CELL TRANSFER MECHANISM I: DIFFUSION & OSMOSIS (FINAL)

• Simple Diffusion: Area of higher concentration --> Equilibrium is achieved.
• Diffusion involves the movement of molecules in a solvent from an area of higher solute concentration to an area of lower solute concentration which eventually results in the state of dynamic equilibrium.
• Simple Diffusion: (PNMHS) passive transport; no energy required; movement of molecules; high to low concentration; state of dynamic equilibrium.
• Facilitated Diffusion: Molecules such as ions and water outside the cell are being transported across the cell membrane through channel proteins via facilitated diffusion.
• The channel protein facilitates the movement of molecules hence the term  “facilitated diffusion”. 
• Osmosis: semi-permeable membrane; high water, low solute concentration; low water, high solute concentration.

  
• Movement is from the region of high water concentration to one with lower water concentration.

  
• Osmosis is similar to diffusion. However, osmosis refers to the movement of water from higher to lower concentration.
• Tonicity: relative concentration of solutes in fluids; ability of a surrounding solution to cause a cell to gain or lose water; depends on the concentration of solutes; can be isotonic, hypotonic, or hypertonic.
• Isotonic solution: Solutions of equal solute concentration.

  solute molecules outside the cell = solute molecules inside the cell
• Isotonic solution is when water molecules move at the same rate in both directions.
• Hypotonic solution: Has lower solute concentration and has higher water concentration (i.e., less solute, more water).

  solute molecules outside the cell < solute molecules inside the cell
• Hypotonic solution can cause the cell to swell or even burst due to the intake of water more than the cell can accommodate.
• Hypertonic solution: has higher solute concentration and has lower water concentration (i.e., more solute, less water).

  solute molecules outside the cell > solute molecules inside the cell
• Hypertonic solution can cause an animal cell to shrink or shrivel due to water loss.
• Hypotonic solution

  
• Isotonic solution

  
• Hypertonic solution

  
• Plant cells, relative to animal cells, do not change cell size that much with varying concentrations of water.
• Diffusion is the movement of molecules down their concentration gradient, i.e., from an area of higher concentration to an area of lower concentration.
• A solution contains both the solute, which is usually solid and a solvent, which is usually a liquid. A solute added in a solvent will naturally diffuse to form a solution.
• Facilitated diffusion involves the movement of molecules across the membrane but with the aid of either channel or carrier proteins. These molecules are usually those that cannot cross due to their molecular size or chemical nature.
• Diffusion is an example of passive transport in which molecules are moved across the membrane without spending energy.
• Osmosis is the diffusion of water across a selectively permeable membrane from high to low concentration.
• Solutions with an equal solute concentration are said to be isotonic.
• Hypotonic solution has a lower concentration of solutes than inside the cell.
• Hypertonic solution is one with a higher concentration of solute outside of the membrane.