4.3- OSMOSIS Flashcards
(25 cards)
What molecules does osmosis only involve?
water molecules only
What is the definition of osmosis?
passage of water from region where it has higher water potential to region where it has lower water potential through selectively permeable membrane
Examples of selectively permeable membranes?
cell-surface membranes and other plasms membranes i.e. those around organelles
How are plasma membranes and cell-surface membranes selectively permeable?
permeable to water molecules and a few other small molecules, but not to larger molecules
What is a solute?
any substance that’s dissolved in a solvent i.e. water
What does a solute and solvent form?
solution
What Greek symbol is water potential represented by?
psi (Ψ)
What unit is water potential measured in?
unit of pressure, usually kiloPascals (kPa)
What is water potential?
pressure created by water molecules
What is standard conditions of temperature and pressure?
25°C and 100kPa
Under standard conditions of temperature and pressure, pure water is said to have what water potential?
zero
What will happen to the water potential when a solute is added to pure water?
lower its water potential
What must the water potential of a solution always be less than?
less than zero, negative value
What will happen to water potential when more solute is added?
water potential becomes lower (more negative)
When water molecules move by osmosis from which region of water potential do they go to?
region of higher (less negative) water potential to one of lower (more negative) water potential
What is one way of finding the water potential of cells or tissues?
place them in a series of solutions of different water potentials
where there’s no net gain/loss of water from cell or tissues, water potential inside cells/tissues must be same as that of external solution
What do animal cells i.e. red blood cells contain a variety of?
solutes dissolved in their watery cytoplasm
What would happen if a red blood cell is placed in pure water?
it will absorb water by osmosis as it has a lower water potential
How thin are cell surface membrane?
very thin (7nm)
Although the cell surface membrane is flexible, what can it not do?
cannot stretch to any great extent
As the cell-surface membrane cannot stretch what will happen?
it will break, bursting the cell and releasing its contents
What is it called when red blood cells burst?
haemolysis
To prevent the animal cells from bursting where do they normally live?
in a liquid which has the same water potential as the cells
What does red blood cells have the same water potential as?
blood plasma
