Rogers, L. L. 1999. American black bear. Pages 157-160 in D. E. Wilson and S. Ruff, Editors. The Smithsonian Book of North American Mammals . However, as they can be valuable sources for a student, I have formulated a citation format for Introductory Biology classwork.
Most pages report the date of the last update.
The most reliable sources you will encounter will probably be university or corporate sites. Last Name, First Name. Associated University or Company. University of Massachusetts, Amherst. Spelling and Grammar Students of biology often have one of two reactions to scientific communication.