Question 22M.2.HL.TZ1.1c
| Date | May 2022 | Marks available | [Maximum mark: 2] | Reference code | 22M.2.HL.TZ1.1c |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Explain | Question number | c | Adapted from | N/A |
In winter when temperatures drop, brown bears (Ursus arctos) enter a cave and hibernate. The graph shows the mean values for the body temperature, heart rate and activity of 14 brown bears throughout the year. The grey shaded areas indicate the periods when the bears are in transition between hibernation and normal activity.
[Source: Adapted from Evans, A.L., Singh, N.J., Friebe, A., Arnemo, J.M., Laske, T.G., Fröbert, O., Swenson, J.E. and Blanc,
S., 2016. Drivers of hibernation in the brown bear. Frontiers in Zoology, 13(7). This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/).]
Explain the change in heart rate during the period of hibernation.
[2]
- decreased/slower heart rate because bears less active/use less energy;
- less (cell) respiration / lower (rate of) metabolism;
- less oxygen/glucose required / less CO2 produced/needing to be removed;
- less muscle contraction/muscles require less blood;
- conserves energy;
Many candidates mentioned lack of activity as a reason for lower heart rate and some went on to mention reduced respiration rates or other aspects of physiology. Other candidates failed to offer an explanation and instead just described the data. A few claimed wrongly that bone porosity was directly proportional to age, in which case all those of a certain age would have the same degree of osteoporosis, which is plainly not the case.
