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.
