The primary reasons for citing sources in a research paper are to give credit to the authors whose work you have drawn upon and to allow readers to track down your sources, should they wish to explore further. There are many style guides for formatting citations and creating bibliographies. The CSE (Council of Science Educators) Style Guide is frequently used in biology, but your professor may specify another format.
For articles with 2 authors, names are separated by a comma in the end reference but by “and” in the in-text reference:
Mazan MR, Hoffman AM. 2001. Effects of aerosolized albuterol on physiologic responses to exercise in standardbreds. Am J Vet Res. 62(11):1812–1817.
(Mazan and Hoffman 2001)
For articles with 3 to 10 authors, list all authors in the end reference; in the in-text reference, list only the first, followed by “et al.”:
Smart N, Fang ZY, Marwick TH. 2003. A practical guide to exercise training for heart failure patients. J Card Fail. 9(1):49–58.
(Smart et al. 2003)