Question 22N.2.HL.TZ0.c
| Date | November 2022 | Marks available | [Maximum mark: 1] | Reference code | 22N.2.HL.TZ0.c |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Suggest | Question number | c | Adapted from | N/A |
Common shrews (Sorex araneus) are small mammals found in Northern Europe. Their diet includes insects, slugs, spiders, worms and amphibians. They do not hibernate in winter because their bodies are too small to store sufficient fat reserves.
[Source: [Shrew], n.d. [image online] Available at: https://www.pxfuel.com/en/free-photo-jslkw [Accessed 29 October 2021].]
To study brain size in shrews, researchers anesthetize them, X-ray their skulls and measure the height of the braincase (BCH) where the brain is located. The graph shows the relationship between BCH and the brain mass of individual adult shrews.
[Source: adapted from Lá zaro, J., Hertel, M., LaPoint, S., Wikelski, M., Stiehler, M. and Dechmann, D.K.N., 2018.
Journal of Experimental Biology 221. http://doi.org/10.1242/jeb.166595.]
Suggest a reason that researchers use BCH rather than brain mass to indicate brain size.
[1]
easier to measure/doesn’t require dissection/non-invasive / shrew not harmed/killed/more ethical;
The mark can be awarded for one of these reasons even if it is not the first reason given in the answer.
Many candidates came up with unlikely reasons for using BCH as a measure, rather than that it was easier to measure and less harmful to the shrew. A common misconception was that brain mass was an inaccurate measure of brain size because brain density might be variable. It was surprising that so many candidates thought the height of the brain case would give a better measure of brain size, especially as the scatter graph showed that BCH is not directly proportional to brain mass.
