what are light and dark reactions.where do they occur in plants name the parts and full chemical equation and detail about light and dark reactions

Asked by dakmayank17 | 16th Aug, 2015, 04:16: PM

Expert Answer:

Photosynthesis takes place in two stages:

  • Light reaction
  • Dark reaction

Light reaction:

  • The light reaction of photosynthesis occurs only in the presence of sunlight in the thylakoid membranes of grana and stroma lamellae.
  • It mainly involves absorption of sunlight by the pigments of photosystems and the conversion of their energy into usable chemical energy in the form of ATP and NADPH + H+.
  • Light reaction is also called the photochemical reaction or Hill reaction or photophosphorylation.

Steps in light reaction:

  • Absorption of Light
  • Excitation of Reaction Centres
  • Photosynthetic Electron Transport and Formation of Assimilatory Power
  • Photophosphorylation

Chemical equation:

begin mathsize 11px style 2 straight H subscript 2 straight O space plus space 2 NADP to the power of plus space plus space nADP space plus space nPi space plus space hv space rightwards arrow space straight O subscript 2 space plus space 2 NADPH space plus space 2 straight H to the power of plus space plus space nATP end style

Dark reaction:

  • The dark reaction is the second phase of photosynthesis which occurs in the stroma of chloroplasts.
  • The reaction is also known as the biosynthetic phase or Blackman’s reaction or carbon dioxide fixation or Calvin cycle.
  • It uses ATP and NADPH2 for the fixation and reduction of CO2 to form carbohydrates.
  • The dark reaction is independent of light and may take place in the light or dark without the use of light energy.
  • In the dark reaction, CO2 is reduced to carbohydrates in the form of sugar.

Steps in dark reaction:

  • Carboxylation to form 3-phosphoglyceric acid (PGA).
  • Reduction to form carbohydrates using ATP and NADPH
  • Regeneration to form ribulose 1,5-biphosphate

Chemical equation:

begin mathsize 11px style 6 CO subscript 2 space end subscript plus space 6 RuBP space plus space 18 ATP space plus space 12 NADPH space rightwards arrow with space Enzymes on top space straight C subscript 6 straight H subscript 12 straight O subscript 6 space plus space 6 RuBP space plus space 18 ADP space plus space 18 Pi left parenthesis straight H subscript 3 PO subscript 4 right parenthesis space plus space 12 NADP to the power of plus end style

Answered by Sheetal Kolte | 17th Aug, 2015, 11:14: AM