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Two molecules, A and B, and their distribution inside and
outside of a cell are represented in the diagram.
State one possible reason why molecule A could diffuse
across the membrane of the cell but molecule B could not.
Answer:
Molecule A is small enough to pass, molecule B is too big.
Aim: How does
Osmosis and Diffusion
compare?
What is the diffusion of
water called?
Osmosis
OSMOSIS
 The
movement of water from an
area of high concentration to an
area of less concentration.
What is meant by concentration?
The amount of solute!
Solvent: The liquid (ex. Water)
Solute: The solid added to the liquid (ex.
Salt/sugar)
Distilled water
100% pure water
Concentration Differences:
1)
A 90% salt solution vs. a 20% salt
solution
Which solution has more salt particles?
Which solution has more water molecules?
2) A 60% salt solution vs. 80% salt
solution?
Which container has a greater
concentration of water molecules?
= Solute (salt)
= Solvent (water)
Which container has a greater
concentration of solute molecules?
In which direction is osmosis going
to occur?
= Solute (sugar)
= Solvent (water)
Selectively Permeable
Why does this happen?
Why are the water molecules
diffusing to the left?
Water molecules are red
The
water is moving
from an area of high to
low!
Why does water go in and out
of the cell?
EQUILIBRIUM
If soluteTo
is maintain
equal, DYNAMIC
then so is
water amt.,
molecules still move back and forth!
What happens to an animal
cell if it is surrounded by a
high concentration of water?
Water will enter the cell! Cell will swell and burst!
What happens to an animal
cell if it is surrounded by a
low concentration of water?
The Cell will shrink!! Salt sucks!!!!
Practice Questions
1. A cell containing 98% water in its cytoplasm is
placed in a 20% salt solution. What will happen to
the cell?
2. What will happen to a cell if it is placed into a
concentrated salt solution?
3. What will happen if a cell is placed in distilled water?
In which direction will
osmosis happen?
How is osmosis a form of
passive transport?
Osmosis is the movement of water from
an area of high concentration to an
area of low concentration. No ATP