Limiting factors

• Temperature

  • Rate of photosynthesis increases as temp increases up to an optimum, decreases after

  • Limits light independent reaction as it’s enzyme controlled (rubisco)

  • Increasing temp up to optimum…

  • More Ek.

  • More E-S complexes (rubisco).

  • Above optimum…

  • H bonds in tertiary structure break active site changes shape / enzyme denatured (rubisco)

  • Fewer E-S complexes
• Light intensity

  • Rate of photosynthesis increases as light intensity increases (then plateaus)

  • If light intensity was dramatically reduced …

  • Levels of ATP and reduced NADP would fall, because…

  • Light dependent reaction limited as less photoionisation of chlorophyll (and less photolysis)

  • So, the light independent reaction would also slow/stop…

  • GP can’t be reduced to TP (requires ATP and reduced NADP)

  • TP can’t regenerate RuBP (requires ATP)
• CO 2 concentration

  • Rate of photosynthesis increases as CO 2 conc increases (then plateaus)

  • If carbon dioxide concentration dramatically decreased…

  • Limits light independent reaction

  • Less CO 2 to combine with RuBP to form GP

  • Less GP reduced to TP

  • Less TP (and GP) converted to organic substances e.g.

  hexose and to regenerate RuBP
• Common agricultural practices used to overcome the effect of these limiting factors

  • You might be asked to evaluate data relating to common agricultural practices used to overcome the effect of these limiting factors

  • For example, growing plants under artificial lighting to maximise light intensity, or heating a greenhouse to increase the temperature and burning fuel, such as paraffin burners, to release more carbon dioxide
• If limiting factors are minimal, rate of photosynthesis will increase, so:

  Faster production of glucose allowing faster respiration.

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

  Higher yield so more profit.