Biology 2e is designed to cover the scope and sequence requirements of a typical two-semester biology course for science majors. The text provides comprehensive coverage of foundational research and core biology concepts through an evolutionary lens. Biology includes rich features that engage students in scientific inquiry, highlight careers in the biological sciences, and offer everyday applications. The book also includes various types of practice and homework questions that help students understand—and apply—key concepts. The 2nd edition has been revised to incorporate clearer, more current, and more dynamic explanations, while maintaining the same organization as the first edition. Art and illustrations have been substantially improved, and the textbook features additional assessments and related resources.

By the end of this section, you will be able to do the following:

Understand how the cell cycle is controlled by mechanisms that are both internal and external to the cell
Explain how the three internal “control checkpoints” occur at the end of G1, at the G2/M transition, and during metaphase
Describe the molecules that control the cell cycle through positive and negative regulation

This pathway provides an introduction to the cell cycle and how its regulation is important to normal cell division. Cancer is often caused by unregulated cell division. For a deeper look at this topic, we recommend the pathway Cell Reproduction from the OpenStax textbook Biology for AP® Courses.