2selective permeability Chapter 7.2Membrane Structureresults inselective permeabilityMembrane- A supramolecular structure. Many molecules ordered into a higher level of organization.Membrane regulates the cells molecular traffic. A steady traffic of small molecules and ions moves across the plasma membrane in both directions.Cell is selective permeability, to allow a variety of small molecules, but then excluding the ones it does not want. The membrane can also determine what rate the substances travel in and out.
3The Permeability of the Lipid Bilayer Chapter 7.2The Permeabilityof the Lipid BilayerHydrophobic molecules can dissolve in the lipid bilayer of a membrane and cross it with ease without the aid of membrane proteins.Polar molecules only pass slowly through the membranes lipid bilayer.
4Transport Proteins Chapter 7.2 There are many kinds that transport substances in many different ways, some cells membranes differ from others.Transport Proteins- Allows hydrophilic substances to avoid contact with the lipid bilayer by passing through this. They also span the membrane.An example of this is aquaporins. These are channel proteins that facilitate the passage of water molecules through the membrane in certain cells.Carrier proteins hold on to its “passengers” and then changes shape in a way that shuttles them across the membrane.The selective permeability of a membrane depends on both the discriminating barrier of the lipid bilayer and the specific transport proteins built into the membrane.
6Passive Transport is diffusion of a substance across a membrane with Chapter 7.3Passive Transport is diffusion of a substance across a membrane withno energy investmentA result of thermal motion is diffusionDiffusion- the tendency for molecules of any substance to spread out evenly into the available space.Any substance will diffuse down its concentration gradient.Concentration gradient- in the absence of other forces, a substance will diffuse from where it is more concentrated to were it is less concentrated.Diffusion is spontaneous.The diffusion of substance across a biological membrane is called passive transport because the cell does not have to expend energy to make it happen.
7Effects of Osmosis on Water Balance Chapter 7.3Effects of Osmosis onWater BalanceOsmosis- the diffusion of water across a selectively permeable membrane.The movement of water across cell membranes and the balance of water between cell and its environment are crucial to organisms.
8Water Balance of Cells Without Walls Chapter 7.3Water Balance of CellsWithout WallsTonicity- the ability of a solution to cause a cell to gain or lose water.Isotonic – iso means sameSo the isotonic solution would be the same environment as the cell.Hypertonic- hyper means moreSo, in the instance of a cell, the hypertonic solution would have more non-penetrating solutes than the cell.-causes water to leave cell and shrivel and dieHypotonic- hypo means lessFor a cell in a hypotonic solution with less non-penetrating solutes, water will enter the cell faster than it leaves.-causes cell to swell and burst or lyseOsmoregulation- the control of water balanceAnimals and other organisms without rigid cell walls living in hypertonic or hypotonic environments must have special adaptations for osmoregulation.
9Water Balance of Cells with Walls Chapter 7.3Water Balance ofCells with WallsFlaccid- limpIf the cells and their surroundings are isotonic, there is no net tendency for water to enter, and the cell becomes this.Turgid- very firmElastic walls of cells will only expand so much before it exerts a back pressure on the cell that opposes further water uptake.*Like a Bush*
10Facilitated Diffusion Chapter 7.3Facilitated DiffusionFacilitated diffusion- when polar molecules and ions impeded by the lipid bilayer of the membrane diffuse passively with the help of transport proteins that span the membrane.-material moves down concentration gradientChannel proteins simply provide corridors that allow specific molecules or ions to cross the membrane.An ion channel is one of these groups. Many of these function as gated channels. Gated channels are stimulated to open and close by electrical or chemical stimulus's.Carrier proteins simply change conformational shape as they bind to and transport solutes across the membrane