A.
In addition to chlorophylls, thylakoid membranes contain secondary lightabsorbing pigments, or accessory pigments, called carotenoids.
B.
Carotenoids may be yellow, red, or purple. The most important are β-carotene, which is a red-orange isoprenoid, and the yellow carotenoid lutein.
C.
The carotenoids absorb light at wavelengths not absorbed by the chlorophylls and thus are supplementary light receptors.
D.
They also protect downstream components from a highly reactive form of oxygen (singlet oxygen) that is formed when intense light exceeds the system’s capacity to accept electrons.