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:

Name examples of prokaryotic and eukaryotic organisms
Compare and contrast prokaryotic and eukaryotic cells
Describe the relative sizes of different cells
Explain why cells must be small

Bacteria, being single-celled prokaryotic organisms, do not have a male or female version. Bacteria reproduce asexually. In asexual reproduction, the "parent" produces a genetically identical copy of itself. Learn more about bacteria reproduction in this learning module produced by CK-12.

A free CK-12 account is required to view all materials.

This video segment explores the astounding diversity of the world's smallest life forms: single-celled organisms. [3:43]

The elephant is a creature of epic proportions- and yet, it owes its enormity to more than 1,000 trillion microscopic cells. And on the epically small end of things, there are likely millions of unicellular species, yet there are very few we can see with the naked eye. Why is that? Why don't we get unicellular elephants? Or blue whales? Or brown bears? Murry Gans explains. [4:06]