BIOLOGY Volume 1 - A Guide to General Biology - 2004

7. AUTOTROPHIC NUTRITION

7.5. Photosynthetic Pigments

7.5.2. Carotenoids

Carotenoids are yellow, orange, red, or brown pigments that strongly absorb light in the blue-violet region. They are referred to as accessory pigments because they transfer the light energy they capture to chlorophyll. The absorption spectrum of carotenoids (Fig. 7.9) exhibits three peaks in the blue-violet region. In addition to acting as accessory pigments, carotenoids protect chlorophylls from excess light and photooxidation by oxygen produced during Photosynthesis. They are normally masked by green chlorophylls, but become visible in leaves before leaf fall begins, as chlorophylls break down first. Carotenoids are also found in certain flowers and fruits, where their bright coloration attracts insects, birds, and mammals, thereby ensuring successful pollination and seed dispersal; for instance, the red Skin color of tomatoes is due to the presence of carotenes.

Carotenoids are divided into two types: carotenes and xanthophylls. The most widespread and important carotene is p-carotene, well known as the orange pigment of carrots. In vertebrate Digestion, this pigment is cleaved into two vitamin A molecules.