In oxygenic photosynthesis, what is the primary role of accessory pigments (e.g., chlorophyll b and carotenoids) in light harvesting?

• A. They serve as the terminal electron acceptors of the photosynthetic electron transport chain.
• B. They broaden the range of wavelengths absorbed and transfer excitation energy to chlorophyll a in the reaction center.
• C. They directly split water to release $O_2$ in photosystem II.
• D. They catalyze the fixation of $C_{O}2$ into sugars during the Calvin cycle.

Answer: (B)

Verified step by step guidance

1. Understand that accessory pigments, such as chlorophyll b and carotenoids, are molecules that absorb light energy at different wavelengths than chlorophyll a.
2. Recognize that the primary function of these accessory pigments is to capture a broader spectrum of light, which increases the efficiency of light harvesting during photosynthesis.
3. Know that after absorbing light energy, accessory pigments transfer this excitation energy to chlorophyll a molecules located in the reaction center of the photosystem.
4. Recall that chlorophyll a is the pigment directly involved in the photochemical reactions that convert light energy into chemical energy.
5. Conclude that accessory pigments do not participate directly in electron transport, water splitting, or carbon fixation, but instead enhance the light absorption capacity of the photosynthetic apparatus.