Entry Quiz

When you are writing a short report, you need to try to get out of the habit of writing up your experiment under the traditional style of aim, methods, results and discussion. This applies particularly to the methods stage which is NOT written as a separate section but is included in the LEGEND which accompanies the RESULTS.

The main problems students have with writing the legend are deciding on:

  • what content or information to put in and how much to put in;
  • how to structure this content;
  • where to put this content.

Remember that there is particular emphasis on the detailing of the conditions under which the data were obtained. WE WANT CONDITIONS NOT PROCEDURES. Sufficient methodological information must be provided to enable the reader to see how the experiments were performed and to allow critics to repeat and/or pick holes in the experimental approach.

Legends sit under your graphs and figures but above your tables. The information in a legend should tell the reader how you obtained the data in the figure/table by answering the following questions:

  1. What were the conditions or circumstances under which the data was obtained, eg: the concentrations, pH, temperature etc during the reaction?
  2. How was the experiment performed?

Legends provide enough information to allow the reader to repeat the experiment in their lab and with their equipment.

Click on the highlighted text for more explanation

Figures 1 and 2. Effect of high-and low-cholesterol diets on blood cholesterol concentration.

Subjects (Table 1) consumed a high (n=3) or low (n=4) cholesterol diet for up to 3 months. Plasma obtained from samples obtained at the times shown were analysed for cholesterol by incubation in 100 mM Tris-HCl, pH 7.7 containing 1 mM aminoantipyrine (AAP), 6 mM phenol, 1 mM sodium cholate, 2.8 U/ml peroxidase, 7.4 mM Triton X-100, 0.65 U/ml cholesterol esterase and 0.45 U/ml cholesterol oxidase. After 10 min at room temperature, the absorbance of the incubation mixture was determined at 500 nm.

This information tells the reader the conditions or circumstances under which the data was obtained; concentrations, pH, temperature, wave length etc.

This information tells the reader in what way or how the experiment was performed and when or for how long certain actions were carried out.

Use this quiz to find out what you already know about writing the legend.

Compare the paired extracts in each set and decide which is appropriate. You will receive your feedback immediately.

Legend extracts a-d are from student reports where the activity of the enzyme alcohol dehydrogenase was measured.

Extract a
The assay had a total volume of 1.0 ml and contained 0.5 ml 0.8 M glycine, pH 9.5, 50 µl of 60 mM NAD, 50 µl of 1 M ethanol and distilled water to 980 µl. We placed this mix in a 1 ml cuvette and zeroed the spectrophotometer at 340 nm. 20 µl of liver extract is then added. This extract was prepared by homogenising 400 mg of liver with 4 ml of a homogenising buffer, containing 50 mM Trid pH 7.5 and 1 mM dithiothreitol (DTT) to stabilise the enzymes.
Extract b
Liver homogenates (0.1 g wet weight/ml prepared in 50 mM Tris, pH 7.5, 1 mM DTT) were assayed in 0.4 M glycine pH 9.5, containing 3 mM NAD and 5 mM ethanol. The assay contained 2 mg liver tissue/ml reaction mixture.
extract a is appropriate | extract b is appropriate

Correct. Well done.

Incorrect - Write about the conditions of the experiment not the procedure, i.e.: don't write the list of instructions that you followed.

 
Extract c
The progress of the reaction was monitored by the increase in absorbance at 340 nm over a 5 minute time period and the reaction rate calculated using the extinction coefficient for NADH at 340 nm, ε = 6.2 mM-1 cm-1.
Extract d
  • Then measure the absorbance at 340nm every 15s for 5 min.
  • Convert the linear rate, expressed as a change in absorbance per min, to the number of umoles of product (NADH) per min using the extinction coefficient for NADH at 340nm, 6.2 mM-1 cm-1.
extract c is appropriate | extract d is appropriate

Correct. Well done.

Incorrect - This extract needs to be more concise. Leave out details about when measurements were taken and conversion of the linear rate and write the legend in complete sentences and not in point form.

 

Legend extracts e and f are from the report entitled 'Varying the Dietary Intake of Cholesterol May Cause Changes in Plasma Cholesterol Concentration in Middle-Aged Subjects'

 
Extract e
100 mM Tris-HCl, pH 7.7 containing 1 mM aminoantipyrine (AAP), 6 mM phenol, 1 mM sodium cholate, 2.8 U/ml peroxidase, 7.4 mM Triton X-100, 0.65 U/ml cholesterol esterase and 0.45 U/ml cholesterol oxidase
Extract f
0.1 M Tris, 1mM 4-aminoantipyrine, 60mM phenol, 1mM sodium cholate 280U peroxidase, 7mM Triton X-100, 65U cholesterol esterase, 45U cholesterol oxidase, pH 7.7
extract e is appropriate | extract f is appropriate

Correct. Well done.

Incorrect - The most serious mistake in this legend extract is the concentration of phenol as phenol is a very strong chemical and a ten fold increase in concentration would have a marked effect on the reaction. There is a small mistake in the concentration of Triton. There is no mistake in the concentration of Tris as 100 mM is the same as 0.1 M. Also it is better to give the concentrations rather than the amounts of chemicals.

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