Homeostasis

All cells must maintain an internal balance
For animal cells:
 Allow glucose, oxygen and water in
 Export wastes and carbon dioxide out
Selectively Permeable

The ability of a membrane to allow some
substances to pass through while keeping
others out
 Strainer
 Filter
 Screen
 ???
door
Structure of the Plasma
Membrane

Phospholipid
Phosphate
Lipids
http://telstar.ote.cmu.edu/biology/downloads/membranes/
Phospholipid Bilayer
 Meaning
that there is two layers of
the phospholipid molecule
http://www.wiley.com/college/pratt/0471393878/student/animations/membrane_transport/index.html
Protein Molecules
 Are
embedded throughout the bilayer,
serve as channels for materials to pass
through the membrane


http://home.earthlink.net/~shalpine/anim/Life/memb.htm
http://www.wisc-online.com/objects/index_tj.asp?objid=AP1101
Fluid Mosaic Model
 The
phospholipids are not bonded to
each other and can freely move
sideways throughout the bilayer


http://www.stolaf.edu/people/giannini/flashanimat/lipids/membrane%20fluidity.swf
http://telstar.ote.cmu.edu/Hughes/tutorial/cellmembranes/bil.swf
Diffusion

The movement of particles from areas of high
concentration to areas of low concentration

http://www.stolaf.edu/people/giannini/flashanimat/transport/diffusion.swf

http://www.wisc-online.com/objects/index_tj.asp?objid=AP1903

Movement occurs until dynamic equilibrium is
reached – continuous movement with no overall
change
 Smells,
dyes, ??
Osmosis


The diffusion of water molecules through
a membrane from a high to low
concentration
http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm
Active Transport
Movement of materials against the
concentration gradient
 Requires energy!!!


http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html
http://www.stolaf.edu/people/giannini/flashanimat/cellstructures/phagocitosis.swf

http://www.wisc-online.com/objects/index_tj.asp?objid=AP11203
