& Data Analysis
Protein gel electrophoresis
Protein gel analysis
Concepts and theory
Writing Sample– Materials and Methods
The following methods and materials section was prepared for a study on flagellar regeneration by Chlamydomonas reinhardi. The style is much more terse than the style one would use to instruct someone in the methodology. Notice that the focus is strictly on the methodology itself, not on the experimental design or the whys or wherefores of the various methods. The text in the results section, supported by figures and/or tables, will make the design of the experiment clear. Volumes of cultures, sampling times, and even the volumes of sample that were fixed and stained need not be specified, since an investigator could scale the experiment up or down without affecting results. This section simply documents the methodology that was employed.
Materials and Methods
Chlamydomonas reinhardi (Carolina Biological Supply Company, Burlington NC) were cultured in 10% Ward's basic culture medium in spring water (Ward's Natural Sciences, Rochester NY), pH 7. Motile cells were obtained by inoculating medium from an agar tube and exposing a culture to bright sunlight in a shallow glass containers for four days. Flagella were amputated by adding 0.5M acetic acid dropwise to 100 ml culture while stirring, to bring pH to 4.5 within 30 seconds, then raising pH to 6.8 by dropwise addition of 0.5 M KOH. Following centrifugation for 3 min at 500 x g, room temp., pellets were resuspended in 30 ml 10% culture medium. Cycloheximide and colchicine (SIGMA Chemical Co, St. Louis MO) were used at concentrations 10 µg/ml and 3 mg/ml respectively. Treatment and sampling were begun within five minutes of amputating flagella. Lugol's iodine (4% iodine crystals, 6% KI) was used to fix and stain samples in the proportion 1 part iodine to 3 parts culture (1:6 for cultures containing colchicine). Flagella in fixed samples were measured to the nearest µm at 400x with phase contrast or dark field optics.
More comments on style and content
We describe materials and methods strictly in past tense because this section describes the precise methodology used in this particular study. We nearly always avoid use of first person in this section of a paper.
Notice that this section was written as part of a research paper, not as a "lab report." Reference to the biology lab, the instructor, or names of individuals are inappropriate.
Students often use the definite article, inappropriately, to describe materials. For example, why refer to "the" Chlamydomonas or "the" control culture. Presumably there is more than one Chlamydomonas culture in the world and other control cultures could be prepared. A sequence of procedures is usually implied by a methodology, thus there is no need to report that "first we did this, then we did that." In fact, this part is not to be a history of what you did in the lab. It's purpose is to allow the reader to judge the merits of your methodology and perhaps to employ all or part of the methodology for his/her own studies. There is usually no significance to a numerical order. For example, why refer to the cycloheximide treated culture as the "first" one, the untreated as the "second" one, etc.?
Notice that no mention is made of supplies or equipment when their use is implied in a procedure and a specific brand or type is not required. For example, a centrifuge run is defined by g force, time, and temperature. The type of centrifuge, rotor type, etc. do not matter. It does not matter what brand of microscope was used. The material is written for a reader who is familiar with common laboratory procedures, thus there is usually no need to specify that test tubes were used, how slides were prepared, etc. Note that because the paper is not focused on the chemicals used, it is not pertinent to the study to report the chemical compositions of chemicals used. For example, we used acetic acid and need not report its atomic composition (CH3COOH).
Pay attention to spelling! For example, the name of the species was Chlamydomonas reinhardii, a scientific name. Scientific names must be spelled correctly and are, by convention, written in italic font. Spell checkers won't help you with chemical names. For example, there probably is a compound called cyclohexamide, but it probably doesn't affect protein synthesis. Amides are not the same as -imides.
Notice that it took more space to describe the features of a materials and methods section than it took to actually write it!