Question 19M.2.SL.TZ2.1g
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.2.SL.TZ2.1g |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Suggest | Question number | g | Adapted from | N/A |
Mice (Mus musculus) have various defence systems against predators such as foxes (Vulpus vulpus) or stoats (Mustela erminea). The mice release specific alarm compounds when under threat that serve as danger signals for other mice. Predators also release scents that the mice can detect.
In one study, mice were exposed to paper soaked in compounds taken from other mice, foxes or stoats in a test chamber. The scientists then measured the reaction of three different groups of neurons used in smelling: G1, G2 and G3, as shown in the diagram.
The percentage of G1, G2 and G3 neurons responding to the mouse, fox and stoat compounds, as well as a control compound, are shown in the chart.
Percentage of response of neurons in mice
[Source: Julien Brechbühl, et al., (2013), PNAS, 110 (12), pages 4762–4767]
The scientists recorded the neural traces (action and resting potentials) of six G1 neurons exposed to the compounds from the different animals. The horizontal bar beneath each trace corresponds to the time of exposure to the test compound.
[Source: adapted from J Brechbühl, et al., (2013), PNAS, 110 (12), pages 4762–4767]
The molecular structures of the mouse alarm compound and fox scent are very similar. Suggest an evolutionary advantage for this chemical similarity.
[1]
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.
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.
