Increased mucus production can block airways and reduce airflow.

### Why this is right The material identifies increased mucus production as an effect of smoking and states that mucus can block airways, reducing airflow. This can add to the breathing difficulty caused by airway swelling and narrowing. ### The concept Mucus is produced in the airways, but excess mucus can obstruct the passages through which air moves. Airway inflammation can also swell and narrow those passages. These effects concern airflow through the airways, while alveolar damage concerns gas exchange deeper in the lungs. Both can contribute to impaired breathing, but they involve different structures. ### Terms - **Mucus**: A substance produced in the airways that can obstruct airflow when present in excess. - **Airway**: A passage that carries air into and out of the lungs. - **Airflow**: The movement of air through the respiratory passages. ### Remember Excess mucus can physically narrow the space available for air to move.