What are OER - Open Educational Resources?
Open Educational Resources for Biology
OER books come from many sources. Some are developed by the author specifically to teach a course, some are new textbooks from a commercial publisher that the author negotiated to be published open access, some are older textbooks where the copyright has reverted to the author. Here are some examples of the variety of OER books you can find.
More Biology Open Textbooks
Anatomy and Physiology
Cell and Molecular Biology