How to write
a lab report Methods section
This handout will use the spontaneous generation procedure II as an example of how to write a methods section. In each section of this worksheet there are questions include that should be answered in reference to your “student designed experiment”. You can then use the answers to these questions to your methods section for the assigned lab report.
General Rules for a methods section:
1. Do not list supplies used for the experiment as in a recipe.
2. Do not use narrative style writing, for example:
On Tuesday we put five seeds into six Petri dishes.
Two students took half of the seeds home and
watered
them each day.
3. A methods section should include a description of the
experimental treatments and sample sizes for each trial.
Experimental factors that were held constant and dependent
variables should also be described.
To effectively write a methods section you will need to know some aspects about the hypothesis.
Sample hypothesis: The spontaneous generation of life from inorganic matter may require the presence of “air” to occur.
This
hypothesis implies methodology for an experiment. Included in the methods should be description
of how the independent variable of exposure to air was
manipulated. However, the
experimental methodology should also include controlling factors. For the spontaneous generation hypothesis all trials should include sterilized
conditions. Having sterilized conditions
allows for conclusions about life from inorganic matter. If the trial flasks were
not sterilized, the experiment would not be testing life from inorganic
matter but would test life arising from pre-existing cells.
Information needed before writing a methods section:
1. The supplies used during the experiment: growth substrate – nutrient agar broth
350 ml Erlenmeyer flasks
shape and straight glass tubing
sterilized cotton
an autoclave
From the list of supplies you should be able to identify the variables to include in a methods section.
A. independent variable: type of exposure to “air”
B. dependent variable: turbidity of agar broth (number of organisms)
C. control variables: nutrient agar broth (same broth for all treatments)
sterilized equipment and growth substrate
Assignment 1.
List the supplies used for your “student designed experiment”
Assignment 2.
A. independent variable:
B. dependent variable(s):
C. control variables:
Although you will use aspects of the hypothesis in the methods section, the statement of hypothesis is not included in the methods section (it is included in the introduction). There is an example of the format for a methods section on the following page.
Methods and Materials
We used five 350ml Erlenmeyer flasks with 75 ml of nutrient agar broth as a culturing media. The covering over the flask opening varied the exposure of air to the culture media. One flask was sealed with cotton to prevent air from entering the flask. Two of the flasks were sealed with cotton and glass tubing anchored in the center of the cotton plug. Both of the glass tubes allowed air to enter the flask opening. One of the glass tubes was “s” shaped the other was straight. The fourth flask did not have a cover treatment, so the flask opening allowed for air exposure. All flasks were autoclaved and then allowed to culture for five days. The number of organisms present at the end of the culture period was measure by the turbidity of the nutrient agar broth.