# Emerson effect

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{{Short description|Increase in the rate of photosynthesis after exposure to a certain light}}
{{refimprove|date=October 2011}}

The '''Emerson effect''' is the increase in the rate of [photosynthesis](/source/photosynthesis) after [chloroplasts](/source/chloroplasts) are exposed to light of wavelength less than 680&nbsp;nm (deep red spectrum) and more than 680 nm (far red spectrum). When simultaneously exposed to light of both wavelengths, the rate of photosynthesis is higher than the sum of the red light and far red light photosynthesis rates. The effect was early evidence that two [photosystem](/source/photosystem)s, processing different wavelengths, cooperate in photosynthesis.<ref name="govin">{{cite book|title=Photosynthesis|last2=Rabinowitch|first2=Eugene|date=1969|publisher=John Wiley & Sons, Inc.|isbn=0-471-70423-7|edition=1|location=New York City|page=[https://archive.org/details/photosynthesis0000rabi/page/172 172]|last1=Govindjee|url=https://archive.org/details/photosynthesis0000rabi/page/172}}</ref>

==History==
[Robert Emerson](/source/Robert_Emerson_(scientist)) described the eponymous effect in 1957.<ref>{{cite journal|last1=Emerson|first1=Robert|title=Dependence of yield of photosynthesis in long wave red on wavelength and intensity of supplementary light|journal=Science|date=1957|volume=125|pages=746}}</ref> In his paper he observed that:
# When plants are exposed to light having wavelength greater than 680&nbsp;nm, then only one photosystem is activated; i.e. [PS700](/source/photosystem_I) resulting in formation of ATP only.
# When plants are exposed to light having wavelength less than 680&nbsp;nm, the rate of photosynthesis was very low.
# On giving both shorter and higher wavelengths of light, the efficiency of the process increased, because both photosystems were working together at the same time, resulting in higher yield.

==Description==
When Emerson exposed green plants to differing [wavelengths](/source/Wave_length) of [light](/source/light), he noticed that at wavelengths of greater than 680&nbsp;nm the efficiency of [photosynthesis](/source/photosynthesis) decreased abruptly despite the fact that this is a region of the spectrum where chlorophyll still absorbs light ([chlorophyll](/source/chlorophyll) is the green [pigment](/source/pigment) in plants - it absorbs mainly the red and blue wavelengths from light). When the plants were exposed to short-wavelength light, (less than 660&nbsp;nm), the efficiency also decreased.
Emerson then exposed the plants to both short and long [wavelengths](/source/wavelengths) at the same time, causing the efficiency to increase greatly. He concluded that there must be two different [photosystem](/source/photosystem)s involved in [photosynthesis](/source/photosynthesis), one driven by short-[wavelength](/source/wavelength) light and one driven by long-wavelength ([PS1](/source/Photosystem_I) and [PS2](/source/Photosystem_II)). They work together to enhance efficiency and convert the light [energy](/source/energy) to forms that can be absorbed by the plant.<ref>plantphysiol.org</ref>

The light excites the [chlorophyll](/source/chlorophyll) molecules at the reaction centre and causes an increase in energy. As the [molecule](/source/molecule) becomes less excited, its energy is transported through a chain of [electron](/source/electron) carriers to the next [photosystem](/source/photosystem) which does much the same thing and produces energy-carrying [organic molecules](/source/organic_molecules).

==References==
{{Reflist}}

==External links==
*[http://botanydictionary.org/emerson-effect.html Emerson Effect at Botany Dictionary]
*[http://everything2.com/title/Emerson+Enhancement+Effect everything2.com]
*[http://www.plantphysiol.org/cgi/reprint/39/1/10.pdf Emersion Effect in details at Plantphysiol.org]

Category:Photosynthesis
Category:Biochemistry

{{photosynthesis-stub}}

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Adapted from the Wikipedia article [Emerson effect](https://en.wikipedia.org/wiki/Emerson_effect) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Emerson_effect?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.