BIOL107 Lecture 7: Cell Membrane Part 2
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22 Sep 2015
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Biol 107 - lecture 7 - cell membrane part 2. A substance can freely diffuse across the phospholipid bilayer. These substances are generally small and non-polar, but are always uncharged. A substance that cannot cross the hydrophobic core of the membrane. These substances are too large, or charged, or polar (with h2o as an exception) Ions are the least permeable as they are charged. Water molecules surround sodium ions through dipole attraction. This causes the molecule to become too large to pass through the bilayer. In water molecules the electrons can rearrange and remove the dipole charge just long enough for the molecules to pass through the membrane. Moves down the concentration gradient until an equilibrium is reached. More solute in the cell than outside the cell. Water follows solute and enters the cell. Animal cells can fill with too much water and burst. Cell wall prevents the cell from bursting. Hypertonic (hyper: too much ; tonic: solution )