Cell Biology/Membranes/Semi-permeability and osmosis

<< Cholesterol | Semi-permeability and Osmosis | Proteins and channels >> The membranes of cells are a fluid, they are semi-permeable, which means some things can pass through the membrane through osmosis or diffusion. The rate of diffusion will vary depending on the its: size, polarity, charge and concentration on the inside of the membrane versus the concentration on the outside of the membrane. When something is permeable it means that something can spread throughout, like (The perfume is permeating the room.). Here is a list of some molecules and how they relate to passing through the membrane without assistance, in other words, through diffusion: Hydrophobic Molecules O2 - Oxygen N2 - Nitrogen benzene Small uncharged Polar Molecules H2O - Water urea glycerol Large Uncharged Polar Molecules Glucose Sucrose nucletide Ions H+ - Hydrogen ion Na+ - Sodium ion K+ - Potassium ion Ca2+ - Calcium ion Cl- - Chloride ion Various substances will pass through the membranes at varying rates through diffusion.