Thus when white light shines on chlorophyll-containing structures like leaves, green light is transmitted and reflected and the structures appear green. Carotenoids Chloroplasts also contain carotenoids. These are also pigments with colors ranging from red to yellow. Carotenoids absorb light most strongly in the blue portion of the spectrum. They thus enable the chloroplast to trap are larger fraction of the radiant energy falling on it.
Carotenoids are often the major pigments in flowers and fruits .
The red of a ripe tomato and the orange of a carrot are produced by their carotenoids. In leaves, the carotenoids are usually masked by the chlorophylls. In the autumn, as the quantity of chlorophyll in the leaf declines, the carotenoids become visible and produce the yellows and reds of autumn foliage. The figure below shows the structure of beta-carotene , one of the most abundant carotenoids. Note again the system of alternating single and double bonds that in this molecule runs along the hydrocarbon chain that connects the two benzene rings.