What creates selective permeablility of plasma membrane?
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this would be easier to google if you spelled it correctly, i imagine.\n\nlets assume you arent asking: what 'makes' it selectively permeable, but what 'causes' selective permeability.\n\nthe easy answer would be the code of the construction of the membrane (what makes me a boy--my code--genetics, what makes my air filter let air pass but not dog hair--the code--the engineering diagram) which usually defines permeability in one of three ways: rate, shape or size.\nrate: how fast can water go through my reverse osmosis (LOL) filter. 50 gallons a day. but ALL h20 goes through.\nshape: what can get through the cell membrane, anything that matches the shape of the protein that carries it across.\nsize: large rocks get caught on the screen, but small rocks go through.\n\nmaybe you can define a little...clarify seletively permeable or selective permeability, human biology or water filtration? \n\neither way, this link might help (or might be 5 years behind you! sorry, dont know!)
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It would depend on several factors. Small, uncharged molecules can pass through the cell membrane through diffusion. When it is water, it is called osmosis. Diffusion can only occur into the cell when the concentration of the substance is greater outside the cell than within it, and likewise only out of the cell when the concetration is greater inside the cell than outside. This is called the concentration gradient.\n\nWhen the molecule is charged or is large (such as a chlorine ion or a lactose molecule), it requires active transport by carrier proteins. There are also carrier proteins that help to transport against the concentration gradient.\n\n[Edit] \nAfter thinking for a bit, I believe it would be pertinent to include something about the more complex methods of active transport.\n\nThere are two "directions" of the complex forms of active transport: in (endocytosis) and out (exocytosis).\n\nExocytosis is when a vesicle, after being released from the Golgi complex, fuses to the cell membrane, releasing the contents.\n\nEndocytosis is done by three main means: Phagocytosis, Pinocytosis, and Receptor-Mediated Endocytosis.\n\nPhagocytosis is the process of enveloping a large particle, such as how many unicellular organisms "eat" other organisms. The large particle comes in contact with the cell membrane, stimulating the formation of a vesicle. This vesicle then enters the cell and depending on the contents may fuse with a lysosome to help to digest it.\n\nPinocytosis also forms a vesicle, but differs from phagocytosis because it forms a much smaller vesicle.\n\nReceptor-mediated endocytosis is when particles that cannot normally enter the cell bond to receptor proteins embedded in the cell membrane. These proteins then congregate and form a vesicle. \n\nIn all forms of endocytosis and exocytosis, ATP is required for energy.
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The cell membrane is a phospholipid bilayer, meaning there are two chains. Each chain has a serious of long non-polar tails (hydrophobic, hate water, non-permeable to polar molecules) with polar heads (hydrophilic, love water, permeable to polar molecules). The polar heads are on the outside of the membrane and the non-polar tails face the middle of the membrane. This structure prevents molecules from freely moving across the membrane. Embedded within the membrane are protein channels that are designed to specifically allow certain molecules through. Some of these channels open randomly, others require some kind of signal. They are selective by allowing molecules of certain size and/or charge (positive or negative) cross the membrane, also keeping in mind concentration gradients (molecules will move down their gradients). In some cases, molecules move against their gradients, but require energy to do it.
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The interior of the lipid bilayer is hydrophobic; ions, by definition, are hydrophillic.  If the ion interacts with the hydrophobic environment of the lipid bilayer, this is energetically unfavorable.  It will cause the ion to move back out of the membrane, preventing ions from passing through the membrane at a useful rate.  Ion channels allow the passage of ion by preventing the ion from interacting with the lipid bilayer, or by orienting the ion so that it interacts favorably.
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plasma membrane-bouncer or security\ncell wall-Berlin Wall\nmitochondria-power plant\nER-Ups of the cell\nlysosome-decomposers\nvacuole-water and septic tank\nchloroplast-dye
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chemiosmosis makes the Hydrogen gradient in the inner membrane space where it then channels through the ATP sythesis to make ATP and water
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I do not know just how scientific you want this to be, so I will give you the reason to a collegiate level. The plasma membrane in your dermal cells (as in most somatic cells) is made up of a lipid bilayer. Water can travel through a protein channel called the aquaporin or it can go directly through the lipid bilayer in certain occasions (though large amounts cannot as the middle of the bilayer is made up of hydrophobic tails). When water is exposed to the skin, diffusion occurs since there is a greater concentration of water outside the dermal cells than inside, and this is called osmosis. Therefore, these cells take in large amounts of water (up until a point where the aquaporin is closed to prevent cytolysis, or the death of cells due to overexpansion). The interstitial tissue also absorbs water, and thus, the dermal area expands. Since the dermal area is larger than it really should be, it "folds" to a point, causing wrinkles. Hope that helped.
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From the interior of the lipid bilayer?  Because the interior is hydrophobic, and ions would tend to get in and get stuck, eventually probably gumming up the membrane.
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mostly phospholipids (the bulk of the membrane is the phospholipid bilayer, with hydrophobic tails pointed towards each other and hydrophilic heads pointing out), with a bunch of proteins stuck in it like little potatoes :) \n\nmixed in the sea of phospholipids are small amounts of cholesterol (roughly the same size) to help prevent weakening of the cell membrane at high temperatures.\n\nAs for proteins, there are many types with many functions!\n- transport proteins\n- identity markers\n- junctioning proteins (stick to other cells)\n- anchors for cytoskeleton\n- enzymes\n- hormone receivers
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Visking tubing is partially permeable.\ncut 2 pices of Visking tubing 12cm long.tie one end of each with cotton.fill "cell A" with sugar solution & "cell B" with water.tie the other end & weigh each "cell".put "cell A" into a beaker of water.put "cell B" into a beaker of sugar solution.after 30 minutes reweigh each "cell".Cell A increases in weight because water has passed into the cell,into the srong solution by osmosis.Cell B decreases in weight because water has passes out of the cell,into the strong solution by osmosis.\nhope that helped-cheers!
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external barriers, then mucous membrane, then nonspecific, then specific.
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Glucose, sodium ions and choride ions are just a few examples of molecules and ions that must efficently get across the plasma membrane but to which the lipid bilayer of the membrane is virtually impermiable. Their transport must therefore be "facilitated" by proteins that span the membrane and provide an alternative route or bypass. Facilitated diffusion is the name given this process. It is similar to simple diffusion in the sense that it does not require expenditure of metabolic energy and transport is again down an electrochemical gradient. \n\nTwo major groups of integral membrane proteins are involved in facilitated diffusion: \n\nCarrier proteins(also known as permeases or transporters) bind a specific type of solute and are thereby induced to undergo a series of conformational changes which has the effect of carrying the solute to the other side of the membrane. The carrier then discharges the solute and, through another conformational change, reorients in the membrane to its original state. Typically, a given carrier will transport only a small group of related molecules.\n\nSome important and illustrative groups of transporters are: \nCertain of the hexose transporters, which transport glucose and similar monosaccharides into and out of cells.\n \nBand 3, the anion transporter, which facilitates transport of bicarbonate and chloride ions \n\n\nIon Channels do not really bind the solute, but are like hydrophilic pores through the membrane that open and allow certain types of solutes, usually inorganic ions, to pass through. In general, channels are quite specific for the type of solute they will transport and transport through channels is quite a bit faster than by carrier proteins. Additionally, many channels contain a "gate" which is functions to control the channel's permiability. When the gate is open, the channel transports, and when the gate is closed, the channel is closed. Such gates can be controlled either by voltage across the membrane (voltage-gated channels) or have a binding site for a ligand which, when bound, causes the channels to open (ligand-gated channels).\n\nIon channels allow currents the be carried across the membrane and are thus of particular importance in the physiology of excitable cells like neurons and muscle cells.
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Alkanes-such as methane (CH4) can pass through the lipid bilayer.
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Lipid soluble molecules diffuse through membrane lipids. Small soluble molecules and ions diffuse through membrane channels.
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facilitated diffusion
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Passive transport is when subtances can move across the plasma membrane without any input of energy by the cell\n\nEg : Simple Diffusion, Osmosis and Facilitated diffusion\n\nWhile active transport is the movement of molecules or ions against the concentration gradient across the plasma membrane.\n\nEg :Carrier protein
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osmosis is the movement of water across a membrane. \nWikipedia on the subject: \n\n"Osmosis is the diffusion of a solvent through a selectively-permeable membrane from a region of low solute concentration to a region of high solute concentration, or in other words, from a high water concentration to a low water concentration. The higher the solute concentration the lower the water concentration will be. The selectively-permeable membrane is permeable to the solvent, but not to the solute, resulting in a chemical potential difference across the membrane which drives the diffusion. That is, the solvent flows from the side of the membrane where the solution is weakest to the side where it is strongest, until the solution on both sides of the membrane is the same strength (that is, until the chemical potential is equal on both sides)."\n\nin short, if you put the potato in fresh water, the potato cells will burst, because water will enter the cells in an attempt to equalize the concentration of salt, etc. inside the cell to what is outside the cell.. if you put a potato in salt water, the cells will shrink, because water will exit them in an attempt to equalize the concentration of salt in the cell and outside of it. I realy don't know what the temperature of water will affect though.