Limiting factors of photosynthesis

Requirements for photosynthesis

  • photosynthetic pigments

    • eg. chlorophyll

    • absorb light energy

  • carbon dioxide

    • provides carbon to make glucose

  • water

    • provides electrons and is a source of hydrogen ions

  • light

    • provides energy to:

      • split water

      • produce ATP

      • reduce NADP

  • suitable temperature

    • provides kinetic energy

Limiting factors

  • light intensity

  • carbon dioxide concentration

  • temperature

Light intensity

  • low light intensity

    • limits the light dependent stage so not much ATP and reduced NADP produced

    • less electrons are excited

    • slows the light dependent stage

    • rate of photosynthesis is low

  • intermediate light intensity

    • produces more ATP and reduced NADP in the light dependent stage

    • more electrons excited

    • photophosphorylation increases

    • in turn regenerates RuBP in light independent stage more quickly

    • more GP is converted to TP

    • rate of photosynthesis increases

  • very high light intensity

    • more light than needed

    • another factor becomes limiting

    • rate plateaus 

light intensitylight intensity and the Calvin cycle

Carbon dioxide concentration

  • low CO2 concentration

    • limits light independent reaction as less CO2 is fixed

    • reduces production if GP and TP

    • rate of photosynthesis is low

  • intermediate CO2 concentration

    • allows faster production of GP and TP

    • rate of photosynthesis increases

  • high CO2 concentration

    • another factor becomes limiting

    • graph plateaus

    • saturation point

CO2 concentration

Temperature

  • low temperature

    • provides little kinetic energy

    • slows enzyme catalysed stages

      • fixation of CO2 controlled by rubisco

    • rate of photosynthesis is low

  • intermediate temperature

    • increases kinetic energy supplied to these reactions

    • increases rate of photosynthesis up to optimum

  • very high temperature

    • denatures enzymes

    • rate of photosynthesis drops sharply

Temperature and relationship with light intensity

Water stress

  • when water is scarce - stomata close to prevent water loss

  • can cause leaves to wilt

  • severe water loss can halt photosynthesis completely