Q.Apart from chlorophyll, algae have several other pigments in their chloroplast. What pigments are found in blue-green, red and brown algae that are responsible for their characteristic colours?

Besides chlorophyll, algae contain additional pigments that give different algal groups their characteristic colours.

• Blue-green algae (Cyanophyceae): contain chlorophyll a together with the blue pigment phycocyanin; the combination of the green chlorophyll and the blue phycocyanin gives these algae their distinctive blue-green colour.
• Red algae (Rhodophyceae): contain the red pigment phycoerythrin, which dominates over their chlorophyll and other pigments to give them their red colour. …

All algae contain chlorophyll and are photosynthetic, but many groups also contain additional, accessory pigments in their chloroplasts. These accessory pigments can be present in large enough amounts to mask the underlying green of chlorophyll, which is why different groups of algae look so different in colour even though all of them photosynthesise using chlorophyll.

Blue-green algae (Cyanophyceae / cyanobacteria) contain chlorophyll a as their main photosynthetic pigment, along with the accessory pigment phycocyanin, a blue-coloured pigment belonging to the phycobilin group. The combined effect of the green chlorophyll a and the blue phycocyanin is what produces the characteristic blue-green colour these algae are named for.

Red algae (Rhodophyceae) owe their colour mainly to phycoerythrin, a red-coloured phycobilin pigment. Phycoerythrin is present in large enough quantity to dominate over chlorophyll and any other pigments present, giving red algae their typical red colour — this pigment is also useful to the algae because it can absorb the blue-green light that penetrates to greater ocean depths, where red algae are commonly found. …