In which of the following would cartilage NOT be found?

Cartilage is a flexible connective tissue that provides support and structure to various parts of the body. It can be found in several locations, particularly in the respiratory system and the skeleton.

In the case of the alveoli, these are tiny air sacs located in the lungs where gas exchange occurs. They are primarily composed of simple squamous epithelium, a type of tissue that facilitates efficient gas exchange due to its thinness. Alveoli lack cartilage because they need to maintain a very flexible and elastic structure to expand and contract during breathing. The absence of cartilage allows the alveoli to be highly compliant, which is essential for their function in the respiratory system.

In contrast, structures like the trachea, bronchi, and larynx are supported by cartilage. The cartilage in these areas helps maintain open airways and provides structural integrity while allowing some flexibility. Therefore, understanding the function and composition of these different components of the respiratory system highlights why cartilage would not be present in the alveoli.