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OCR Question membranes

Just a quick question, but as the centre of the bilayer of a membrane is hydrophobic how is water able to go through it? It doesn't allow water soluble substances to pass through?
Some water is allowed to pass through as water molecules are small and non-polar. Only a certain amount though, as far as I'm aware that's just how it is. I'd say the fatty acid tails aren't in contact with the water for long though.
^water is a polar molecule for a start, but it is uncharged. But yeah it's a small molecule and it can pass through the bilayer by osmosis down a concentration gradient. remember that the lipid bilayer is a fluid mosaic model which means the layers move around and slide along, allowing water and some other small molecules (such as O2 and CO2) to pass through. There are also aquaporins in the membrane which are protein channels specific to water which allows them passage in and out of the cell.
Original post by rm_27
Just a quick question, but as the centre of the bilayer of a membrane is hydrophobic how is water able to go through it? It doesn't allow water soluble substances to pass through?


Water is a tiny molecule, so it can just go through by osmosis. From high Concn to low Concn

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