4.3 Osmosis

Question 1

Define osmosis

Answer 1

The movement of water from an area where it has a higher water potential to an area where it has a lower water potential through a selectively-permeable membrane

Question 2

What is the water potential of pure water?

Answer 2

0

Question 3

What happens to water potential when you add a solute

Answer 3

Water potential gets more negative

Question 4

What would happen if cells were placed in a hypertonic solution?

Answer 4

Lower water potential than the cells
Water moves out of cells by osmosis
Cell shrinks

Question 5

What would happen if cells were placed in a hypotonic solution?

Answer 5

Higher water potential than cells
Water moves into cells by osmosis
Cell swells/bursts

Question 6

What would happen if cells were placed in a isotonic solution

Answer 6

Same water potential as cells
No osmosis
Nothing happens to cell

Question 7

Describe a method which could be used to investigate the water potential of potato cells

Answer 7

1. Make up six boiling tubes with different concentrations of sucrose solution
2. Control the temp by placing all the tubes in a water bath at 30 degrees
3. Cut six identical cylinders from the potato using a borer.Cut all of the cylinders to the same length, e.g. 2cm, using a ruler, scalpel and white tile.
4. Blot the potato chips dry with a paper towel, but do not squeeze the chips.
5. Place each potato chip onto a labelled paper towel which is numbered to indicate which sucrose solution each potato chip will be placed in.
6. Measure and record these initial masses of each potato chip.
7. Place each potato into its own boiling tube and start the stop clock. After 20 minutes, remove the chips from the boiling tubes and blot dry.
8. Reweigh each chip and record the final masses.
9. Calculate the change in mass and then calculate the percentage change in mass.
10. Plot a graph of your percentage change in mass and use this to determine the concentration of sucrose which has the

Question 8

What equation is used to work out the volume of initial solution needed for dilutions

Answer 8

v1=m2 x v2÷m1
m1=conc of initial solution
m2=conc you want
v1= volume of initial solution
v2=volume of final solution

Question 9

Why is it essential that the temperature is controlled?

Answer 9

Temperature affects the rate of osmosis because temperature affects kinetic energy.

Question 10

Why do the potato chips have to be the same size and have the same surface area?

Answer 10

Surface area affects the rate of diffusion for example the larger the surface area the faster the rate of diffusion

Question 11

Why do the potato chips have to be blotted dry?

Answer 11

To remove any excess moisture that could alter the initial mass of the potato chips

Question 12

Why does change have to be calculated as a percentage?

Answer 12

To standardise for variation in initial masses allowing you to compare the data

Question 13

How would you determine the concentration of sucrose that has the same water potential of potato cells?

Answer 13

Use a calibration curve
Use a conversion table