Experimental work in biology. Introduction
Ideally, students would be expected to make or be presented with observations, generate alternative hypotheses to explain the observations, and design experiments to test one or more of the hypotheses. This is a very desirable, if idealistic, approach but, in the context of a 50 minute lesson, by the time you have worked through this, there will not be enough time to set up and complete an experiment.The experiments which follow have been designed and tested so that most of them can be completed within the lesson. Accordingly, precise instructions are given for conducting the experiment and recording the results, but the expected outcome is not given.
Instructions.The instructions are worded in such a way that, if students follow them, significant results can be expected. To ensure this outcome, the quantities of the reagents and living material to be used are stated.
The discussion.Even if the experiment is introduced as a test for a hypothesis, many students will still not understand the logic of the experimental design. However, once they have completed the experiment and achieved meaningful results, the design and its purpose become clear. This may seem counter to current educational thinking, but the consequence is that the students do acquire an appreciation of experimental design. The discussion questions encourage the students to state the results clearly, offer an interpretation of the results, consider alternative interpretations, criticise the experimental design and suggest further experiments.
Teachers notes.It may be that the teacher wishes to introduce and conduct the experiment in a completely different way from the one suggested above. Nevertheless, the notes contain all the information needed for preparing the experiment: quantities and strength of reagents, suitable living material and apparatus.
Safety.It is essential that good laboratory practice is observed as set out in Safeguards in the School Laboratory published by the Association for Science Education
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