Which pigments contribute to photosynthesis and why is pigment diversity important?

• A. Carotenoids; they broaden light absorption spectra and provide photoprotection against excess light.
• B. Carotenoids only; they perform all functions.
• C. Chlorophyll a only; other pigments are nonfunctional.
• D. Phycobilins; they are the primary light-harvesting pigments in higher plants.

Answer: (B)

Pigments beyond the main chlorophyll a are there to broaden the range of light that plants can use and to keep the photosynthetic machinery safe. Chlorophyll a does the core job of capturing light and driving the chemical reactions, but it doesn’t absorb every wavelength equally. Carotenoids step in as accessory pigments, soaking up light in wavelengths where chlorophylls are weaker and then transferring that energy to the reaction centers. They also help protect the system by quenching excess energy and neutralizing reactive oxygen species that can form under bright light.

This diversity matters because natural light varies a lot—cloud cover, shade, and leaf age change the spectral quality reaching the chloroplasts. Having multiple pigments ensures more of the available light is harvested efficiently and that the damage from too much light is mitigated. In higher plants, chlorophylls stay central for the actual photochemistry, while carotenoids support and safeguard that process. Phycobilins, meanwhile, are used by some algae and cyanobacteria, not by higher plants.