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The production of carbon neutral fuel - biodiesel - from cooking oil, animal fat and plants. At a biodiesel refining plant in Motherwell, 35,000 tonnes of old cooking oil and animal fat is filtered each year and chemically converted into diesel fuel. The fuel is mostly mixed with normal diesel to power lorries and some cars. Biodiesel is produced from plant material so is, in theory, carbon neutral. The reason for this is that the plants that biodiesel is produced from consume the same amount of carbon dioxide as is produced when the biodiesel is burned

Divide students into two groups – one to investigate how petrol and diesel are used in Scotland today, as well as the implications of this use – and one to research biodiesel as an alternative source of fuel. How could biodiesel be used to reduce the waste of energy caused by ordinary petrol and diesel and the impact on the environment caused by CO2 gases? Would it be practical to replace all petrol and diesel with biofuel?

Students could write letters to imaginary lorry companies in the UK, urging them to switch to biodiesel, citing the reasons for doing so. Students could also write replies from the lorry companies, explaining why they would be willing to discuss the proposal or why it is not a viable option for them. .