Photosynthetic pigments


The role of pigments is to absorb light energy, converting it into chemical energy.  They are found on the chloroplast membranes and the chloroplasts are arranged in the cells so that their membranes are at right-angles to the light source to maximize light absorption.  In most plants, the photosynthetic pigments can be grouped into two classes; the chlorophylls and the carotenoids.

Within the main classes, there are several slightly different pigments, which each absorb light of slightly different frequencies.  This allows the plant to make use of a broad frequency spectrum.  Details of the different pigments are given in the table below.

Class of pigment with examples Color Distribution
Chlorophylls
chlorophyll a yellow-green All photosynthetic organisms except some photosynthetic bacteria
chlorophyll b blue-green Higher plants and green algae
chlorophyll c green Brown algae, and a few unicellular algae including diatoms
chlorophyll d green Some red algae
bacteriochlorophylls a-d pale blue Photosynthetic bacteria
 
Carotenoids carotenes and xanthophylls
Carotenes
beta-carotene orange All photosynthetic organisms except photosynthetic bacteria
 
Xanthophylls (carotenols)
Great variety all yellow Fucoxanthin helps give brown algae their color. It has a very broad absorption spectrum.