- Help pupils to work out a technique for determining dry mass, using either secondary sources or preliminary work,
eg leaving a slice of apple in an oven and weighing it at regular intervals until the mass is constant, trying different oven temperatures and different time intervals for weighing.
- Ask pupils to consider the available apparatus, identify the hazards and decide what they would need to do to minimise the risks from each of these.
- Help pupils to decide how to calculate the percentage of water in an apple from the dry mass of a slice.
- Ask pupils to carry out procedures safely and effectively, record their data and carry out the calculations needed to determine approximately how much of an apple is water.
- Ask pupils to evaluate the method used and identify ways in which their results may be inaccurate,
eg water vapour may be reabsorbed if the apple is left to cool in the air and a desiccator is not available; the apple may not be of uniform composition; substances other than water may have been driven off, and to consider how many measurements they would need to make to have confidence in their results.
- Ask pupils to explain the significance of the amount of water in an apple by using their knowledge of the ways in which water is used by plants and in plant cells.
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- suggest an appropriate way of determining the dry mass of an apple,
eg through research or by carrying out preliminary work
- explain why each step in their technique is necessary
- use suitable apparatus,
eg an oven, digital balance, and carry out procedures safely
- calculate the percentage of water in an apple
- evaluate the accuracy of their technique
- explain why plants have a high percentage of water
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