CIE A Level Biology

Revision Notes

Syllabus Edition

First teaching 2020

Last exams 2024

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13.1.4 Chloroplast Pigments

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Chloroplast Pigments

  • 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

Thylakoid membrane photosystem, downloadable AS & A Level Biology revision notes

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

Chloroplast Pigments Table, downloadable AS & A Level Biology revision notes 

  • 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

Exam Tip

Remember – the pigments themselves have colour (as described in the table). This is different from the colours of light that they absorb.

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