Photosynthesis: light-dependent reactions

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In the light dependent reactions:

  • light energy is trapped
  • ATP is synthesised in photophosphorylation
  • water is split by photolysis to give hydrogen ions (H+) that reduce the hydrogen carrier molecule NADP and electrons that pass to chlorophyll.

Oxygen is a waste product of photolysis.

Light energy is trapped in the chloroplast lamellae by photosynthetic pigments that are either:

  • chlorophylls e.g. a and b
  • carotenoids e.g. B-carotene and xanthophyll

Different pigments absorb different wavelengths of light and the absorbance can be plotted on its absorption spectrum. The effectiveness of the different wavelengths of light in promoting photosynthesis can be shown as an action spectrum.

The photosynthetic pigments are arranged as photosystems in the chloroplast lamellae.

A photosystem contains:

  • a central primary pigment molecule (P), which is one of two forms of chlorophyll a with

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