Maintaining Homeostasis
Passive and Active Transport
Lesson Objectives
• Understand how equilibrium is established as a
result of diffusion.
• Distinguish between diffusion and osmosis.
Cellular Membrane
• Membrane: function is to control what enters
and exits the cell
▫ Selectively permeable
Homeostasis
• All living cells exists in a liquid environment
• Internal conditions need to remain constant
▫ Homeostasis
▫ Equilibrium=everything is balanced
• Maintain homeostasis by regulating movement of
molecules across the membrane
▫ Passive Transport (no energy required)
▫ Active Transport (energy required)
Passive Transport: Diffusion
• Movement of materials across the cell membrane
without using energy
• Diffusion:
▫ Movement of material/molecules from an area of
high concentration to an area of low concentration
 Concentration Gradient
Passive Transport: Osmosis
• When water diffuses across the cell membrane
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.htm
l
Effects of Osmosis on Cells
Hypotonic:
• Lower solute
concentration
outside of the
cell
Hypertonic:
• Higher solute
concentration
outside of the
cell
Isotonic:
• Concentration is
the same inside
and out
▫ Water moves
into the cell
▫ Cell swells
▫ Water moves
out of the cell
▫ Cell Shrinks
▫ Water moves in
and out
How does water move? “Salt Sucks”
How does water move? “Salt Sucks”
How does water move? “Salt Sucks”
v
v
Osmosis In Nature
• Cytolysis: in a hypotonic solution red blood cells
will continue to swell until they burst
▫ Penicillin killing bacteria
• Contractile Vacuole: organelle in protist cells that
pumps excess water out
▫ http://www.youtube.com/watch?v=pahUt0RCKYc&feature=related
• Turgor Pressure: water pressure placed on the cell
wall to give plant cell its shape
▫ Plants wilting if solution is hypertonic
• Don’t drink salt water
• Diarrhea
▫ Something in stools that is drawing out the water
Facilitated Diffusion
• Movement of particles from higher concentration
to lower concentration
• Large molecules may require “help”, they use
carrier proteins
• Nervous system uses Na and Ca pumps
Lesson Objectives
• Distinguish between passive and active
transport.
• Explain how sodium-potassium pumps operate.
• Compare and contrast endocytosis and
exocytosis.
Active Transport
Passive Transport: down concentration gradient
Active Transport
Active Transport
Passive
Active
Active Transport
• Requires energy to move molecules up their
concentration gradient
▫ Low concentration to high concentration
• Sodium-Potassium Pump
• Exocytosis
• Endocytosis
Cell Membrane Pumps
• Requires a carrier protein
• 3 Na-2 K
• Requires energy
•
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_p
ump_works.html
Endocytosis
• Phagocytosis
• Pinocytosis
Exocytosis