Question

The role of phycobilins in photosynthesis is to
A. Absorb and transfer energy to chlorophyll
B. Donate electrons to the electron transport system
C. Fix carbon dioxide
D. Carry hydrogen or electrons

Answer 1

Photosynthesis needs light to be absorbed first then the light is used to make food in autotrophic organisms. Phycobilins are the accessory photosynthetic pigment. They do not directly help in photosynthesis.

Complete answer: Chlorophyll is the main primary photosynthetic pigment in plants and many organisms. These photosynthetic pigments help in the absorption of light energy to synthesize complex organic material from an inorganic supply of nutrients.
-There are some pigments that do not directly participate in photosynthesis but are important in a photoautotroph. Photoautotrophs are organisms which require light to prepare their own food. These organisms have additional pigments called accessory pigments. Some examples of accessory pigments are carotenoids and phycobilins. These pigments transfer light energy to the primary pigment (chlorophyll).
-Phycobilins are found in red algae (eukaryotes), cyanobacteria, and also cryptomonads. These are photoautotrophs and transfer the light absorbed from the sun to their primary pigment. In eukaryotes, these are found in the stroma of the chloroplast. In prokaryotes, they are found in the cytoplasm of the cell. This absorbed light energy is important for photosynthesis and thus, these are important.
-Phycobilins are characterized by other accessory pigments by their water solubility. Phycobilins are water-soluble while carotenoids are water-insoluble. Phycobilins are linked to proteins that assist their absorption of light and are known as phycobiliproteins. They act as chromophores. Some examples of phycobiliproteins are phycocyanin, phycoerythrin, etc.
Thus, phycobilins absorb the light and transfer the energy to their primary pigments, chlorophyll. The correct option is A.

Note: The phycobilins are not the primary pigments in the photoautotrophs. The proteins associated with them help them to get soluble in water. They absorb wavelengths of light which are not greatly absorbed by the green pigment (chlorophyll).