Unit 3 - Biofuels
Biogas generators can be filled with faeces.

Unit 3 - Biofuels

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.

What are biofuels made from?
Animal and plant material
Biofuels come from organisms
Biogas is primarily made up of which gas?
Carbon dioxide
Methane is a useful fuel
Biogas is made by which process?
Aerobic respiration
Alcoholic fermentation
Anaerobic fermentation
Biogas is made by a special type of anaerobic respiration called anaerobic fermentation. This is not the same process which occurs in the muscles of our body
Biogas generators can be filled with which of the following?
Human and animal faeces can be used as well as food waste. So it helps to keep the environment clean as well as providing a useful fuel
In a biogas generator, what does the animal or plant material supply?
Carbohydrate (sugar)
The carbohydrate is changed into the product methane
Methane is a greenhouse gas and contributes to...
the weather
global warming
ozone depletion
Global warming is the gradual increase in the average temperature of the surface of the Earth
Which of the following is not caused by global warming?
Increased temperature of the Earth
Rise in sea levels
Increased biodiversity
Climate change
Global warming leads to reduced biodiversity
What is biodiversity?
The number of species
The population of humans
The variety of birds
The number of trees
Biodiversity is important to the health of the planet. It refers not just to the number of different species but also to the genetic variations within each species
Biogas is produced at a faster rate if the temperature is...
heated for longer
About 35 degrees C is the optimum temperature
Biogas generators are useful in developing countries such as Africa, because they easily and cheaply get rid of what?
The raw materials are free and recycled into a useful product, biofuel, which can be used for many purposes
Author:  Donna Maria Davidson

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