Flashcards in osmosis Deck (21):
what is osmosis?
the passive movement of water from an area of high water potential (hypertonic) to an area of low water water potential (hypotonic) across a selectively-permeable membrane.
what is meant by the phrase 'water potential'?
the pressure created by water particles, how freely water particles can move.
what is the unit of water potential
represented by Ψ (psi)
measured in units of pressure, usually kilopascals (kPa)
what are the standard conditions of pressure and temperature?
temperature = 25°C
pressure = 100 kPa
under standard conditions of pressure and temperature, pure water has a water potential of...
ZERO - water particles can move freely
what is the highest rate of water potential?
what effect will the addition of a solute to pure water have on WP?
it will lower its water potential (become more negative) - the water particles are attracted to the solute and so are less free to move around.
water potential of a solution must always be...
the more concentrated a solution is...
the lower its WP
describe a way of finding the WP of cells/tissues?
1. place them in a series of solutions of different WP's.
2. no net gain or loss of WP of cell/tissue - WP of external (solution) and internal (cell/tissue) environment are the same.
solute and water particles move in a...
random motion due to kinetic energy.
what do red blood cells contain?
a variety of solutes in their watery cytoplasm.
what will happen if a red blood cell is placed in pure water?
it wall absorb water via osmosis because the RBC has a lower water potential than pure water. Although cell surface membranes are thin and flexible, they cannot stretch to any extent, therefore the CSB will break, the red blood cell will swell and burst (haemolysis). Contents including haemoglobin are released.
what is done to prevent animal cells from bursting?
animals cells live in liquid conditions with the same WP as the cells.
what will happen if the red blood cell has a higher WP than the solution?
water will leave the cell via osmosis and the cell will shrink and become shrivelled. Haemoglobin will become more concentrated giving cell darker appearance.
what will happen if a plant cell is placed in pure water?
water will enter the cell via osmosis and the cell will swell and become turgid. It will not burst due to the rigid protection of the cell wall.
what will happen if the plant cell has a higher WP than the solution?
water will leave the cell via osmosis and the cell will shrink (plasmolysed).
what is meant by the phrase '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 - change water potential
you must control the temperature during your osmosis practical - HOW?
using a water bath and check the temperature at regular intervals using a thermometer