Unit 3 – Lecture 3
Diffusion
Diffusion – movement of substances from an area of
high concentration to an area of low concentration
 works to balance the concentration gradients of
substances
 ex: perfume in a room,
dye in a glass of water…
Diffusion – cont’d
Concentration Gradient – difference in concentration of
a substance over a certain area
 “with/down” the gradient = particles move from area
of high conc. to low conc.
Diffusion – cont’d
Concentration Gradient – difference in concentration of
a substance over a certain area
 “against” the gradient = particles move from area of
low conc. to high conc.
 non-natural movement;
requires E
Diffusion – cont’d
Dynamic Equilibrium – a balance of the distribution of
particles in an area acknowledging the constant
movement of the particles
 dynamic – opposite of sta(tic/sis)
 indicates constant change
Discuss
 What is the purpose / point of diffusion?
 What does it mean to move
“against” a concentration gradient?
 What is dynamic equilibrium?
Diffusion – cont’d
Diffusion often occurs through one of two types of
membranes:
 permeable membrane
 allows all molecules [solute, solvent, or other
particle] to pass through
 semi/selectively permeable membrane
 allows only certain substances to pass through
Discuss
 What type of membrane,
permeable or selectively permeable,
do our cells have?
Diffusion Drawings #1
Problem: In a beaker with a permeable membrane there
are:
 4 particles of X [3 left, 1 right]
 12 particles of O [2 left, 10 right]
Based on the given information,
 identify & understand the type of membrane
 draw before & after beaker with membrane
Problem: In a beaker with a permeable membrane there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
Based on the given information,
 identify & understand the type of membrane
 draw before & after beakers with membrane
Problem: In a beaker with a permeable membrane there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
before beaker:
 under beaker, record # of particles per side
 draw # particles in beaker
X=3
O=2
X= 1
O = 10
Problem: In a beaker with a permeable membrane there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
before beaker:
 determine directions of particle movement
 above, draw arrows specifying how particles will move
X=3
O=2
X= 1
O = 10
Problem: In a beaker with a permeable membrane there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
before beaker:
 large arrow = larger movement [specify type of particle]
O
X
X=3
O=2
X= 1
O = 10
Problem: In a beaker with a permeable membrane there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
before beaker:
 small arrow = smaller movement [specify type of particle]
O
X
X=3
O=2
X= 1
O = 10
Problem: In a beaker with a permeable membrane there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
after beaker:
 under beaker, record new # of particles per side
O
X
X=3
O=2
X= 1
O = 10
X=2
O=6
X= 2
O=6
Problem: In a beaker with a permeable membrane there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
after beaker:
 draw # of particles in beakers
O
X
X=3
O=2
X= 1
O = 10
X=2
O=6
X= 2
O=6
Problem: In a beaker with a permeable membrane there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
after beaker:
 draw appropriate arrows [specify type of particle]
O
O
X
X
X=3
O=2
X= 1
O = 10
X=2
O=6
X= 2
O=6
Diffusion Drawings #2
Problem: In beaker with a membrane selectively
permeable to X molecules, there are:
 4 particles of X [3 left, 1 right]
 12 particles of O [2 left, 10 right]
Based on the given information,
 identify & understand the type of membrane
 draw before & after beaker with membrane
Problem: In a beaker with a membrane selectively permeable to X
molecules, there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
Based on the given information,
 identify & understand the type of membrane
 draw before & after beakers with membrane
Problem: In a beaker with a membrane selectively permeable to X
molecules, there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
before beaker:
 under beaker, record # of particles per side
 draw # particles in beaker
X=3
O=2
X= 1
O = 10
Problem: In a beaker with a membrane selectively permeable to X
molecules, there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
before beaker:
 determine directions of particle movement
 above, draw arrows specifying how particles will move
X=3
O=2
X= 1
O = 10
Problem: In a beaker with a membrane selectively permeable to X
molecules, there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
before beaker:
 large arrow = larger movement [specify type of particle]
X
X=3
O=2
X= 1
O = 10
Problem: In a beaker with a membrane selectively permeable to X
molecules, there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
before beaker:
 small arrow = smaller movement [specify type of particle]
X
X=3
O=2
X= 1
O = 10
Problem: In a beaker with a membrane selectively permeable to X
molecules, there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
after beaker:
 under beaker, record new # of particles per side
X
X=3
O=2
X= 1
O = 10
X=2
O=2
X= 2
O = 10
Problem: In a beaker with a membrane selectively permeable to X
molecules, there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
after beaker:
 draw # of particles in beakers
X
X=3
O=2
X= 1
O = 10
X=2
O=2
X= 2
O = 10
Problem: In a beaker with a membrane selectively permeable to X
molecules, there are:
4 particles of X [3 left, 1 right]; 12 particles of O [2 left, 10 right]
after beaker:
 draw appropriate arrows [specify type of particle]
X
X=3
O=2
X
X= 1
O = 10
X=2
O=2
X= 2
O = 10
Osmosis
Osmosis – diffusion of water across a selectively
permeable membrane
 membrane allows ONLY water to go through
 solute particles NEVER move
 water must be used to reach dynamic equilibrium
 more water moves to where there is more solute
Discuss
 Which has the higher concentration of solute?
 5 scoops of lemonade in a pitcher
filled with 8 ounces [1 cup] of water
 5 scoops of lemonade in a pitcher
filled with 1 gallon of water
 How can you make the concentrations equal?
Osmosis Drawings
Problem: With a membrane selectively permeable to
water, there are:
 4 particles of X [3 left, 1 right]
Based on the given information,
 identify & understand the type of membrane
 draw before & after tubes with membrane
Problem: With a membrane selectively permeable to water, there
are:
4 particles of X [3 left, 1 right]
Based on the given information,
 identify & understand the type of membrane
 draw before & after tubes with membrane
Problem: With a membrane selectively permeable to water, there
are:
4 particles of X [3 left, 1 right]
before tube:
 under tube, record # of particles per side
 draw # particles in tube
X=3
X= 1
Problem: With a membrane selectively permeable to water, there
are:
4 particles of X [3 left, 1 right]
before tube:
 determine directions of particle movement
X=3
X= 1
Problem: With a membrane selectively permeable to water, there
are:
4 particles of X [3 left, 1 right]
before tube:
 above, draw arrows specifying how particles will move
X=3
X= 1
Problem: With a membrane selectively permeable to water, there
are:
4 particles of X [3 left, 1 right]
before tube:
 large arrow = larger movement [specify type of particle]
H2O
X=3
X= 1
Problem: With a membrane selectively permeable to water, there
are:
4 particles of X [3 left, 1 right]
before tube:
 small arrow = smaller movement [specify type of particle]
H2O
X=3
X= 1
Problem: With a membrane selectively permeable to water, there
are:
4 particles of X [3 left, 1 right]
after tube:
 under tube, record # of particles per side
H2O
X=3
X= 1
X=3
X= 1
Problem: With a membrane selectively permeable to water, there
are:
4 particles of X [3 left, 1 right]
after tube:
 draw # of particles in beakers AND water level
H2O
X=3
X= 1
X=3
X= 1
Problem: With a membrane selectively permeable to water, there
are:
4 particles of X [3 left, 1 right]
after tube:
 draw appropriate arrows [specify type of particle]
H2O
X=3
H2O
X= 1
X=3
X= 1
What happens to cells?
Hypertonic Solution – solution outside of
the cell has a higher concentration of
solute than inside of the cell.
 “hyper” = more than normal
 water moves out of cell
 cell shrinks
Why is this bad for the cell?
What happens to cells? – cont’d
Isotonic Solution – solution outside of the
cell has the same concentration as the
solution inside of the cell.
 concentrations are equal [“iso”]
 cell remains the same size
What happens to cells? – cont’d
Hypotonic Solution – solution outside of
the cell has a lower concentration of
solute than inside of the cell.
 “hypo” = less than normal
 water moves into the cell
 cell swells
 animal cell – may burst
 plant cell – rigid [preferred for plants]
Discuss
 Hypertonic, Hypotonic, Isotonic
 Compare each term [how are they similar?].
 Contrast each term [how are they different?].