light absorption, which pigments are involved?
All photosynthetic organisms contain one or more organic pigments capable of absorbing visible radiation, which will initiate the photochemical reactions of photosynthesis. The three major classes of pigments found in plants and algae are the chlorophylls, the carotenoids and the phycobilins. Carotenoids and phycobilins are called accessory pigments since the quanta (packets of light) absorbed by these pigments can be transferred to chlorophyll. Chlorophylls chlorophyll a - present in all higher plants and algae chlorophyll b - present in all higher plants and green algae chlorophyll c - diatoms and brown algae chlorophyll d - red algae (chlorophyll a is present in all photosynthetic organisms that evolve O2.) Chlorophyll molecules contain a porphyrin 'head' and a phytol 'tail'. The polar (water-soluble) head is made up of a tetrapyrrole ring and a magnesium ion complexed with the nitrogen atoms of the ring. The phytol tail extends into the lipid layer of the thylakoid membrane. Carotenoids (carotenes and xanthophylls) Carotenes: -carotene - higher plants and most algae $-carotene - most plants some algae xanthophylls: luteol, fucoxanthol and violaxanthol Carotenoids contain a conjugated double bond system of the polyene type (C-C=C-C=C). Energy absorbed by carotenoids may be transferred to chlorophyll a for photosynthesis. Phycobilins (found mostly in red and blur-green algae): phycoerythrin phycocyanin allophycocyanin )
