LIR and limiting factors

• Light independent reaction (LIR)

  - Calvin cycle

  - Uses CO2, reduced NADP and ATP to form hexose sugar

  - Occurs in stroma which contains the enzyme Rubisco

  - Temperature-sensitive
• Calvin cycle

  
• RuBP


  - Ribulose biphosphate

  - A five-carbon molecule
• GP


  - Glycerate-3-phosphate

  - A 3-carbon molecule
• TP


  - Triose phosphate

  - 3-carbon molecule
• Producing hexose sugar in LIR

  - Takes 6 cycles

  - Glucose can join to form disaccharides (sucrose) or polysaccharides (cellulose)

  - Can be converted to glycerol to combine with fatty acids to make lipids
• Limiting factors


  - A factor which, if increased, the rate of the overall reaction also increase
• Limiting factors of photosynthesis

  - Light intensity

  - Carbon dioxide concentration

  - Temperature
• How light intensity limits photosynthesis?

  - If reduced, levels of ATP and reduced NADP would fall

  - LDR limited - less photolysis and photoionization

  -GP cannot be reduced to TP in LIR

  
• How temperature limits photosynthesis?

  -LIR inhibited-enzyme controlled (Rubisco)

  - Up to optimum, more collisions and E-S complexes

  - Above optimum, H bonds in tertiary structure break, active site changes shape - denatured
• How CO2 concentration limits photosynthesis?

  - If reduced, LIR inhibited

  - Less CO2 to combine with RuBP to form GP

  - Less GP reduced to TP

  - Less TP converted to hexose and RuBP regenerate
• Agricultural practices to maximise plant growth

  - Growing plants under artificial lighting to maximise light intensity

  - Heating in greenhouse to increase temperature

  - Burning fuel to release CO2
• Benefit of agricultural practices for plant growth


  - Faster production of glucose -> faster respiration

  - More ATP to provide energy for growth e.g. cell division + protein synthesis

  - Higher yields so more profit
• Products of LIR


  glucose, ADP, NADP