Topic 2---B: Cell Membranes- 3. Osmosis

Question 1

What is osmosis?

Answer 1

It’s the net movement of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane.
(from a dilute solution to a concentrated solution)
- Passive process

Question 2

What does it mean if there is a high water potential?

Answer 2

A higher concentration of water particles so there are fewer solute particles present to restrict the movement of the water particles.

Question 3

What does it mean if there is a lower water potential?

Answer 3

• A lower concentration of water molecules so there are more solute particles available to restrict the movement of water particles due to the attractive forces that exist between solute and water particles.
• So this will lower the kinetic energy and water potential.

Question 4

What is pure water’s water potential?

Answer 4

0kpa

Question 5

How does the water potential get lower?

Answer 5

By adding more solutes to it so the more negative the water potential the stronger the solutes in the solution so it will be negative

Question 6

What is water potential?

Answer 6

• It’s a measure of the kinetic energy of water molecules.
• When water molecules collide with the cell membrane they create a pressure known as water potential.
• Measured in Kpa

Question 7

Isotonic solution

Answer 7

• Solution surrounding the cell has the same water potential as the cell itself.
• Cells in a isotonic solution won’t gain or lose any water.
• Theres no movement of water molecules because there is no difference in water potential between the cell and surrounding solution.

Question 8

Hypotonic solution

Answer 8

• Solution surrounding the cell has a higher water potential (less solutes) compared with the inside of the cell.
• When the cell is placed in the solution it will swell as water moves into it by osmosis.

Question 9

Hypertonic solution

Answer 9

• Solution surrounding the cell has a lower water potential (more solutes) compared with the inside of the cell.
• When the cell is placed in the solution it maay shrink as water moves out by osmosis.

Question 10

Isotonic solution (animal cell)

Answer 10

• No change in cell volume as they have the same water potential.

Question 11

Hypotonic solution (animal cell)

Answer 11

• Cell bursts if too much water enters (lysis) as solution surrounding the cell has a higher water potential compared with the inside of the cell.

Question 12

Hypertonic solution (animal cell)

Answer 12

• Cell shrinks if too much water leaves (crenation) as solution surrounding the cell has a lower water potential compared with the inside of the cell.

Question 13

Isotonic solution (plant cell)

Answer 13

• No change in cell volume as they have the same water potential.

Question 14

Hypotonic solution (plant cell)

Answer 14

• Vacuole swells and the cell becomes turgid (prevents it from bursting).
• Pressure pushing outwards from inside prevents water entering.

Question 15

Hypertonic solution (plant cell)

Answer 15

• Vacuole shrinks.
• Cell membrane begins to pull away from cell wall.
• Cells becomes flaccid and plasmolysed.

Question 16

Factors affecting the rate of osmosis?

Answer 16

• The surface area of the exchange surface ( the larger the surface area the faster the rate of osmosis).
• The thickness of the exchange surface (the thinner the exchange surface the faster the rate of osmosis).
• The water potential gradient (the higher the water potential gradient the faster the rate of osmosis) but as osmosis takes place the difference in water potential on either side of the membrane decreases, so the rate of osmosis levels off over time.