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.