Emerson’s effect and pigment systems

what is Emerson’s effect and pigment system? :- Robert Emerson (1932,58) Studied the quantum Yield in a green alga named chlorella under different wavelength of monochromatic light beam only one type of wavelength of light was given to green plant at a time. They observed that in tha monochromatic light beam of wavelength of more than 680 nm, there is a sudden drop in tha quantum yield i.e., the rate of photosynthesis is reduced. Since, this wavelength is related with red region of visible spectrum, hence, this phenomenon is called ‘Red Drop.’

Emerson and his Co-Workers, further extended the previous experiment and observed that the quantum yield is enhanced, if monochromatic light of longer wavelength (Above680nm) and shorter wavelengths (Below 680nm) were given simultaneously to Chlorella. This enhancement of quantum yield in photosynthesis is called Emerson’s enhancement effect.

Pigment System

The discovery of red drop and Emerson’s enhancement effect clearly indicated that at least two group of pigment are present for the absorption of light. These group of pigment are called pigment system or Photosystems. They are also called pigment system-I (PS-I) and pigment system -II (PS-II)

  • Pigment System-I (PS-I): –

It has a special type of chlorophyll-a molecule called P P700 is the reaction center of pigment system-I .it is surrounded by other chal-a, chl-b and carotenoid molecules. It absorbs light both wavelength shorter as well as longer than 680 nm. It takes part in both cycle and non-cycle photophosphorylation. In cyclic photophosphorylation, the pigment system-I takes part independently.

  • Pigment system-II (PS-II): –

The pigment system-II (PS-II) also has a special chlorophyll-a molecule called P P680 is the reaction Centre of Ps-II. It is also surrounded by other chl-a, chl-b and carotenoid molecules. It absorbs light of wavelength shorter than 680 nm only. it takes part in non-cycle photophosphorylation along with PS-I

All the pigment system of pigment system is in contact with one another. the energy absorbed by each pigment is received by reaction Centre (P700or P680) of pigment system which alone take part in further light reaction.

Difference between pigment system-I and pigment system-II

         Pigment system-I                Pigment system-II
Its reaction Centre is P700. Its reaction Centre is P680.
Both wavelength of light, shorter and longer than 680nm are absorbed by it. Only wavelength of light shorter than 680 m, are absorbed by it.
It is located on the outer surface of thylakoid. It is located on the inner surface of thylakoid.
Molecular oxygen is not released in this system. Molecular oxygen is released by the photolysis of water in this system.
It is involved both in cyclic and non-cyclic photophosphorylation It is involved only is non-cyclic photophosphorylation.