Osmosis

Question 1

Osmosis definition

Answer 1

The net movement of water molecules from an area of an area of high water potential to an area of low water potential through a semi-permeable membrane (PASSIVE)

Question 2

What is water potential?

Answer 2

Same as concentration gradient. Potential for water to move through something
Ψ (water potential)
The pressure created by water molecules

Question 3

What is wp measured in?

Answer 3

kPa

Question 4

What is the relationship between increases the solute and wp?

Answer 4

Increasing the solute
Decreases the wp

Zero is the highest wp

Question 5

Effect of higher wp on red blood cell

Answer 5

Net movement in
Cell swells and bursts

Question 6

Effect of equal wp on red blood cell

Answer 6

No change of net movement of water
No change in state of cell

Question 7

Effect of lower wp on red blood cell

Answer 7

Net movement of water out
Cell shrinks

Question 8

Effect of higher wp on plant cell

Answer 8

Net movement of water in
Protoplast swells
Cell turgid

Question 9

Effect of equal wp on plant cells

Answer 9

No change in net movement
No change in protoplast
State of cell: incipient plasmolysis

Question 10

Effect of lower wp on plant cell

Answer 10

Net movement - water leaves cell
Protoplast shrinks
State of cell - plasmolysed

Question 11

What is hypotonic?

Answer 11

Lower concentration of dissolved solute, so higher wp

Question 12

What is hypertonic?

Answer 12

Higher concentration of dissolved solute, so lower wp

Question 13

What is isotonic?

Answer 13

Equal water potentials

Question 14

Factors affecting the rate of osmosis

Answer 14

• water potential gradient (higher = faster rate of osmosis)
  over time the difference in wp on either side of the membrane decreases, so rate levels off over time
• thickness of exchange area (thinner = higher rate of osmosis)
• surface area of exchange surface (larger sa, faster rate of osmosis)

Question 15

How to make a serial dilution?

Answer 15

1. 5 test tubes in a rack
2. Add 10cm3 of initial 2M sucrose solution to first test tube and 5cm3 of distilled water to other tubes
3. Using a pipette, draw 5cm3 of solution from the first tt and add to the 2nd and mix. Now have 10cm3 half as concentrated as the 1st solution (1M)
4. Repeat 3 times to create solutions of 0.5M, 0.25M and 0.125M
5. Always wipe glass rod between mixing to prevent contamination

Question 16

Finding the wp of potato cells

Answer 16

1. Use cork borer to cut potatoes into identically sized chips
2. Measure the mass of each chip using balance
3. Place one in each solution
4. Leave them all in for 20mins
5. Remove the chips and pat dry with a paper towel
6. Find mass again and record
7. Calculate % change in mass for each conc
8. Make a calibration curve (change in mass % against solution conc)

Question 17

Explain the potato wp experiment

Answer 17

Chips will gain water and mass in solutions with higher wp than the chips and lose water in solutions with lower wp
Where the curve crosses the x axis (% change is 0) is when the wp of solution is equal to wp of potato cells