Leah.J
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"Water and small solutes enter and leave the cell by diffusing through the lipid bilayer of the plasma membrane or by being pumped or moved across the membrane by transport proteins. However, large molecules—such as proteins and polysaccharides, as well as larger particles—generally cross the membrane in bulk, packaged in vesicles. Like active transport, these processes require energy."


In bulk means in large amounts right ? So when they say "Bulk transport across the plasma membrane occurs by exocytosis and endocytosis"
Do they mean that when a large number of sth wants to cross the membrane it occurs by exo and endocytosis or do they mean that when a large object wants to cross it occurs by exo/endocytosis or do they mean both ?
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dwji
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(Original post by Leah.J)
"Water and small solutes enter and leave the cell by diffusing through the lipid bilayer of the plasma membrane or by being pumped or moved across the membrane by transport proteins. However, large molecules—such as proteins and polysaccharides, as well as larger particles—generally cross the membrane in bulk, packaged in vesicles. Like active transport, these processes require energy."


In bulk means in large amounts right ? So when they say "Bulk transport across the plasma membrane occurs by exocytosis and endocytosis"
Do they mean that when a large number of sth wants to cross the membrane it occurs by exo and endocytosis or do they mean that when a large object wants to cross it occurs by exo/endocytosis or do they mean both ?
If an object is too large (or has unsuitable properties) to diffuse across the membrane it will cross using exo/endocytosis (theres different types but dw about those for now). Bulk transport is literally just 'the movement of macromolecules into or out of the cell'. Hope that clears it up.
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Leah.J
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(Original post by dwji)
If an object is too large (or has unsuitable properties) to diffuse across the membrane it will cross using exo/endocytosis (theres different types but dw about those for now). Bulk transport is literally just 'the movement of macromolecules into or out of the cell'. Hope that clears it up.
Can't macromolecules move through facilitated diffusion ?
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dwji
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(Original post by Leah.J)
Can't macromolecules move through facilitated diffusion ?
No they are too large, need bulk transport. However macromolecules such as carrier or channel proteins may be the ones facilitating diffusion of smaller molecules such as ions.
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Leah.J
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(Original post by dwji)
No they are too large, need bulk transport. However macromolecules such as carrier or channel proteins may be the ones facilitating diffusion of smaller molecules such as ions.
Ohhhh
So in what cases are substances like glucose ( which can pass through the membrane by other methods ) transported through exo and endocytosis ?
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dwji
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(Original post by Leah.J)
Ohhhh
So in what cases are substances like glucose ( which can pass through the membrane by other methods ) transported through exo and endocytosis ?
Glucose is a monosaccharide, not a macromolecule. It is transported by facilitated diffusion or active transport. You will look at it more in upper sixth.

For now this might help: http://www.phschool.com/science/biol...1/glucose.html
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