Osmosis
• Osmosis is simply a type of diffusion.
• It is when water moves from areas of HIGH
concentration to areas of LOW concentration
through a membrane.
• We have already witnessed osmosis in TWO of
the experiments we’ve done this year. Can you
name which two?
There were LESS water molecules inside the gummy bear, so the
water diffused INTO the gummy bear to try to achieve
homeostasis.
Egg Experiment
Syrup Egg
LESS water molecules outside the egg, so the
water diffused out of the membrane to try to
achieve balance
Control Egg
Water Egg
MORE water molecules outside the
egg, so the water diffused out of the
membrane to achieve balance.
Starch & Iodine Experiment
Starch & Iodine Experiment
What does osmosis and diffusion have
in common?
• They are both examples of PASSIVE transport.
• Passive transport is when molecules are
transported throughout a cell or through a
membrane WITHOUT the use of energy
___________.
How can I get the green molecules on
the top to move across the
membrane?
• Will they diffuse?
• NO. They won’t
move against their
concentration gradient
with PASSIVE
transport.
How can I get the green molecules to
move across the membrane?
• Molecules can use
ACTIVE transport
to move molecules.
It requires energy
to make the protein
“transporter”
function
Osmosis/Diffusion Web Resources
• http://www.phschool.com/science/biology_pl
ace/labbench/lab1/ex1.html