Energy is funny stuff. It cannot be made or got rid of, it can only be changed from one form to another. Every time that happens some is lost to outer space as "low-grade" heat.
We get our energy from the Sun. Plants use "high-grade" energy - sunlight - to turn water and carbon dioxide into lower-grade chemical energy as part of the photosynthesis process. Plants store energy as sugars, fats and proteins. In turn, we get our energy by eating plants or the products of farm animals - this is the so-called food chain.
As we turn food into human energy, the heat we produce helps to keep us warm and we warm up the environment around us. The harder we work the more we have to eat and the hotter we get. We sweat, puff and pant to keep our bodies at the right temperature. When we get ill, our temperature changes as the energy supply of c our bodies is being used by bacteria and viruses, and our temperature often goes up to warn us that something is wrong.
Other forms of energy keep our schools warm in the winter and provide light for classrooms when it gets dark early. Dinner ladies need energy to cook lunch, and some of us travel to school by train, bus or car, which also uses fuel.
Our main sources of energy are coal, oil and natural gas - fossil fuels made by plants millions of years before dinosaurs ruled the Earth. These can be turned into electricity, which is one way in which energy can be easily brought into our homes and schools. Electricity is convenient and clean in the home - just imagine how your computer would look if it was gas-powered, or how your television might work if it needed stoking with coal.
Most electricity is produced by burning fossil fuels, but these are finite. There may be huge stocks of fossil fuels on Earth but, as we use up the stocks that are easy to reach, fossil fuels become less economical. We can turn them into plastics or hot air, but we can't make more of them. There is a danger they could run out in your lifetime.
India, which will soon be home to a billion people, is the world's largest producer of tropical hardwood, 80 per cent of which is used as fuel.
Burning wood is still the most common way for people around the world to cook and heat their homes. But constantly chopping down trees does the soil no good and eventually new trees will not grow - and trees are being chopped down faster than they are being grown.
As if chopping down trees - which help stabilise the soil - is not bad enough, they are then burnt. The burning of any fuel releases carbon dioxide back into the atmosphere, where it acts like panes of glass in a greenhouse, trapping the energy of the Sun and warming up the planet.
The temperature of the Earth's atmosphere is rising - not much, but enough to warn that something may be wrong. If the temperature continues to rise, it could melt the glaciers and ice caps. If that were to happen, the sea level would rise by about 100 metres, flooding most of the world's towns and much agricultural land. Burning things to release energy also produces toxic waste, acid rain, choking gases, particles and ash.
Some say that atomic power is the answer to the problem. This is power generated from the inner core, or nucleus, of the atom. A tiny particle called a neutron hits the nucleus of an atom in a material such as uranium-235. The tremendous release of energy that follows is kept in check by neutrons in control rods, which absorb any excess energy. But atomic power also produces very harmful substances which cost lots of money to deal with and can cause terrible problems if something goes wrong, as was proved by the accident at the Chernobyl nuclear power station in 1986.
Fortunately, there are many other power sources all around us - rain drops, wind energy, waves and tidal rivers that run into the sea. Engineers can capture and turn them into electricity. But these forms of alternative energy can have some side-effects and must be developed with care. For instance, wave and tidal barriers can adversely affect wildlife: without proper planning, they can let sewage and pollution (such as chemical waste from agricultural land) gather in environmentally sensitive estuaries, poisoning fish and birds. Windmills that generate electricity can be noisy, offending residents and frightening away tourists who provide vital money for the region.
However, scientists are busy perfecting solar cells and super conductors so that future generations can behave like plants and tap directly into the sun.
Until that happens, there is another form of energy we must all plug into and so do our bit to help save the world.
I like to call it "complementary energy", the energy we can all save by using what we have as efficiently as possible. Just to keep all the schools in Britain well lit and at the correct temperature costs around pound;400million a year. Many studies show that it is easy to save 30 per cent of the energy we use in our everyday lives. Just think, if you could make your school that energy efficient, you could have pound;5,000 or more to invest in other things every year. To save money, you could encourage teachers and governors to:
* Make sure your school roof is adequately insulated. This will stop heat escaping and can reduce the school's energy bill by 20 per cent.
* Get the caretaker to turn the thermostat down by 1 LESS THAN C. You won't notice the difference, but could reduce the energy bill by 10 per cent.
* Buy long-life light bulbs. These use only 25 per cent as much energy as ordinary ones and last eight times longer.
You can also make sure:
* Lights and electrical appliances are switched off when not in use. A television on standby uses almost as much power as when it is full on.
* Stop draughts, close doors and windows, and wear warmer indoor clothes in the winter. In the summer, open windows and let cooling breezes in.
Schools, quite literally, hold the key to our future. The Earth is in your hands, and every one of you can make a difference.
* Openings, a booklet from the Centre for Research, Education, and Training in Energy, lists and reviews energy education resources for all age ranges. pound;2 from CREATE, Kenley House, 25 Bridgeman Terrace, Wigan, Lancashire, WN1 1SY. 01942 322271.
* Visit the CREATE website at www.create.org.uk.