In photosynthesis, which pigment primarily absorbs light for photosystem II?

• A. Chlorophyll b
• B. Carotenoids
• C. Phycobilins
• D. Chlorophyll a

Answer: (D)

Chlorophyll a serves as the main light-absorbing pigment in photosystem II. The reaction center of PSII contains a special pair of chlorophyll a molecules (P680) that directly capture photons and kick off the electron transfer chain. Other pigments, such as chlorophyll b, carotenoids, and phycobilins, act as antenna pigments that broaden the range of light detected and funnel that energy toward chlorophyll a, but they don’t drive the primary charge separation themselves. Chlorophyll b helps harvest additional light and transfers energy to chlorophyll a; carotenoids extend absorption and provide photoprotection; phycobilins serve as supplementary antenna pigments in some organisms and also feed energy into the chlorophyll a pool. So, the pigment that primarily absorbs light for photosystem II is chlorophyll a.