2. Cells - Osmosis

Question 1

What does hypotonic mean?

Answer 1

The water potential of the external solution is higher than the water potential of the cell solution.

Question 2

What does isotonic mean?

Answer 2

The water potential of the external solution is equal to the water potential of the cell solution.

Question 3

What does hypertonic mean?

Answer 3

The water potential of the external solution is lower than the water potential of the cell solution.

Question 4

What is the result of a hypotonic solution for a plant cell?

Answer 4

The net movement of water enters the cell, the protoplast swells and the cell becomes turgid.

Question 5

What is the result of an isotonic solution for a plant cell?

Answer 5

The net movement of water neither enters nor leaves cell, there is no change to the protoplast and the cell is in incipient plasmolysis.

Question 6

What is the result of a hypertonic solution for a plant cell?

Answer 6

The net movement of water leaves the cell, the protoplast shrinks and the cell becomes plasmolysed.

Question 7

What is the water potential of pure water?

Answer 7

Zero.

Question 9

What does the addition of a solute to pure water do to the water potential?

Answer 9

It lowers the water potential.

Question 10

Give a brief explanation for osmosis:

Answer 10

• Both solute and water molecules are in random motion due to their kinetic energy
• Selectively permeable plasma membrane only allows water molecules across it, not solute molecules
• Water molecules diffuse from area of higher to lower water potential, down a water potential gradient