Final answer:
The metabolic rate can be measured with a respirometer by monitoring oxygen consumption to indirectly calculate energy expenditure (option D). This process, based on oxygen being directly proportional to energy produced during food oxidation, is exemplified by techniques like the Benedict-Roth spirometer method or pulse oximetry.
Step-by-step explanation:
The metabolic rate can be measured with a respirometer by measuring oxygen consumption in order to indirectly measure heat production and energy expenditure. This method, known as indirect calorimetry, is based on the principle that oxygen consumption is directly proportional to energy expenditure, as the process of digestion is essentially an oxidation of food. To calculate the metabolic rate, one can employ the Benedict-Roth spirometer method or use a pulse oximeter to assess oxygen levels in the blood, which reflects the metabolic rate.
By using a respirometer, the volume of O₂ consumed per time unit is tracked, often in correlation to the subject's mass. As per the Benedict-Roth spirometer technique, as oxygen in the closed-circuit system is consumed, the movement of the drum, which represents the rate of oxygen consumption, is recorded. This oxygen consumption is converted into energy expenditure, since approximately 20 kJ of energy are produced for each liter of oxygen consumed, with no dependence on the type of food.
This approach is valuable as it can provide insights into a person's overall health and level of athletic conditioning, as well as detecting possible medical issues related to energy metabolism.