Why does it make a difference if you measure metabolic rate in terms of O2/animal or O2/g?

Measuring metabolic rate in terms of O2/animal or O2/g can provide different insights into how an organism utilizes energy. The choice of measurement unit depends on the specific research question and the physiological characteristics of the organism being studied.

When metabolic rate is measured in terms of O2/animal, it provides information about the total amount of oxygen consumed by an individual organism. This measurement is useful when comparing metabolic rates between different individuals within a species. For example, if you want to compare the metabolic rates of different animals of the same species, such as mice or humans, measuring in O2/animal would be appropriate. This unit of measurement helps evaluate the overall energy requirements of individual organisms and can be useful in understanding differences in energy expenditure between individuals.

On the other hand, measuring metabolic rate in terms of O2/g provides a measure of how efficiently an organism utilizes energy per unit of body mass. This measurement is especially informative when comparing metabolic rates between different species or individuals of vastly different sizes. By normalizing metabolic rate to body mass, it allows for a fair comparison and accounts for the potential bias introduced by size differences. For instance, when comparing metabolic rates between a mouse and an elephant, measuring in O2/g would be more appropriate. This unit of measurement helps evaluate the relative energy expenditure of different organisms, regardless of their size.

In summary, measuring metabolic rate in terms of O2/animal or O2/g provides different perspectives on energy utilization. O2/animal helps understand the absolute energy requirements of individual organisms, while O2/g allows for fair comparisons between different species or individuals of varying sizes. The choice of measurement unit should be based on the specific research question and the characteristics of the organisms being studied.