Methods

The specific words used in this section title may vary by discipline. “Materials and Methods” or simply “Methods” are common titles.
Tense: Past

The intent of the materials and methods section is to give your reader enough information to repeat the experiment. The key is to present this information as concisely as possible in past tense. Only include what is absolutely necessary. For ecology or other outdoor activities, this is where you would include site information such as weather, site description, etc. if appropriate.

The materials and methods section should be written in paragraph form; therefore it should be presented as an overview, not in recipe format. Think of your reader as someone who was not in the lab when you performed the experiment. This will force you to include the small details which you would assume otherwise. Yet frequently students will, incorrectly, include everything that they did during the time period of the experiment, even if it is irrelevant to the procedure itself; only information that is pertinent should be presented. As you move into upper-level courses it is expected that you will become more proficient at translating the procedure you performed into a few well organized and concise paragraphs. The three basic questions to be answered are “where,” “when” and “how”. Usually the data analysis is described last within the Methods section. Cite sources of the Methods used where relevant. Here are some things to keep in mind as you write your materials and methods section:

1. For field studies, site descriptions are first priority. Start with broad geographic location, and narrow down to precise location or geographic feature, including key descriptors that would allow someone to pick a similar site to duplicate your study somewhere else in the world. This will usually need to be in the present tense. Describing conditions during the study, and describing the actions performed at that site will be in the past tense.
2. For reaction mixtures, translate all of the volumes of solutions used into final concentrations for the assay. The reason for this is that someone else may not have the same stock solutions available, or will be making on a different scale altogether (such as microlitres vs. litres):
   Example:
   In brief, the procedure states: add 20μl of water, 5μl of 1M Tris-Buffer (pH 8.0), 1μl of Eco RI(20,000units/ml), 1μl of Hind III (20,000units/ml), 1μl of 600ng/μl plasmid to your test tube. Incubate for 1hr at 37oC.
   This should be rewritten as: Plasmid digestion was carried out at 37oC for 1 hour in 0.25M Tris (pH 8.0) with 20units of Eco RI, 20 units of Hind III and 600ng of plasmid.
3. Condense lengthy procedure into a single succinct paragraph.
   

Below is a procedure from TWU’s Biology 384 Lab Manual:

Part 2: Velocity vs. Substrate Concentration

1. The purpose of the following procedure is to test the effect substrate concentration has on the reaction velocity.
2. Complete Table 3.3 to use as a guide for preparing your blank and assay tubes. Since the enzyme concentration will not change in this portion of the experiment, only one blank needs to be prepared for all 7 assay tubes.
3. Be sure to adjust the water volume accordingly to make up a total assay volume of 6ml.
4. Add water and buffer to the appropriate tubes (Table 3.3).
5. Prepare your blank by adding ADH and NAD+ to tube 1. Mix your blank well. Pour into a cuvette. Autozero the spectrophotometer (A340) to the blank.
6. When you are ready to measure the reaction rate of your first substrate concentration, add ADH and NAD+ to test tube 2. Mix well.
7. Initiate the reaction by pipetting the Ethanol into Tube 2. Start timing, this is time zero.
8. Quickly mix by inverting the tube with a gloved hand and then transfer the solution to a cuvette and take absorbance (A340) readings 15, 30, 45, 60 and 75 seconds from the point of mixing.
9. Repeat steps 6-10 for each substrate concentration. Be sure to only add ADH and NAD+ immediately before mixing the assay components with the EtOH.
   

Table 3.3 Assay of ADH activity as ethanol concentrations vary

Here is how you might rewrite this procedure in past tense:
To test the activity of ADH as substrate concentration changes, ADH activity was measured with 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, and 4.5M ethanol. Reactions were carried out with 0.3units of ADH in 0.005M NAD+ and 0.05M sodium pyrophosphate (pH 8.5), and were initiated by the addition of ethanol. Velocity was monitored by the change in absorbance at 340nm over 75 seconds; measurements were taken every 15 seconds.
Notice that the paragraph still contains no personal pronouns (I, we, us etc.) even though all the actions were performed by the author.

3. Insert citations when describing certain methods or statistical analysis
A Burlese funnel was used to isolate invertebrates from the soil as per Schaller (1968). One liter of soil was extracted from the top layer of the site and placed in the funnel under a 40 W heat lamp (40cm from sample) for 48hours. Statistical calculations (ANOVA) were calculated at a 95% confidence level (Lowery, 2013).

4. Precision and model number of all equipment is indicated
Triplicate readings of absorbance were taken at 595nm with a Genesis S10 UV/Vis spectrophotometer (+/- 0.005A).

*The intent of the materials and methods section is to give your reader enough information to repeat the experiment. The key is to present this information as concisely as possible in past tense.