<unk>  is any material that is burnt or altered in order to obtain energy.<unk>  releases its energy either through a chemical reaction means, such as combustion, or nuclear means, such as nuclear fission or nuclear fusion. An important property of a useful<unk>  is that its energy can be stored to be released only when needed, and that the release is controlled in such a way that the energy can be harnessed to produce work.
All carbon-based life forms—from microorganisms to animals and humans—depend on and use<unk> s as their source of energy. Their cells engage in an enzyme-mediated chemical process called metabolism that converts energy from food or solar power into a form that can be used to sustain life.  Additionally, humans employ a variety of techniques to convert one form of energy into another, producing usable energy for purposes that go far beyond the energy needs of a human body. The application of energy released from<unk> s ranges from heat to cooking and from powering weapons to combustion and generation of electricity.
Fuel
Boil
Hydrocarbon
Colloid
Phytochemical
Metal
Carbide
Electron