Editing Photosystem (section)

{{Short description|Structural units of protein involved in photosynthesis}}
'''Photosystems''' are functional and structural units of [[protein complex]]es involved in [[photosynthesis]]. Together they carry out the primary [[photochemistry]] of [[photosynthesis]]: the [[Absorption (electromagnetic radiation)|absorption of light]] and the transfer of [[Förster resonance energy transfer|energy]] and [[Electron transfer|electrons]]. Photosystems are found in the [[thylakoid membrane]]s of plants, algae, and cyanobacteria. These membranes are located inside the [[chloroplast]]s of plants and algae, and in the cytoplasmic membrane of photosynthetic bacteria. There are two kinds of photosystems: PSI and PSII.
[[File:Photosystem Model.jpg|center|thumb|650x650px|Model of a photosystem and how it uses light energy to carry out processes.]]
PSII will absorb red light, and PSI will absorb far-red light. Although photosynthetic activity will be detected when the photosystems are exposed to either red or far-red light, the photosynthetic activity will be the greatest when plants are exposed to both [[wavelength]]s of light. Studies have actually demonstrated that the two wavelengths together have a synergistic effect on the photosynthetic activity, rather than an additive one.<ref>{{Cite journal|date=2017-02-01|title=Far-red light is needed for efficient photochemistry and photosynthesis|journal=Journal of Plant Physiology|language=en|volume=209|pages=115–122|doi=10.1016/j.jplph.2016.12.004|issn=0176-1617|last1=Zhen|first1=Shuyang|last2=Van Iersel|first2=Marc W.|pmid=28039776|doi-access=free|bibcode=2017JPPhy.209..115Z }}</ref>[[Image:Thylakoid membrane 3.svg|thumb|400px|right|Light-dependent reactions of photosynthesis at the thylakoid membrane]]Each photosystem has two parts: a reaction center, where the photochemistry occurs, and an [[Light-harvesting complexes of green plants|antenna complex]], which surrounds the reaction center. The antenna complex contains hundreds of [[chlorophyll]] molecules which funnel the excitation energy to the center of the photosystem. At the reaction center, the energy will be trapped and transferred to produce a high energy molecule.<ref name=":0">{{Cite book|author=Taiz, Lincoln|url=http://worldcat.org/oclc/1035316853|title=Fundamentals of plant physiology|year=2018|publisher=Oxford University Press |isbn=978-1-60535-790-4|oclc=1035316853}}</ref>

The main function of PSII is to efficiently split water into oxygen molecules and protons. PSII will provide a steady stream of electrons to PSI, which will boost these in energy and transfer them to NADP{{sup|+}} and [[Hydronium|H{{sup|+}}]] to make [[Nicotinamide adenine dinucleotide phosphate|NADPH]]. The hydrogen from this NADPH can then be used in a number of different processes within the plant.<ref name=":0" />