photosynthetic. Many, but not all, phototrophs often photosynthesize: they anabolism convert carbon dioxide into Biomolecule to be utilized structurally (e.g. cellulose and Membrane lipid), functionally (e.g. Vitamin, Nucleotide, and Amino acid), or as a source for later catabolism processes (e.g. Starch, Sugar and Fat). All phototrophs either use electron transport chains or direct to establish an electrochemical gradient, which is utilized by ATP synthase to provide adenosine triphosphate (ATP) for the cell. Phototrophs can be either or . If their electron and hydrogen donors are inorganic compounds (e.g., , as in some purple sulfur bacteria, or , as in some green sulfur bacteria) they can be also called , and so, some photoautotrophs are also called photolithoautotrophs. Examples of phototroph organisms are Rhodobacter capsulatus, Chromatium, and Chlorobium.

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History Originally used with a different meaning, the term took its current definition after Lwoff and collaborators (1946).Lwoff, A., C.B. van Niel, P.J. Ryan, and E.L. Tatum (1946). Nomenclature of nutritional types of microorganisms. Cold Spring Harbor Symposia on Quantitative Biology (5th edn.), Vol. XI, The Biological Laboratory, Cold Spring Harbor, NY, pp. 302–303, [1].Schneider, С. K. 1917. Illustriertes Handwörterbuch der Botanik. 2. Aufl., herausgeg. von K. Linsbauer. Leipzig: Engelmann, [2].

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Photoautotroph Most well-known phototrophs are Photoautotroph, which means they synthesize their own food from inorganic substances (i.e. carbon dioxide) in a process called carbon fixation, using light as an energy source. Green plants and most photosynthetic bacteria are photoautotrophs. Photoautotrophic organisms are sometimes referred to as holophytic.

Robert Hine (2025). 9780816056484, Infobase Publishing. ISBN 9780816056484

Oxygenic photosynthetic organisms use photosystem II to capture light-energy and oxidize water (H₂O), splitting it into molecular oxygen (O₂) and 4 protons (H⁺) in the process called photolysis.

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Ecology In an ecology context, photoautotrophs are often the food source for neighboring heterotrophic life. In terrestrial environments, are the predominant variety, while aquatic environments include a range of phototrophic organisms such as algae (e.g., kelp), other (such as euglena), phytoplankton, and bacteria (such as cyanobacteria).

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 chloroplast in plants that carries out photosynthesis is derived from an endosymbiotic cyanobacterium.

This bacterium can use water as a source of electrons in order to perform CO₂ Redox reactions.

A photolithoautotroph is an Autotroph organism that uses light energy, and an inorganic electron donor (e.g., H₂O, H₂, H₂S), and Carbon dioxide as its carbon source.

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Photoheterotroph In contrast to photoautotrophs, photoheterotrophs are organisms that depend solely on light for their energy, and consumption of organic compounds for biomolecules. Photoheterotrophs produce ATP through photophosphorylation but use environmentally obtained to build structures and other biomolecules.

(2025). 9780805368444, Pearson Benjamin Cummings. ISBN 9780805368444

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Classification by light-capturing molecule Most phototrophs use chlorophyll or the related bacteriochlorophyll to capture light and are known as chlorophototrophs. Others, however, use retinal and are retinalophototrophs.

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Flowchart

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See also

• Primary nutritional groups
• Prototroph

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