Draw a labelled diagram to show the fluid mosaic model of the plasma membrane.

Outline how neurons generate a resting potential.

Hydrogen bonds can exist both within and between molecules in living organisms and have an impact on their structure and function. Explain the importance of hydrogen bonding for living organisms.

a. two correctly orientated layers of phospholipids/phospholipid bilayer shown withheads facing in opposite directions 

b. phospholipids shown with two parts labelled hydrophilic/phosphate head AND hydrophobic/hydrocarbon tail

c. protein (any) shown as a globular structure embedded in one/both layers of phospholipid 

d. peripheral protein shown as globular structures at the surface of the membrane AND integral protein shown as embedded globular structures 

e. glycoprotein shown as embedded globular structure with antenna-like carbohydrateprotruding 

OR 

carbohydrate shown as branched/antenna-like structure attached either to a protein or to a phospholipid 

OR 

channel protein(s) shown with a pore passing through it 

OR 

pump protein shown as a transmembrane globular structure 

f. cholesterol shown in between adjacent phospholipids 

Do not award the mark unless the structure is labelled with the underlined name. 

a. sodium-potassium pump 

b. sodium /Na⁺ out and potassium /K⁺ in 
OR
sodium/Na⁺ concentration higher outside and potassium/K⁺ higher inside 

c. three Na⁺ pumped for every two K⁺ (hence negative inside) 
OR
inside of axon holds negative ions/Cl^- ions/negatively charged proteins/organic anions (hence negative inside) 

d. by active transport / using ATP 

e. inside (of axon/neuron) is negative in comparison to outside 
OR
electrochemical concentration/charge difference (across the membrane) is the resting potential 

f. resting potential is –70 mV

a. cohesion in water/water molecules stick together (due to hydrogen bonds) 

b. cohesion helps transport under tension of water/sap in xylem / transpiration stream

c. adhesion between water and cell walls/cellulose/polar molecules 

d. adhesion/capillary action helps water to rise in plants/stems/xylem / helps keep leaf walls moist 

e. solvent properties (due to hydrogen bonds) with polar/hydrophilic molecules 

f. solvent properties exemplified by glucose/other example of a polar solute 

g. high latent heat of evaporation / (much) energy required for evaporation so water useful as coolant/for sweating 

h. high (specific) heat capacity so water temperature changes less 

i. base pairing between bases/nucleotides/strands in DNA by hydrogen bonding 

j. base pairing between bases in RNA and DNA for transcription/between codon and anticodon for translation 

k. proteins have hydrogen bonding in secondary structure/α helix/β pleated sheet 

l. proteins have hydrogen bonding between R groups/in tertiary structure/to maintain conformation 

m. habitats because water is liquid due to high boiling point/due to water freezing on the surface 

n. habitats on water surface due to surface tension