State the minimum ratio at which some mice showed no symptoms.

Analyse the effect of increasing the ratio of rAChE to OP on the symptoms in mice.

Predict what would happen if a mouse received 300 mg of rAChE and 600 mg of OP.

Calculate the difference in median area of synapse between the control mice and mice treated with rAChE and OP, giving the units.

Describe the evidence for damage to synapses by OP provided by data in the box plot.

Using the data from both graphs, evaluate the hypothesis that plant-produced rAChE could be used to protect humans or other mammals from damage caused by exposure to OP.

0.38 (allow any value in the range 0.37–0.39)

a. as the ratio increases, the symptoms decrease;
b. between 0 and 0.16 (accept 0.14 – 0.18) symptoms decrease/are moderate;
c. between 0.16 (accept 0.14 – 0.18) and 0.4 (accept 0.38 – 0.42) symptoms are mild;
d. between 0.38 and 0.41 mice may have mild or no symptoms;
e. after 0.4 (accept 0.38 – 0.42) there are no symptoms;

a. (ratio would have been) 0.5/1 to 2;
b. no symptoms;

90 μm² (accept 75 – 100) (units required)

a. higher/highest median area of synapses;
b. higher/highest maximum/minimum area of synapses;
c. higher/highest 25^th/75^th percentile;

a. the higher the RAChE, the milder the symptoms/damage (first graph);
b. with or without OP, RAChE decreases area of synapses / RAChE reduces the damage to synapses (second graph);
c. (but still) some increase in area/damage to synapses (with OP) even with RAChE;
d. the study was done on mice with no evidence that its results extend to humans;

Most candidates gave answers within the accepted range of 0.37-0.39. Those who gave 0.40 were not credited.

Many candidates recognized that as the RAChE to OP ratio increases, the symptoms decrease. Some others also saw that after a ratio of 0.4 (accept 0.38 - 0.42) there were no symptoms. Additional marking points were available but often not awarded because candidates did not think to give more details or were not precise enough when analyzing the graph. For example, for ratios between 0 and 0.16 (accept 0.14 - 0.18) the symptoms decrease; or, between 0.16 (accept 0.14 - 0.18) and 0.4 (accept 0.38 - 0.42) the symptoms are mild. The given tolerances provided adequate leeway to candidates who observed those features of the graph and made careful measurements.

Much success was seen here. The prediction of 0.5 and “no symptoms” was very common. It was based on using the supplied data in a simple calculation.

This additional calculation for candidates also produced widespread success. It involved finding a difference using box plot data presented in the second graph. There was a generous acceptable range for the answer (from 75-100 μm2). Units were required.

 Often, at least one mark was gained for describing the evidence. Candidates usually mentioned “highest median area of synapses” or “highest maximum area of synapses” or, sometimes, both for two marks

Again, many candidates gained at least one mark. In this case the task was to evaluate an hypothesis. True evaluative statements were not seen very often. A few candidates pointed out that the study was done on mice with no evidence that its results could extend to humans. Other candidates said that since humans and mice are mammals the RAChE might offer protection to humans. Both types of reasoning were accepted. The marks gained most frequently were for more descriptive answers such as “the higher the RAChE, the milder the symptoms” from the first graph or “RAChE decreases area of synapses” or “RAChE reduces the damage to synapses” from second graph.