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Limiting factors of photosynthesis summary (A-Level 2nd Year)
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Limiting factors of photosynthesis summary
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Limiting factors in photosynthesis Factors that restrict rate of photosynthesis
Some affect LDR/LIR
Light intensity – AM
Temp – Cold day
CO2 – warm, sunny day
Def:
the factor that determines/limits rate of photosynthesis.
Limiting factor is the one that is in shortest supply
Light intensity
Affects light dependent reaction but is going to affect Light Independent Reaction
produces ATP + produces NADPH
If light intensity low = ATP decreases, NADPH decreases, O2 decreases
When Light intensity = 0, rate of photosynthesis also = 0 (directly proportional)
Above a certain amount of light intensity, photosynthesis rate = constant so another
factor is limiting photosynthesis rate. (co2)
Light Intensity – Effect on Calvin Cycle
Less light = NO NADPH or ATP
Relative conc of glycerate phosphate increases
Its accumulating cuz no NADPH or ATP to turn it GP into Triose Phosphate
Thus, less TP because no NADPH or ATP from LDR for synthesis and because TP is
being converted into sugars
RuBP decreases therefore, no ATP for regeneration
CO2 Conc
Affects Light Independent Reaction - Calvin Cycle
Co2 conc in air = 0.04%
0 co2 = 0 photosynthesis rate (directly proportional)
Above certain co2 conc = constant photosynthesis rate so another limiting factor
CO2 Conc – Effect on Calvin Cycle
, No co2 in carbon cycle = reduced production of GP as co2 has to react with ribulose
bisphosphate to make GP
Accumulation of RuBP cuz no co2 for it to react with
Reduced TP cuz no GP to make it
Temp
Affects light independent reaction directly
Cuz enzyme – catalysed process and thus temperature sensitive
The LIR is just FAR MORE affected by temp because every part of the Calvin cycle is
enzyme catalysed.
the LIR is affected by temp while the LDR isn't
low temps: rate directly proportional to temp so, increased kinetic energy of
molecules when temp starts to increase making enzyme-substrate complexes
above optimum temp, enzyme denature
Temperature – Effect on Calvin Cycle
at temps above optimum, but below causing denaturation, photorespiration can
occur
this is when instead of co2 it is o2 that binds w enzyme RuBisCO’s active site which
catalyses RuBP
so decreased co2 fixed into GP
so, decreased (less) GP and decreased TP produced
initial accumulation of RuBP as it is being held back as it can’t react with co2 but in
the end the amount goes down anyways because it isn’t being regenerated by TP
because no TP is being made.
GRAPH
low co2 = low temp
low co2 = high temp
high co2= low temp
high co2 = high temp
possible limiting factors: Light intensity, Temperature, CO2 Conc or something
else…
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