Lab Reports

A very important aspect of laboratory work is being able to communicate your results effectively. Although each teacher may have different preferences, there are certain, accepted standards for the preparation of a lab report.

The lab report is divided into several sections in order to organize the contents and make it easy for the reader to follow and to find the information he is looking for.



For Biology

Title

Should be one simple sentence that describes the purpose of the lab. For example, if you are investigating how quickly a plant will grow in response to sunlight in a sunny window, your title might be "The effect of sunlight on plant growth." Your reader should be able to tell what the experiment was about just by reading the title.

Introduction

This section provides the reader with any background information or concepts he might need in order to understand what you have done in the experiment. The Introduction defines the subject of the report. It defines the nature and scope of the area to be investigated, as well as the motivation behind the experiment. In the introduction to our plant experiment above, you might explain what photosynthesis is and why it is dependant on sunlight. Remember, you are trying to give some basic background, not a PhD in plant biochemistry. Background material should be used only if it is relevant to the experiment being performed. Major topics which you wish to discuss later (i.e., in the Discussion) should be introduced here. Conclude the Introduction with a brief statement as to the purpose of the experiment. After reading this section a person should have a good idea of what was done experimentally by you and why.

Hypothesis

Your teacher may require you to have a hypothesis before you begin the experiment. Your hypothesis should be stated in the positive and using the "If . . . then" format. For example, "If a plant is placed in direct sunlight, then it will grow more quickly." Do not state negative hypotheses such as "If a plant is removed from the sunlight, then it will not grow as quickly." The hypothesis should actually be tested in the experiment. For example, you would not use "If a plant is well-watered and placed in direct sunlight, then it will grow more quickly" as your hypothesis if you do not plan to test the effects of watering on the growth of the plant.

Materials and Methods

You would be more familiar with calling this section a "Procedure" but many scientific journals refer to it as "Materials and Methods." The Materials & Methods section contains the technical information and methods used to obtain the results; it tells the reader what you did. This section should contain enough detail to allow another scientist to repeat your experiment, but should not be overwhelming. It should not be a regurgitation of the lab manual. Any procedural changes from the original outline (lab manual) must be included, however. Do not use lists of equipment or a numbered list of steps that you followed. Rather, present the materials and methods as if it were a story. Mention the equipment or apparatus used as you describe the steps you followed in completing the experiment. Procedures are presented in chronological order for each part (avoid mixing experimental procedures even if this was what was done in the lab) and subdivided using paragraphs and headings. Your teacher may require you to construct a flowchart of the procedure you will follow to accompany the materials and methods. Include items such as growth conditions, organisms, and the chemicals used in the experiment. Avoid using trade names for chemicals (e.g., sucrose not sugar); describe organisms with their scientific names (e.g., Vicia faba not bean). Examples of methods include sampling techniques, types of microscopy, and statistical analyses. Sources for major/unusual items (e.g., cell cultures, special chemicals, etc.) should be included. For specialized equipment (e.g., microscopes, centrifuges, etc.) the manufacturer and model should be included. Serial numbers are not necessary. Experiments described in a scientific paper must be reproducible. For this reason, the quality of the Materials & Methods section is judged by the reader's ability to repeat the experiment (and obtain similar data). If a colleague cannot repeat your experiment using only this section it is probably poorly written. This section is always written in past passive tense, as are all sections. This means that there are no references to the first person, or pronouns. For example, you would not state "I/we/Jack/Jill looked at the cells using a microscope", but would state, "The cells were examined using a Leica Galen III compound light microscope." Or, in our plant experiment above, you might write "A geranium plant was placed in a sunny window and the temperature was recorded using an alcohol thermometer. The number of hours of exposure to sunlight was measured using a timer and recorded on a daily basis." Notice that you have explained a few of the steps and indicated the equipment necessary at the same time.

Results

This is where all your data belongs. Both quantitative (measured values) and qualitative (observed characteristics) are included. You might use tables, charts or graphs. Remember that you must show your raw data (i.e., what you actually observed or recorded) as well as the results of any calculations. Imagine that you are answering the questions "What did you find?" or "what did you see or measure?" The results section should summarize the data and observations from your experiments without discussing their implications. Organize the data into figures (graphs, drawings, etc.) and tables, each with a descriptive title and a separate number, so they can be referred to in the text of your Discussion section. Remember, each table or figure should be self-explanatory; the reader should be able to understand each without referring to the written text . Keep titles simple and to the point.

Note: There are no labels "Drawing" or "Graph" used in formal reports. Only use Figure (for drawings, diagrams, flow-charts, graphs, etc.) or Table (for tabulated data).

All results must be fully described. Presentation of data (figures or tables) without adequate description, in words, is inadequate and incorrect. Present only what was actually observed/obtained in the experiment and not what theoretically or by inference should have occurred. If calculations are included present an example.

The most common error is to begin discussion of the results (ie., discussing their implications) in this section. For example, consider these sentences:

1. A cell, 50 pm in diameter, was observed.

2. A cell, identified as B. bunnyus based on its size of 50 pm, was observed.

The first sentence belongs in the Results section as it describes an observation (cell size). The second sentence belongs in the Discussion section as it describes an observation (cell size) and interprets this information (identifies the cell).

Discussion

The discussion is perhaps the most important part of your lab report. This is where you provide an interpretation or explanation of your results. It is not enough to only report your findings (results), you must also discuss what they mean and why they are important. Discuss what you are able to learn from your results. In this section the author (you) is expected to analyze and interpret the experimental data relative to the objectives described in the Introduction.

If the experiment appears to have gone well and you find results that you were expecting (i.e., agree with generally accepted values), you need to interpret those results. This means that you explain for the reader what your results mean. If you find some unexpected results, you face the difficulty of explaining those results. In other words, you must provide a possible explanation as to why you did not find what you had expected to find. Don't worry if your results seem strange - discuss the results you got. Remember, a great deal of science comes from finding the unexpected. be sure to validate or disregard your hypothesis.

Discuss the topic concisely and succinctly, with direct reference to your experimental results. Attempt to present the principles, relationships and generalizations shown by the results but do not repeat the results more than absolutely necessary. Attempt to explain the theoretical basis for your results (e.g., reaction mechanisms for stains, or role of sunlight in photosynthesis) where possible. Compare your results with the literature on the subject (textbooks, journal articles, etc.). If questions are provided for the lab, they are meant to be a guide to build your discussion around. Do no limit your Discussion to only answering the questions.

A good discussion section should do each of the following:

  1. Discuss the results, that is, present relationships, principles and generalizations.
  2. Point out exceptions and lack of correlations; define unsettled points.
  3. State how the results relate to the existing knowledge. All experimental results must be addressed, whether they agree or disagree with the literature.
  4. State the significance and implications of the data. What do the results mean?

Conclusion

Your teacher may require that you provide a short, one or two sentence conclusion. This will usually sum up the experiment, what was found and whether the hypothesis was validated or rejected.



For Chemistry

Purpose

This is completed after reading over the assigned laboratory, and before the laboratory period. Please place it on the front desk of the pre-lab room as you enter. It will be marked before you begin the laboratory and must be included with the final report.

Tabulation of Data

Record data in ink, data recorded in pencil will result in a less professional and less permanent record. Each new piece of data is recorded immediately, and only in your data table (you mus, therefore, take your data table with you to the balance rooms, etc). If a piece of data is recorded incorrectly it should be crossed out with a single straight line. Give thought to your data table prior to the lab. Do not "list" data when it can be tabulated. The data table must be initialed by an instructor before you leave the lab.

The data (usually numbers) tabulated (i.e., headings with units) must be complete enough for the calculations. If you have trouble with your procedure (e.g., a lack of information), you are also encouraged to include a second data table of things such as procedural observations.

Procedure

Written sections of the report (such as this) are worth a significant portion of the mark. Write in third person, using the past tense. Be concise. Describe observations briefly in brackets, at the appropriate point in the procedure. Start sentences with words, not numbers. Your procedure must be in your own words and tell exactly what you did.

Consider the following draft:

0.342 g of some salt was weighed by my partner into a flask. It was brown. About 20 mL of sodium hydroxide was added to the salt in the flask.

There are several mistakes and omissions:

A possible revision would be:

Unknown salt #4 (brown) powder, 0.3 g was weighed into a dry 125 mL Erlenmeyer flask. Sodium hydroxide (colorless), 20 mL, was added (turned blue).

Any technique that is being done for the first time should be designated with an asterisk (*), then, at the end of the experimental procedure, described fully. If the technique is used again in a future lab, it should not be described again.

Calculations

Your calculations must be neat and organized. When running duplicates, each trial is to be calculated separately and the final results averaged. Any graphs must be completed on graph paper and included in this section.

Conclusion

In the conclusion, you state what was learned from the work. Include how you have, or have not, met the objective(s). Ensure you include any calculated results and, where possible, compare them with known values. Also, describe the product (e.g., caffeine (white powder)) when appropriate. you are encouraged to discuss a draft copy of your report with a student colleague and or with an instructor.

Sources of Error

In this section you suggest reasonable causes which could account for discrepencies between your results and the expected (or known) results. Do not include every conceivable error. Ensure that it is reasonable or probable that the error(s) influenced the results. Suggest ways to prevent (or minimize) these errors in the future.

Assigned Problems/Questions

Occasionally there are assigned problems/questions included in the laboratory manual. these constitute part of the mark for that lab and must be completed and submitted with the report.