Why does it make a difference if you measure metabolic rate

Why does it make a difference if you measure metabolic rate in terms of CO2/animal or CO2/gram?

Why does measuring changes in CO2 allow you to measure metabolic rate?

Solution

Answer:

It makes a difference to measure metabolic rate in whole animal against tissues (measured in grams) because:

1. When tissue respiratory rates and sums of the individual rates are compared to the respiratory rate of the intact animal several problems become apparent. It is uncertain to what extent in vitro measurements reflect the in vivo situation. Tissues often maintain active respiration in vitro for several hours. However, it is not known how these rates compare with those of the tissues at the time they were removed from the animal.

2.  In the case of mammalian tissues, gas supplies (carbon dioxide and oxygen) to the tissues do not diffuse as readily in vitro as they did when the tissue was provided through gases through a system of capillaries permeating the tissue. It is difficult to assess to what degree diffusion in vitro duplicates physiological conditions for tissues normally serviced by an open circulatory system.

Whole-body carbon dioxide (CO2) production is an index of substrate oxidation and energy expenditure; therefore, it may provide information about the metabolic response and help calculate the metabolic rate.