Xref: utzoo sci.bio:3860 sci.chem:2447 sci.physics:15376 sci.misc:4545 Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!gatech!ncar!elroy.jpl.nasa.gov!turnkey!orchard.la.locus.com!fafnir.la.locus.com!fafnir.la.locus.com!richard From: richard@locus.com (Richard M. Mathews) Newsgroups: sci.bio,sci.chem,sci.physics,sci.misc Subject: Re: Osmosis - the cause at the molecular level. Message-ID: Date: 9 Nov 90 23:54:04 GMT References: <3703@stl.stc.co.uk> <1990Nov6.235518.8507@alchemy.chem.utoronto.ca> <839@inews.intel.com> Organization: Locus Computing Corporation, Los Angeles, California Lines: 29 bhoughto@cmdnfs.intel.com (Blair P. Houghton) writes: >In article <1990Nov6.235518.8507@alchemy.chem.utoronto.ca> mroussel@alchemy.chem.utoronto.ca (Marc Roussel) writes: >> This is certainly true. You are both focussing on the wrong aspect of >>the problem however. It is not the size of the molecules that matters, >>but their area of contact with the membrane. >If the contact plugs a hole then it plugs traffic in both directions. I'm not sure I agree. This would be true if the molecule plugs the hole for some length of time, but not if a point on the molecule just bounces off of the membrane. Say that when a water molecule hits the membrane, it has a certain probability of passing through. If it approaches from the opposite side as the other molecule and gets there just before the other molecule bounces, it will be able to pass through the membrane before striking the other molecule. Similarly, if it gets there just after the bounce, it will be able get through. Water molecules on the same side of the membrane as the other molecule, on the other hand, will be excuded from that neighborhood of the membrane for a short time. Put another way, the pressure of the water on one side will be able to push the plug out of the way, but the water on the same side as the plug will be blocked. Richard M. Mathews D efend Locus Computing Corporation E stonian-Latvian-Lithuanian richard@locus.com I ndependence lcc!richard@seas.ucla.edu ...!{uunet|ucla-se|turnkey}!lcc!richard