1. **Problem:** Determine which organ is responsible for respiration from the options: heart, kidney, liver, lung, ear. 2. **Understanding the problem:** Respiration is the biological process of gas exchange, primarily involving oxygen intake and carbon dioxide release. 3. **Key fact:** The organ responsible for respiration in humans is the lung. 4. **Explanation:** - The heart pumps blood but does not perform gas exchange. - The kidney filters blood but is not involved in respiration. - The liver processes nutrients and detoxifies but does not handle respiration. - The ear is involved in hearing and balance, not respiration. - The lung contains alveoli where oxygen and carbon dioxide are exchanged with the blood. 5. **Final answer:** (d) lung