Chloroplast Pigments (CIE A Level Biology)

• Chloroplasts contain several different photosynthetic pigments within the thylakoids, which absorb different wavelengths of light
  • In places, these thylakoids stack up to form structures known as grana (singular – granum)
  • The thylakoid membrane system provides a large number of pigment molecules in an arrangement that ensures as much light as necessary is absorbed
  • The pigment molecules are arranged in light-harvesting clusters known as photosystems
  • In a photosystem, the different pigment molecules are arranged in funnel-like structures in the thylakoid membrane (each pigment molecule passes energy down to the next pigment molecule in the cluster until it reaches the primary pigment reaction centre)

• The light-dependent stage of photosynthesis occurs in the thylakoid membranes and the thylakoid spaces (the spaces inside the thylakoids)
• This is why the thylakoid membranes contain the pigments, enzymes and electron carriers required for the light-dependent reactions

An example of a photosystem in a chloroplast thylakoid membrane: a light-harvesting cluster of photosynthetic pigments involved in the light-dependent stage of photosynthesis

• There are two groups of pigments
  • Chlorophylls
    • Chlorophyll a and b
  • Carotenoids
    • Carotene and xanthophyll

Chloroplast pigments table

• Chlorophylls absorb wavelengths in the blue-violet and red regions of the light spectrum
  • They reflect green light, causing plants to appear green

• Carotenoids absorb wavelengths of light mainly in the blue-violet region of the spectrum