Why some algae have red , …

Algae are mainly classified on the basis of their pigments. Flagellation, storage products and chemistry of cell wall are also taken into account. The three classes of algae are Chlorophyceae (green algae), Phaeophyceae (brown algae) and Rhodophyceae (red algae).

1. Chlorophyceae: The members of Chlorophyceae are commonly called green algae. The pigments, chlorophyll-a, chlorophyll-b, carotene and xanthophyll are present in them. They are usually grass green in colour due to the dominance of pigments i.e.chlorophyll a and b.
2. Phaeophyceae: The members of Phaeophyceae are commonly called brown algae. Brown algae are found primarily in marine habitats. They possess the pigments chlorophyll a and c, carotenoids and xanthophylls.
3. Rhodophyceae: The members of Rhodophyceae are commonly called Red Algae. The pigments present in them are r-phycoerythrin, r-phycocyanin, chlorophyll-a and chlorophyll-d. The characteristic red colour is due to the predominance of the red pigment r-phycoerythrin.