Interpreting and evaluating experimental results
Oxygen use by mice and lizards
- Units 2 and 8
- 9 points
- About 25 minutes
You can use a calculator on this question, just like on exam day.
A long question built around a real-world experiment and its data in a table or graph. You describe the biology behind it, pick out the experiment's variables and controls, analyze the data or do a calculation, and make and justify a prediction. On the exam: Question 1 of 6 in Section II (90 minutes, 50% of the exam score); about 25 minutes suggested.
The question and its sources
Animals differ in how they control body temperature. Deer mice are endotherms, and many lizards are ectotherms. Researchers compared the oxygen consumption of deer mice and of a lizard species with a similar body mass (about 20 g). Because almost all O₂ an animal uses is consumed by cellular respiration, the rate of O₂ consumption is a measure of metabolic rate.
Experiment
None of the animals were fed for 12 hours before testing. Each animal was placed alone in a sealed chamber held at one of five air temperatures from 5°C to 35°C. After 1 hour in the chamber, the researchers measured the animal's rate of O₂ consumption for 30 minutes and divided it by the animal's body mass. Six different animals of each species were tested at each temperature.
At the end of each test, the researchers measured body temperature. The mice had a body temperature of about 37°C at every air temperature. Each lizard's body temperature was within 1°C of the air temperature.
Source: Hypothetical study
Table 1. Rate of O₂ consumption (mL O₂/g/h), mean ± 2SE
| Air temperature (°C) | Deer mouse | Lizard |
|---|---|---|
| 5 | 7.8 ± 0.5 | 0.05 ± 0.02 |
| 15 | 5.6 ± 0.4 | 0.13 ± 0.03 |
| 25 | 3.3 ± 0.3 | 0.29 ± 0.05 |
| 30 | 2.4 ± 0.3 | 0.43 ± 0.06 |
| 35 | 2.5 ± 0.3 | 0.62 ± 0.07 |
Source: Hypothetical data
Suggested time: 25 minutes
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Part (a)
1 pointDescribe the source of the thermal energy that an endotherm such as the deer mouse uses to keep its body temperature constant.
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Part (b)
3 points(i) Identify the independent variable that the researchers varied for each species. (ii) Justify the researchers' decision not to feed any of the animals for 12 hours before testing. (iii) Based on Table 1, describe the effect of increasing air temperature from 5°C to 35°C on the lizard's rate of O₂ consumption.
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Part (c)
3 points(i) Calculate how many times greater the deer mouse's rate of O₂ consumption is than the lizard's rate at 25°C. (ii) Based on Table 1, determine whether the deer mouse's rate of O₂ consumption at 30°C is significantly different from its rate at 35°C. Support your answer with the data. (iii) Explain why the deer mouse's rate of O₂ consumption increases as air temperature decreases from 30°C to 5°C.
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Part (d)
2 pointsA shrew is an endotherm with a body mass of about 5 g. (i) Predict the shrew's rate of O₂ consumption per gram of body mass at 15°C compared with the deer mouse's rate at 15°C. (ii) Justify your prediction.
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