Question 19M.2.SL.TZ2.i
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.SL.TZ2.i |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Outline | Question number | i | 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]
Another study was carried out on the defence systems in aphids (Myzus persicae) which feed on thale cress plants (Arabidopsis thaliana). Individual aphids release an alarm compound containing the chemical (E)-β-farnesene (EBF) when attacked by a predator. Other aphids are repelled and leave the thale cress plant or hide.
The gene for EBF was inserted to produce transgenic (T) thale cress plants to test aphid reaction to EBF over several generations. Aphids were raised on wild type (W) thale cress and then allowed to feed for three generations on either W or T thale cress. Aphids were tested in each generation for their reaction when EBF was added to a choice chamber. The percentages of aphids attracted to or repelled by EBF and those which made no choice were recorded.
[Source: M De Vos, et al., (2010), PNAS, 107 (33), pages 14673–14678]
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).
[2]
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 ✔
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.
