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In my A level revision guide and places on the internet it states that at low temperatures levels of RuBP, GP and TP all fall. However I don't quite understand how this is the case, because as far as I can see, a reduction in temperature would give the molecules less kinetic energy and reduce the rate of reaction of the enzymes and so there would be no change to relative concentrations, because everything is slower all equally. Could anybody explain to me why all three decrease in concentration at low temperatures?

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Enzymes don't universally reduce their catalytic ability when the ambient temperature is lower. Some will be affected more than others. You could probably look up the KM values with relation to temperature if you're curious. – MCM Jun 8 '14 at 1:55
Note that reaction rates depend exponentially on temperature as per Arrhenius equation. So the change won't be linear. Moreover the activation energies for different reactions will be different. $\\k=Ae^{-E_a/{RT}} \\\frac{k_1}{k_2}=e^{-E_aR(\frac{1}{T1} - \frac{1}{T2})}\\\\$ – WYSIWYG Jun 8 '14 at 6:59
@MCM so, if the enzyme to convert TP into the respiratory substrates works faster than all the other enzymes, and given that Carbon Dioxide will diffuse slower in lower temperatures (hence less input), all the levels of intermediates should decrease? – J_mie6 Jun 8 '14 at 10:36
@WYSIWYG that's an interesting equation, I will look into it, I love a bit of exponential decay from physics! – J_mie6 Jun 8 '14 at 10:38
@J_mie6 I missed it then but after a while looked at this question again. The answer to your question requires the model parameters and other reactions. Can you provide the link to the source where you read this? – WYSIWYG Dec 14 '14 at 13:31

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