Cell Transport

 

	In order to survive, cells must maintain a biological balance (homeostasis) with their environment; they do this by regulating what comes into and goes out of the cell

-Passive vs. Active Transport

	Passive	Active
Cell Energy (ATP) Required	No	Yes
Concentration Gradient & Molecular Movement	molecules move  along the gradient ("high to low")	molecules are forced  against the gradient ("low to high")
Transport Methods	diffusion osmosis facilitated diffusion	transport pumps endocytosis exocytosis

 

-Crossing the Membrane

-to enter or leave a cell you can:

     1. move directly through the lipid bilayer
          -works for small molecules that are chemically similar 
            to the phospholipids
                -gases (O₂ and CO₂) and water
          -typically associated with diffusion and osmosis

     2. cross the bilayer through a channel / transport protein
           -works for small, polar molecules 
                 -sugars and ions
           -typically associated with facilitated diffusion

     3. manipulate the bilayer with the use of vacuoles / vesicles
           -works for large substances
                  -enzymes, hormones, food bits and waste particles
           -typically associated with endo- and exocytosis

 

-The Movement of Water

	water molecules do move via diffusion but water is so important to a cell that its natural movement gets its own term (osmosis)

-Osmosis
     -the diffusion of water
          -movement of water from high to low concentration
                -passive transport - no energy required

-Sometimes, cells will force water against the concentration gradient
     -ex: paramecium in a pond must expel water to avoid cytolysis
     -this requires energy & is not osmosis

		active transport is involved anytime water is forced against its natural flow

     
   

 

to great cell transport animations

-Short Animations of
     -diffusion: Ohio University 
      -osmosis: Westminster Secondary School
      -transport proteins: The College of St. Scholastica  

-Animated Movies
     -Pearson Prentice Hall  (includes audio narration)   
      -Northland Community and Technical College 

 

to more detailed notes

-Florida State University
-Clinton Community College
-University of Connecticut