This GCSE Biology quiz takes a closer look at biofuels. These are either combustible gases like methane or combustible liquids such as plant oils, which can be burnt to release energy.
Biofuels are more environmentally friendly alternatives to fossil fuels because they are part of the current carbon cycle. Burning fossil fuels releases carbon that has been locked out of the carbon cycle for millions of years. This causes a problem because it overloads the Earth's natural recycling system that keeps the level of gases in the air in balance. It only takes small increases in the percentages of gases like methane and carbon dioxide to create a runaway greenhouse effect in which the surface temperature of the Earth increases beyond that which could sustain life. Most scientists believe that human use of fossil fuels is creating this greenhouse effect and causing global warming, whilst some believe that the changes we are seeing are natural.
Liquids obtained from plants can help to lessen the amount of carbon imported to the present day from the past. Petrol can be diluted with a percentage of ethanol (an alcohol) that is made from the fermentation of plants. These plants are part of the current carbon cycle and so will not increase the overall level of carbon dioxide in our atmosphere. There are other advantages too, such as lower emissions of other gases like the toxic carbon monoxide. The main argument against this is that land that could be used for growing food crops will be taken up by crops grown to produce bioethanol to add to petrol. Diesel can be replaced with biodiesel. This is made from plant oils that have been treated to make them burn in diesel engines. Biodiesels can be made from used cooking oils, soya bean oil or even animal fats.
Biogas is made in a generator which is loaded with human waste, animal dung or food waste which would otherwise end up in the environment. Waste materials like these release methane and carbon dioxide into the atmosphere as they decay. This biofuel is mainly methane and is produced by anaerobic fermentation of the waste products. Aerobic fermentation would produce carbon dioxide instead of methane and that cannot be usefully used. Biogas can be passed through pipes to local homes where it can be used as a fuel for cooking. In some places, the biogas is used as a fuel for generating electricity for the local community.
Which biofuels are combustible liquids? Is methane a biofuel? See how much you understand about biofuels by trying this quiz.