EXPERIMENTAL FIGURE 12-40 The rate of photosynthesis is greatest at the wavelengths of light absorbed by three plant pigments. The action spectrum of photosynthesis in plants (the relative ability of light of different wavelengths to support photosynthesis) is shown in black. The energy from light can be converted into ATP only if it can be absorbed by pigments in the chloroplast. Absorption spectra (showing how well light of different wavelengths is absorbed) for three photosynthetic pigments present in the antennas of plant photosystems are shown in color. Comparison of the action spectrum of photosynthesis with the individual absorption spectra of these pigments suggests that photosynthesis at 680 nm is primarily due to light absorbed by chlorophyll a; at 650 nm, to light absorbed by chlorophyll b; and at shorter wavelengths, to light absorbed by chlorophylls a and b and by carotenoid pigments, including β-carotene.