“Principles of Biology: Animal Systems” 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 principles of anatomy and physiology in the biological systems, including evolution and the functions of each organ 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.