Chloroplasts contain several photosynthetic pigments, molecules that absorb particular wavelengths of light. A mixture of pigments lets the plant use a wider range of wavelengths than any single pigment could.The main pigments are:
• Chlorophyll a: the primary pigment. It is found in the reaction centres of the photosystems, where absorbed light energy excites electrons that drive the light-dependent reactions.
• Chlorophyll b: an accessory pigment with a slightly different structure, absorbing slightly different wavelengths.
• Carotenoids (carotene and xanthophylls): yellow and orange accessory pigments that absorb blue-violet light. They also protect chlorophyll from damage by excess light.Accessory pigments absorb wavelengths that chlorophyll a absorbs poorly and pass the energy on to chlorophyll a.Chlorophylls absorb mainly red and blue-violet light. Green light is mostly reflected or transmitted, which is why leaves look green.
A chlorophyll molecule has two parts:
• a flat porphyrin ring with a magnesium ion at its centre, which absorbs light;
• a long hydrocarbon tail, which anchors the molecule in the thylakoid membrane.Because magnesium is part of chlorophyll, a plant growing in soil lacking magnesium ions cannot make enough chlorophyll, and its leaves turn yellow. This is called chlorosis.In autumn, many trees break down their chlorophyll, revealing the yellow and orange carotenoids that were there all along.
• Chlorophyll a: the primary pigment. It is found in the reaction centres of the photosystems, where absorbed light energy excites electrons that drive the light-dependent reactions.
• Chlorophyll b: an accessory pigment with a slightly different structure, absorbing slightly different wavelengths.
• Carotenoids (carotene and xanthophylls): yellow and orange accessory pigments that absorb blue-violet light. They also protect chlorophyll from damage by excess light.Accessory pigments absorb wavelengths that chlorophyll a absorbs poorly and pass the energy on to chlorophyll a.Chlorophylls absorb mainly red and blue-violet light. Green light is mostly reflected or transmitted, which is why leaves look green.
A chlorophyll molecule has two parts:• a flat porphyrin ring with a magnesium ion at its centre, which absorbs light;
• a long hydrocarbon tail, which anchors the molecule in the thylakoid membrane.Because magnesium is part of chlorophyll, a plant growing in soil lacking magnesium ions cannot make enough chlorophyll, and its leaves turn yellow. This is called chlorosis.In autumn, many trees break down their chlorophyll, revealing the yellow and orange carotenoids that were there all along.