Photosynthesis at different wavelengths. (a) The action spectrum of photosynthesis in plants; that is, the ability of light of different wavelengths to support photosynthesis. (b) The absorption spectra for three photosynthetic pigments: chlorophyll a, chlorophyll b, and b-carotene. Each spectrum shows how well light of different wavelengths is absorbed by one of the pigments. A comparison of the action spectrum with the individual absorption spectra suggests that photosynthesis at 680 nm is primarily due to light absorbed in the antenna complex by chlorophyll a; at 650 nm, to light absorbed by chlorophyll b; and at shorter wavelengths, to light absorbed by chlorophyll b and by carotenoid pigments, including b-carotene.

(figure and text (c) 2000 WIlliam Freeman Company)