3.2.3.3 - Osmosis Flashcards
The passive movement of water from an area of high water potential to an area of low water potential through a selectively permeable membrane is…
OSMOSIS
Osmosis involves the movement of
water ONLY
By adding more solute the a solution how does this affect the water potential
it lowers the WP - becomes more negative
Why does pure water have a higher water potential than a solution of sugar
there are more ‘free’ water particles in pure water
A potato has a WP of -200kPa was placed in pure water WP 0kPa, what happens?
Water ENTERS the potato by osmosis (water moved from a high WP to a lower WP)
water potential is represented by
psi (greek letter)
water potential is measured in units of pressure which are
kPa
Pure water has a WP of
0kPa
How can you determine the the WP of a potato
place potato in a series of solutions of different WP. Where there is no net gain of water by the potato is the WP of the potato.
What happens if a red blood cell is placed in pure water
it swells and bursts - water enters the cell
What happens if a red blood cell is placed in strong sugar solution
It shrinks - water leaves the cell
What happens if a plant cell is placed in pure water
It swells - water enters the cell - it becomes turgid
What happens if a plant cell is placed in strong salt solution
water leaves the cell - it shrinks - it plasmolysed
What is meant by selectively permeable
Membrane only allows certain molecules through; it is only permeable to water and other small molecules `
During an osmosis practical, how and why do you dry the potato chips?
with a paper towel. To remove surface water - This would add to the mass - which we do not want
You must control the temperature during your osmosis practical - HOW?
Using a water bath and check the temperature at regular intervals using a thermometer
give 2 similarities in the movement of substances by diffusion and osmosis
- down a gradient (High to Low)
2. passive not active (does not use energy)
when preparing cells for observation the scientist placed them in a solution that had a slightly higher (less negative) water potential than the cytoplasm. this did not cause the cells to burst but moved the chromosomes further apart in order to reduce the overlapping of chromsomes when observed with an optical microscope.
suggest how this procedure moved the chromosomes apart?
- water moves into cells by osmosis
- cell gets bigger
osmosis potato practical method?
- cut potato cubes to same size
- put potato cubes in solution
- make sure all potato cubes exposed to solution by shaking tube or stirring it
- take cubes out
- blot dry with paper towel
