Photosynthesis consists of two steps : in light reaction light energy is trapped to form ATP and in dark reaction carbon dioxide is reduced to form glucose, The dark reactions or Blackman's reactions or biosynthetic phase involves three steps: (i) Fixation of ${\mathrm{C}\mathrm{O}}_2$ , (ii) Reduction of ${\mathrm{C}\mathrm{O}}_2$ and (iii) Synthesis of glucose. It is independent of light but product of light reaction are consumed.