When you cite references to articles or books, you will need to put your citations into a specific style. There is no one style that biologists use. They use a lot of them. Psychologists always use the APA style. You can use APA style if you don't have another style to use. Below are some help pages.
Citing Books (electronic or not)
When you cite sources I've listed for Finding Background Information like encyclopedia sections, they will be cited as books or chapters of books. Note whether the section or chapter you're citing has its own authors. If so, cite the title and authors of the chapter as well as the title and editors of the whole book. If it was from an electronic source, you will also need to add in information about when you accessed the source.
When you get articles through searching the internet or a database like PubMed, cite the article, the journal title, the volume, date, and its authors. Do not cite the information as coming from "PubMed"! PubMed or Google are merely finding tools for the articles, but do not contain the information themselves. You can cite online journals the same as hardcopy journals.
Citing other Web Sites
You need to pay careful attention to what type of electronic material you are citing. If it is an online book, follow instructions for citing books. If it is an online journal, follow instructions for citing journal articles. If it is a Web document that is neither of the above, follow general APA instructions for citing Web-based material.