1. Demonstrating transport in plants
Practical work is a very good way to engage your students with an idea or problem and help them to see the relevance of the theories that you want them to learn. As a teacher you will be keen to explain the scientific ideas. Often teachers are too ready to offer an explanation and miss the opportunity to really engage and interest their students. If you can show your students something that surprises or intrigues them, they will be keen to find out more. Sometimes, therefore, it is better to withhold information and let your students ask questions or suggest an explanation. In Case study 1, the teacher gets her students to set up an experiment but does not tell them why they are doing it. This is important; she wants them to think about what might happen and give them the opportunity to share their ideas. In Activity 1 a slightly different way of presenting the same experiment is suggested.
Case study 1: Organising a demonstration
At the end of the topic on nutrition Mrs Ngnomo found that she had 15 minutes at the end of the lesson. The next topic she was due to teach was transport, and she had been collecting plants and flowers for a while. She got out her plants, some jars and some food colouring. She asked some of the students to half-fill the jars with water and to add a few drops of food colouring to each one. A pale coloured flower or a stick of celery was placed in each jar and they were left on the window sill of the classroom until the next lesson. The class were intrigued. Mrs Ngnomo gathered them round the front and asked them what they thought might happen. She did not tell them any answers.
She wrote all their suggestions on the board. Then she gave them five minutes to talk to each other. She asked each pair to write down a prediction and a reason for their prediction. She collected in their suggestions and kept them until the next lesson.
The next day the class rushed into the lab, keen to see what had happened to their flowers. The white carnations had gone blue and the veins could be seen all the way through the celery.
The students were really interested in what had happened and Mrs Ngnomo let them cut thin sections of the stems of the plants and look at them with a hand lens. She gave out the predictions they had made, gathered them round the front and asked them questions about the experiment. She started with simple, closed questions, based on their observations and moved on to harder questions that challenged their thinking.
Activity 1: Encouraging student questions
Set up a plant in a beaker of coloured dye. Choose a plant or flower that clearly shows the path of water through vascular bundles and that has a stem that you can cut easily with a razor. Your school text book should suggest suitable plants found in your area.
You should do this at the end of a lesson, so that the students can see what you are doing – but don’t tell them anything about it. Leave it until the next lesson so the dye has time to move up the stem. (If you have not done this before try it beforehand to see how long it takes. If it is a long time until the next lesson, you might need to set up another one).
You should use probing questions aimed at helping students to predict, observe and explain what the experiment shows. You may also choose to show the same experiment with a plant that has a pale coloured flower where the dye is seen moving through the flower. Ask students to suggest what further questions this experiment raises. Write all suggestions on the board. Then ask students to predict the answers to their questions and to suggest how scientists could investigate these questions.