Which one of the following is not a function of the pigment carotenoid ?

Carotenoids are accessory pigments found in plants and some microorganisms. The correct answer is (D) because the reaction centre in a photosynthetic pigment system (Photosystem I or II) is always composed of a specific pair of chlorophyll a molecules. Carotenoids act as antenna pigments that harvest light energy and transfer it to the reaction centre, but they do not serve as the centre themselves.

• Option A: Carotenoids are responsible for the yellow-orange hues of autumn leaves, which become visible as green chlorophyll degrades.
• Option B: They perform a vital role in photoprotection, shielding chlorophyll from damage caused by photo-oxidation.
• Option C: In the human body, specific carotenoids like lutein and zeaxanthin accumulate in the retina, providing a photoprotective role by filtering harmful blue light and acting as antioxidants.