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Photosysnthesis

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Photosysnthesis

Postby davidtrees » Wed Feb 01, 2012 11:00 am

I have just started reading a book unrelated to biology but in the foreword it uses photosynthesis as a metaphor for something else. It describes photosynthesis like this:

"During the light of day a tree absorbs carbon dioxide through its leaves. Then at night during the dark phase of photosynthesis, the carbon dioxide molecule is separated into one carbon atom and two oxygen atoms. The tree releases the oxygen atoms back into the air and forms the carbon atoms into a six carbon simple sugar ring which is a building block for cellulose."

It's been a while since I was at school, but this seems wrong to me. The "dark phase of photosynthesis" especially. But maybe I am misremembering.

Would anyone care to comment?
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Postby JackBean » Wed Feb 01, 2012 11:43 am

1) the absorption of CO2 by leaves (entrance by stomata) is not dependent on light. Rather contrary because excess heat causes closing of stomata to prevent drying. The light is used to break down water to produce some high-energy electrons etc.
2) yep, the dark phase of photosynthesis doesn't take place during night. It actually requires light to proceed, although the light is not used directly as an energy source, but there are some light-dependent changes in Mg concentration and pH.
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Re: Photosysnthesis

Postby sachin » Wed Feb 01, 2012 5:42 pm

It's not carbon dioxide that splits to give oxygen its water molecule.

H2O + e- = 2H+ + half O2 + 2e- Oxygen is released and e- and H+ is utilized to make 2 NADPH molecules and

Please check ...
Non cyclic photo-phosphorylation
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Postby JackBean » Wed Feb 01, 2012 6:27 pm

That's right!

Here is something about the light regulation http://en.wikipedia.org/wiki/Light-inde ... regulation
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Re: Photosysnthesis

Postby jonmoulton » Wed Feb 01, 2012 9:30 pm

This separation of photosynthesis into day and night phases sounds like CAM photosynthesis. However, I think that's giving the author too much credit. I suspect this is a misinterpretation of "dark reactions" as something that happens at night.
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Re: Photosysnthesis

Postby sachin » Thu Feb 02, 2012 11:16 am

jonmoulton wrote:This separation of photosynthesis into day and night phases sounds like CAM photosynthesis. However, I think that's giving the author too much credit. I suspect this is a misinterpretation of "dark reactions" as something that happens at night.


That is what we understood in lower school. Then in higher school realized the truth about it.

One question is there in my mind for so long.

Can we increase the efficiency of photosynthesis by providing light for 24 hrs and of required frequency in green houses to get faster yield? :idea:
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Postby JackBean » Thu Feb 02, 2012 11:33 am

what do you mean by frequency? The wavelength? Or intensity?

The plants are sensing photoperiodism, so 24-hrs light wouldn't be probably good for them (at least not long-term)
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Postby sachin » Thu Feb 02, 2012 12:10 pm

Oh... I didn't mention it clearly...

I mean Wavelength and Intensity.
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Postby JackBean » Thu Feb 02, 2012 12:21 pm

The wavelength of course influences the yield, but it's not like increasing with monochromatic light, because the other wavelengths just pass away.
The intensity has classical shape of dependence on any nutrient. First it grows until some saturation, but then it may decline because of photoinhibition etc.
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Postby sachin » Thu Feb 02, 2012 12:31 pm

Ok......

Any ways I don't want plants to work like slave.... :lol:
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Re: Photosysnthesis

Postby Adz795 » Thu Feb 02, 2012 3:43 pm

Anyway what book was that? So grossly wrong. :roll:
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