CELLS: Osmosis

Question 1

Osmosis.

Answer 1

Passage of water from a region where it has higher water potential to an area where it has a lower water potential through a selectively permeable membrane.

Question 2

Water potential.

Answer 2

Likelihood of water molecules to diffuse out of or into a solution.

Question 3

Isotonic.

Answer 3

Two solutions have same water potential.

Question 4

Solute.

Answer 4

Any substance that is dissolved in a solvent.

Question 5

What has the highest water potential?

Answer 5

Pure water.

Question 6

Under standard conditions of temperature and pressure, what is the water potential or pure water?

Answer 6

0

Question 7

The addition of a solute to pure water…

Answer 7

… will lower its water potential.

Question 8

The water potential of a solution (water + solute) must always be what?

Answer 8

Less than 0 - a negative value.

Question 9

The rate of osmosis depends on what factors?

Answer 9

• Water potential gradient
• Thickness of exchange surface
• Surface area of the exchange surface

Question 10

How does the water potential gradient affect the rate of osmosis?

Answer 10

The higher the water potential gradient, the faster the rate of osmosis.

As osmosis takes place, the difference in water potential on either side of membrane decreases, so the rate of osmosis levels off.

Question 11

How does the thickness of exchange surface affect the rate of osmosis?

Answer 11

The thinner the exchange surface, the faster the rate.

Question 12

How does the surface area of the exchange surface affect the rate of osmosis?

Answer 12

The larger the surface area, the faster the rate.

Question 13

How would you make 5 serial dilutions?

Answer 13

1. Add 10cm³ of 2 M sucrose solution to 1st test tube
2. Add 5cm³ distilled water to other 4 test tubes
3. Use a pipette to add 5cm³ of solution from first test tube to second test tube + mix
4. Repeat taking 5cm³ from second test tube and adding to third.
5. Results = 2M , 1M, 0.5M, 0.25M, 0.125M

Question 14

How would you investigate the water potential of potato cells?

Answer 14

1. Cut potatoes into identical sizes
2. Divide into groups of 3 and measure mass of each group
3. Place 1 group into each sucrose solution
4. Leave for set period
5. Remove and pat dry
6. Weigh using mass balance
7. Calculate % change in mass
8. Use results to make calibratio curve, showing %change in mass vs sucrose concentration.
9. Gain mass = higher water potential of solution than chips
10. Where curve crosses x-axis = WP of sucrose is same as potato