What molecules limit a membrane's permeablility?
829422
Yes, lipoproteins and cholesterol do limit a membrane's permeability - but it's also important to note that they are there for a reason.  Molecules like cholesterol also add to the fluid mosaic model and actually make molecules more fluid in colder temperatures by pushing around the bilipid layer.
37484
All cells have membrane-spanning proteins that serve as channels.  They can move materials across the cell membrane, either in or out, by passive diffusion, active transport (ie ATP-consuming energy-burning motors that sort materials against a chemical gradient) or facilitated transport (ie coupled transport systems where the movement of one chemical down a chemical gradient is coupled with the transport of another chemical up a gradient).  Some combination of these methods is used to transport wastes from the bacterial cell.\n\nIn eukaryotic cells (ie not bacteria, but possibly including single-celled protists and fungi) there can also be excretion of materials by the means of small vessicles made of the same lipid bilayer that the membrane is made of.  When these vessicles fuse to the cell membrane, the contents spill out, and the vessicle lipids become part of the cell membrane.
773799
Cell walls surround the cell outside of the plasma membrane.  When water flows into the cell by osmosis, the cell swells until its membrane builds up pressure against the cell wall.  The cell wall prevents the cell from swelling and bursting in a hypotonic solution.
237624
here's a basic answer about stuff we were recently talkin' about in class.... there are intrinsic and extrinsic proteins... also called integral and peripheral proteins... the first guys completely span the membrane bilayer and the second guys just touch the surface of the membrane or only partially go into it.  Proteins can diffuse laterally in the membrane.  They also decrease the fluidity of the membrane and increase its rigidity.  I believe it's oligosaccarides or carbohydrates can also bind to the proteins.  Most of the proteins function though as transporters.  There's so many transporters that that's a new questions in itself and i don't feel like the typing! ;)
1133718
A. Yes, the use of ATP against the gradient is active\nB. This is diffusion or osmosis\nC. Nope\nD. This is passive transport
980593
Dialysis tubing can come in various pore sizes that allow selective passage of materials. This is like a cell membrane that is also selective, but not really in terms of the size of the material. It has to do with the polarity (cell membrane is bipolar-has polar head with long, non-polar tail, but two chains of this with non-polar ends facing inward on the membrane and polar heads facing the outside of the membrane). Polar molecules (such as Na+ or K+) need to go through membrane-bound protein channels or receptors.
764226
Semi = partially, half\npermeable = can pass through\nmembrane= a cover\nSemi-permeable membrane = A membrane which only lets a certain things to pass through.
702562
Because of osmosis (the diffusion of water through a membrane) the water will move from the higher concentration of water to the lower concentration of water. (From the solution with less sugar, to the solution with more sugar, because it has less water in it with the sugar taking up the space.)
854233
Basically the semi-permeable membranes and capillary beds carry out osmosis. Osmosis is the passive diffusion of water molecules from a higher water potential to a lower water potential. Water moves from an area with higher concentration of water to an area with less water until the concentration of water in both areas become equal. Semi-permeable membranes and capillaries have thin walls that allow the passage of water. Thus water can move according to its concentration across the membranes.
449266
Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration...
192408
Ionophores- They havea negatively charged channel that allows the solute to enter\n\nFacilitated diffusion- Essentially they capture a solute and tug it into the cell.\n\nactive transport- i believe they look similarly to proteins that facilitate diffusion
767841
In order to have osmosis first of all you need to have a semi-permeable membrane separating two solutions. In order to have net water movement from one solution to the other you need to have different concentrations of solutes that CANNOT pass through the membrane. These solutes are osmotically active: since they cannot pass through the membrane water has to move in order to equilibrate the osmotic pressures. If they could pass through the membrane then they would just diffuse from one solution to the other until their concentration equilibrates and thus they would not contribute to the generation of osmotic pressure. \n\nSo in two words, osmotically active substances with respect to a given semi-permeable membrane are solutes that cannot pass through the membrane.
552863
Cell surface hydrophobicity
864874
"Aquaporin" is a class of molecules, so which one are you looking for the formula for?  And what possible reason might you have for wanting to know? LOL\n\nHere's a link that explains what they are, (they are basically conglomerate protein molecules) and as you can see the 'chemical formula' might be somewhat clumsy and unenlightening!
98589
Transmembrane proteins form channels through the lipid bilayer.\nThere are different sorts of channels, ion channels for example.\nIn the case of ions, they would not normally be able to cross the membrane, a channel protein (plus associated mechanisms) make it possible.
1072970
You best resource is the internet. Since you are the only on who knows what your level of understanding is, only you can choose from the multitude of sources.  Please choose the one that comes closest to what you need:\nhttp://www.google.com/search?num=100&hl=en&lr=lang_en&q=cell+membrane+loose+stability+%2B+oxygen+depletion&btnG=Search\nhttp://search.yahoo.com/search?fr=ytff1-&p=cell%20membrane%20loose%20stability%20%2B%20oxygen%20depletion&ei=UTF-8
815455
blocked pores and bacteria.