lecture 7

Question 1

Tonicity

Answer 1

Tonicity: the effect the solution has on cell
volume
* The tonicity of the solution is determined by
the concentration of the solution in
nonpenetrating solutes (the penetrating
ones are rapidly equally distributed between
ECF and ICF)
* Isotonic solutions: result in a constant cell
volume
* Hypotonic solutions: tend to swell the cell
* Hypertonic solutions: tend to shrink the cell

Question 2

osmolarity

Answer 2

Osmolarity: the measure of solute
concentration per unit volume of solvent.
* Its not the same as tonicity! Osmolarity
takes into account ALL of the solute
concentrations (penetrating and
nonpenetrating solutes)
* Iso-osmotic; hypo-osmotic; hyper-osmotic

Question 3

2 types of assisted membrane transport

Answer 3

Carrier-mediated transport (for small water-soluble molecules)
* Vesicular transport (larges molecules and multi-molecular particles)

Question 4

carrier-mediated transport

Answer 4

Carrier proteins span the plasma membrane
* They can reverse shape so binding sites are alternately exposed to the
ECF and ICF (flip-flops)

Question 5

carrier mediated transport have three charactrasitics

Answer 5

Specificity (amino acids cannot bind to glucose carriers)
* Saturation (limited number of carrier binding sites)
* Competition (closely related compounds compete for access)

Question 6

carrier-mediated transport Facilitated diffusion

Answer 6

Facilitated diffusion: uses a carrier molecule to facilitate (assist) the
transfer of a substance across the membrane from high to low
concentration (downhill)
* Passive process (Does not require
energy)
* Occurs naturally down a concentration
gradient
* Rate is limited by saturation of the
carrier binding sites
* E.g.: glucose is transported into the
cells from the blood stream via GLUTs