Science at key stage 3    (Year 9)

• Review pupils' knowledge and understanding of feeding relationships by asking them to draw food chains representing a typical meal that they may have eaten. Help them to combine their responses to show the wide variety of foods that humans eat, and the complexity of the human food web.
• Ask pupils questions about why plants can be food sources and the importance of the Sun as an energy source for food chains. Check pupils' understanding and relate their ideas to the food web produced.

• Provide examples of food from plants, eg carrot, pea, potato, wheat, maize, lettuce, apple, rice, mango, soya bean, grape, radish, coconut, onion. Ask pupils for further examples and to identify which parts of a plant each represents. Explain that each of these foods contains materials produced by the parent plant. Ask them how plants produce this material, and why plants keep large stores of starch in certain parts (roots, stems, seeds), emphasising that it was not produced for humans or animals to eat. Remind pupils about plant respiration.
• Ask pupils to test the samples for the presence of starch, and invite them to suggest why some parts do not give positive results. Explain how the products of photosynthesis may be converted into other substances by the plant.
• Provide microscope slides showing starch grains inside cells, eg of a potato, and help pupils to interpret what they see.

• Ask pupils to make a concept map using appropriate terms, eg producer, consumer, food web, photosynthesis, energy, Sun, glucose, starch, root, leaf, stem. Ask pupils to exchange maps and to suggest additional connections, explaining these.

• Ask pupils to use samples of fertiliser packs of different types and other sources to find out about nutrients, eg the range of nutrients that plants need, what role these nutrients play in the life of the plant, which nutrients each fertiliser provides, how much a plant requires, and to summarise the information in a table. Tell pupils the cost of a pack of fertiliser, and the recommended application rate, and ask them to calculate the cost per 100 square metres of crop.
• Show images, eg video clips, photographs, of large-scale fertiliser application to farmland. Ask pupils to consider the great costs involved, and any other implications of this practice.

• Extend this work by asking pupils to plan and carry out an investigation into the effects of fertiliser, eg of nitrate fertiliser concentration on duckweed growth, providing information about culturing the plant and a maximum concentration; the effect of different fertilisers on wheat growth. Ask pupils to produce a report of their investigation and to contribute conclusions to a class summary, indicating whether they think they should have confidence in what they found out.

• Ask pupils to suggest what the term 'weed' means, why weeds might affect yields from food crops, and ways in which weeds compete with crop plants for resources. If possible, provide pupils with data about the yields of crops with, and in the absence of, weeds, and ask them to explain whether the data supports their ideas. Ask pupils to suggest what the effects of killing the weeds might be on other living things on the farm.
• Provide pupils with examples, eg specimens, photographs, of weeds that often grow alongside food crops and show photographs or video clips of workers in protective gear spraying food crops with weedkiller. Ask pupils to find out about the chemicals used and their effects, eg using information from packaging, and to present this information as a table.

• Extend this work by asking pupils to carry out a survey of weeds growing, eg in a lawn, allotment or crop field. Provide a key for identifying weed plants and remind them how to use quadrats to sample a population.
• This could be set in the context of having to produce a report for the landowner about the types and numbers of weeds on the land. In the report, pupils could be asked to explain the problems that weeds present and to make suggestions about how to treat the land to remove them, and to identify possible consequences of the treatment.

• Ask pupils about the types of animals that might feed on the crops grown and establish that these are competing with humans for the crops. Ask pupils to find out what these animals, eg fieldmouse, cabbage white butterfly, aphid, snail, slug, feed on, and emphasise that, for these animals, the food crops are part of the food web. Help pupils construct pyramids of numbers for some of the feeding relationships identified.
• Ask pupils how farmers respond to pests, and consider methods of management, including the use of pesticides. Show packaging or advertisements, eg for insecticides, snail and slug treatment, and ask pupils to find out about what chemicals are used, how dangerous they are, and whether they are specific to one type of animal.
• Show a food web and identify a pest species that could be eliminated by a pesticide. Ask pupils to predict some effects of this on the pest species and on other populations, eg fewer insect pests leads to a decrease in the bird population, and to relate this to pyramids of numbers.

• Remind pupils how to select information from a text and ask them to suggest ways in which information about toxins in food chains might depend on the author of the text. Provide pupils with secondary sources of information, eg textbooks, videos, environmental leaflets, about the effects on the wild bird population of bio-accumulation of toxins in the food chain, eg the effect of DDT used as a pesticide on the heron population, the osprey and other birds of prey such as sparrowhawks, and the decline in populations of some UK native birds as a result of pesticide use on farms.
• Ask pupils to consider and evaluate the information provided, and to extract from it the key points to explain why the bird populations have declined.
• Provide pupils with secondary sources of information about the use of pesticides, eg in controlling populations of locusts, malarial mosquitoes. Ask pupils to consider and evaluate the information provided and to extract from it the key points about which pesticides were used and why they were used.

• Use the examples above to draw out issues and ask pupils to reflect on questions, eg
• Why are pesticides used?
• Are there alternatives?
• Who develops alternative, less harmful pesticides?
• What could be done to protect vulnerable populations such as birds?
• Should pesticides be used to produce more food for humans at the expense of other animals?
• How are pests managed on organic farms?

• Ask pupils about the conditions that plants need for healthy growth, eg light, water, minerals, warmth, carbon dioxide. Reinforce by showing examples of plants that have been deprived of one of these, eg grass seedlings grown in the dark, in the cold, in dry conditions, or with a mineral deficiency, and ask pupils to suggest reasons for the plants' conditions.
• Show images of commercial greenhouses in operation. Supplement with information about smaller-scale greenhouses, eg from a catalogue. Discuss the advantages of growing crops this way, eg control of climate, longer growing season, no weeds, and consider and evaluate any problems associated with this type of production, eg appearance in the environment, possible variation in taste.

• Ask pupils to use their knowledge of the needs of plants and of growers to design an ideal greenhouse environment for crop production on farms. They may include control-technology devices to monitor and control the internal environment. Their plans should be presented as annotated drawings that include the reasons for each design feature.
• Ask pupils why most food crops are not grown under protective cover.

• Draw together the concepts and issues from the previous activities, eg
• the need to provide food for humans and domestic animals
• the reasons for, and effect of, the removal of hedges and woodland
• why pesticides and weedkillers are used

and provide comparative information about alternatives, eg organic farming.
• Ask pupils to produce a piece of work that summarises the issues of plant production for food, based on their scientific knowledge of the problems, eg
• a magazine article highlighting the main issues for the general public
• a script for a radio or TV documentary
• a classroom debate in which individuals or groups argue the case for and against intensive agriculture
• a carefully scripted role play where individuals act the parts of participants in a meeting to discuss the issues