Science at key stage 3 (Year 7)
Unit 7A: Cells
Section 10: What causes pollen tubes to grow?
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Objectives |
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- how to frame a question that can be investigated
- about the importance of sample size and the number of observations in biological investigations
- to identify trends shown in graphs
- to evaluate the strength of the evidence
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Activities |
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Outcomes |
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Children: |
- Remind pupils of their observations of pollen tubes and explain that they are going to find the sugar concentration that is best for pollen tube growth. Help them to frame a question for investigation. Suggest an appropriate range of sugar concentrations and discuss with pupils the control of variables and the sort of observations which would provide the information needed to answer the question.
- Explain issues relating to sampling in biological investigations,
eg sufficient sample size to account for variables that cannot be controlled or to provide reliable data.
- Help pupils to collect and present data relating to the number of germinated grains, in a sample of approximately 20, from each sugar concentration.
- Ask pupils to produce an account of their investigation in which the importance of sampling is clearly explained.
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- identify a suitable question
- explain why they needed to use a particular number of pollen grains,
eg 20 grains at each concentration
- make accurate observations and record these appropriately
- draw an appropriate graph of data collected
- use the graph to identify trends and make generalisations
- compare graphs produced by different groups, and use these to evaluate the strength of evidence
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Points to note |
- This investigation provides an opportunity to help pupils understand the importance of sampling in biological investigations. A suitable approach involves preparing slides of pollen in a range of sugar concentrations, observing,
eg 20 pollen grains from each slide, and counting how many of these have germinated. The use of 20 pollen grains should enable a conclusion to be drawn about the optimum concentration for the process. However, within each 20 grains there will be differences arising from variables that cannot be controlled,
eg the genetic make-up of the grain. In smaller samples these differences may mask the effect of the different concentrations of sugar.
Safety
- pupils' plans must be checked for health and safety, before practical work begins
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This unit is divided into sections. Each section contains a sequence of
activities with related objectives and outcomes. You can view this unit by
moving through the sections or print/download the whole unit.
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