CBSE Class 10 Answered

a) Alveoli present in the lungs are covered with blood capillaries so that the exchange of gases can take place between the membranes of the alveoli and the surrounding capillaries. The blood capillaries covering alveoli have a low oxygen and high carbon dioxide concentrations. This allows oxygen to diffuse into the blood and carbon dioxide to diffuse out of the blood.

b) The walls of the trachea are strengthened by several C-shaped rings of cartilage. The cartilage rings provide flexibility. They keep the trachea open, thus facilitating continuous airflow. In the absence of cartilage rings, the trachea would collapse under the partial vacuum formed while inhaling.