Light independent reaction

• The light independent reaction is also known as the Calvin Cycle
• LIR happens in the stroma of the chloroplast
• The stroma contains the enzyme RuBisCo, which catalyses the LIR
• LIR is temperature sensitive due to enzymes
• Uses CO2, reduced NADP and ATP
• LIR forms a hexose sugar
• ATP is hydrolysed to provide energy for the LIR
• Reduced NADP donates the hydrogen to reduce GP molecules
• Light independent reaction

  A) Rubisco

  B) CO2

  C) 2 GP molecules

  D) 2 TP molecules

  E) 2x 3C

  F) 2x 3C

  G) Hexose sugars, lipids, amino acids

  H) RuBP

  I) 5C

  J) ATP

  K) ADP

  L) 2 ATP

  M) 2 ADP

  N) 2 NADPH

  O) 2 NADP

  
• Light independent reaction

  1. CO2 reacts with RuBP to form 2 molecules of GP- catalysed by the enzyme RuBisCo
  2. GP is reduced to form TP using energy from ATP and accepting a hydrogen from reduced NADP
  3. Some of the carbon from TP leaves the cycle each turn and is converted into useful organic substances
  4. The rest of the molecule is used to regenerate RuBP with the energy from ATP
• Products of the LIR

  • Glucose (most common)
  • Disaccharides (sucrose)
  • Polysaccharides (cellulose and starch)
  • Glycerol (-> fatty acids)
• Limiting factors- anything that could reduce the rate of photosynthesis
• Limiting factors of the LIR

  • Temperature
  • CO2 concentration
  • Light intensity
• Knowledge of limiting factors is important in agriculture in order to know how to overcome them
• Farmers can provide artificial conditions to overcome limiting factors and promote optimum growth
• Limiting factors can be overcome by heating crops, buying lights, and burning wood for CO2, however all of these are expensive so a cost benefit analysis must be run