Limiting Factors of Photosynthesis
Limiting Factors
- A limiting factor is something which inhibits or slows the rate of reaction when it is in short supply.
- 'The rate of a physiological process is limited by the factor in which there is the shortest supply'
- Factors affecting the rate of photosynthesis are:
- Light Intensity; a lack of light means the light dependant stage cannot function, inhibiting photosynthesis. Optimum amounts of light maximise the rate of production for ATP and NADP.
- CO2 Concentration; a lack of this substrate means there cannot be carbon fixation in the Calvin cycle, so no GP or TP molecules are made so there are no products. Large quantities of CO2 mean that there is always CO2 available for fixation by RuBisCo, and RuBisCo will not begin catalysing photorespiration.
- Temperature; as an enzyme controlled reaction, the calvin cycle will stop if the temperature is too low for RuBisCo to function or too high causing it to denature, stopping photosynthesis. The same is true for all other proteins involved, such as the ferredoxin carrier, NADP reductase coenzyme etc. Optimum temperatures mean the rate of photosynthesis is as efficient as possible.
- Although water is required for photosynthesis, it is never considered a limiting factor as if water availability is so low to limit the rate of photosynthesis, the plant would have already closed its stomata and ceased photosynthesis, as a result of other processes stopping.
Investigating Limiting Factors
- Dataloggers record physical properties such as light intensity, temperature, pressure, pH and humidity over a period of time, producing a graphical representation of the changes that occur.
- These readings are highly accurate.
- Rate of photosynthesis can be used by measuring the change in CO2 levels or O2 levels.
Artificial Photosynthesis
- Burning fossil fuels releases large quantities of carbon dioxide, leading to global warming. These non-renewable fuels will run out and lead to a fuel (and therfore food)shortage.
- Photosythesis can utilise this excess carbon dioxide to produce large quantities of carbohydrates which can be used as both biomass fuel and food.
- By improving the relatively inefficient natural process of photosynthesis, we can harbour the sun's energy in a more effective way than current solar power. This would mean there is more fuel, food and less CO2.
- Most plants perform C3 photosynthesis, which is most efficient in cool, wet conditions with intermediate light intensities. It is the one we have learnt about.
- Plants in high temperatures with low water supply undergo....
- C4 photosynthesis; They fix CO2 more effeciently so stomata do not need to be open as often, reducing water lost through transpiration.
- It first uses PEP Carboxylase, not RuBisCo, for carbon fixation, which is not inhibited by oxygen.
- It produces 4 carbon molecules which are tightly packed together, later decarboxylated again in the calvin cycle in isolation of atmospheric oxygen.
- CAM Photosynthesis; Plants open their stomata at night when temperatures are cooler, to reduce water lost through transpiration.
- CO2 absorbed is converted into an acid for storage during the night, which is broken down again during the day for photosynthesis and use by RuBisCo in isolation of oxygen to maximise efficiency.
- CAM plants are able to keep their stomata closed day and night to have a closed circuit of recycled CO2 and O2.
- C4 photosynthesis; They fix CO2 more effeciently so stomata do not need to be open as often, reducing water lost through transpiration.