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Topic: Photosynthesis  (Read 2272 times)

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Offline INeedSerotonin

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Photosynthesis
« on: October 30, 2019, 10:49:32 PM »
6 CO2(g) + 6 H2O(ℓ) <---> C6H12O6(s) + 6 O2(g) ∆H° = + 2816 kJ

How can we make it easier for glycosis glucose to be formed?

a) Remove some of the glycosis;
b) Add oxygen;
c) Remove some of the CO2;
d) Add water;
e) Raise the temperature.

Why is (D) not the answer, but only (E)? I think that, if you add water, the equilibrium will shift right.

Could you guys help me find the explanation?
« Last Edit: October 31, 2019, 11:00:20 AM by Borek »

Offline AWK

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Re: Photosynthesis
« Reply #1 on: October 31, 2019, 03:24:22 AM »
And what happens to the CO2 concentration if you add water?
AWK

Offline INeedSerotonin

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Re: Photosynthesis
« Reply #2 on: October 31, 2019, 09:04:10 AM »
I think that it stays the same. Indeed there wouldn't be enough material to form more glucose, because there would be more water and not sufficient CO2 to compensate the increase on water. But this confuses me. I learnt that increasing reagents shifts the equilibrium to the products.

Or, maybe, if I add water, there would be a discrepancy, and glucose would begin to be consumed to make CO2. Is that it? This confuses me, because I learnt that, if you add to the concentration of one compound on one side, it shifts the equilibrium to the other side.
« Last Edit: October 31, 2019, 11:56:56 AM by INeedSerotonin »

Offline Babcock_Hall

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Re: Photosynthesis
« Reply #3 on: October 31, 2019, 10:16:21 AM »
I do not know what glycosis is.  Do you mean glucose, which has the molecular formula that you provided?  Glycolysis is a pathway.
EDT
One question that you might want to ponder is how does nature make photosynthesis favorable. 
« Last Edit: October 31, 2019, 10:47:26 AM by Babcock_Hall »

Offline INeedSerotonin

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Re: Photosynthesis
« Reply #4 on: October 31, 2019, 10:33:28 AM »
I do not know what glycosis is.  Do you mean glucose, which has the molecular formula that you provided?  Glycolysis is a pathway.

Oops! Sorry! In my native language it is "glicose". I meant glucose. I can't edit the first post anymore.  :(

Offline AWK

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Re: Photosynthesis
« Reply #5 on: October 31, 2019, 04:32:16 PM »
There is a big problem with this reaction.
With such phase notation (g, l, s) these questions do not make sense. Chemical equilibrium analysis only applies to one phase. The process of photosynthesis occurs in the liquid phase from the absorption of CO2 gas to the release of O2. In addition, photosynthesis never achieves chemical equilibrium. Increasing the amount of CO2 in the air and then in the cell only to a limited extent increases the efficiency of photosynthesis if there is sufficient "amount of light". Increasing the temperature is only possible to a limited extent because the increased amount of oxygen produced at a higher temperature inhibits photosynthesis. Removal of glucose from the cell is impossible - it may be possible in the process of artificial photosynthesis.
This question is extremely unsuccessful.
AWK

Offline Enthalpy

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Re: Photosynthesis
« Reply #6 on: November 01, 2019, 09:36:24 AM »
And since this reaction is not an equilibrium but needs light input, laws of equilibrium shift don't apply.

More generally, biology and equilibrium don't fit easily together. Biology is change. Equilibrium is death.

Offline INeedSerotonin

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Re: Photosynthesis
« Reply #7 on: November 01, 2019, 10:53:34 AM »
Thank you, guys! I'm convinced this exercise is not well-formulated.

Offline Babcock_Hall

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Re: Photosynthesis
« Reply #8 on: November 02, 2019, 08:36:27 AM »
Glucose is converted into sucrose or starch; therefore, it can be removed.  However, increasing the temperature increases the problem that the enzyme that fixes CO2 can use O2 as an alternate substrate, as AWK indicated.

It is very difficult to write good exercises without doing some simplifications.  Nevertheless, this exercise forces us to ponder some important ideas.  One is that light energy is needed to make the process favorable.   It also implies that living organisms must be able to couple favorable and unfavorable processes together.  How coupling happens is a topic in some biochemistry courses.  In this instance absorption of light changes the reduction potentials of P680 and P700, chromophores within photosystem II and photosystem I, respectively.

Offline AWK

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Re: Photosynthesis
« Reply #9 on: November 02, 2019, 07:59:11 PM »
But the starch formula is rather close to (C6H10O5)n
AWK

Offline Babcock_Hall

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Re: Photosynthesis
« Reply #10 on: November 04, 2019, 05:52:34 PM »
Starch is just a 1,4 polymer of glucose (formally there is a loss of water in creating each acetal bond).  Offhand I cannot recall whether or not there is branching analogous to the branching in glycogen.

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