Osmosis Flashcards
Osmosis definition
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)
What is water potential?
Same as concentration gradient. Potential for water to move through something
Ψ (water potential)
The pressure created by water molecules
What is wp measured in?
kPa
What is the relationship between increases the solute and wp?
Increasing the solute
Decreases the wp
Zero is the highest wp
Effect of higher wp on red blood cell
Net movement in
Cell swells and bursts
Effect of equal wp on red blood cell
No change of net movement of water
No change in state of cell
Effect of lower wp on red blood cell
Net movement of water out
Cell shrinks
Effect of higher wp on plant cell
Net movement of water in
Protoplast swells
Cell turgid
Effect of equal wp on plant cells
No change in net movement
No change in protoplast
State of cell: incipient plasmolysis
Effect of lower wp on plant cell
Net movement - water leaves cell
Protoplast shrinks
State of cell - plasmolysed
What is hypotonic?
Lower concentration of dissolved solute, so higher wp
What is hypertonic?
Higher concentration of dissolved solute, so lower wp
What is isotonic?
Equal water potentials
Factors affecting the rate of osmosis
- 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)
How to make a serial dilution?
- 5 test tubes in a rack
- Add 10cm3 of initial 2M sucrose solution to first test tube and 5cm3 of distilled water to other tubes
- 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)
- Repeat 3 times to create solutions of 0.5M, 0.25M and 0.125M
- Always wipe glass rod between mixing to prevent contamination
Finding the wp of potato cells
- Use cork borer to cut potatoes into identically sized chips
- Measure the mass of each chip using balance
- Place one in each solution
- Leave them all in for 20mins
- Remove the chips and pat dry with a paper towel
- Find mass again and record
- Calculate % change in mass for each conc
- Make a calibration curve (change in mass % against solution conc)
Explain the potato wp experiment
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
