Question 19M.2.SL.TZ2.1b
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.2.SL.TZ2.1b |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Identify | Question number | b | 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]
Using evidence from the chart, identify, giving a reason, which group of neurons responded most to the chemicals.
[1]
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
many lost the mark by not stating the reason that the G1 responses were higher than the others (G2 and G3)
