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Photosynthesis/carbon fixing

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Photosynthesis/carbon fixing

Postby johnboy » Thu May 24, 2012 11:48 am

Hello

I am fairly new to plant biology and was hoping someone could point me in the right direction regarding a question in an assignment i am doing at this moment in time.

It is about photosynthesis and carbon fixing, and although I understand the process and the complex stages involved, I cannot seem to get to grips with the graphs in this question.

There are three graphs. In all the graphs the oxygen levels, illumination and temperature are constant. The only variation is the level of the enzyme rubisco carboxylase which is set at normal for the first graph, 40% of normal in the second and 10% of normal in the third. The x-axis represents the uptake of carbon dioxide and the oxygen evolution in micromoles and the y-axis represents carbon dioxide concentration.

What I don't understand is why the graph with 40% of the normal rubisco carboxylase level produces the highest levelsof oxygen evolution and carbon dioxide uptake. The normal level seems to become saturated quicker and also the levels decrease quicker. In the graph with 10% the levels are much lower but there is a steady increase.

I just don't get how higher levels of the enzyme can become saturated sooner than lower levels, it just doesn't make sense to me and I cannot find an answer in my course materials.

In addition, purely for personal interest as this is not in the question, why is the oxygen evolution levels higher than carbon dioxide uptake?

If anyolne could help me I would be eternally greatful.

John
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Postby JackBean » Thu May 24, 2012 12:06 pm

Because oxygen is not released from CO2.

Are you sure you haven't switched the axises?
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.
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Re: Photosynthesis/carbon fixing

Postby johnboy » Thu May 24, 2012 12:41 pm

Hello JackBean

Yes i made a mistake I did switch the axises thank you for noticing.

I thought that was the reason for the O2 levels being higher but in the third graph, the one with 10% the normal level, the O2 levels are consistent with CO2 and are sometimes lower, that is what confused me.
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Postby JackBean » Thu May 24, 2012 2:26 pm

Why should that matter?
http://www.biolib.cz/en/main/

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Re: Photosynthesis/carbon fixing

Postby johnboy » Thu May 24, 2012 3:08 pm

Well, if the O2 evolution is consistently higher than CO2 uptake when the enzyme levels are normal or at 40%, but are not when the level is 10%, I found it reasonable to assume that the enzyme level had an affect on oxygen evolution.
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Postby JackBean » Thu May 24, 2012 7:09 pm

Is it decreased to 40% and 10%?
http://www.biolib.cz/en/main/

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Re: Photosynthesis/carbon fixing

Postby johnboy » Fri May 25, 2012 10:43 am

Yes, the second example is decreased to 40% and the third decreased to 10%.
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Postby JackBean » Fri May 25, 2012 11:58 am

the oxygen production?
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.
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Re: Photosynthesis/carbon fixing

Postby johnboy » Fri May 25, 2012 4:28 pm

No, the level of rubisco carboxylase.

In the first example, rubisco carboxylase is normal level and the oxygen evolution is consistently higher than CO2 uptake.

In the second example, rubisco carboxylase is at 40% its normal level. O2 evolution is again consistently higher than CO2 uptake. Both O2 evolution and CO2 uptake are at higher levels in this example than with example one.

In the third example, rubisco carboxylase is at 10% its normal level. O2 evolution is equal to CO2 uptake throughout and the levels are far lower.


I need to know why the example 2 produced better results than example. I also need to know the relationship between oxygen evolution and carbon dioxide uptake in photosynthesis.
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