Final answer:
Increased metabolism results in a higher demand for oxygen, leading to an increase in both the respiratory rate and tidal volume to ensure proper oxygenation and carbon dioxide elimination.
Step-by-step explanation:
When metabolism is increased, the body requires more oxygen to produce energy, resulting in a change in the breathing pattern. Specifically, if ventilation is high, both the respiratory rate and the volume of air per breath, or tidal volume, will increase to meet the higher oxygen demands and to remove carbon dioxide efficiently.
This physiological response ensures that adequate oxygenation of the blood is maintained to support the increased metabolic activity.
In summary, the correct answer to the question 'What happened to the breathing when metabolism was increased?' is 'd. the breaths per minute and the tidal volume increased' as more oxygen is needed and carbon dioxide needs to be expelled at a faster rate.