CIE A Level Biology (9700) 2019-2021

Revision Notes

13.1.4 Absorption Spectra & Action Spectra

Absorption Spectra & Action Spectra

  • An absorption spectrum is a graph that shows the absorbance of different wavelengths of light by a particular pigment
  • Chlorophylls absorb wavelengths in the blue-violet and red regions of the light spectrum
  • Carotenoids absorb wavelengths of light mainly in the blue-violet region of the spectrum
  • An action spectrum is a graph that shows the rate of photosynthesis at different wavelengths of light
  • The rate of photosynthesis is highest at the blue-violet and red regions of the light spectrum, as these are the wavelengths of light that plants can absorb (ie. the wavelengths of light that chlorophylls and carotenoids can absorb)
  • There is a strong correlation between the cumulative absorption spectra of all pigments and the action spectrum:
    • Both graphs have two main peaks – at the blue-violet region and the red region of the light spectrum
    • Both graphs have a trough in the green-yellow region of the light spectrum

Author:

Alistair graduated from Oxford University in 2014 with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems and Societies.
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