<P> Some organisms employ even more radical variants of photosynthesis . Some archea use a simpler method that employs a pigment similar to those used for vision in animals . The bacteriorhodopsin changes its configuration in response to sunlight, acting as a proton pump . This produces a proton gradient more directly, which is then converted to chemical energy . The process does not involve carbon dioxide fixation and does not release oxygen, and seems to have evolved separately from the more common types of photosynthesis . </P> <P> In photosynthetic bacteria, the proteins that gather light for photosynthesis are embedded in cell membranes . In its simplest form, this involves the membrane surrounding the cell itself . However, the membrane may be tightly folded into cylindrical sheets called thylakoids, or bunched up into round vesicles called intracytoplasmic membranes . These structures can fill most of the interior of a cell, giving the membrane a very large surface area and therefore increasing the amount of light that the bacteria can absorb . </P> <P> In plants and algae, photosynthesis takes place in organelles called chloroplasts . A typical plant cell contains about 10 to 100 chloroplasts . The chloroplast is enclosed by a membrane . This membrane is composed of a phospholipid inner membrane, a phospholipid outer membrane, and an intermembrane space . Enclosed by the membrane is an aqueous fluid called the stroma . Embedded within the stroma are stacks of thylakoids (grana), which are the site of photosynthesis . The thylakoids appear as flattened disks . The thylakoid itself is enclosed by the thylakoid membrane, and within the enclosed volume is a lumen or thylakoid space . Embedded in the thylakoid membrane are integral and peripheral membrane protein complexes of the photosynthetic system . </P> <P> Plants absorb light primarily using the pigment chlorophyll . The green part of the light spectrum is not absorbed but is reflected which is the reason that most plants have a green color . Besides chlorophyll, plants also use pigments such as carotenes and xanthophylls . Algae also use chlorophyll, but various other pigments are present, such as phycocyanin, carotenes, and xanthophylls in green algae, phycoerythrin in red algae (rhodophytes) and fucoxanthin in brown algae and diatoms resulting in a wide variety of colors . </P>

What is the site of photosynthesis in plant