Question 22N.2.HL.TZ0.j
| Date | November 2022 | Marks available | [Maximum mark: 1] | Reference code | 22N.2.HL.TZ0.j |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Outline | Question number | j | 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.]
The researchers found that the BCH of any individual adult shrew could vary seasonally. They collected shrews at different times of the year. The BCH of each shrew was compared with its body mass. The results are displayed in the chart.
[Source: adapted from Schaeffer, P.J., O’Mara, M.T., Breiholz, J., Keicher, L., Lázaro, J., Muturi, M.,
Dechmann, D.K.N., 2020. R. Soc. Open Sci. 7. http://dx.doi.org/10.1098/rsos.191989.]
Shrews were observed in different seasons and the time they spent on a particular activity was recorded and expressed as a percentage of the total observation time. The circles in the kite shapes represent the mean value of time for each activity.
[Source: adapted from Schaeffer, P.J., O’Mara, M.T., Breiholz, J., Keicher, L., Lázaro, J., Muturi, M.,
Dechmann, D.K.N., 2020. R. Soc. Open Sci. 7. http://dx.doi.org/10.1098/rsos.191989.]
The researchers were interested in the seasonal differences in searching for food. They set up a square arena with sides of 110 cm and four entrances (A, B, C and D). Containers were placed in the arena, some with food and others with no food. The diagram shows a top-down view of the arena.
[Source: adapted from Lázaro, 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.]
Each shrew was starved of food for two hours before its cage was opened at one of the entrances to the arena. The length of the path taken by the shrew to obtain food was measured. This was standardized by dividing the path length by the straight-line distance from the entrance to the containers with food. Each shrew was used for 10 trials.
The graph shows the standardized mean path length taken by all the shrews at different seasons of the year. The letters show where the cages were placed for each trial.
[Source: adapted from Lázaro, 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.]
Outline a reason that the path length was standardized.
[1]
compensates for the different distances between entrances and food/OWTTE;
OR
to enable (fair/valid) comparison/OWTTE;
Do not accept unspecific answers such as ‘to be consistent’.
This was another question that tested candidates' ability to express a relatively simple idea clearly, rather than having to understand a more complicated idea. The key part of the answer was that standardizing path lengths allowed results to be compared to find the effect of the intended independent variable, by cancelling out another variable.
