Final answer:
The apparatus for measuring respiratory gas exchange requires the addition of a carbon dioxide absorbent to accurately measure oxygen consumption, as animals produce CO2 while consuming oxygen.
Step-by-step explanation:
The apparatus described seems to be used for measuring respiratory gas exchange, and the key component that would need to be added to account for the carbon dioxide production is a carbon dioxide absorbent. This is essential because while the animals consume oxygen, they also produce carbon dioxide. The presence of a CO2 absorbent such as soda lime would ensure that the measurements of oxygen consumption are not confounded by the volume of carbon dioxide produced.
An apparatus designed to measure the respiratory gases needs to accurately reflect the oxygen-carrying capacity, which is the amount of oxygen transported in the blood, and the partial pressure of oxygen, representing the pressure exerted by oxygen within a mixture of gases. These are critical concepts reflected in the oxygen dissociation curve. By absorbing the CO2 produced, the apparatus can more accurately measure the oxygen consumed which reflects the metabolic rate of the animal.