The different type of photosynthetic pigments and their roles are as follows :
(1) Chlorophylls : The chlorophylls are most abundant and important pigments of plants . They are green pigments soluble in organic solvent and insoluble in water.
The chlorophylls are of seven types, viz., chlorophyll-a, chklorophyll-b, chlorophyll-c, chlorophyll-d, chlorophyll-e , bacterio-chlorophyll and bacterioviridin. Of these chlorophyll -a, chlorophyll b. chlorophyll-c, chlorophyll-d and chlorophyll-e are most important.
(i) Chlorophyll -a : :Chlorophyll -a is blue green in colour. Its chemical formula is `C_(55)H_(72)N_(4)Mg.` With the exception of photosyn- thetic becteria, chlorophyll-a is found in all photosynthetic organisms.
The pigment chlorophyll-a is considered as an essential pigment as it converts the light energy into chemical energy.
(ii ) Chloropohyll-b : Chlorophyll-b is yellow green in colour. Its chemical formula is `C_(55)H_(70)O_(6)N_(4)Mg`. It is found in higher plants such as green algae, bryophytes and all vascular plants. The pigment chlorophyll-b absorbs and transfers the light energy to chloropohyll-a. Hence it is called an accessory pigment.
(iii ) Chlorophyll-c, d and e. These are found in brown and red algae in association with chlorophyll-a.
(2) Carotenoids : Carotenoids are widely distributed in chloroplasts and chromoplasts. There are two types of carotenoids, viz., carotenes and xanthophylls. Carotenes are orange yellow in colour while xanthophylls are yellow in colour. The major carotene is `beta` carotene.
Carotenoids absorb blue violet light and transfer it to chlorophyll-a and as such function as accessory pigments. Besides, carotenoids protect chlorophyll-a from photoxidation.
(3) Phycobillins : Phycobillins are accessory pigments found in red algae and cyanobacteria. They are of two types, viz., phycocyanin and phycoerythrin.
