The respiratory system is responsible in regulating gas exchange between the body and the external environment. Differences in respiration rate indirectly influence basal metabolic rate (BMR) by providing the necessary components for adenosine triphosphate (ATP) formation (Williams et al., 2011). Observation of gas exchange were measured and recorded for two mice (mus musculus) weighing 25 g and 27 g under the conditions of room temperature, cold temperature (8°C), and room temperature after fasting using a volumeter. The rates of oxygen consumption and carbon dioxide production were measured and used to calculate BMR, respiratory quotient (RQ) and oxidation rate. The mouse at room temperature was calculated to have a BMR of 2361.6 mm3/g/hr. Under conditions of cold temperature and fasting, the BMR values decreased to 2246.4 mm3/g/hr and 2053.2 mm3/g/hr respectively. Rates of glucose oxidation increased under these treatments while rates of fat oxidation decreased. Respiratory quotient (RQ) values were calculated to determine the fuel source for metabolic activity. On a relative scale, protein or fat appeared to be the primary fuel source for all three treatments although the mouse at 8°C had the highest RQ and may have relatively used the most glucose. It was also concluded that BMR in mice are greater than in humans.
In this experiment mice were studied as examples of organisms that employ physiological mechanisms to maintain and regulate internal body temperature.
The respirometer uses the principle of water displacement. As the amount of gas in the respirometer changes, this will be reflected by an equivalent displacement of water in the pipette. Remember that at the same temperature and pressure, equal moles of different gases occupy the same volume (i.e. 1 mole of gas occupies 22.4L), so one can compare different gases such as CO2 and O2 directly in volume units.
Refer to McMaster University, Biology 2A03. 2014. Lab Manual: Respiratory Gas Exchange in the Mouse, p5-11 for complete procedure.
For this study, a control mouse weighing 25 g was measured for oxygen consumption and carbon dioxide production. Carbon dioxide production was determined by subtracting total gas exchange from only oxygen consumption. The oxygen consumption and carbon dioxide production rates were found to be 0.0164 ml/sec and 0.0124 ml/sec respectively.
Figure 1: Rates of oxygen consumption (blue) and carbon dioxide production (red) of a 25 g mouse at room temperature, measured at 15-second intervals over a period of 435 seconds.
The same mouse was used to analyze the effects of low temperatures, specifically at 8°C, on rates of respiratory gas exchange. The rates of oxygen consumption and carbon dioxide production for the 25 g mouse at 8°C were determined as 0.0154 ml/sec and 0.0121 ml/sec respectively.
Figure 2: Rates of oxygen consumption (blue) and carbon dioxide production (red) of a 25 g mouse...