Editing Photosynthesis (section)

==Photosynthetic membranes and organelles==
{{Main|Chloroplast|Thylakoid}}
[[File:Chloroplast.svg|thumb|upright=1.4|right|'''Chloroplast ultrastructure''':{{ordered list
|outer membrane
|intermembrane space
|inner membrane (1+2+3: envelope)
|stroma (aqueous fluid)
|thylakoid lumen (inside of thylakoid)
|thylakoid membrane
|granum (stack of thylakoids)
|thylakoid (lamella)
|starch
|ribosome
|plastidial DNA
|plastoglobule (drop of lipids)}}
]]
In photosynthetic bacteria, the proteins that gather light for photosynthesis are embedded in [[cell membrane]]s. In its simplest form, this involves the membrane surrounding the cell itself.<ref>{{cite journal |vauthors= Tavano CL, Donohue TJ |date= December 2006 |title= Development of the bacterial photosynthetic apparatus |journal= [[Current Opinion in Microbiology]] |volume= 9 |issue= 6 |pages= 625–631 |doi= 10.1016/j.mib.2006.10.005 |pmc= 2765710 |pmid= 17055774 }}</ref> However, the membrane may be tightly folded into cylindrical sheets called [[thylakoid]]s,<ref name="Mullineaux-1999">{{cite journal |vauthors= Mullineaux CW |year= 1999 |title= The thylakoid membranes of cyanobacteria: structure, dynamics and function |journal= [[Australian Journal of Plant Physiology]] |volume= 26 |issue= 7 |pages= 671–677 |doi= 10.1071/PP99027 |bibcode= 1999FunPB..26..671M }}</ref> or bunched up into round [[vesicle (biology)|vesicles]] called ''intracytoplasmic membranes''.<ref>{{cite journal |vauthors= Sener MK, Olsen JD, Hunter CN, Schulten K |date= October 2007 |title= Atomic-level structural and functional model of a bacterial photosynthetic membrane vesicle |journal= [[Proceedings of the National Academy of Sciences of the United States of America]] |volume= 104 |issue= 40 |pages= 15723–15728 |bibcode= 2007PNAS..10415723S |doi= 10.1073/pnas.0706861104 |doi-access= free |pmc= 2000399 |pmid= 17895378 }}</ref> 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.<ref name="Mullineaux-1999"/>

In plants and algae, photosynthesis takes place in [[organelle]]s called [[chloroplast]]s. 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.

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 [[carotene]]s and [[xanthophyll]]s.<ref>{{cite book |vauthors=Campbell NA, Williamson B, Heyden RJ |title=Biology Exploring Life |publisher=[[Prentice Hall]] |location=Upper Saddle River, New Jersey |year=2006 |isbn=978-0-13-250882-7 |url=http://www.phschool.com/el_marketing.html |access-date=2009-02-03 |archive-url=https://web.archive.org/web/20141102041816/http://www.phschool.com/el_marketing.html |archive-date=2014-11-02 |url-status=dead }}</ref> Algae also use chlorophyll, but various other pigments are present, such as [[phycocyanin]], [[carotene]]s, and [[xanthophyll]]s in [[green algae]], [[phycoerythrin]] in [[red algae]] (rhodophytes) and [[fucoxanthin]] in [[brown algae]] and [[diatoms]] resulting in a wide variety of colors.

These pigments are embedded in plants and algae in complexes called antenna proteins. In such proteins, the pigments are arranged to work together. Such a combination of proteins is also called a [[light-harvesting complex]].<ref>{{cite journal | title=Molecular mechanism of SRP-dependent light-harvesting protein transport to the thylakoid membrane in plants | vauthors = Ziehe D, Dünschede B, Schünemann D | journal=Photosynthesis Research | volume=138 | issue=3 | pages=303–313 | date=December 2018 | pmid=29956039 | pmc=6244792 | doi=10.1007/s11120-018-0544-6 | bibcode = 2018PhoRe.138..303Z }}</ref>

Although all cells in the green parts of a plant have chloroplasts, the majority of those are found in specially adapted structures called [[leaf|leaves]]. Certain species adapted to conditions of strong sunlight and [[arid]]ity, such as many ''[[Euphorbia]]'' and [[cactus]] species, have their main photosynthetic organs in their stems. The cells in the interior tissues of a leaf, called the [[mesophyll tissue|mesophyll]], can contain between 450,000 and 800,000 chloroplasts for every square millimeter of leaf. The surface of the leaf is coated with a water-resistant [[wax]]y [[Plant cuticle|cuticle]] that protects the leaf from excessive [[evaporation]] of water and decreases the absorption of [[ultraviolet]] or [[blue]] [[light]] to minimize [[heat]]ing. The transparent [[Leaf#Epidermis|epidermis]] layer allows light to pass through to the [[Mesophyll tissue|palisade]] mesophyll cells where most of the photosynthesis takes place.