Science at key stage 3 (Year 9)
Unit 9C: Plants and photosynthesis
Section 3: a. What is the role of the leaf in photosynthesis?
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Objectives |
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- to test for the presence of starch in a leaf
- to heat flammable liquid safely
- that chlorophyll and light are necessary for photosynthesis
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Activities |
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Outcomes |
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Children: |
- Explain to pupils that the glucose formed is usually stored as starch and ask them about a test for starch. Demonstrate how this can be carried out on a leaf.
- Provide pupils with a variety of leaves,
eg variegated leaves, leaves kept in the dark for a few days, leaves covered with cut-out templates, copper beech leaves, so they can investigate starch distribution.
- Discuss the results with pupils and ask them to explain their observations. Compile a summary of all the observations and establish that starch is stored in the green parts of leaves and those parts that have been exposed to light. Establish with pupils that the chlorophyll in plants enables them to absorb light, which is necessary for photosynthesis.
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- detect the presence of starch in a photosynthesising leaf and relate it to the presence of chlorophyll
- relate photosynthesis to exposure of the leaf to light,
eg etiolation
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Points to note |
- Pupils will have carried out a test for starch in unit 8B 'Respiration'.
- Pupils may need to sketch the pattern of green and white/pink on a variegated leaf before testing it for starch, to be better able to correlate starch distribution with presence of chlorophyll.
- Extension: some pupils could be asked to find out about the molecular structures of glucose, sucrose and starch and the relationship between them. They will have seen models and representations of large molecules in unit 8E 'Atoms and elements'.
Safety
- emphasise the hazards of heating flammable liquids and show an appropriate way to heat ethanol, eg using water from an electric kettle or a water bath
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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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