Cigarette smoking causes emphysema. Give reason. 

Explanation

Emphysema is a chronic disorder of respiratory system, where inflation or abnormal distension of alveolar wall occurs. Cigarette smoking and the inhatation of other smoke or toxic substances over a period of time causes the damaging of septa between the alveoii, and of its elastic tissue is replaced by the connective tissue in lungs.
Hence, the respiratory surface decreases. thus causing the emphysema. tt causes Shortness of breath. production of sputum, chronic bronchitis, etc.