Biology is a complete educational tool for the high school student. The book will be introduced in two phases, covering 10 units. Each unit has 2 - 6 chapters, and each chapter has 2 - 4 lessons. Together the 10 units of CK12 Biology have 40 chapters and over 120 lessons. These lessons, written by renowned experts in high school biological science education, are designed to address both state and national standards.