Passive Transport

About Cell Membranes

1.All cells have a cell membrane

2.Functions: 

a.Controls what enters and exits the cell to maintain an internal balance called homeostasis

b.Provides protection and support for the cell

•cell uses no energy

•molecules move randomly

•Molecules spread out from an area of high concentration to an area of low concentration.

•(HighàLow)

•Three types:

​1.Diffusion: random movement of particles from an area of high concentration to an area of low concentration.

(High to Low)

•Diffusion continues until all molecules are evenly spaced (equilibrium is reached)-Note: molecules will still move around but stay spread out.

​2. Facilitated diffusion: diffusion of specific particles through transport proteins found in the membrane

a.Transport Proteins are specific – they “select” only certain molecules to cross the membrane

b.Transports larger or charged molecules

​3.Osmosis:  diffusion of water through a selectively permeable membrane

•Water moves from high to low concentrations

​Water moves freely through pores.

Solute (green) to large to move across.

​Hypotonic:  The solution has a lower concentration of solutes and a higher concentration of water than inside the cell. (Low solute; High water)

​Result: Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)!

​Hypertonic:  The solution has a higher concentration of solutes and a lower concentration of water than inside the cell. (High solute; Low water)

​Result: Water moves from inside the cell into the solution Cell shrinks (Plasmolysis)!

​Isotonic:  The concentration of solutes in the solution is equal to the concentration of solutes inside the cell.

​Result:  Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium)