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C3 and C4 plants

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Postby 2810712 » Tue Mar 29, 2005 6:03 am

I'm a bit confused here, how do theC4s need less CO2 as to carry out equal no. of photosynth reactions, CO2 required should be the same. Also, the require ment is given in 'ppm' units [ parts per million] The above q arises if this ppm quantity corrosponds to the conc. of CO2 in plasma of cell, but if it is about the conc. of CO2 in air, the above q will not arise. I think the more % CO2 stored in C4 is used in photosynthesis, so they need less CO2 conc. in air.
Also, how do CAMs save water in photosynthesis ? ? ?
Please help, i'm really confused. :oops: :cry:

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Postby MrMistery » Tue Mar 29, 2005 6:39 pm

Ok, i see you are really confused so i'll try to clear up things for me: hope i can
Both C3 and C4 plants need the same amount of co2 to produce glucose: all processes bow down to the laws of chemistry. But in c3 plants, under higher temperatures, occurs a process called fotorespiration. RuDP-carboxylase(the enzime that fixes CO2 in c3 plants) has a hish afinity for oxygen. Under high intensity of heat and light, c3 plants close their stomates, therefore reducing the quantity of water. when there is no water, there is no energy to enable fixing CO2, therefore oxigen is fixed on that enzime. Through this process photosynthesis in c3 plants drops dramatically, by aprox 50%. The enzime that fixes co2 in c4 and cam plants does not have an afinity for o2, therefore it does not have this problem.
Because C4 plants do not have this problem, photosynthesis is 6 times more efficient in their case. That is why they need less co2.
How do CAM plants save water? Good question. CAM plants live in places with less water, that is true. THEY DO NOT SAVE WATER IN PHOTOSYNTHESIS. They save it by reducing transpiration. CAM plants keep their stomas open during the night when it is colder so transpiration is reduced greatly, almost 0. They take CO2 from the air then and transform it into malic or aspartic acid, which filles the vacuoles of the plant. During the day the plant turns these acids into glucose, so the stomas are closed.

Hope i made it clear for you.
Regards,
Andrew
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Postby mashimaro » Sat Aug 05, 2006 3:56 am

I got a question...
Our teacher tell us that c3 is same with CAM. It's true? We all got a bit confuse about that....
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Postby mith » Sat Aug 05, 2006 5:20 am

nope, depends on which part, some part are the same.but they're not identical
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Postby mashimaro » Mon Aug 07, 2006 8:46 am

In which part it is same? According our teacher explaination, c3 plant undergoes Crussulacean Acid Metabolism while c4 plant undergoes Hatch- Slack Pathway...i rily confused wif it...can u explain to me? :cry:
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Postby MrMistery » Mon Aug 07, 2006 6:39 pm

Your teacher is wrong.
All plant assimilation types(C3, C4 and CAM) undergo the Calvin cycle.
C4 and CAM plants have an additional cycle witch fixes CO2 into malic acid(usually) first and then "gives" it to Rubisco and runs the Calvin cycle. The two types of plan ts differ in 2 main ways:
1. C4 plants have certain anatomical adaptations, while CAM plants do not
2. C4 plants separate the 2 cycles spatially(one occurs in the mesophil cells and the other in the bundle sheeth cells) while CAM plants separate them temporally(one occurs during the day and the other at night)

Hope i was as clear as possible...
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Postby bio_is_my_best_friend » Wed Aug 09, 2006 4:48 am

I thought that C4 was use by the evil terrorists of the Middle East.
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Re: C3 and C4 plants

Postby Justazz » Wed Mar 12, 2008 11:35 pm

Hi, I have 1 little question. How CAM plants prevent fotorespiration? or don't they? I understand why in C4 plants fotorespiration doesn't occures, but CAM is mystery for me.
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Postby mith » Thu Mar 13, 2008 1:23 am

read mrmistery's post above.
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Postby MrMistery » Thu Mar 13, 2008 10:24 am

and don't double post...
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Postby tittu » Tue May 13, 2008 4:32 pm

Bringing alive this old thread,
If you keep a c3 plant and a c4 plant under the same bell jar, adequate licght, then what happens to the co2 conc in the jar?
a. [co2] drops to co2 compensation point of c3 plant
b. [co2] drops to co2 compensation point of c4 plant
c. [co2] goes on decreasing.
d. [co2] drops below co2 compensation point of c4 plant

This came in Indian Biology Olympiad 2008. I just dont get the rationale.
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Postby mith » Tue May 13, 2008 4:42 pm

You basically find which C02 binding enzyme has greater affinity.
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