Draw an annotated diagram of the fluid mosaic model of membrane structure.

Describe the processes involved in absorbing different nutrients across the cell membrane of villus epithelium cells lining the small intestine.

Explain the events that occur during a nerve impulse and how the impulse is propagated along an axon.

a. phospholipid bilayer – with head and tails 

b. hydrophilic/phosphate/polar heads AND hydrophobic/hydrocarbon/fattyacid/non-polar tails labelled. Both needed.

c. integral/intrinsic protein – embedded in the phospholipid bilayer 

d. protein channel – integral protein showing clear channel/pore 

e. peripheral/extrinsic protein – on the surface 

f. glycoprotein with carbohydrate attached 

g. cholesterol – shown embedded in bilayer

Award [1] for each structure clearly drawn and correctly labelled.

a. «simple» diffusion of nutrients along/down a concentration gradient 

b. example of simple diffusion, eg: fatty acids 

c. facilitated diffusion of nutrients involves movement through channel proteins 

d. example of nutrient for facilitated diffusion eg: fructose 

e. active transport of nutrients against a concentration gradient / involving protein pumps 

f. example of active transport, eg: (iron) ions/glucose/amino acids 

g. endocytosis / by means of vesicles 

h. example of nutrient for endocytosis, eg: cholesterol in lipoprotein particles

a. nerve impulses are action potentials propagated along axons of neurons 

b. resting potential is −70 mV
OR
relatively negative inside in comparison to the outside 

c. Na⁺/K⁺ pumps maintain/re-establish «the resting potential» 

d. more sodium ions outside than inside «when at the resting potential»
OR
more potassium ions inside than outside «when at the resting potential» 

e. action potential stimulates «wave of» depolarization along the membrane/axon 

f. «when neuron is stimulated» if threshold potential is reached Na⁺ channels open 

g. sodium ions diffuse/move in 

h. «Na⁺ move in» causing depolarization / inside of the neuron becomes more positively charged than the outside of the neuron 

i. potassium ion channels open
OR
potassium ions diffuse/move out 

j. «K⁺ move out» causing repolarization 

k. local currents
OR
description of Na⁺ ion diffusion between depolarized region and next region of axon to depolarize 

l. myelination increases propagation speed/allows saltatory conduction

Accept any of the points clearly explained in an annotated diagram.