membranes as permeability barriers

Question 1

what is a semi permeable membrane

Answer 1

a layer through which only allowed substances can pass

Question 2

what is passive transport dependent on

Answer 2

permeability- how easily a substance can dissolve into lipid and transport across it.
concentration gradient
rate of passive transport increases linearly with increasing conc gradient

Question 3

how do you measure permeability

Answer 3

use black film apparatus
consist of two chambers separated by septum with small pin hole in the middle
phospholipids are painted across the whole so that lipid bilayer forms.

Question 4

permeability of lipid bilayer to different classes of molecules

Answer 4

hydrophobic molecules- pass easily across hydrophobic domain of membrane as they are small dn uncharged. e.g oxygen , carbon dioxide, N2, benzene
small and uncharge polar molecules- also pass. e.g water, urea, glycerol
anything larger than glucose as well as glucose cannot pass
ions are thermodynamically unfavourable as there is a charge so cannot pass

Question 5

what are the roles of transport processes

Answer 5

maintenance of ionic composition and intracellular pH
regulation of cell volume
conc of metabolic fuel and building blocks
extrusion of waste products of metabolism and toxic substances.
generation of ion gradients necessary for the electrical excitability of nerve and muscle

Question 6

how do proteins contribute to membrane permeability

Answer 6

amplify the amount of substance transported
enhance permeability
facilitated diffusion
channels and transporters