The correct answer to the question “The light-harvesting pigment NOT used by Cyanobacteria for photosynthesis is” is (A) Rhodopsin. Cyanobacteria rely on phycobilins as key accessory pigments in their phycobilisomes for efficient light capture.​

Correct Answer

Rhodopsin serves as a light-sensitive protein in archaea and animals for phototaxis and vision, but cyanobacteria do not employ it in photosynthesis. Instead, they use chlorophyll a alongside phycobiliproteins for oxygenic photosynthesis.​

Option Explanations

• (A) Rhodopsin: This retinal-based pigment enables light detection in halophilic archaea and eukaryotes but plays no role in cyanobacterial light harvesting.​

• (B) Phycobilin: These water-soluble tetrapyrrole pigments form phycobilisomes in cyanobacteria, optimizing light absorption in low-light aquatic environments.​

• (C) Phycoerythrobilin: A red-absorbing phycobilin bound to phycoerythrin in cyanobacteria, aiding complementary chromatic adaptation.​

• (D) Phycocyanobilin: A blue-absorbing phycobilin attached to phycocyanin, crucial for transferring energy to photosystem II in cyanobacteria.​