1. Diffusion & Osmosis Lab

2. Positive tests for starch and glucose.
What is the “test for starch”?
Iodine turns purple in the
presence of starch
What is the “test for glucose”?
Benedicts solution (heated) indicates
presence of sugar by turning color.
(green, orange or red depending
upon concentration)

3. Semi-permeable membrane
Did iodine move across the membrane? Evidence?
Did starch move across the membrane? Evidence?
Did glucose move across the membrane? Evidence?
Did water move across the membrane? Evidence?

4. Part 1 Follow up questions
Why was it important to rinse the bag with H2O before putting it in water with iodine?
Describe the permeability of the membrane .
Did you draw the set up for part 1 on top of page 5?

5. Part II One potato slice in pure H2O, 1 potato slice in salt water.
What did you observe about the potato slices after letting them sit in the solutions for a time?
Observation: The slice in dis. H2O was normal stiffness, the slice in salt H2O was limp.
What happened here?
Turgor pressure: internal pressure resulting from being filled with a fluid.
A water balloon would show turgor pressure. (The membrane of the balloon is supported by internal water pressure.)

6. Elodea in fresh and saltwater
In which situation (fresh vs. saltwater) did the Elodea cells have the greatest level of turgor pressure?
Why?
Cell membrane is NOT visible because water is pushing it up against the cell wall
Cell membrane is visible because cell lost water
Distilled (100%) water around cell is hypotonic to cell & water moves into the cell by osmosis pushing the membrane against the cell wall.
Salt Solution around cell is hypertonic to cell & water moves out of the cell by osmosis causing the cell to lose turgor (fluid) pressure.

7. Egg Demonstration In which environment did the egg gain mass?
In which environment did the egg lose mass?
Which environment was hypotonic when compared to the egg?
Which environment was hypertonic when compared to the egg?

8. Increased turgor pressure
Decreased turgor pressure

9. Water has a net flow out of the bag (or from left to right)
The hypertonic solution has a higher concentration of water & less solute compared to the hypertonic solution.