Essay Types - How to Write a Science Lab Report

The scientific report takes various formats and the exact format will depend on the teacher's requirements. In formal reports the first section is called the Abstract and is a one paragraph summary of the whole experiment including results.

In all sections the writing is done in the passive voice. This will offend your grammar checker if you use one in your word processing program. The passive voice removes the subject from the sentence in most cases. Chemical A was mixed with chemical B; not: We mixed chemical A with Chemical B. This is important because the whole idea of the scientific method is to remove the subjective element.

Thesis (Hypothesis) or Introduction

In science we call the thesis the hypothesis. Although the words have different roots and slightly different meanings, they essentially have the same function in your writing. The hypothesis is the thing which your experiment is testing. It is usually worded as the effect of one thing on another thing. (This experiment will determine the effect of salt on cell volume.) The significance of this effect is part of the discussion. Sometimes the hypothesis is stated as a single sentence in a separate section. Other times it can be included in a section entitled Introduction in which background information and the general theory behind the hypothesis are presented.

Often in a science lab report the hypothesis is worded as "The effect of ... on ..." This is an essential part of the scientific method. The purpose of the experiment is to determine one particular effect. It is only by breaking down the physical world into small pieces that we can examine individually, can we really begin to understand how the parts work. This is a reductionist point of view which sometimes proves wrong, as the whole may sometimes be more than the sum of the parts.

A key issue for many science students is to identify the dependent and independent variables. The independent variable is the thing you control. The dependent variable is the thing that you measure. In essence, your hypothesis is "the effect of the independent variable on the dependent variable." In the scientific method, an experiment is performed to determine if the independent variable has an effect on the dependent variable. In order to do that, you need to create two cases. The two cases must be identical except for the difference in the independent variable.

Think about it this way. If you wanted to measure the effect of water (independent variable) on plant growth (dependent variable), you would take two plants in identical containers, with identical soil, and identical light. You would give water to one plant and no water to the other. (The one without the water is called the control). Then you would measure the difference. If the plant without water dies, then you could conclude that water is essential to plant survival. (Don't do this with a cactus; it might be a long experiment.) But if you put one plant in the sun and the other plant in the shade, then you can't tell whether it is the lack (or excess) of light that has caused the difference.

Methods or Methods and Materials

Some formats include materials and methods together; some formats keep them separate. The important thing is this is where the description of all activities is made. Someone should be able to read this section and reproduce your experiment. It is important to be very detailed: what size beakers were used, what was the temperature of water, what was the room temperature, what was the atmospheric pressure? Try to be very detailed in your observations of conditions under which the experiment was undertaken. Whether the hypothesis ends up being proven or not proven, the details of the conditions will be important for the discussion.

The methods and materials section often includes a detailed drawing of the apparatus as it is set up for the experiment.

Results

This is usually a chart or brief presentation of data collected. Minimal discussion of results happens in the Results section; save the discussion for the Discussion section. Don't forget that for all measurements, an estimate of uncertainty is important. (This is usually in grade 10 or higher). This must be shown in any calculations. Additionally, in Biological Sciences especially, calculations of probability are necessary to show whether or not the result is significant. (Advanced grades only).

Often you will display your results in a graph. Normally the independent variable is on the horizontal axis (across) and the dependent variable is on the vertical axis (up and down). See this page for info on making great graphs.

Discussion

Was the hypothesis proven? If not, why not? What were the important factors in the experiment? What further experimentation does this suggest? How could the experiment be refined to obtain better results? In the discussion you need to demonstrate your understanding of the scientific method and how you used it in your experiment.

What is the marker looking for?

Despite your hopes, science students, clear writing and good grammar will help you get a good mark. Neatness counts! Unfortunately many science graduate students and even professors don't know grammatical rules very well. However, you may end up with someone like me who did an English degree before doing a science degree and who will mark you down for grammatical faults. Don't worry, the most important thing in the formal lab report is that you show that you understand the concept of the experiment, what the essential elements were and how they came into play during the experiment.

Even if the experiment was a failure (ie the hypothesis was not proven when you know it should have been) you can still achieve a high grade by a proper examination of the factors which were important in the experiment. In a course on experimental design I totally screwed up my most important experiment, but still managed an A on the formal lab report because I identified the error and correctly analyzed all parts of the experiment.

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