AP Lab 4: Osmosis and Diffusion
Purpose
1. Investigate processes of
diffusion and osmosis in a
model membrane system, and
2. Investigate effect of solute
concentration on water
potential as it relates to living
plant tissues.
Key Concepts
• Diffusion: The mvmt of materials from high to
low concentrations…passive transport = no
energy.
• Osmosis: Mvmt of water from high to low.
Key Concepts
Key Concepts: Water Potential
• Tendency of water to leave one place in favor
of another.
• PP: amt of pressure in cell
• SP: solute concentration: As solute is added,
value for solute potential becomes more
negative  decreases wp.
Key Concepts: Molarity
• 1 M Sucrose: 342.3 g/mol + 1000 mL (1 L)
• 1 M NaCl: 58.44 g/mol + 1000 mL (1 L)
• To make a 0.5 M, cut the grams amount
by ½.
Procedure Pt 1
• 1) Tie off one end of a wet
dialysis bag. Fill with a 10 mL
sugar/salt solution of a
concentration (like 1M NaCl).
Tie off and weigh.
• Fill cup with diff. sugar/salt
concentration (like 0.5M
NaCl).
• Let sit for 30 mins.
• Reweigh
Procedure Part 2
• 1) Obtain 6 wet dialysis bags.
• 2) Fill with different concentrations of sucrose.
Weigh to get initial weights (OM, 0.2 M, 0.4
M, 0.6 M, 0.8 M, 1 M)
• 3) Place dialysis bags in distilled water.
• 4) Wait and then weigh bags to see what
happened. Graph results.
• Hint: Be sure that the entire dialysis bag and
tie are submerged!
Procedure Part 3
• 1) Like Ex 2, but
w/ potatoes. 1st
weigh potatoes.
• 2) Put potatoes
(no skin) in
solutions of
varying sucrose
concentrations.
• 3) Calculate
weight gain or
loss.
Procedure Part 4
• Use the value for the molar concentration of
the potato cores that you obtain in Exercise 3
to determine the water potential for the
potato cells.
• Calculate water potential (pressure potential
on open beaker is zero).
Procedure Part 5
• Watch the effect of placing an onion cell into a
solution that has a lower or higher
concentration of water than the cell.