Inspiration and expiration typically account for what ratio of breathing in the lungs?

The correct choice reflects the typical ratio of inspiration and expiration during a normal breathing cycle at rest. In a healthy adult, the duration of expiration is generally longer than that of inspiration due to the physiological processes involved in breathing. The breathing cycle can be broken down into specific phases: during inspiration, the diaphragm and intercostal muscles contract, allowing air to flow into the lungs, while expiration involves relaxation of these muscles and passive recoil of the lung tissues.

In normal, relaxed breathing, the ratio of inspiration to expiration is often approximated to be 1:2. This means that for every one part of time spent inhaling, two parts are spent exhaling. Therefore, this translates to the choice indicating 1/3 for inspiration and 2/3 for expiration, effectively illustrating this ratio.

While the other choices suggest different proportions, they do not accurately reflect the typical respiratory cycle of a healthy adult, where expiration takes a longer duration compared to inspiration, leading to the most accurate answer being the indicated ratio of 1/3 for inspiration and 2/3 for expiration.