3. Planning investigations
Students enjoy planning experiments for themselves. In doing so, they develop thinking skills and the ability to ask questions, both of which will help them to learn. In order to plan an experiment, students need a question to answer or a hypothesis. It might be something like ‘which plastic bag is the strongest?’ or ‘which design of paper airplane flies the furthest?’
In Case study 3 the teacher chooses a simple question that she thinks will interest her students. Activity 3 describes an investigation linked to the topic of transport which involves thinking about where on the leaf the water is coming from. You will to need to lead them to the idea that spreading petroleum jelly on the surface of the leaf will prevent water from leaving, but leave the details of the plan to them. Use questioning to encourage them to think about how they will detect water loss, how they will decide on where the water is coming from, what the control will be and why they need a control. Some groups will need more help than others.
When students plan their own experiments, they don’t always come up with the best way of doing it, but that doesn’t matter because you want them to learn about the process as much as the theory. If you make sure that they evaluate their experiment carefully they will still learn and will be receptive to your suggestions of how it might be improved. The more investigations you do, the better they will be at doing them.
Case study 3: A simple investigation
Mr Machacha did an investigation with his class in biology. However, it was not a very successful lesson as his students found it very difficult – they were not used to designing experiments. They did not appreciate the importance of a ‘fair test’ or the benefit of testing their idea before they started collecting data. He realised that they needed the opportunity to do a really simple investigation that would help them to understand the principles involved in planning experiments.
Mr Machacha made two different paper helicopters (see Resource 5). He asked the class which one was the best. This got them thinking about how to decide what was ‘best’ and how to measure it. He got them to predict how the size of the rotors would affect the time it took to fall. He purposefully didn’t tell them how to do the experiment or how to record the results. They soon realised that they had to drop it from the same height each time and that they needed to think about how best to record the results.
His class spent about 20 minutes taking readings and plotting a graph. Mr Machacha went round asking them questions about how best to record the results and helping them plot a graph. At the end he asked the group who had done the best to draw their table of results on the board so everyone could see what they had done. They had a lot of fun and learnt a lot about how to plan experiments.
Activity 3: Investigating leaves
Tell the students that they are going to plan their own investigation into how water is lost from leaves. Ask them to predict whether more water will be lost from the upper or lower surface of leaves. If they have done Activity 2, ask them to think about what they observed when they put leaves in boiling water. Do not tell the answer to this, but ask them to work in groups to design an experiment to answer the question. You will need to give them some clues and prompts (see Resource 5) but should not give them more information than they need.
Collect the written plans. Check whether they are reasonable and collect apparatus to do as many different ones as possible. In the next lesson, give them feedback on their suggestions and allow students to set up all the ones that are possible.4
2. Organising a class practical
