why does it make a difference if you measure metabolic rate in terms of o2/animal or o2/g
When measuring metabolic rate, it can make a difference whether it is expressed in terms of oxygen consumption per animal (O2/animal) or oxygen consumption per gram (O2/g) of body mass.
The choice of how to express metabolic rate depends on the specific research question or context in which the measurement is being used. Here's why:
1. Comparing Metabolic Rates: One common reason to express metabolic rate in O2/animal is to compare the absolute metabolic rates between different individuals or species. For example, if you want to compare the energy expenditure of two animals, expressing it in O2/animal allows you to directly observe and compare the total amount of energy being utilized by each animal.
2. Comparing Metabolic Efficiency: On the other hand, expressing metabolic rate in O2/g is useful when you want to compare the metabolic efficiency or energy consumption per unit body mass. Since larger animals typically have higher absolute metabolic rates due to their higher body mass, expressing it in O2/g allows for comparisons across different-sized animals. This can help understand the relative efficiency of energy utilization between species or individuals.
To obtain either measure, researchers generally use indirect calorimetry, which involves measuring the oxygen consumption and/or carbon dioxide production of an animal. By measuring the difference in oxygen concentrations between inhaled and exhaled air, scientists can calculate the amount of oxygen consumed during a given time period. This information, combined with the mass of the animal, allows them to express metabolic rate in terms of O2/animal or O2/g.
In summary, whether you choose to express metabolic rate in O2/animal or O2/g depends on the research question at hand and what you want to compare. O2/animal allows for direct comparisons of the absolute energy expenditure, while O2/g facilitates comparisons of metabolic efficiency across different-sized animals.