[Unit 4.3] | Osmosis

Question 1

Define Osmosis.

Answer 1

The movement of water from a dilute solution to a concentrated solution across a selectively permeable membrane. (High - Low Conc)

Question 2

What is a selectively permeable membrane?

Answer 2

A membrane that is permeable to water and small molecules, but not large molecules.

Question 3

What is water potential?

Answer 3

• The pressure created by water molecules.
• Under standard conditions, water should have a water potential of 0.
• It is measured in kPa and is represented by the symbol psi.

Question 4

What happens to the water potential of a solution as you add more solute?

Answer 4

• It becomes increasingly negative.
(The water potential of a solution is always negative.)

Question 5

Does water move via osmosis from:
• A: High -> Low Water Potential
Or
• B: Low -> High Water Potential

Answer 5

A: High -> Low Water Potential

Question 6

How can the water potential of a tissue/cell sample be determined using solutions of varying water potentials?

Answer 6

• Record the mass of the samples
• Place each sample into a separate solution
• After an intermission period, remove the samples and record their final mass and the percentage change.
• A percentage change of 0 means the water potential of the solution equals that of the sample.

Question 7

What are the 3 conditions of animal cells when they are hypertonic, isotonic or hypotonic solutions?

Answer 7

• Hypertonic: Water leaves the cell. The cell is shrivelled.
• Isotonic: There is no movement of water. The cell is normal.
• Hypotonic: Water enters the cell. It becomes lysed and can burst.

Question 8

What are the 3 conditions of plant cells when they are hypertonic, isotonic or hypotonic solutions?

Answer 8

• Hypertonic: Water leaves the cell. The cell is plasmolysed.
• Isotonic: There is no movement of water. The cell is flaccid.
• Hypotonic: Water enters the cell. It becomes turgid/normal.

Question 9

What is a hypertonic solution?

Answer 9

A solution with a water potential higher than that of the other solution it interacts with. (Water is moved away from the hypertonic solution during osmosis.)

Question 10

What is an isotonic solution?

Answer 10

A solution with a water potential equal to that of the other solution it interacts with. (Water does not move away from either solution during osmosis.)

Question 11

What is a hypotonic solution?

Answer 11

A solution with a water potential lower than that of the other solution it interacts with. (Water moves into the hypotonic solution during osmosis.)