This chapter focuses on how living organisms obtain oxygen from their environment and release carbon dioxide. It covers the difference between breathing and cellular respiration, detailing the human respiratory system (including the nasal cavity, trachea, bronchi, bronchioles, and alveoli). The text explains the mechanics of inhalation and exhalation, common respiratory disorders like bronchitis, emphysema, asthma, and lung cancer, as well as the harmful health effects of smoking.