Had some hw questions and was confused on the following:
How the following factors influences the rate of diffusion:
- molecule size
- charge
- solubility
- SA:V ratio
What does it mean when no net diffusion occurs?
Why do vesicles need to be formed for proteins to be secreted from the cell?
Any help would be much appreciated!
1) I definitely know molecule size and solubility influence the rate of diffusion; alcohol molecules are non-polar and can hence readily diffuse through the lipid bilayer, whereas a large polar molecule would have to go through a protein channel, and I assume the former process would be shorter in time. Likewise, smaller molecules generally don’t need to do through the protein channels, so size would influence rate of diffusion. As for charge and SA;V rain, I’m not 100% sure but I would think that they would affect rate since they would most likely impact the manner in which the molecule enters/leaves the cell. Perhaps check these with a quick google search or with your teacher to get the full understanding of these mechanisms (in Biol, don’t memorise facts, rather learn the reasoning behind these processes - just a tip to kill the subject
)
2) No net diffusion would mean that the amount of a molecule entering the cell would be equal to the amount leaving - so there is movement, but no NET movement; one direction of movement is not preferential
3) Proteins are hydrophilic and so can’t diffuse through the lipid bilayer. So, you’d think that the alternative is travelling through a protein channel, right? Well, if you think about it, the protein wouldn’t be able to diffuse through a protein channel since the protein molecular would be too large. Therefore vesicles are necessary to enable this movement!
Hopefully this made sense
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