3. Osmosis Flashcards
Define osmosis.
Diffusion of water molecules across a partially permeable membrane, from an area of high water potential to an area of lower water potential.
What is water potential?
Its the likelihood of water molecules do diffuse out of or into a solution.
What can and can’t diffuse through cell membrane?
Water molecules can as they’re small.
But.
Large solute molecules can’t.
What is pure waters water potential like?
It has a water potential of zero.
Adding solutes to pure water lowers its water potential - water potential of any solution is always negative.
The more negative the water potential =
The stronger the concentration of solutes in the solution.
EXAMPLE.
Give an example of water potential?
Glass A contains pure water - WP is zero.
Glass B contains a solution of orange squash - orange squash molecules are a solute, they lower the concentration of water molecules.
Water potential of orange squash is lower than water potential of pure water.
What does isotonic mean?
When 2 solutions have the same water potential.
No net movement of water
What happens to cells in an isotonic solution?
They don’t gain or lose water.
As there is no net movement of water molecules because there’s no difference in water potential between cell and surrounding solution.
What happens if a cell is placed in a solution that has a higher water potential?
The cell will swell as water moves into it by osmosis.
Solutions with higher water potential compared with inside of the cell are called hypotonic.
What happens if a cell is placed in a solution that has a lower water potential?
It may shrink as water moves out of it by osmosis.
Solutions with lower water potential than the cell are called hypertonic.
What 3 factors affect the rate of osmosis?
Water potential gradient.
Thickness of exchange surface.
Surface area of exchange surface.
How does water potential gradient affect the rate of osmosis?
Higher the water potential gradient = faster the rate of osmosis.
Over time, difference in water potential on either side of membrane decreases.
How does thickness of exchange surface affect the rate of osmosis?
Thinner the exchange surface, the faster the rate of osmosis.
How does surface are of exchange surface affect the rate of osmosis?
Larger the surface area, faster the rate of osmosis.
Hypertonic
Net movement of water OUT of cell
