ch17 - limiting factors

What is a limiting factor?

An environmental factor which restricts the rate of reaction of a process when it is in short supply, increasing this factor will increase the rate to a certain point where a new factor will then become limiting

What are the three main limiting factors?

Light intensity, Carbon dioxide concentration, and Temperature

Why is water not a limiting factor?

If water is in such short supply the plant will close its stomata to prevent water loss via transpiration, which consequently prevents CO₂ uptake, so CO2 concentration would be the limiting factor

How does light intensity affect photosynthesis at low, intermediate and high intensity?

Low = limits light-dependent stage so small amounts of ATP and reduced NADP are produced which slows the light-independent stage so rate of photosynthesis is low 

Intermediate = more ATP and reduced NADP produced meaning RuBP is regenerated quicker and more GP will be reduced into TP so rate of photosynthesis increases 

High = more light than is needed is present so rate of photosynthesis plateaus because another factor becomes limiting 

How does carbon dioxide concentration affect photosynthesis at low, intermediate and high concentration?

Low = limits light-independent stage as less CO2 is fixed with RuBP, reducing the production of GP and TP so rate of photosynthesis is low

Intermediate = allows faster production of GP and TP so rate of photosynthesis increases 

High = more CO2 conc. than is needed is present so rate of photosynthesis plateaus because another factor becomes limiting

How can you tell if CO2 concentration is the limiting factor

In an experiment, if you increase CO2 conc. and the rate increases that means it was limiting 

How does temperature affect photosynthesis at low, intermediate and high concentration?

Low = provides little kinetic energy which slows the activity of all enzymes such as RuBisCO (which catalyses the reaction of carbon fixation) so rate of photosynthesis is low

Intermediate = increases kinetic energy for all enzyme-catalysed reactions so rate of photosynthesis increases up to an optimum point

Very = denatures enzymes, so rate of photosynthesis drops sharply