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# Endotherms vs. Ectotherms

APBIO-VL3VYF

To measure the rate of organismal respiration, a 1000 mL respirometer was constructed. These measure relative volume as oxygen is consumed by respiring organisms. However, as oxygen gas is consumed during aerobic respiration, it is replaced by $CO_2$ gas at a ratio of one molecule of $CO_2$ for each molecule of $O_2$.

As such, in the following protocol, the $CO_2$ produced is removed by a small piece of cotton treated with potassium hydroxide ($KOH$).

$KOH$ reacts with $CO_2$ to form the solid potassium carbonate ($K_2CO_3$). Over the course of 20 minutes, changes in the volume were measured by following the distance of a red soap bubble placed on the end of a 40 uL capillary tube at time = 0.

Due to the larger sized respirometer, relatively larger sized organisms were used for the setup. What would be the results if equal volumes of an ectotherm (ex. small snake) were compared for oxygen consumption with an endotherm (ex. small mouse), in two different setups?

An external temperature of 10 °C was used in one experimental setup. Another experiment had a temperature of 30 °C. Both experiments used a respirometer with an equal volume of glass beads to represent a control group. External pressure was constant in all cases.

Which of the following would the results from these experiments show?

A

The snake would respire faster in the 10 °C experiment as compared to the mouse at 10 °C since the snake needs to keep more active to stay alive.

B

There would be no difference in oxygen consumption between the snake and mouse in both temperatures since they have equal volumes and equal effects of temperature and pressure.

C

The mouse would show no overall change in respiration rate in 10 °C and 30 °C temperature while the snake would show a low rate in 10 °C and a higher rate of respiration at the warmer temperature.

D

A temperature of 30 °C is too high for both snakes and mice to live. Since most respiratory enzymes would denature at this temperature, the respiration rates in both animals would be lower than they would be at 10 °C.