Terrestrial and aquatic phototrophs: Plants grow on a fallen log floating in algae rich water.

Photoautotrophs or Phototroph (Gk: photo = light, auto = self, troph = nourishment) are organisms (usually plants) that carry out photosynthesis to acquire energy. Energy from sunlight, carbon dioxide and water are converted into organic materials to be used in cellular functions such as biosynthesis and respiration. In an ecological context, they provide nutrition for all other forms of life (besides other autotrophs such as chemotrophs). In terrestrial environments plants are the predominant variety, while aquatic environments include a range of phototrophic organisms such as algae (e.g. kelp), other protists (such as euglena) and bacteria (such as cyanobacteria). One product of this process is starch, which is a storage or reserve form of carbon, which can be used when light conditions are too poor to satisfy the immediate needs of the organism. Photosynthetic bacteria have a substance called bacteriochlorophyll, live in lakes and pools, and use the hydrogen from hydrogen sulfide instead of from water, for the chemical process. (The bacteriochlorophyll pigment absorbs light in the extreme UV and infra-red parts of the spectrum which is outside the range used by normal chlorophyll). Cyanobacteria live in fresh water, seas, soil and lichen, and use a plant-like photosynthesis.

A photolithotrophic autotroph is an autotrophic organism that uses light energy, and an inorganic electron source (eg. H₂O, H₂, H₂S), and CO₂ as its carbon source. Examples include plants.

The depth to which sunlight or artificial light can penetrate into water, so that photosynthesis may occur, is known as the phototrophic zone.

[edit] Flowchart

Flowchart to determine if a species is autotroph, heterotroph, or a subtype

• Autotroph
  • Chemoautotroph
  • Photoautotroph
• Heterotroph
  • Chemoheterotroph
  • Photoheterotroph

[edit] See also

• Primary nutritional groups
• Prototroph

[edit] References