Light Absorbing Pigments

In order to capture energy from light, cells need pigments that absorb light efficiently in the visible and near-infrared portions of the spectrum. The light absorbing portions of these pigments are called chromophores. Structures of a few common chromophores are shown in Figure 17.7. Figure 17.8 shows that chromophores absorb light that completely spans the visible spectrum.

Chlorophyll a and chlorophyll b are the most abundant pigments in higher plants. Both pigments are related to protoporphyrin IX of hemoglobin and myoglobin. One important difference is that the metal bound in chlorophylls is Mg2+ versus Fe2+ in the blood proteins.

Chlorophylls are located in the thylakoid membranes of the chloroplast.

Chlorophylls a and b absorb deep blue and red light strongly (Figure 17.8). The reflected light (the light not absorbed) is (green) and is what we see when we look at most plants. The other colors of plants arise from the colors of accessory pigments. Loss of chlorophylls in the autumn allows the accessory pigments (and nonphotosynthetic pigments) of leaves to become apparent.

Some photosynthetic bacteria use pigments that absorb wavelengths in the near infrared portion of the spectrum.

See also: Light Gathering Structures, Energy of Light, The Chloroplast, Photosystem II, Photosystem I, Thylakoid Membranes, Porphyrin and Heme Metabolism (from Chapter 21)

INTERNET LINK: Photosynthetic Pigments