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AP Lab 4: Osmosis and Diffusion
Purpose1. 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.