# Temperature effect on RuBP

Hello, I'm doing OCR A Biology, this is A2 unit f214, about photosynthesis.

The specification states "describe the effect on the rate of photosynthesis, and on the levels of GP, RuBP and TP, of changing carbon dioxide concentration, light intensity and temperature".

I understand how the rate of photosynthesis and the concentration of GP, TP and RuBP are effected in terms of light intensity and carbon dioxide concentration.

What I need help on is how the concentration of the molecules are effected by temperature...

(Ignore temperatures above 25 degrees as I understand how photo-respiration will act to decreases rate of photosynthesis)...

If I increase the temperature, for example from 10 degrees to 20 degrees.....

The rate of photosynthesis increases, because molecules have more kinetic energy hence more successful collisions per unit time.

From this it is clear that TP concentration must increase.
Therefore GP concentration must have increased, correct?

Now, how is RuBP concentration effected?

RuBP concentration increases? --> if so, how can they all increase? then there is a gain of carbon, is there not?

RuBP concentration decreases? --> this is what was suggested at college, but is this correct? An explanation was not given.

Please explain this to me it has been annoying me for months now.

All the books on the topic seem to avoid answering this.
And it can't be the concentration of all TP, GP, and RuBP all stay the same, can it? Because TP concentration must increase as this is the product of the Calvin Cycle, to use to make glucose/etc.
(edited 9 years ago)

Posted from TSR Mobile
Hello,

So if you increase the temperature, the rate of photosynthesis increases because Rubisco, RuBP and CO2 move more and there is more likely to be successful collisions between the active site of Rubisco, the RuBP, and the CO2. So this means that the concentration of GP increases. Since there's more GP, there's more GP to be converted into TP, so the concentration of TP increases. Then because there's more TP, the concentration of RuBP increases, but you could say the concentration of RuBP would also decrease because it was being converted into GP more quickly...

I get what you mean! It's confusing...perhaps the concentrations stay the same, but the Calvin cycle just speeds up? Have you tried asking your teacher? I'd quite like to know the answer now too!
Original post by supergrace
Hello,

So if you increase the temperature, the rate of photosynthesis increases because Rubisco, RuBP and CO2 move more and there is more likely to be successful collisions between the active site of Rubisco, the RuBP, and the CO2. So this means that the concentration of GP increases. Since there's more GP, there's more GP to be converted into TP, so the concentration of TP increases. Then because there's more TP, the concentration of RuBP increases, but you could say the concentration of RuBP would also decrease because it was being converted into GP more quickly...

I get what you mean! It's confusing...perhaps the concentrations stay the same, but the Calvin cycle just speeds up? Have you tried asking your teacher? I'd quite like to know the answer now too!

Yes we actually did it in class, and she said RuBP concentration would decrease, but I asked why and she couldn't properly explain it haha, and this also conflicts with one of my textbooks, and then websites on the Internet all conflict with each other! So it really is very confusing :-(

I had this theory on why RuBP would decrease but I'm not so sure...

RuBP + CO2 ---> GP
Occurs faster than TP is combined to regenerate RUBP, because
TP --> RuBP occurs over multiple steps, hence although all the steps would increase in rate, RuBP concentration would actually decrease from what it was previously?

Let me know what you think and if you have any other ideas on what happens.

Posted from TSR Mobile
So if RuBP concentration decreases, the conversion of RuBP to GP must be faster than GP to TP, TP to RuBP...that's the only explanation I can think of. Perhaps it's faster because it's enzyme controlled, and the temperature rise affects this step in particular?
It really depends, because if you increase temperature above 45 degrees, RUBISCO activase (an enzyme required for the proper functioning of RUBISCO) will denature, thus leading to a build-up of RuBP. As a rule of thumb increased temperature would also increase the rate of reaction of the other reactions in the Calvin cycle as they too depend upon the number of successful reactant collisions per second, and thus (up to 45 degrees) there would be very little change in the relative concentrations of GP, TP and RuBP.