Lesson 4 of 12 · 7 min
Pigments involved in photosynthesis
NCERT §11.4
Crush a rice leaf in a mortar with a little alcohol and run it up a strip of chromatography paper, and the single 'green' turns out to be at least four different colours climbing at four different speeds.
The lesson in notes
In short
Separating leaf pigments by paper chromatography reveals four of them: chlorophyll a (bright or blue-green), chlorophyll b (yellow-green), carotenoids (yellow to yellow-orange) and xanthophylls (yellow).
Chlorophyll a is the chief pigment of photosynthesis.
An absorption spectrum shows chlorophyll a absorbs most strongly in the blue and red regions of light.
The action spectrum (rate of photosynthesis versus wavelength) peaks in the blue and red regions too, and roughly matches the absorption spectrum of chlorophyll a, confirming most photosynthesis occurs in blue and red light.
Some photosynthesis also occurs at other visible wavelengths because accessory pigments (chlorophyll b, xanthophylls, carotenoids) absorb them and pass the energy to chlorophyll a.
Accessory pigments widen the range of usable wavelengths and also protect chlorophyll a from photo-oxidation.