Osmosis Flashcards
osmosis definition
osmosis is the diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of lower water potential
which solution has the highest water potential?
pure water all other solutions have lower water potentials
what does isotonic mean?
if two solutions have the same water potential they are isotonic
which factors affect the rate of osmosis?
-the higher the water potential gradient the faster the rate of osmosis
which experiment is used to investigate water potential?
- serial dilution
- you can use potato cylinders to find out the water potential of plant tissue however
- you need to make up several solutions of different know concentrations to test the cylinders in
(stage 1) serial dilution
line up 5 test tubes in a rack
(stage 2) serial dilution
- add 10cm3 of a known concentration sucrose solution to the first test tube
- add 5cm3 of distilled water to the other 4 test tubes
(stage 3) serial dilution
- use a pipette to take 5cm3 of solution from the first test tube and add it to the second
- mix thoroughly so you have 10cm3 of solution (half the concentration of the first)
(stage 4) serial dilution
-repeat this process for the remaining test tubes
how do you work out the scale factor?
- start with a solution of a known concentration
- find the scale factor by dividing the concentration of this solution with the one you want to make
- the solution you want to make is X amount of times weaker than your current concentration so make a solution that much weaker than your current one
- finally top up the test tube with distilled water to make the volume you want
what does water potential mean?
it is the likelihood of water molecules of water molecules to diffuse out of or into a solution
what happens to the water potential gradient during osmosis?
as osmosis takes place the difference in water potential on either side of the membrane decreases so the rate of osmosis levels off overtime
how is concentration measured?
in moles (M)
how do you work out the water potential of potato cells? (stage 1)
use a cork borer to cut potatoes into identically sized chips about 1cm in diameter
how do you work out the water potential of potato cells? (stage 2)
divide the chips into groups of three and measure the mass of each group using a mass balance
how do you work out the water potential of potato cells? (stage 3)
place one group into each of your previously prepared sucrose solutions and leave for 20 minuets
how do you work out the water potential of potato cells? (stage 4)
remove the chips and gently pat dry with a paper towel
how do you work out the water potential of potato cells? (stage 5)
-weigh each group again and record your results
how do you work out the water potential of potato cells? (stage 6)
calculate the % change in mass for each group then create a calibration curve
hypothesis for the water potential of potato cells
the potato chips will gain water (mass) in solutions with a higher water potential than themselves and loose water in solutions with lower water potentials
what does it mean when the change in mass of potato cells is 0?
the sucrose solution is the same as the water potential of the potato cells
