CELLS: Osmosis Flashcards
Osmosis.
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.
Water potential.
Likelihood of water molecules to diffuse out of or into a solution.
Isotonic.
Two solutions have same water potential.
Solute.
Any substance that is dissolved in a solvent.
What has the highest water potential?
Pure water.
Under standard conditions of temperature and pressure, what is the water potential or pure water?
0
The addition of a solute to pure water…
… will lower its water potential.
The water potential of a solution (water + solute) must always be what?
Less than 0 - a negative value.
The rate of osmosis depends on what factors?
- Water potential gradient
- Thickness of exchange surface
- Surface area of the exchange surface
How does the water potential gradient affect the rate of osmosis?
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.
How does the thickness of exchange surface affect the rate of osmosis?
The thinner the exchange surface, the faster the rate.
How does the surface area of the exchange surface affect the rate of osmosis?
The larger the surface area, the faster the rate.
How would you make 5 serial dilutions?
- Add 10cm3 of 2 M sucrose solution to 1st test tube
- Add 5cm3 distilled water to other 4 test tubes
- Use a pipette to add 5cm3 of solution from first test tube to second test tube + mix
- Repeat taking 5cm3 from second test tube and adding to third.
- Results = 2M , 1M, 0.5M, 0.25M, 0.125M
How would you investigate the water potential of potato cells?
- Cut potatoes into identical sizes
- Divide into groups of 3 and measure mass of each group
- Place 1 group into each sucrose solution
- Leave for set period
- Remove and pat dry
- Weigh using mass balance
- Calculate % change in mass
- Use results to make calibratio curve, showing %change in mass vs sucrose concentration.
- Gain mass = higher water potential of solution than chips
- Where curve crosses x-axis = WP of sucrose is same as potato