L3

Question 1

define osmosis

Answer 1

diffusional movement of water from a region of greater water activity to an area of lower water activity where the change in the water activity is due to a difference in solute concentration

activity of water in low amounts can be considered the same as concentration

Question 2

if you have pure water and you add solutes to it, what happens to the concentration of that water

Answer 2

it decreases

this is because the more solutes you add, the more water that is displaced (because solutes take up space) therefore decreasing the concentration

Question 3

if you had pure water in a U tube with sides A and B separated by a semi-periable membrane that was selective to water, what would happen when you added solutes to side B

Answer 3

initially the solutes in side B would take up space so water would travel to side A. this causes an osmotic gradient and water will want to flow back into side B as it goes from high to low conc

this movement causes an increase in volume on side B

Question 4

what is osmotic pressure

Answer 4

the external pressure required to prevent the osmotic flux of water

Question 5

how can you measure osmotic pressure in a U tube

Answer 5

by applying a force to side B (where the volume has increased) so that the volumes on side A and B are =

this applied force is = to the osmotic pressure

Question 6

what is the unit for osmotic pressure

Answer 6

atmospheres

Question 7

what does the van’t Hoff equation describe

Answer 7

the osmotic pressure of a solution

π = RTECoi

Question 8

what does osmotic pressure (π) tell us

Answer 8

where the water is going to move to

Question 9

how do we calc osmolarity

Answer 9

concentration x number of solute molecules formed by disassociation

Ci

Question 10

when does osmotic pressure occur

Answer 10

only when osmosis exists

in the body this is always because all membranes are selective for water

Question 11

what is the difference between osmolaRity and osmolaLity

Answer 11

osmolaRity = Osmol/L
is about volume therefore it is temperature dependent

osmolaLity = Osmol/Kg
this is about mass therefore it is temperature independent

in PHSL these mean the same thing

Question 12

J = P dC is the equation for flux

what is the equation for water flux

Answer 12

Jv = Lp x A x (dP - dπ)

however it is only dπ (osmotic pressure) that is applicable in the human body therefore

water flux is = to osmotic pressure

Question 13

what does Lp in the equation Jv = Lp x A x (dP - dπ) stand for

Answer 13

hydraulic conductivity (how easily a fluid can move)

Question 14

what does dP in the equation Jv = Lp x A x (dP - dπ) stand for

Answer 14

hydrostatic pressure

dP - dπ is the driving force for water movement

NOTE in the U tube example this is the applied force

Question 15

what is important to note about hydrostatic pressure in PHSL

Answer 15

this does not happen in cells as they dont have a cell wall to protect them from this pressure therefore it would cause the cells to burst

to avoid this the cells move ions around (water follows salt)

Question 16

what are the 2 ways that water can get through the membrane

Answer 16

through the lipid bilayer or through aquaporins

Question 17

how is water able to diffuse through the lipid bilayer

Answer 17

because of hydraulic conductivity of the membrane however this process is unregulated and slow

Question 18

do all cells have the same hydraulic conductivity

Answer 18

no

different membranes have different hydraulic conductivities

Question 19

what can alter a cells hydraulic conductivity

Answer 19

vasopressin/antidiuretic hormone

it does this by altering the number of aquaporins in the membrane

aquaporins increase the hydraulic conductivity of the membrane

Question 20

what are aquaporins

Answer 20

water channels

small proteins that create pores

these proteins have polar, non polar, negative and positive parts to the protein

Question 21

how much do aquaporins increase permeability

Answer 21

by 100 fold

however osmotic pressure is still the driving force as water moves from a high to low conc but this can be regulated by the movement of ions

Question 22

what do aquaporins allow for

Answer 22

regulation of hydraulic conductivity

Question 23

what is osmolarity

Answer 23

number of osmotically active molecules dissolved in a solution

285 - 300 mOsmol/L in the human body

it indicates to us where the water wants to go

Question 24

what is tonicity

Answer 24

the relative solute concentration of two solutions separated by a membrane

it describes the effect a solution has on cells

Question 25

what does tonisity take into account for

Answer 25

the ability of molecules to cross the cell membrane

Question 26

what does isosmotic mean

Answer 26

same osmolarity on the inside and the outside of the cell

Question 27

what does hyperosmotic mean

Answer 27

greater osmolarity on the outside of the cell compared to the inside

this will cause the cell to shrink (a hypertonic solution)

Question 28

what does hypo-osmotic mean

Answer 28

lower osmolarity on the outside of the cell compared to the inside

O stands for cell swelling (a hypotonic solution)

Question 29

what should you note from isosmotic, hyperosmotic and hypo-osmotic

Answer 29

that it always has to do with the environment outside of the cell because the inside should always be relatively constant

285-300mOsmol/L