State the percentage of G2 neurons in the mice that respond to the fox scent.

. . . . . . . . . . . . . . . . . . . .%

Using evidence from the chart, identify, giving a reason, which group of neurons responded most to the chemicals.

State the name of the instrument used to make these traces.

Distinguish between the effects of the mouse alarm compound and the effects of the control compound on the G1 neurons.

Compare and contrast the effects of the mouse alarm compound and stoat scent on the G1 neurons.

Deduce whether there is a correlation between the neural traces and the percentage of responding G1 neurons.

The molecular structures of the mouse alarm compound and fox scent are very similar. Suggest an evolutionary advantage for this chemical similarity.

Identify, with a reason, the aphids that were most strongly repelled by EBF.

Outline the conclusions that can be drawn from the data in the graph for the group of aphids fed for three generations on transgenic thale cress plants (T).

Discuss whether natural selection would favour the transgenic EBF-producing thale cress plants if they were released into the wild.

10–25 «%» ✔

G1 always respond more than 25% «except control», while G2 and G3 always respond 25% or less ✔

G1 always responds more than G2 and G3/all of the others ✔

OWTTE

oscilloscope ✔

mouse chemicals cause action potentials «in all six neurons» while control ones cause none «remain in resting potential»/mouse chemicals cause greater responses ✔

OWTTE

a. both chemicals cause action potentials
OR
both chemicals respond in the majority of/five/most neurons ✔

b. stoat scent causes a higher action potential/longer/bigger response than mouse alarm compound «in each neuron»
OR
neuron 2 reacts strongly to the stoat scent but has a minimal/no response to the mouse alarm compound ✔

a. there is a positive relationship/correlation between the size of neural traces and the percentage of responding G1 neurons Accept vice versa
OR
the chemicals that cause stronger/higher neural traces also cause the greatest percentage of responding G1 neurons ✔

b. fox and stoat scents have «approximately» the same/similar neural traces and the same percentage of responding neurons/>75 % ✔

c. mouse alarm compounds cause smaller neural traces and smaller percentage of responding neurons/25–75 % ✔

d. control chemicals have no response in both cases
OR
no percentage of «G1 neurons» response and no action potential «in neural traces» ✔

the mice would have the same response to another mouse’s danger signal as to the actual presence of the predator/fox
OR
adaptation to fool predator by producing a scent similar to predator’s own scent
OR
allows a group response to a predator/fox/danger when just one mouse detects the danger ✔

Accept any other feasible answer.

the aphids that were fed on wild-type thale cress/W as they had 80 % «or more» repelled each generation/ always had the higher % response
OR
the aphids that fed on wild-type thale cress plants/W of G3 as they had «about» 85 % repelled/had the higher % response ✔

Answer should refer to a percentage.

a. «over the generations» fewer are repelled by EBF ✔

b. «over the generations» more are attracted to EBF ✔

c. by G3 a «slight» increase in no choice ✔

d. aphids respond less to EBF/alarm compound if they feed on plants that produce it/exposed to it constantly ✔

e. mutant aphids with attraction to transgenic plants can arise from aphids with no attraction or repulsion to transgenic plants
OR
aphids with no attraction or repulsion to transgenic plants may produce new type of aphids with attraction to transgenic plants ✔

a. mutant aphids/varieties may be indifferent to/attracted to transgenic plants as these do not present a hazard «not favour» ✔

b. initially/for limited time the plants would thrive as the aphids would be «largely»repelled and thus not eat the plants «so natural selection would favour them» ✔

c. over time/in a few generations, the aphids population become more resistant/more attracted/less repelled to EBF and return to feed on the plants so long-term benefit very limited «so natural selection would not favour them» ✔

d. the aphids resistant to EBF would not respond to other aphid alarms and «likely»be more readily eaten by predators «so the long-term benefit to plants could be supported by natural selection» ✔

The answers must indicate whether natural selection would support or not for each statement.

Nearly all were able to state the answer of 10-25%.

many lost the mark by not stating the reason that the G1 responses were higher than the others (G2 and G3)

Fewer than 1 in 10 were able to name the oscilloscope. There were some G2 comments about this, but the students should have seen traces like this and should know how they were obtained. 

Many missed the mark in d as they did not state that the control remained at zero.

Answers to e were encouraging as most were able to give both the similarity and the difference.

Similarly, in 1f most could see the positive correlation, albeit not stating it, between the size of the trace and the percentage of responding G1 neurons.

In g, better candidates were able to suggest an evolutionary advantage either from the point of view of one mouse being able to bring about a group response, or from the point of view that the fox could not distinguish between mice and other foxes.

There was some discussion in the G2 forms about the amount of reading before points h, I and j. Good candidates could be seen to have read it carefully, underling the key words. Weaker candidates not so. In 1h a reason in terms of the highest percentage was looked for and was missed by weaker candidates.

There was some discussion in the G2 forms about the amount of reading before points h, I and j. Good candidates could be seen to have read it carefully, underling the key words. Weaker candidates not so. In i. a large proportion gained both marks for stating that the percentage of attraction had increased and the percentage of repulsion had decreased. 

There was some discussion in the G2 forms about the amount of reading before points h, I and j. Good candidates could be seen to have read it carefully, underling the key words. Weaker candidates not so. Very few candidates scored both marks in j as they just wrote about one possibility. Perhaps the answer box should have been larger.