Limiting factors

• limiting factors of photosynthesis:

  Factors required for photosynthesis:

  • Presence of photosynthetic pigments
  • Supply of co2
  • supply of water
  • light energy
  • A suitable temperature
• if there is a shortage of any of these factors, photosynthesis cannot occur at it's maximum possible rate

  Main external factors that affect the rate of photosynthesis are:

  • light intensity
  • CO2 conc
  • Temperature
  • These are known as limiting factors of photosynthesis
  • If any one of these factors is below the optimum level for the plant, it's rate of photosynthesis will be reduced, even if the other two factors are at the optimum level
• when temperature and carbon dioxide concentration remain constant, changing light intensity affects the rate of photosynthesis
• the rate of photosynthesis increases as light intensity increases:

  • greater the light intensity, the more energy is supplied to the plant and therefore the faster the light-dependent stage of photosynthesis can occur
  • produces ATP and reduced NADP for the calvin cycle which can then also occur at a greater rate
  • During this stage of the graph below, light intensity is said to be a limiting factor for photosynthesis
• at some point, if light intensity continues to increase, the relationship above will no longer apply and the rate of photosynthesis will reach a plateau

  • at this point, light intensity is no longer a limiting factor, thus another factor is limiting the rate of photosynthesis

  The factor which could be limiting the rate when the line on the graph is horizontal including temperature being too low or too high, or not enough co2 available

  
• Carbon dioxide conc

  the rate of photosynthesis increases as carbon dioxide conc increase

  • carbon dioxide is one of the raw materials required for photosynthesis
  • Required in the light independent stage of photosynthesis when CO2 is combined with the 5c compound Ribulose Bisphosphate (RuBP)
  • This means that more co2 is present, the faster the step of the Calvin cycle can occur and the faster the overall rate of photosynthesis
• Trend of Co2 conc will continue until some other factor for photosynthesis prevents rate from increasing (limiting)

  • the factor which could be limiting the rate when the line on the graph s horizontal including temperature being too low or too high or not enough light

  
• Temperature

  • As temp increases the rate of photosynthesis increases as the reaction is controlled by enzymes
  • however as controlled by enzymes, only continues to a certain temp due to denature and RoR decreases

  
• for most metabolic reactions, temp has a large effect on the RoR

  • For photosynthesis, temp has little sig effect on the light-dependent reactions, as driven by energy from light rather than kinetic energy of reacting molecules
  • however, calvin cycle is affected by temp, as the light independent reaction are enzyme controlled reactions (Rubisco catalyze reaction between co2 and 5c compound)
• Investigating the rate of photosynthesis: redox indicators

  • light-dependent reactions of photosynthesis happens in the thylakoid membrane and involves the release of high-energy electron from chlorophyll a molecules
  • picked up by electron acceptors then passed down ETC
  • however, if redox indicator such as DCPIP or methylene blue is present, indicator takes electron instead
• causes indicator to change colour:

  • DCPIP: Oxidized (blue) -> accepts electrons -> reduced (colourless)
  • Methylene blue: Oxidized (blue) -> accepts electrons -> reduced (colourless) 

  • THE COLOUR OF REDUCED SOLUTION MANY APPEAR GREEN COZ CHLOROPHYLL