Biology · Kingdom Protista

Blue-green algae or cyanobacteria also contain chlorophyll a, yellowish carotenoids, and blue-pigment phycobilins. Only the appearance of these pigments causes the blue-green colour of the algae. Chlorophyll is a true green pigment. Xanthophylls are yellow pigments. Carotene are yellow and orange pigments. Hence A, B and C are incorrect.

a) Chlorophyll: Chlorophyll is a green pigment found in plants and cyanobacteria (blue-green algae). It plays a key role in photosynthesis by capturing light energy and converting it into chemical energy. 

b) Xanthophyll: Xanthophylls are yellow pigments found in the chloroplasts of plant cells. They assist in capturing light energy and also help protect the plant from excess light. 

c) Carotene: Carotenes are orange pigments found in various plants and some photosynthetic bacteria. They are important in photosynthesis and serve as antioxidants. 

d) Phycobilin: Phycobilins are water-soluble pigments found in cyanobacteria (blue-green algae) and red algae. They help capture light energy and transfer it to chlorophyll during photosynthesis.