Photosynthesis question

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maccha
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Photosynthesis question

Post by maccha » Sun Dec 13, 2009 4:12 am

If plants cells can get ATP from oxidizing water why do they have to make glucose?

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JackBean
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Post by JackBean » Sun Dec 13, 2009 4:18 am

You can get energy from reducing the oxygen, right? So, why do you need to break down the glucose?
What if you didn't have enough oxygen at some moment?
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maccha
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Re: Photosynthesis question

Post by maccha » Sun Dec 13, 2009 5:09 am

Ooh makes sense, thanks!

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JackBean
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Post by JackBean » Sun Dec 13, 2009 5:13 am

Really? :lol: OK, I thought, I will have to explain a little :lol:
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jwalin
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Post by jwalin » Sun Dec 13, 2009 3:49 pm

and secondly glucose is used further to make up other structures
it isn't what you do that matters but it is how you do it

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Post by jwalin » Sun Dec 13, 2009 3:51 pm

and one more thing that although i am not very sure of is
its easier to harvest energy from glucose and can act as an immmediate source of energy as compared to water

and one more thing again i doubt this
energy amounts that are released differ

but i would preffer if our botanist clarifies.
am i right?? jackbean
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MrMistery
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Post by MrMistery » Mon Dec 14, 2009 10:30 pm

There are numerous reasons for using the ATP to make glucose instead of just having the ATP around. the most important is that glucose can be stored in an insoluble form. ATP on the other hand is soluble. As you continue to make more and more of it, it builds up, the cell osmolarity increases and the cell swells. For plants this in itself isn't a problem, because they have a cell wall to protect them from bursting. However, as osmolarity rises water potential also rises, and after a while the water potential for anything is so high that you can't get anything inside the cell. This problem can be overcome by storing the energy in an insoluble form. Plant cells store a polymer of glucose (starch) for this reason.
Another important reason is that sometimes you need to export the energy: the ATP is made in the leaf cells, while energy is also required by root cells. If you simply had a pump that would pump ATP into the phloem then it would be hard to regulate how much ATP you export and how much you keep - ATP is ATP. Plants take care of this problem by turning the ATP for export into sucrose and that for keeping in the same cell into starch. This is done by a rather complicated mechanism of balancing the amount of phosphorylated trioses in the choloroplast vs the cytoplasm, but that's the principle behind it.

Hope this clears things up a little
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