AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
The tiny balloon-like structures in the lungs where exchange of gases takes place are called alveoli (singular: alveolus).
The examiner expects the specific term "alveoli." This is a direct one-line factual answer worth 1 mark. The source passages reference lungs and capillaries in the context of gas exchange, and alveoli is the standard NCERT term from Chapter 5 (Life Processes). No further detail is needed for 1 mark.