The photosynthetic pigments are all fat-soluble to some degree, and therefore are embedded in the thylakoid membrane. It consists of a hydrophobic tail that is imbedded in the thylakoid membrane of the chloroplast, and a tetrapyrrole ring consisting of four smaller pyrrole rings, each with four carbon atoms and one nitrogen atom. Together, the four pyrrole rings sequester a magnesium atom . Chlorophyll a has two peaks of light absorption , one at 430, in the violet-blue range, and the other at 662 nm, in the red range. The action spectrum for photosynthesis , or the range of light wavelengths that result in significant photosynthesis, does not precisely match the absorption spectrum of chlorophyll a, which suggests the involvement of other pigments .
Plants usually contain about half as much chl b as chl a.
The other important accessory pigments are the carotenoids , which are red, orange, and yellow in color. The maximum absorption of the carotenoids is between 460 and 550, in the blue and green range. The carotenoids are entirely fat-soluble, and are therefore fully embedded in the membrane. When the absorption spectra for chl a and the accessory pigments involved in photosynthesis are overlaid, they approximate the action spectrum for photosynthesis. Light energy is captured by antennae complexes , groups of chloroplast pigments arranged in aggregates on thylakoid membranes , and consisting of about three hundred molecules of chlorophyll a and fifty molecules of carotenoids and chlorophyll b .