A Level Biology Practice Exam

What does total lung capacity encompass?

1. just the amount of air inhaled during vigorous exercise

2. only the functional residual capacity of the lungs

3. the sum of vital capacity and residual volume

4. the maximum amount of air that can be inhaled

The correct answer is: the sum of vital capacity and residual volume

Total lung capacity is a critical measurement in respiratory physiology and refers to the maximum volume of air the lungs can hold. It is calculated by adding vital capacity, which is the maximum amount of air a person can exhale after maximal inhalation, and residual volume, the volume of air that remains in the lungs after a complete exhale. Vital capacity includes tidal volume, inspiratory reserve volume, and expiratory reserve volume, representing the air exchanged during breathing. Residual volume is not involved in the breathing cycle but ensures that the lungs do not collapse and are always partially filled with air. Therefore, by summing these two components, total lung capacity is effectively a comprehensive measure of lung volume, reflecting both the air that can be actively exchanged and the air that is always present in the lungs. The other options incorrectly define total lung capacity. It is not limited to the air volume during vigorous exercise, nor is it solely represented by functional residual capacity, which only includes the air remaining after normal exhalation. Additionally, although total lung capacity does relate to a maximum air volume, the phrase "the maximum amount of air that can be inhaled" overlooks the significance of residual volume, which is essential for a complete understanding of total lung capacity.