Question

Characteristic pigment of cyanobacteria is
a. Fucoxanthin
b. Anthoxanthin
c. Chlorophyll C
d. Phycocyanin

Answer 1

Hint: Cyanobacteria are commonly known as blue-green algae because of its appearance. These bacteria are photosynthetic in nature, which means they produce their own food in the presence of sunlight. Cyanobacteria include both free-living bacteria and endosymbiotic plastids.

Complete answer:
Cyanobacteria are prokaryotic bacteria found mostly in freshwater as well as terrestrial habitat. Photosynthesis is performed in thylakoids which are flattened structures present in chloroplast. Cyanobacteria possess a pigment Phycocyanin which is a blue photosynthetic pigment. This pigment is produced by cyanobacteria as a phycobiliprotein complex. It gives the cyanobacteria its characteristic bluish colour. Phycocyanin is a Greek word, ‘psycho’ means algae, and ‘cyanin’ stands for the blue colour also called ‘cyan’.

Hence, the correct answer is option (D).

Additional information:
Phycocyanin is an accessory pigment for chlorophyll and is usually soluble in water. It is a protein complex produced in the phycobiliprotein family. Phycobiliproteins have fluorescent property and they are also used in immuno-assay kits for performing experiments. They group together as clusters and stick to the membrane called a phycobilisome. Phycolibiproteins has two subunits – alpha and beta.

Phycocyanin absorbs light in the range of approximately 620 nm (red and orange), and emits a fluorescence at 650 nm. Thus phycocyanin fluorescence is also used to check cyanobacteria biomass in a water sample. C-phycocyanin is a type of phycocyanin which is stable at hot springs (upto 70 °C).

Note: Cyanobacteria are both beneficial and harmful for humans. Some of these bacteria produce cyanotoxins that are poisonous and thus harmful for not only humans but animals as well. Although some cyanobacteria are also used in production of bioethanol, supplements for dietary and food colourings.