An experiment to measure the rate of respiration in crickets and mice at 10 C and 25 C was performed using a respirometer, an apparatus that measures changes in gas volume. Respiration was measured in mL of O2 consumed per gram of organism over several five-minute trials, and the following data were obtained. [graph of mouse/ cricket data at 10 & 25 degrees]. According to the data, the mice at 10 C demonstrated greater oxygen consumption per gram of tissue than did the mice at 25 C. This is most likely explained by which of the following statements?