membrane permeability

Question 1

how can small, non-polar molecules like oxygen and carbon dioxide diffuse across a membrane

Answer 1

rapidly diffuse

Question 1

what is phospholipid bilayer permeability

Answer 1

partially permeable

Question 2

how can small, polar molecules diffuse across membrane eg. water, urea

Answer 2

slowly and require proteins

Question 3

how can charged particles diffuse across membrane

Answer 3

unlikely
even if small , require proteins

Question 4

what are the factors that affect membrane permeability

Answer 4

temperature
solvent concentration

Question 5

what part of the plasma membranes are affected by temperature

Answer 5

proteins and lipids

Question 6

how can temperature affect membrane permeability

Answer 6

temp increase = kinetic energy increase , particles crossing membrane move more, diffusion takes place more quickly, phospholipids are constantly moving, gain kinetic energy, increase in fluidity creates gaps between phospholipids provide pathways through which substances might pass, membrane become more permeable –> more movement across the membrane ; high temp = membrane starts to become disrupted, phospholipid bilayer breaks down completely, loss of structure increases membrane permeability, large increase in movement across membrane , changes in fluidity is reversible –> when temp decrease, phospholipid will return to normal levels of fluidity; proteins denature at 40 degrees, disrupts membrane structure, no longer forms an effective barrier, substances can pass freely through the disrupted membrane, irreversible
temp decrease = phospholipids vibrate much less, packing together tightly, only rarely providing pathways between themselves through substances pass; cells defrosted, membrane permeability increase, channel/carrier protein deforming, ice crystals pierce membrane, highly permeable; low temp= proteins remain in place, transporter proteins may not work as well, low temp make it difficult for the cell to provide ATP needed for active transport, molecules and ions move less

Question 7

can water affect membrane permeability

Answer 7

no, phospholipids will not dissolve in it, water is a polar solvent

Question 8

how can less polar solvent and non-polar solvent affect permeability

Answer 8

less polar : e.g. alcohal
non-polar : e.g. benzene

organic solvents dissolve the phospholipid bilayer, cholesterol within disrupts cell membranes, prevent normal functioning –> become more permeable

less concentrated alcohol doesn’t dissolve membranes but damage them, –> more fluid and permeable