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biology_06er
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Post by biology_06er » Wed Jun 07, 2006 4:24 am

Is it possible to completely delete posts if you no longer want to post them?

Also could someone please help me with this question I have an exam tomorrow and am unsure of the answer

The diffusion of sodium across a cell membrane:
1-is directed into the cell
2-involves the direct hydrolyses of ATP
3-is an example if faciliated diffusion
4-uses the engery stored in ion gradients
5-is coupled by the removal of potassium ions from the cell

I think 1 3 and 4 are clearly wrong as doesn't Na+ create an ion gradient and it uses a transport protein and as the membrane is impermeable to charged ions it can't be directed into it so my guess would be 2 or 5 but not really sure

Please help!!!!
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Post by canalon » Wed Jun 07, 2006 2:26 pm

For removal you have to kindly ask the nice moderators to do that for you. usually, the easiest way is to edit your post and replace whatever it contained with "please delete" and when one of us will find this we will do it. We are nice and helpful ;-)

As for your answer, I am not sure but if I consider the existence of Na/K ATPases who degrades ATp to transfer Na+ out and K+ in, I would say that 2 AND 5 are OK.
Patrick

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any proof. (Ashley Montague)

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Post by MrMistery » Wed Jun 07, 2006 5:21 pm

Well i don't know what answer your teacher wants from you, but here is the correct one:
Diffusion, in the context off cellular biology, involves transport of solutes down their concentration gradient, from higher to lower concentration. Since there is much more sodium outside the cell, it's diffusion occurs from outsite of the cell towards the cytoplasm. Therefore 1 is correct.
2 is incorect as it refers to the Na/K pump, which is not diffusion but active transport
3 is correct, as Na passes through a proteic ion channel(facilitated diffusion)
4 is corect, as dffusion releases free energy(ΔG=-RTln(c2/c1) - nFΔΨ). Since this energy was initially stored in the ion gradient, i guess you can mark it as correct, although i am not 100% OK with the term "uses the energy"
5 - again refers to the Na/K pump, so incorect.
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canalon
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Post by canalon » Wed Jun 07, 2006 7:55 pm

You are right Mr Cheese, you win a raw milk camembert for read the question, and not just replied as it first come. Yeah when Na+ diffuse it does it through ion channels passively and towards the inside of the cell.

Mea culpa.
Patrick

Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)

biology_06er
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Post by biology_06er » Thu Jun 08, 2006 5:06 am

Hi there

Thanks for the replies...however the question itself is pretty weird as its multi choice and only ONE CORRECT answer (as its marked electronically)..so after discussing with some others I think 3 is the MOST correct...

Thanks again for replies
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MrMistery
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Post by MrMistery » Thu Jun 08, 2006 6:18 pm

If you need to only pick one, i would agree to be 3...
I also made a mistake out of not being careful: substances with a charge(like sodium ions)diffuse down their ELECTROCHEMICAL gradient. This is composed of their electrical gradient and their chemical gradient.

@patrick
thanks. lack of attention happens to me all the time too. By the way, what is that raw milk camembert i won?
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

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Post by canalon » Thu Jun 08, 2006 6:32 pm

Camembert is a typical (if not stereotypical) french cheese. More details here and traditionally made from raw milk, which gives it a really different flavor than the industrial thing bearing the same name made from pasteurized milk.
Luxury product in a way for gourmet cheese eater.

Th perfect gift for a Mr Cheese...
Patrick

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Post by MrMistery » Thu Jun 08, 2006 6:34 pm

Actually i don't really love cheese that much! The title was assigned to my by Kyle. But i'll take it. You can mail it to me :D
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

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