Writing Style Guide

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General Information on essays and literature reviews

Unless told otherwise, the style you will use for departmental essays is the style used in the Primers sections of PLoS Biology. PLoS Biology is an open-access (that is to say, free) online journal that publishes top tier papers from all areas of biology. Note that PLoS Biology publishes articles it calls “essays”, but you aren’t using these as your guide. PLoS essays are more like editorials than literature reviews. The PLoS Primer articles are more similar to what you will be doing in essays and literature reviews.

Go to the latest issue of PLoS Biology, then scroll down to the Primer section.

Written instructions from PLoS Biology for authors of their Primer essays are available here. The guidelines are very brief and it will probably be more helpful to look at sample Primer essays and use them as guides for how to structure and format you essay. Of more use may be the instructions for authors on how to format figure captions.

Sample essays and literature reviews

Here are some Primer articles published by PLoS Biology that you can use as guides. Look at these articles in the PDF format to see the style you should use. Don’t look at the pages in the web or html format – use the PDF format for viewing the articles to see the proper formatting.

Page Layout

Just use a single double-spaced column of text. You should NOT divide your page into two columns of text.

Use one inch margins on all sides of your page (top, bottom, right, left.)

Page numbers on upper left of the page

Make a separate title page. It will start with the article title in bold, left justified. Below that, will be your name in regular font, left justified. Start the text proper on the next page.

Each page except the first page should have a running title in the page’s header region consisting of author’s name (Initials + surname), a colon, then a shortened title for the essay. If your title is already short, you can use the whole title.  For example, if your essay title is, “Stem Cells:  There Is Nothing Immoral About Them, In Fact They Might Lead To All Sorts Of Wonderful Treatments For Horrible Diseases And At The Very Least They Are Very Useful For All Sorts Of Basic Research Into Important Cell Biology Processes”  You might use as a running title on each page, “IM Student:  Stem Cells”


Do not use direct quotations. As a general rule, scientific writing paraphrases everything and almost never uses direct quotes. You must cite what you paraphrase, but you must not plagiarize what you paraphrase.


Figures should be incorporated in the middle of the text, not grouped together on separate pages at the end of the essay. Figures should be incorporated into the text as close as possible to the first reference in the text to that figure.

Number your figures sequentially. Figure 1, Figure 2, etc.

Figures should be boxed with straight lines to make it easier for the reader to k now how to distinguish between the text and figures. (This is not done in PLoS Biology primer essays, but you should do it in your essays.)

All figures need a figure legend underneath the figure. The figure legend should provide enough information to be able to make sense of the figure without having to read the surrounding text. It should provide information about how the data was collected, why it was collected, and what it means.

Here is an example of a figure with an appropriate figure legend underneath it. Notice the amount of detail in the legend. The legend provides details both about the experimental protocol and about the conclusions that can be drawn from the data in the figure.


From: Konrad M, Vyleta ML, Theis FJ, Stock M, Tragust S, Klatt M, Drescher V, Marr C, Ugelvig LV, Cremer S (2012) Social transfer of pathogenic fungus promotes active immunization in ant colonies. PLoS Biol 10: e1001300.

See the sample Primer essays from PLoS Biology for examples on how to incorporate figures and how to write figure legends:


When to use citations

Every statement that is not common knowledge should be referenced with a citation. In a densely written essay, sometimes virtually every sentence in the essay ends in citations. Any piece of material that you didn’t know before hand, that comes from some reference or text, must be referenced with a citation.

How to format citations

Use numbers in square parentheses for your citations. E.g., “[4].”  Do not put periods inside the parentheses.

Number your citations sequentially in the order they appear in the text. The first reference you cite is [1], the second reference you cite is [2], etc.

If you cite the same reference more than once, use the same number each time. That is, once you decide a particular reference is “[7]”, use [7] each time you cite it.

Citations usually go at the end of the sentence. E.g., “Strigolactones belong to the sesquiterpene lactones, which are believed to have a wide distribution in the plant kingdom [11].”

If, however, you have a sentence that contains information from more than one reference, you can put the citation in the middle of the sentence. E.g., “The Glomeromycota are considered the fifth fungal phylum [1] and their common ancestor dates back 600 million years [7], yet all of these fungi exist in symbiosis with phototrophic organisms.”

How to refer to authors being cited

You can occasionally put the name of  the author(s) of a reference, followed by a citation, before summarizing the information from that reference, but don’t overdo this sort of thing as it begins to sound affected if used too much. Only use the authors’ surnames, not their first names or even initials. Do not give them a title or description.

The following is an example of how to properly identify authors: “Recently, Akiyama et al. [10] provided a major breakthrough in our understanding of the very early recognition events in this process.”

The following are examples of how not to identify authors unless the striked-out sections are removed:

“Recently Dr. K. Akiyama and colleagues at Oksaka Prefecture University Akiyama et al. [10] provided…”

“Recently three scientists in Japan named Akiyama, Matsuzaki, and Hayashi Akiyama et al. [10] provided…”

Citations do not replace author names

If you are going to put citations in the middle of your sentences, the sentence must still be comprehensible when the citation is read out loud without the citation numbers. Do not leave out information that would identify the reference in the absence of the citation number. So, do not write a sentence like, “Recently [10] provided a major breakthrough…”. Instead, write, “”Recently, Akiyama et al. [10] provided a major breakthrough…”

More than one citation in a single sentence

If a sentence contains information that is repeated in more than one reference, you indicate that more than one reference was used in the following manner:

two references used:  [3,8]

three or more consecutively numbered references used:  [5-9]

three or more non-consecutively numbered references used:  [5, 8, 12, 20]

Note that if multiple references are cited, you always put the citation numbers in order from smallest to largest.

Entire paragraphs taken from a single reference

If you are using a lot of information within a single paragraph from a single reference, you need to cite that reference for each separate piece of information. Note that if you over-rely on a single reference, it becomes immediately apparent because your paragraphs cite the same source over and over again. In general, this is considered poor form and you should make an effort to find other sources of your information if your paragraph looks like this:

“The heart is located in the thoracic cavity [5]. It consists of four chambers [5]. The upper two chambers are called atria, and the lower two chambers are called ventricles [5]. The left atrium is separated from the left ventricle with a valve called the bicuspidal valve [5].” 

All quoted examples of proper citation style were taken from a PLoS Primer essay by Brachmann and Parniske.


A numbered list of all the references cited anywhere in your proposal.

Only include references you actually cited in your text. Provide all the information for each reference stipulated by the departmental style for references and use the departmental format. 

Reference Format

See some sample research articles from PLoS Biology for examples on how to lay out and format your references:

References should be listed at the end of your essay. There should be a left-justified sub-heading of “References” before your reference list begins.

References should be listed in numerical order by the citation number used to identify them in the text.

All authors should be listed by initials and surname, unless there are more than five authors, in which case only list the first five authors followed by “et al.” Separate different authors with commas. Do not separate surnames and initials with commas. Do not use “and” before the last author.

The full title of the reference should be listed. Do not put the title in quotes.

Use the accepted abbreviations for journal titles. Do not use periods after the abbreviations in the title. For instance, the official abbreviation for the Journal of Biological Chemistry is J Biol Chem, not J. Biol. Chem. Note that some journal titles aren’t abbreviated (e.g., Nature), but most are.

If you don’t know the accepted abbreviation, try looking up the article in PubMed. The PubMed citation will give the journal title in the form of its accepted abbreviation. However, do not just copy the entire PubMed citation. They use a different style than we do; just use PubMed to determine the accepted journal abbreviation (and, if needed, information on the authors, year, title, volume, and pages — just reformat them to fit our departmental style.)

If PubMed does not list the article or journal you are referencing, the CAS (Chemical Abstracts Service) provides an alphabetical list of biology and chemistry journals along with their official abbreviations. Try looking for the journal there. Just remember, do not include the periods in the abbreviations even though the CAS list does.

The second and third lines of a reference should be indented to line up with the beginning of the text on the first line.

Journal Articles

Here is the generic format for journal articles:

1.   Author1 AB, Author2 CB, Author3 DE (year) This is the article title. J Interesting Results 55: 100-110.

For journal articles, start with the authors’ names last name first, followed by initials not separated by any commas and without periods after each initial. Use commas only to separate the different names. Do not put an “and” before the last name. If there are five or less authors, use all the authors’ names. If there are more than five authors, list the first five, followed by “et al.” The “al.” always has a period after it even if it does not end the sentence but the “et” never does.

After the authors names, give the publication year in round brackets. No period before or after the year.

Then give the journal title. Accepted abbreviations should be used for journal titles, but do no put periods after each abbreviated word in the title. Put a period after the article title. Give the volume number of the journal, but do not give the issue number or date. After the volume number, put a colon and give the beginning and end pages of the article, but do not use “pp” or “pg”.

For journal articles that are available both online and in print (hard copy), always format your reference as if you had obtained the article from the print version of the journal. So, even if you go online to read a Nature article, you still format it so the citation includes the journal volume and page numbers, and you do not include the URL or the date accessed. If your online copy of the journal article does not provide the information you need in your citation, look the article up in PubMed. The PubMed listing will give the volume number, the page numbers of the print copy, etc. Use that information in your citation (you will change its formatting slightly, but use the info itself), even if your online copy wasn’t formatted that way. You do not need to provide the DOI information.

For journal articles that are only available online, the online journal will still provide both a volume number for the article and page numbers for the article. Format your reference in the same style as for an article from a print journal with authors, year, title, journal name, volume and page numbers. Do not put the URL or the date accessed info. If you are unsure what volume and page numbers to use for an online article, look the article up in PubMed. The PubMed listing will give the volume number, the page numbers to use. Use that information in your citation (you will change its formatting slightly, but use the info itself), even if your online copy wasn’t formatted that way. You do not need to provide the DOI information.

Here are two examples of how to format references that are journal articles:

5.   Redecker D, Kodner R, Graham LE (2000) Glomalean fungi from the Ordovician. Science 289: 1920–1921.

6.   Weismann D, Hartvigsen K, Lauer N, Bennett KL, Scholl HP et al. (2011) Complement factor H binds malondialdehyde epitopes and protects from oxidative stress. Nature 478: 76-81.

Web Pages

Here is the generic format for web pages:

6.   Author AB (year) Web page title <http://www.sciencewebpages.com/this web page> Accessed 2013 Sept 23.

For web pages that ARE online journal articles, treat the article as if it were a regular journal article, as described in the Journal Articles section above.

For web pages that are NOT online journal articles, you need to provide, if known, the author’s name, space, the date of last revision in parentheses, space, title of document, space, the URL in angle brackets, space, and very importantly the date (year month day, in that order) when you viewed/read the page, period. This last information is the “date of access” and is formatted “Accessed year month day.”

It is sometimes, but not always possible to find the web page author(s), document title, and date of last revision. Look at the top and at the very bottom of the page for the author(s) and revision date; look at the title on the top of your browser window, or sometimes even in the URL itself, for the document title. If some of the information (such as author) just is not available, leave it out and go to the next item in the list of information to include in the reference. If the date of last revision is not available, leave it out and go to the next item of information to include in the reference. But ALWAYS include the page URL and the date accessed.

This style of formatting web page citations is a modified version of the basic format suggested by the Council of Scientific Editors (CSE).

If you can find all the information the formatting of your citation will be some variation of this:

7.   Daneholt B (2006) Advanced Information: The 2006 Nobel Prize in Physiology or Medicine: RNA Interference. <http://www.nobelprize.org/nobel_prizes/medicine/laureates/2006/advanced.html> Accessed 2023 May 28.

If you cannot find an author, your reference listing might look like this:

8.   (2006) Press release: The 2006 Nobel Prize in Physiology or Medicine: RNA Interference. <https://www.nobelprize.org/prizes/medicine/2006/press-release/> Accessed 2028 May 28.

If you cannot find either the author or the date of last revision, you reference listing might look like this:

9.   What is Epigenetics? < https://www.cdc.gov/genomics/disease/epigenetics.htm> Accessed 2023 May 28.


Here is the generic format for entire books, from books where the same author or authors wrote the entire book.

10. Author1 AB, Author2 CD (year) This is the book title. City: Publishing company. p xxx.

For information taken from books, give the authors of the book — last names first followed by their initials without periods. Only put commas between different authors’ names. Follow this with the year published in round parentheses. Then put the title of the book, followed by a period. Give the city where the publisher is located (usually available on the copyright page), colon, name of the publishing company, followed by a period. Put a lower-case p and give the EXACT page number where the information you are citing can be found in the book, followed by a period. Do NOT give the total number of pages for the book, just the pages that provided the information you are citing.

If the information you are citing is from a chapter in a book where every chapter is by different authors, use the format described in the section on Chapter in a book, directly below.

Here is an example of how to format a book in your reference list.

11. Chase JM, Leibold MA (2003) Ecological niches: Linking classical and contemporary approaches. Chicago: University of Chicago Press. p. 212.

Chapter in a book

Here is the generic format for a chapter in a book where each chapter was written by different authors:

12  Author1 AB, Author2 CD (year) This is the chapter title in Editor1Name E, Editor2Name F, editor(s). Book Title. City: Publishing company. pp xxx-xxy.

If your source is a chapter in a book, where each chapter is written by different authors, first give the names of all the authors — last names first followed by their initials without periods. Only put commas between different authors’ names. Follow this with the year published in round parentheses. Then give the title of the chapter, followed by “in” followed by the name or names of the book’s editors. For the editors give their last names first followed by their initials without periods; separate different editors with commas only, no “ands”. Put a period after the editors’ names. Then give the book title, ending with a period. Then give the city where the publisher is located, followed by a colon, followed by the name of the publisher, ending with a period. Finally, use lower-case “pp”, period, followed by the range of pages of the chapter, first page number to last.

Here is an example of how a chapter in a book looks in the reference section:

13. Simberloff D (1997) Eradication. In: Simberloff D, Schmitz DC, Brown TC, editors. Strangers in paradise: impact and management of nonindigenous species in Florida. Washington (D. C.): Island Press. pp. 221–228.

You might want to look through the PLoS Biology archives to find an article similar in theme or content to the report you are writing, to give you a better idea of how to deal with some of the formatting issues you will be encountering.

Return to Writing Style Guide

Written by: Ross E Whitwam
Last updated: 28 May 2023.