Which of the following changes does not occur as the conducting tubes of the respiratory tree become smaller? Group of answer choices Elastin in the walls disappears. Cartilage disappears in the bronchioles. Cartilage rings are replaced by irregular plates of cartilage. The lining epithelium thins.

The change that does not occur as the conducting tubes of the respiratory tree become smaller is "Elastin in the walls disappears."

Here's why:

1. As the conducting tubes of the respiratory tree become smaller, the structure of the tubes changes.

2. Cartilage rings are indeed replaced by irregular plates of cartilage. This happens because as the tubes become smaller, they don't need the same level of structural support that the larger tubes do.

3. Cartilage disappears in the bronchioles. This is because bronchioles are very small tubes and do not require the structural support that cartilage provides.

4. The lining epithelium thins. This is because as the tubes become smaller, the lining also becomes thinner to allow for the exchange of gases.

5. However, elastin does not disappear in the walls. Elastin is a protein in connective tissue that allows many tissues in the body to resume their shape after stretching or contracting. It helps the lungs and airways to return to their resting state after inhalation and exhalation. Therefore, elastin remains present even as the tubes become smaller.