2. Organising a class practical
Demonstrations can be a good way to enthuse and interest your students, but they really begin to learn about being a scientist if they have the chance to do the experiments themselves. Activities 2 and 3 describe two different approaches to class practical work.
Firstly, you can use experiments to illustrate key concepts and to help your students understand the theory, or secondly, you can support them in designing their own experiments in order to investigate a hypothesis. If you do this they will begin to learn about how scientists work as well as understanding the theory. In Case study 2 the teacher does not have very much equipment but manages to do some simple experiments. Rather than get her students to copy notes about the experiments from the board, she uses a sentence matching exercise that will encourage her students to think about what the experiment has shown them. Resource 3 provides ideas about how you can use students’ writing to enhance learning. Activity 2 shows what you could do if you have access to microscopes or balances or a source of heat. Firstly students are encouraged to look very carefully at something they see every day. Then, they put the leaves in special conditions to find out more and finally, they use a microscope to see something invisible to the naked eye. This illustrates three approaches that biologists use to build their understanding of the living world.
Case study 2: Doing practical work with limited resources
Mrs Ogina works in a secondary school near to a large city slum and has very few resources, but she is very resourceful. She is passionate about living things and her students love coming to her room because there are lots of plants growing in pots and pictures of living things that she has collected from old magazines and tourist brochures.
Before the lesson, Mrs Ogina had put a plastic bag over one of the plants in a pot. By the time the lesson began, droplets of water had collected in the bag. She gathered her class round the front and asked them where the water had come from. She didn’t tell them the answer but was encouraged when someone suggested that it might be something to do with the leaves.
She sent them out of the classroom to collect leaves. She asked each group of five students to collect three different types of leaf. (She had also brought some in from where she lives as she knew there was not much variety near the school). She asked them to look at the leaves very carefully and to write down four ways in which they are adapted for photosynthesis. She asked them to think about what they all had in common and what the differences were between them.
When they had been working for a while she stopped them and went back to the suggestion that the water might have come from the leaves. She drew a diagram of a leaf on the board and explained about the stomata. She encouraged them to look carefully at their leaves and see where the stomata should be but explained that they would need a hand lens or microscope to see them.
The next lesson, Sam came rushing into the classroom to show Mrs Ogina a magnifying glass that his uncle had given him. He was happy for the students to take turns in looking for the stomata, provided they were careful with the magnifying glass. To finish the activity, Mrs Ogina wrote statements on the board (see Resource 4) and the students had to match them correctly to make sentences.
Activity 2: Encouraging careful observations
Organise the students into groups of three or four. Ask each group to collect four different leaves. Challenge the groups to find five adaptations for photosynthesis that they can observe without a microscope or hand lens.
Now give each group a beaker or tin of boiling water. Ask them to put each leaf in turn into the water, observe what happens on both sides of the leaf and explain what they see. They should notice that air bubbles appear at the lower surface of the leaf, showing that air is escaping through tiny holes.
Show them a diagram of a section of a leaf seen under a microscope and ask them to relate their observations to the diagram. If your school has a microscope you can show them the stomata or better still get them to make their own slides.