PAG - Determination of water potential by measuring changes in mass Flashcards
1
Q
Osmotic system
A
- cell will lose or gain water by osmosis
- depending on water potential of adjacent cell
2
Q
Preparing boiling tubes -
A
- Label boiling tubes 0, 0.2, 0.4, 0.6, 0.8, 1.0 mol dm3
- Place 30cm3 distilled water in first tube and 30cm3 of appropriate salt solutions in other tubes
- add a stopper to each tube
3
Q
Preparing potato
A
- Use a cork borer and scalpel to prepare 6 potato cylinders of 50 mm long
4
Q
Step 1-
A
- divide and label filter paper into 6 sections, and label 0, 0.2, 0.4, 0.6, 0.8, 1.0
- place a potato cylinder onto each section of filter paper
- blot dry each cylinder
- record mass of cylinder then place into the corresponding test tube
- leave in test tube for 45 minutes
5
Q
After the potato cylinders are left for 45 minutes, what happens
A
- remove cylinders from test tubes and place onto an allocated slot on filter paper
- blot each cylinder to remove excess liquid
- reweigh cylinder
- calculate change in mass in grams
- work out percentage change in mass
6
Q
percentage change in mass -
A
change in mass / original mass x 100
7
Q
why do we weigh potato pieces before and after putting them in the tubes
A
- to compare the change in mass
- to see if water has moved into / out of the cell by osmosis
8
Q
why do we blot dry the surface of the piece of potato
A
- to ensure there was no excess water on the potato
- this would decrease the concentration of salt in test tube solutions
- affecting rate of osmosis
9
Q
osmosis
A
the net movement of water molecules from an area of high water potential to an area of low water potential
10
Q
what is the advantage of calculating the percentage change in mass rather than the change in mass
A
- so you can compare with other potatoes
- each potato would weigh slightly differently, so by comparing percentages it makes the comparison easier/ more accurate
