Osmosis

Question 1

what is osmosis?

Answer 1

the flow of water through a semi-permeable membrane, from a compartment where the solute concentration is lower, to the side of the membrane where the solute concentration is higher

Question 2

what is a semi-permeable membrane?

Answer 2

a membrane that is permeable to water and impermeable to solute.

Question 3

what is Absolute and Relative Impermeability

Answer 3

• Absolute impermeability: No passage
• Relative impermeability: a solute can slowly pass through a membrane, although much slower than water can

Question 4

what are the most important impermeable solutes?

Answer 4

• cytoplasmic proteins
• extracellular Na+ enters the cell but is pumped right back out (functionally impermeable)
• other extracellular solutes like sugars

Question 5

explain cell survival using the Na+/K+ pump?

Answer 5

the Na+/K+ pump is constantly pumping Na+ out of the cell, making it “effectively impermeable” and by drawing water out of the cells by osmosis, balances the tendency of water to move into the cells.
*** Energy (ATP) is required to run the pump.

Question 6

osmosis of water and osmotic pressure uses sheets of cells as membranes in which organ systems?

Answer 6

• endothelial cells of capillaries in all tissues
• epithelial cells lining the GI tract
• epithelial cells making up the walls of the kidney tubules

Question 7

what is osmotic pressure?

Answer 7

is the minimum pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane (osmotic flow)

Question 8

what is Van’t Hoff’s equation used for?

Answer 8

to measure the osmotic pressure difference across a membrane when solutions are dilute and the membrane is absolutely impermeable to solute

π = nRT∆C
- n is the number of particles
(NaCl disassociates into Na and Cl so 2 particles)

Question 9

what does the Reflection Coefficient relate to?

Answer 9

how a semipermeable membrane can reflect solute particles from passing through.
- A value of zero results in all particles passing through.
- A value of one is such that no particle can pass

Question 10

what is osmolarity?

Answer 10

the concentration of the particles in the solution ( 290 is the magic equilibrium number)
- usually measured by freezing point depression

Question 11

what is tonicity?

Answer 11

the concentration of particles in a solution outside the cell that cannot cross the membrane

Question 12

what happens if a cell is placed in an isotonic solution, hypotonic solution and a hypertonic solution?

Answer 12

• maintain its volume
• it will swell
• it will shrink

Question 13

if a solute is impermeable to the cell membrane (σ = 1) a solution that is iso-osmotic will be? hypo-osmotic? hyper-osmotic?

Answer 13

• isotonic
• hypotonic
• hypertonic

Question 14

if a solute is partially permeable in the cell membrane ( σ < 1.0) then a solution that is hypo-osmotic would be?

Answer 14

hypotonic