Jennifer50
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#1
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#1
How does water cross a plasma membrane? Can it just diffuse through like oxygen?
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MrMcBants
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#2
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#2
OSMOSIS!
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kkboyk
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#3
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#3
(Original post by Jennifer50)
How does water cross a plasma membrane? Can it just diffuse through like oxygen?
Water passes through the nuclear pores by osmosis (which is basically diffusion, except its the movement of water down a water potential)
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Jpw1097
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#4
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#4
(Original post by Jennifer50)
How does water cross a plasma membrane? Can it just diffuse through like oxygen?
Some water molecules do passively cross the plasma membrane however water molecules are polar and so do not easily cross the phospholipid bilayer (remember, due to the hydrophobic core). Most water molecules will cross the plasma membrane via aquaporins, which are channel proteins which have a hydrophilic lining which allows water molecules to pass through. However, this is still a passive process known as facilitated diffusion and so a concentration gradient must still exist for water molecules to diffuse across the membrane. Aquaporins are important channel proteins involved in the reabsorption of water in collecting ducts in the nephron in the kidney regulated by anti-diuretic hormone (ADH).

No, it cannot diffuse through like oxygen. Oxygen is non-polar and so is lipid-soluble, it can just dissolve in the phospholipid bilayer and cross the membrane with ease.

Hope that helps.
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MrMcBants
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#5
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#5
(Original post by kkboyk)
Water passes through the nuclear pores by osmosis (which is basically diffusion, except its the movement of water down a water potential)
Aye mate I just said that. Stop stealing my rep.
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Jennifer50
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#6
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#6
Are the aquaporins always open?
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zombiejon
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#7
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#7
(Original post by Jennifer50)
Are the aquaporins always open?
Many are always open, but not all of them.
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Jennifer50
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#8
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#8
How do they open and also are they protein channels?
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zombiejon
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#9
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#9
(Original post by Jennifer50)
How do they open and also are they protein channels?
Not a protein channel.

Usually remain open due to tertiary protein structure.
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Jennifer50
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#10
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#10
So exactly what are they classified as and also I read somewhere that they are water bound, what does that mean?
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zombiejon
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#11
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#11
(Original post by Jennifer50)
So exactly what are they classified as and also I read somewhere that they are water bound, what does that mean?
Integral protein.

Not sure what the term water bound means in relation to an aquaporin.
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Jennifer50
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#12
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#12
So how do they only allow water through?
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zombiejon
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#13
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#13
Constantly open. Probably has a hydrophilic core in order for h2o to pass through, rather than go through the hydrophobic core of tbd the plasma membrane.
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