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Photosynthesis

Site of the Light-Dependent Reaction

The light dependent reaction of photosynthesis takes place in the thylakoids of chloroplasts.
The thylakoids are disc like structures that are stacked together in groups called grana.

Chloroplasts are structurally adapted to their function of capturing sunlight and carrying out the light-dependent reaction of photosynthesis in the following ways:

  • The thylakoid membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the light-dependent reaction
  • A network of proteins in the grana hold the chlorophyll in a very precise manner that allows maximum absorption of light
  • The granal membranes have enzymes attached to them which help manufacture ATP
  • Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for the light dependent reaction

Site of the Light-Independent Reaction
The light-independent reaction of photosynthesis takes place in the stroma of the chloroplasts.

The chloroplast is adapted to carrying out the light-independent reaction of photosynthesis in the following ways:

  • The fluid of the stroma contains all the enzymes needed to carry out the light-independent reaction
  • The stroma fluid surrounds the grana and so the products of the light-dependent reaction in the grana can readily diffuse intro the stroma
  • It contains both DNA and ribosomes so it can quickly and easily manufacture some of the proteins needed for the light-independent reaction