5.5. OSMOSIS Flashcards
What is water potential represented by?
psi/ Ψ
How is a solution formed?
When a solute (i.e. salts) is dissolved in a solvent (water)
What is osmosis measured in?
Water potential (NOT concentration)
What is the definition of water potential?
pressure exerted by water molecules as they hit a container/ membrane
What are the units of water potential?
kPa/ kiloPascal/ 1000Nm-2
What do water potential do?
quantifies the tendency of water to move from one area to another due to osmosis and hydrostatic pressure effects
What does it mean by hydrostatic pressure effects?
movement of water into the cells causes the cell volume to increase - increase in hydrostatic pressure in the cell
What is osmosis?
where water molecues move down a water potential gradient - from high to low - through PARTIALLY permeable membrane
What is osmosis a type of and how does it differ from regular __ ?
- diffusion
- only applies to water molecules
What water potential does pure water have?
At 25*C, and atmospheric pressure of 100kPa, it has a water potential of 0kPa
What is the highest water potential possible?
0kPa, when lower, it goes into the negative numbers
Why is osmosis diffusion?
because it is the solvent molecules (water) moving within the solute molecules/ions.
When is osmosis complete?
When it reaches equilibrium
This can be shown when one side of the partially permeable membrane has a solution higher than the other side
In animal and plant cells, what are the three stages of osmosis?
-hypERtonic
-isotonic
-hypOtonic
-very hypOtonic (only in animals)
What does hypertonic mean in animal cells i.e. red blood cells?
-the solution outside the cell has a lower Ψ than inside, so water leaves the cell
-causes the cells to shrivel up
-cells become CRENALATED
What does isotonic mean in animal cells i.e. red blood cells?
-the solution outside the cells has equal Ψ as inside the cell
-water is moving in equilibrium
-cell is happy
What does hypotonic mean in animal cells i.e. red blood cells?
-the solution outside the cell has a higher Ψ than inside the cell so water moves to inside the cell
-cells swell
What does red blood cells being very hypotonic mean?
-the cell bursts
-causing cytolysis
What does hypertonic mean in relation to plant cells?
-cell wall stays the same shape but membrane shrinks inwards
-becomes plasmolysed
-higher Ψ inside the cell than outside so water leaves the cell
What does isotonic mean in relation to plant cells?
-Ψ inside the cell and outside the cell is the same
-water moves in equilibrium
-cell becomes flaccid
What does hypotonic mean in relation to plant cells?
-Ψ outside the cell is higher than inside so water enters the cell
-develops turgor pressure
-then becomes turgid
-cell cannot burst due to the strong cellulose cell walls
