Class 11 Biology Photosynthesis In Higher Plants Use of ATP and NADPH

Use of ATP and NADPH

  • The phase in which O2 diffuses out of the chloroplast while ATP and NADPH are used to drive the processes leading to the synthesis of sugar is called biosynthetic phase of photosynthesis.
  • Biosynthetic phase does not directly depend on the presence of light but is dependent on the products of the light reaction, i.e., ATP and NADPH, besides CO2 and H2
  • CO2 is combined with H2O to produce sugars.
  • The use of radioactive 14C by Melvin Calvin in algal photosynthesis studies led to the discovery that the first CO2 fixation product was a 3-carbon organic acid.
  • Calvin worked out the complete biosynthetic pathway; hence, it was called Calvin cycle.
  • The first product identified was 3-phosphoglyceric acid (PGA).
  • Another experiment on another plant discovered oxaloacetic acid or OAA as the first stable product of photosynthesis.
  • CO2 assimilation during photosynthesis was said to be of two main types:
  • those plants in which the first product of CO2 fixation is a C3 acid (PGA), i.e., the C3 pathway,
  • the plants in which the first product was a C4 acid (OAA), i.e., the C4



Fig. C3 pathway

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