General Instructions for Writing Scientific Papers or Lab Reports
Prior to writing a report, you may discuss the laboratory experiment with your peers or your instructor. However, the final content, organization, and wording of the report must be of your own design. You may not use figures and graphs or statistical analyses prepared by others and presented to the class in the oral presentations. All data analysis must be your own.
Late reports will be penalized 5% per day.
How to get started?
Our suggestion for writing a lab report is to start by analyzing your data and working on the Results section’s presentation of these data. You should finish with the abstract. It is best to start with the Results section, since you must thoroughly understand your results to form conclusions. When you know what you are able to conclude about the plants or beetles, it is easier to see what background information is appropriate for the introduction. The Methods and Materials section, which should be fairly straightforward, can be written at any point. Use the checklist below after you have written your first draft.
You might also refer to the Carlton College lab report guide as an additional source for science writing suggestions ().
Lab Report Format
A report written in the correct format in most courses will have the following sections, in this order:
Methods and Materials
Results: Tables, Figures and separate results text
References (or Literature Cited)
However, you will only be asked to include a title, methods, results, discussion, and references sections in the sole report in this course.
Compose a title that provides specific information about the variables being tested and reflects the major conclusion of the paper. The major conclusion is often called "the take-home message".
Compare and contrast these potential titles:
"Response of patients to different doses of ice cream"
"Frequent administration of ice cream boosts patients' morale"
“Morale in hospital patients is improved by serving more ice cream”
As you analyze the titles consider these questions:
- Can you easily identify the main topic and the variable that was tested?
- Is the take home message clear?
- Think about the word choices: Are any words in the titles ambiguous e.g. What was the patient response? What doses were used?
In this section, use paragraphs rather than lists, to accurately summarize the final procedures/methods that were employed to collect and analyze your data. The materials (your plants or insects, controlled conditions, equipment used, etc.) are incorporated into the narrative. Provide enough detail so that a reader following this section can evaluate and repeat your experiment.
The Carlton College lab report guide is a great reference if you are struggling with this section. ()
Subheadings: Using subheadings helps organize your method section particularly in big experiment with multiple parts such as the plant lab. Again examine the reference articles you have read for lab for ideas on organizing a methods section. Have a separate paragraph (not a list!) for each subheading. The actual dial settings of equipment used, final concentrations of solutions, number of initial beetles, greenhouse conditions etc. are reported in the methods section, as they will influence the results and their interpretation. It is impossible for your reader to evaluate the results if s/he cannot figure out how you did the experiment. It is more important to be honest and accurate than that you followed the correct procedure. Many experimental errors can be explained by “mistakes” made in methodology.
One subheading, often forgotten is Data Analysis: a section on the mathematical calculations and statistical analyses you used. Tell your reader the variables that were compared, the types of statistical tests used, and for what they were used. What alpha level (threshold significance probability) was used? Were the data transformed in any way (by taking their logarithms, etc.)?
Citations: If you followed a procedure EXACTLY as described in the lab manual you may cite the lab manual for that procedure (don’t forget to include the lab manual in the references cited section).
For example, a subheading identified as photosynthetic rate might be written:
“The photosynthetic rates of leaves were measured at 25 degrees C and light intensities between 0 and 1000 µmol photons m-2 s-1 using a Qubit Model 3750 Infra red gas analyzer (BISC 111, 2009).”
Note: An appropriate reference section citation for the lab manual is: BISC 111. 2011. Introductory Organismal Biology Lab Manual. Wellesley College Biological Sciences Department. Wellesley MA. Labs 3-5.
The text of this section should be double spaced, except for the table/figure captions which should be single spaced.
The result section should contain your data presented in the form of figures and tables and must include an equally important narrative description of the results. Interpretation of your data (why you obtained these results, possible errors, etc.) belongs in the Discussion and should not be reported in the results.
Text of Result Section: The most salient (noteworthy, striking, contrasting) results must be described in a narrative. Reading the results sections from published papers will give you a feel for how results should be presented in text. You should describe general trends, and you should refer specifically to figures and/or tables that pertain to the trends you are describing.
Referring to tables and figures in text: You should eliminate redundancy. You do not need to repeat in text form the values that you list in a table or show in a figure –- these should stand on their own. The reader should be made aware of the main results by reading the narrative without having to look at the figures or tables. The purpose of this section is to draw the reader’s attention to what you think is important about the data.
Example: “The mean transpiration rate was higher for Eichhornia crassipes than Rhoeo (Fig. 1).” Note here you don’t say “Figure 1 shows…” or “As can be seen in Figure 1…” Just tell the reader what you found, then cite the figure (as “Fig.”, or “Figs.” if more than one) or table in parentheses.
Reporting statistics in text: The question often arises as how best to present the results of statistical tests, for example, a t-test. One way to do this, especially if reporting several test results, is to construct a table with appropriate headings. If expressing such a result in Results text form, there are many ways to phrase this. You want to give the basic results of the test and enough detail so that readers can understand the structure of the test data or could check p-values themselves.
When reporting the statistical significance of your results in the Results text, include the name of the test, the test statistic, the degrees of freedom and the p - value.
Citing results of a t-test:
“The mean number of beetles in population E was significantly higher than in population D (t-test, tstat = 2.87, df = 8, p = 0.02, alpha level = 0.05).”
“In Helianthus (sunflowers), the mean stomatal density was 50% higher on the upper than on the lower leaf surface. This difference was significant (t-test, tstat = 3.21, df = 3, p = 0.0023, alpha level = 0.05).
Citing results of an ANOVA - Tukey statistical test:
If we quantified total leaf thickness (by measuring cross-sections of leaves) and if there was a significant difference between two or more of the plants, you might summarize this as:
"Leaf thickness was compared in four plant species adapted to a range of natural habitats from very dry to aquatic. Average leaf thickness ranged from 342 µm in Helianthus to 925 µm in Rhoeo and was significantly different among the four plants (ANOVA, F = 24.4, df = 3, 35, p < 0.0001, alpha level=0.05; Tukey HSD) (you should also cite the table or figure showing these data). Scindapsus leaves were significantly thicker than Helianthus but thinner than Rhoeo while Eichhornia crassipes overlapped with both Scindapsus and Helianthus."
Or if you were comparing beetle growth in different types of flour:
"After 70 days, the mean number of adult beetles in the starting population (20) had increased by a factor of 20 in wheat flour but only by a factor of 10 in corn and 7 in white flour (Fig. 1). Mean population sizes in corn and white flour were not significantly different from each other but were significantly different from the mean population size in wheat flour (ANOVA, F = 22.7, df = 2, 6, p = 0.002, alpha level=0.05; Tukey HSD test)."
Useful tip: Avoid using the term “significant” in most scientific expression, unless referring to the results of a statistical test. This word has a very specific meaning in a scientific paper, as we have seen.
Figures and Tables: The narrative text of Results describes your findings while the data that documents those findings is processed and presented in tables and figures. Tables and figures should be able to stand alone in a scientific paper, meaning that the reader should be able to understand, generally, the experiment and the data’s meaning without reading either the Methods section or the narrative description
Effective figures present information in a format that is easily evaluated by the reader. Remember that tables and figures summarize results, they do not present large amounts of raw data (the individual measurements you each made). When possible, the results should provide some way of evaluating the reproducibility or statistical significance of any numbers presented.
Graphs, pictures, drawings, and computer-generated images are all represented as figures. Figures are numbered consecutively (Figure 1, Figure 2, etc.) in the order they are cited in the text.
Examples of tables and figures and their legends/captions are available throughout this lab manual in addition to the examples presented here. It is very helpful to refer to scientific publications for additional examples.
Most Figures in your reports will be graphs that were prepared using a computer program. Label the axes carefully and specify the units. Put the independent variable on the X-axis (the horizontal axis or abscissa). The experimenter controls the values of the independent variable. Put the dependent variable on the Y-axis (the vertical axis or ordinate). The experimenter measures the dependent variable.
If more than one set of data is plotted on a single graph (e.g., data from different species), be certain to identify each data set plotted using a key. The "key" (called a legend in some graphing programs, such as Excel) to identifying the different data may appear imbedded in the graph itself (labeling the curves or columns) or in the text caption below the graph. Font sizes in figures (and tables) should be such that text is easily readable when printed.
Data may be also be effectively presented in figures as images. Many times, these photos will be taken of specimens under a microscope. Often, the most effective way to use photomicrographs (photos taken of a specimen or sample under a microscope) in figures is to present more than one of them in a single figure with one legend (different photos labeled A, B, etc. representing different levels of your independent variable) This is called a composite figure. Composite figures invite comparisons; therefore, such figures are able to visually and effectively make the point that some aspect of your dependent variable (stomatal density/aperture length/structure of cross section) changed with the independent variable (plant species). That change is easily visible by labeling the relevant parts in the photos presented for comparison.
Tables are used to present numerical data and are numbered separately from figures (Table 1, Table 2, etc.). The numerical data in the table is most often displayed as means ± SD or means ± SE (n= number of replicates) rather than including all measurements. Reporting raw data from each replicate of an experiment is not usually acceptable. Each column of data should have a heading that describes completely what is in that column including the units of measurement. Some columns may need a double heading. For example, when reporting data from different species, you should specify which column of data was collected from each species. It will also be necessary to give an additional heading over all of the species’ data columns indicating what type of data are in these columns. Enter data values so that decimal points are vertically aligned, and align and space all entries for maximum clarity.
Legends/headings/captions (single space): Tables and figures should be able to stand-alone in a scientific paper and should be single-spaced. Each table and figure must have a number and a legend/heading/caption, a brief text description that tells the reader what the table or figure presents, and a brief, general description of how the data were obtained. This description is called a heading in a table and a caption in a figure, but both descriptions can generally be described as a legend. Each scientific journal has its own rules for the detail to be included in a legend, and here we offer some general guidelines. Excessive reporting of methodology is unnecessary in legends if methods have been described adequately elsewhere in the paper (remember, eliminate redundancy).
The information identifying and describing a table is usually placed above the table whereas figure numbers and legends are placed below the graph or picture. In the legend/caption, be sure to explain the meaning of any ambiguous symbols not shown in a figure key. It is also helpful to summarize results of statistical analyses in captions, especially if Tukey test results are presented in the figure rather than in a separate table. If error bars are included in the figure, the caption should tell the reader whether they represent SD or SE.
The legend/caption does not include any interpretation of the data or statement of conclusions. Avoid redundancies; present either a figure or a table as shown below. Similarly, if you cite t-test/ANOVA results in the legend/caption of your illustrations, you do not need to include them in the narrative of the results section.
Figure 1. Population size of adult Tribolium beetles raised in different flour types (mean ± SE). Twenty unsexed beetles were placed in a jar containing one gram of flour per individual. Three replicates per treatment were set up and the beetles were cultured at 29 degrees C and 50% humidity for 70 days. ANOVA, F = 22.7, df = 2, 6, p = 0.002, alpha level = 0.05; Tukey HSD test results are shown as letters above columns. Means not sharing the same letter are significantly different.
Table 1. Test of the hypothesis that food type affects adult flour beetle (Tribolium castaneum) population growth. Twenty unsexed beetles were placed in a jar containing one gram of flour per individual. Three replicates per treatment were set up and the beetles were cultured at 29 degrees C and 50% humidity for 70 days. ANOVA, F = 22.7, df = 2, 6, p = 0.002, alpha level = 0.05. Tukey levels not sharing the same letter are significantly different.
Example of table representing means +/- SE, Tukey HSD test results and an appropriate caption:
Example of a Composite Figure: Composite figures show connected information using multiple formats.
The figures should agree with the final conclusions illustrated by your data and represented in graphs/tables. In other words, if your numerical data shows that plant A has a relatively high stomatal density, be sure to choose a photo of an epidermal peel for your photomicrograph that shows plant A has a high stomatal density relative to the other species of plants. The following is an example of a composite figure from Klich, M.G. (2001):
Fig. 2. Cleared leaves of E. angustifolia and drawings of transverse sections. (a,b) Lower shade leaves; (c,d) medium half sun-exposed leaves; (e,f) upper sun-leaves. (For a,c,e, bar: 1 cm; for b,d,f, bar: 50 mm).
Note in Fig 2 that each photo or drawing in the figure has a bar with its scale noted in the caption of the figure. The caption also describes the contents of each section of the figure and labels specific pictures/drawings with letters to denote different groups. You may also choose to use arrows with labels to point out specific components of the figure that you think should be highlighted for your reader.
Writing a good Discussion section is the most challenging part of composing a scientific paper. Organize your Discussion around the major points (conclusions) that you want to make from your data. Use your results to support these points without restating them, and try to relate your results to the expectations in the introduction.
The discussion is the appropriate place in the paper to evaluate the significance of your findings. In this section you try to explain what the data mean. Show your reader what your results mean in the context of the whole biological system with which you’re working. Begin this section with a general restatement of your experimental goals as a topic sentence to frame the entire discussion; then summarize your main findings, using specific references to tables and figures in your results section. When organizing the discussion, it is best to follow the pattern of organization that you established in the 'Results’ narrative. You might compare your data to published reports from similar experiments (CITE them).
In-text Citations (within the text):
Be sure you cite the source of all background information in proper “in-text” format.
Here are 3 examples of options for citing in your written text:
Albie (2004) found that … In contrast, Hummel and John (2000) reported that ...... Others have found that … (Hold, 2004; VandenBos et al., 2001; Mayer, pers. comm., 2005) .
Note the proper in text citation format for various numbers of authors of publications:
- one author: (Albie, 2004)
- 2 authors (Albee and VanderBos, 2008)
- more than 2 authors (VandenBos et. al, 2001) The first author is the only name reported here, but all authors are listed in the References Cited section of your report.
-You may also include page numbers, particularly for books, (VanderBos et. al, 2001, 781).
Look at your data: Do they support your hypothesis? Do they agree or conflict with published research? Mention the results from your experiments that support or conflict with your hypothesis or related studies, and offer plausible explanations. The Discussion is where you "make your case", much as a lawyer might do in a trial, based on the evidence you have presented. Considering the overall goal of our plant labs, your "case" might consider: How do these plant species illustrate evolutionary adaptation to environment?
An excellent way to organize your Discussion, as well as your Results and Introduction sections, is to lead off each paragraph with a topic sentence, a sentence that summarizes the main point, or “take-home message”, of the paragraph. This is a straightforward statement that basically condenses all that is to follow in the paragraph. Then, the rest of the information in each paragraph flows in illustration of those main points.
As an example – this is a topic sentence appropriate for a Discussion section paragraph:
"The positive effect of the treatment was especially pronounced in the two groups receiving the highest doses. This is perhaps due to?... (Describe possible reasons that explain positive effects in these groups, including those findings and reasons suggested by previous studies).”
The bolded sentence is the topic sentence here. It is the "take-home" message of the paragraph. Try to do this for all paragraphs you write, especially in the Introduction, Results, and Discussion.
Start the Discussion with the most important finding of your research and its interpretation. Don’t dwell on difficulties encountered in the study. Another useful rule of thumb to help you compose your Discussion is to answer the question: “What are three principal findings I can discuss here?” Of course, there may be more or fewer than three, but the point is to focus on the main results and their implications.
Possible experimental or human errors should be mentioned in the discussion, but they should not be the focus of your Discussion. You should suggest further studies that you think should be conducted on this topic, additional questions that could be posed, or ways to modify the present study.
Emphasize the “take-home’ messages of the paper in a concluding paragraph. Your conclusion should summarize the principal findings, interpretations, and implications of your work.