The ability to write well is one of the most important skills that you can develop. Writing is thinking on paper. The ability to write clearly is an indication of your clear thinking and solid logic. You can expect to have several different writing assignments in any Biology course you take.

You should expect to go through several drafts before you have a paper that you are willing to hand in for a grade. It’s a good idea to start your writing well in advance of the deadline. You will find your ability to improve on a draft will be increased greatly if you let the paper sit for a day or two before you start on a new draft.

Good writing is economical and clear. You should to state your points as concisely as possible. Avoid redundancy. Make sure your sentences flow smoothly.

Of course, one hallmark of good writing is correct grammar. No matter how well written a paper is, readers (including Biology instructors!) will look unfavorably on a paper that is filled with grammatical errors and misspellings. Below we provide a list of frequently made grammatical errors in scientific writing. You are well advised to look over this list carefully and make sure you are not committing any of these errors in the papers you submit.

  • Avoid noun phrases.

Poor usage. I conducted a forest ecosystem disturbance investigation.

Better usage. I investigated the effects of disturbance on a forest ecosystem.

  • Affect/effect. In their common uses, affect is a verb meaning “to change something” while effect is a noun meaning “the change itself”.


One of the effects of the drug epiluramide is high blood pressure.

Daylength affects the growth rate of plants.

  • i.e. and e.g. The first is an abbreviation for the Latin “id est” meaning “it is” and is followed by an explanation. The second is an abbreviation for the Latin “exempli gratia” meaning “for example” and should be followed by an example.


The population size of the orchid is perilously low; i.e., the orchid is in danger of extinction.

Several marine invertebrates are commercially important in Maine, e.g., lobsters and steamer clams.

  • If you begin a list with for example or such as, then you do not need to end with “and so on” or “etc.”.
  • An incorrect but widely used construction is and/or. “A or B” does not preclude the inclusion of both A and B; therefore, the and in and/or is redundant. If you wish to specify A or B but not both, you need to be explicit and write “A or B but not both”.
  • Use the passive voice minimally. There is no need to be bashful. Write “I measured the plants daily” instead of “The plants were measured daily”.



  • Hopefully. This word means “full of hope”. It does not mean “I hope that”.



  • Apostrophe. This punctuation mark in used in contractions but not with possessive pronouns.

Its main use is in contractions; it’s not used in possessive pronouns (his, her, hers). If you’re careful, your writing will be a model of clarity.

  • that and which. These are tricky words. Which is used for a phrase, set off by commas, to give further information about a group, which is already specified. Here’s an exampleThat is used to further specify a group.


The Peregrine Falcon, which is on the Endangered Species List, is making a comeback from near-extinction in the western United States.

The Peregrine Falcons that are found in the western United States are making a comeback.

[In the first example which introduced information that related to all Peregrine Falcons; in the second example, that was used to introduce information that pertains to only some Peregrine Falcons, namely those in the western United States.]

  • Subjunctive mood. The subjunctive mood is used to express possibility rather than actuality. In other words, the subjunctive mood expresses what something might be or do rather than what something actually is or does.


If one were to remove the blue crabs from Chesapeake Bay, the survivorship of small clams would increase.

  • Avoid ending a sentence with a preposition.

Incorrect example: Crustaceans were the main item the fish stomach was full of.

Correct example: The fish stomach was mainly full of crustaceans.

  • Although it consists of two words, an infinitive is a unit and should not be split. Compound verbs are not considered units and can be split with an adverb.

Correct examples:

He was able to measure carefully the size of each fruit fly.

He is carefully measuring the size of each fruit fly.

  • Use only directly before the word that is “only”. “


He only turned 21 last week. This sentence means that all he did last week was to turn 21.

He turned 21 only last week. This sentence means that he turned 21 quite recently.

The same advice holds for nearly, even and almost.

  • Less/few. Use less for quantities that aren’t composed of identifiable units and few for units you can count.


Waterville received less rain in July than Augusta.

Fewer moose are found in the southern part of Maine compared to the northern part.

  • Comprise/ Comprise means “include”. The whole comprises the parts. The parts compose the whole.


The central nervous system comprises the spinal cord.

The brain and spinal cord compose the central nervous system.

  • Watch those antecedents. This/these/that/those are probably a lot clearer to you than to your readers. Explicitly say what you mean: “this experiment”, “these predators”, “that orchid”.


High levels of infrared radiation result in reduced plant growth. This indicates that infrared light is stressful to plants. [Does “this” mean “infrared radiation” or “reduced plant growth”? This should refer to the nearest singular noun preceding it, which would be “growth”. The writer probably wishes this to refer to infrared radiation.]

  • As you strive to write with economy, here are a few ways to shorten your prose.

Whether or not usually means no more than whether.

After works very well for subsequent to.

Use indicates rather than is indicative of.

Don’t write In order to determine when To determine is shorter.

  • The reason why is redundant and the reason is because reasons are already why?
  • The fact that one can begin a sentence this way does not mean that one should.
  • Although it may seem obvious that two or more subjects, even when conceptually linked, take a plural verb, errors of this sort abound.

Incorrect examples:

The distribution and abundance of organism constitutes the primary focus of ecology

Wheres my shoes?

Corrected examples:

The distribution and abundance of organism constitute the primary focus of ecology

Where are my shoes?

  • When neither and nor are used, the verb should agree with the part of the subject closest to the verb.

Example In the experiment, neither the newly hatched chicks nor their older sibling was fed by the parents.

  • Be consistent in the use of tense. Use the past tense to describe what you did or observed and present tense for general statements about nature.
  • Capitalize all Latin taxonomic names except the species part of a binomial. You should italicize (or underline) Latin names for genera and species.

Example: Homo sapiens belongs to the Order Primates and the Family Hominidae.

  • Position and emphasis. Words at the beginning or end of a phrase automatically receive extra emphasis. Placing important words there can reinforce your point. “This is an exciting result” emphases not that what you found is exciting but that it is a result. “This result is exciting” is better.



  • Principal as an adjective means most important. Principle is a noun meaning a basic rule or truth.


Altitude is the principal determinant of the distribution of subalpine fir.

The Competitive Exclusion Principle states that two species cannot occupy the same niche.

  • Unique means one of a kind. A thing cannot be most, very or quite unique; it is simply unique.



  • Because and since. Most meanings of since incorporate the notion of time. Because indicates a direct reason whereas since has a more casual meaning, indicating conditions attendant on the main statement.


Average human height has increased over the past 100 years because of improved nutrition.

Global temperature has been rising since the level of carbon dioxide in the atmosphere reached 330 ppm.

  • For positive integers ¾10, spell out the word but use Arabic numerals for larger integers. Use the Arabic form for small integers when used with a symbol.


We saw six Great Blue Herons and 14 Snowy Egrets.       

The spider was 6 cm long.



There are quite a few biological nouns, which have been borrowed directly from, Greek or Latin. Their plurals are not always straightforward. Here are some nouns that have tricky plurals.

Singular    Plural

alga             algae

analysis     analyses

bacterium bacteria

basis            bases

cilium         cilia

criterion     criteria

datum         data

flagellum   flagella

focus            foci

formula      formulae, formulas

fungus        fungi

genus          genera

hypothesis hypotheses

index           indices (for numerical expressions), indexes (in books)

larva           larvae

locus            loci

matrix       matrices

medium    media

nucleus     nuclei

octopus     octopodes1

ovum        ova

phenomenon phenomena

phylum    phyla

protozoan protozoa, protozoans

pupa          pupae

species      species

stimulus  stimuli

stratum   strata

taxon        taxa

testis         testes

1There is no word “octopi” in Greek (octopus is a third-declension noun not a first-declension noun for you classical scholars). Octopi is an English bastardization and should not be used. If you don’t want to use octopodes as the plural of octopus, octopods works just fine.


Standard Symbols and Abbreviations Used in Biology

To conserve space, biologists and other scientists generally use the following abbreviations in their writing.

ångstrom  logarithm (base 10) log
approximately ca. or ‰ logarithm (base e) ln
calorie cal meter, metre m
cubic centimeter cm3 microgram mg
cubic meter m3 microliter ml
day d micrometer mm
degree celsius °C minute (time) min
degree fahrenheit °F month mo
degrees of freedom df number (sample size) n
figure, figures fig., figs. parts per million ppm
gram g percent %
greater than > plus or minus ±
hectare ha second (time) s
height ht species (singular) sp.
hour hr species (plural) spp.
kilocalorie Kcal square centimeter cm2
kilogram kg square meter m2
kilometer km square millimeter mm2
less than < week wk
liter or L weight wt


Goldwasser, L. 1999. A collection of grammatical points. Bull. Ecol. Soc. Amer. 79: 148-150

Johnson, E. D. 1982. The Handbook of Good English. Facts on File Publications, New York.

Strunk, Jr., W. and E. B. White. 1979. The Elements of Style. MacMillan Publishing Company, New York.

Turabian, K. L. 1982. A Manual for Writers. University of Chicago Press, Chicago.