CSE (Council of Science Editors) Style is the citation standard commonly used in the natural sciences, which includes the biological sciences. There are three documentation systems used in CSE, so be sure to ask your professor which system you are supposed to be citing for your paper.
In the citation-sequence system, in-text references are cited with sequential superscript numbers, such as this1. If you are citing more than one reference within a sentence, you can use a superscript sequence of numbers, like this2,3. In the references, list the citations in the numerical order that they appear in your paper.
As in the citation-sequence system, superscript numbers are inserted at the point of reference. However, when you're organizing your reference list, you will first alphabetize all the citations by authors' last names, then number them in your paper by the order they appear in the list of references.
In the name-year system, citations are inserted in your paper using the in-text style, which includes the author's name and year of publication within parentheses, such as (Jefferson 2009). In the list of references, alphabetize all the citations by the authors' last names.