"Respiratory System" is a part of the college-level Principles of Biology course series textbooks. It is a tutorial written in questions and answers format to describe the anatomy and physiology of the respiratory system, including the gas exchange, partial pressure, lungs, breathing mechanisms, neural control of respiration, counter-current exchange system, and evolution of the respiratory system.

It is a study guide with in-depth explanations. Each section is a modular unit that is self-contained for easy reading. The principles and concepts are introduced systematically so students can learn and retain the materials intuitively.