Phycobiliproteins are complex proteins in cyanobacteria that absorb light energy. There are three different kinds of phycobiliprotein molecules used to pass light to chlorophyll: phycoerythrin is responsible for capturing green light, phycocyanin is responsible for capturing orange-red light, and allophycocyanin is responsible for capturing red light.



Since light can only penetrate to certain depths in oceans, phycobiliproteins capture the light available and pass it through various pathways of phycobiliproteins until the emitted light is red, which is absorbed by chlorophyll. Use the figure below to answer the following questions.



a. Explain the relationship between chlorophyll absorption and wavelength.

b. Justify the claim that photosynthetic organisms that live more than 75 feet below the surface of the ocean need phycoerythrin to survive. Provide reasoning that explains this claim.