Define vital capacity. What is its significance?

(N/A) Vital capacity is the maximum volume of air that a person can breathe in after a forced expiration,or the maximum volume of air that a person can breathe out after a forced inspiration. It is calculated as the sum of $IRV + TV + ERV$. In a healthy human adult,it is approximately $3.5-4.5$ litres. Its significance lies in the fact that it provides a reserve of air for increased physical activity,ensures efficient ventilation of the lungs,and facilitates better gaseous exchange between the blood and the environment.