Osmosis

Question 1

What is osmosis?

Answer 1

The diffusion of water molecules across a partially permeable membrane, from an area of higher water potential to an area of lower water potential.

Question 2

What is water potential?

Answer 2

The likelihood of water molecules to diffuse out of or into a solution.

Question 3

What does it mean if a cell is in an isotonic solution?

Answer 3

No net movement of water because same water potential.

Question 4

What are solutions with a higher water potential compared with the inside of a cell called?

Answer 4

Hypotonic

Question 5

What are solutions with a lower water potential than the cell called?

Answer 5

Hypertonic

Question 6

What factors affect the rate of osmosis?

Answer 6

1. Water potential gradient - higher = faster rate but levels off over time
2. Thickness of exchange surface - thinner = faster rate
3. Surface area - larger = faster rate

Question 7

How do you make serial dilutions?

Answer 7

1. Line up 5 test tubes.
2. Add 10cm3 of 2 M sucrose solution to first tube and then 5cm3 distilled water to the rest.
3. Draw 5cm3 from 1st and add to 2nd.
4. Repeat.

Question 8

How do you investigate water potential?

Answer 8

1. Make serial dilutions.
2. Measure change in mass by:
   - cut potatoes into equal 1cm chips
   - measure mass on balance
   - place into solutions and leave for 20 mins
   - remove and pat gently
   - reweigh and calculate percentage change in mass
3. Produce a calibration curve to determine water potential.