When pupils need more than 10 or 20 seconds for their talk it needs to be structured more carefully. Here are some examples:
■ Peer-group discussion to develop an explanation for a phenomenon ('Why do you think bulbs go dim when in series, but stay bright in parallel? You have 45 seconds to discuss this in your groups.').
■ Debating an issue, having been given resources to examine (as in activities you can download from the upd8 ('update') website (www.upd8.org.uk), such as the genetics debate in Box 8.1).
■ Planning a group report or Microsoft PowerPoint presentation on the results of practical work or investigations ('In 2 minutes I will ask each group leader to present the findings of their investigation.' 'You have 5 minutes to prepare two or three PowerPoint slides to explain what you found out.'). Note: set strict and short time limits.
■ Deciding on an explanation prior to devising further investigation (e.g. the reason why white light goes green when it hits a leaf - see Box 8.2).
Having grappled with the fundamentals of genetics and cell division, pupils are in a position to get their teeth into the major issues of today. These are displayed readily on a daily basis via the media. They were epitomised when surgeons crossed a major medical frontier with the transplant of a human windpipe grown from adult 'stem cells', within a month of the Human Fertilisation and Embryology Bill being passed by the government. The bill gave the go ahead for research to take place involving the implantation of human genetic material into an egg taken from another animal, for example a rabbit. Together these advances pave the way for a host of innovative possibilities including regenerative medicine - when damaged body parts are repaired in situ rather than being removed and replaced by whole-organ transplants, for example, brain and nerve tissue regeneration. In one technique stem cells are extracted from cloned embryos created from a patient's skin cells and used to create mature nerve cells that can be transplanted into damaged areas of the brain.
There are many social, moral and ethical issues associated with such research, lending themselves to group and whole-class debate. This however needs to be managed effectively. To ensure that pupils can contribute to such debates they should be encouraged to collect relevant newspaper cuttings or print-outs from websites on the issues to supplement classroom-based theory lessons with their own wider research. They then take part in role-play scenarios whereby they access all aspects of the debate.
The following questions highlight issues that can form the basis of detailed debate and discussion:
■ Should scientists be allowed to alter people's genes? Would it make a difference if the genes they altered were faulty ones, so that an illness like cystic fibrosis could be cured? What if they could alter sex genes, so that the illness would not be passed on to the next generation but the human genetic pool would be irrevocably changed?
■ Should scientists be given the potential to create half-human, half-ape 'hamanzees' or real-life creatures from Greek mythology such as the half-bull, half-human 'Minotaurs'?
■ Should it be possible to patent genes? At present genes of known function can be patented - for example, the cystic fibrosis gene is 'owned' by the universities of Michigan and Toronto - but it is not yet clear whether parts of genes or those of unknown function can be registered.
■ Should food crops be modified to enable greater yields to be obtained? Who should own the patents for such developments?
During a class debate the pupils could have notes to support what they say, but insist that they speak ex tempore, that is, they do not read from a prepared text, but speak from their understanding.
Seal two microscope slides together with a thick band of glue-gun glue along three edges of one face so your pupils can pour into this a strong solution of chlorophyll, in alcohol, which they (or you) make by grinding up grass with ethanol and filtering. Pupil talk at the start is needed to elicit their ideas about how this green 'filter' works - it seems to change everything green. Some may think the light is 'dyed' by the green filter; others may think that the filter removes some of the colours leaving only green. They now use a ray box and prism to make a spectrum (the physics of light and colour) and you ask each group to discuss how the contrasting ideas can be tested. For example, if the green colour dyed the light, all the colours of the spectrum would go green, but if only the green was allowed through and the other colours were absorbed, you would see that the red and blue parts of the spectrum were missing. Following the practical work (or teacher demonstration) with filters the pupils then discuss which explanation of how the filters worked best fitted the experimental results. Finally you can help them apply these ideas to ask what happens to the red and blue sunlight energy captured by green leaves.
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