Energy is created in the Sun and other stars when atoms are fused together. In the core of every star, tiny amounts of mass are destroyed to form enormous amounts of energy over and over again every second. This process is called thermonuclear fusion, and it is the source of all the light radiated by the Sun and all other stars.
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The Sun and other stars create energy through a process called thermonuclear fusion.
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However, in everyday life, energy cannot be created or destroyed. Energy is simply transformed from one form to another all around us every day. Energy in action is classified as kinetic energy, while energy that seems to be inactive or stored is classified as potential energy. As a way of imagining these transformations, think of the energy stored in water contained by a dam (potential energy). When water is released to flow, it drives a turbine generator (kinetic energy) that produces electricity (electrical energy). The energy was not created or destroyed; it was transformed.
There are many different kinds of kinetic and potential energy. A few examples of each are listed in the table below. (Note: There are many more types of energy than the few examples listed on the table.)
Potential (“stored”) Energy |
Gravitational potential energy is the energy of something because it is in an elevated position so that it could fall.
Elastic potential energy is the energy of an object that is stretched or squished out of its natural shape and has the potential to snap back, such as a stretched rubber band or a compressed spring.
Chemical energy is the energy stored in compounds that can be unlocked by chemical reactions, such as when food is digested or gasoline is burned. |
Kinetic (“in motion”) Energy |
Thermal energy is the energy of vibrating particles; it causes the sensation of warmth.
Electrical energy is the energy of charged particles flowing from one area to another, such as through a circuit or from the brain to the muscles through the nervous system.
Light energy is energy made up of particles moving in waves; it is produced by glowing objects, such as stars and light bulbs, and is absorbed by producers to gain energy to carry out photosynthesis. |
The same forms of energy we see at work in the world around us are also at work inside living things. All living things need energy to live and grow. Sunlight is that energy source. Every ecosystem must have producers to start the flow of energy. Producers absorb sunlight and use it to create chemical energy in the form of carbohydrates. Producers use a chemical reaction called photosynthesis to convert carbon dioxide and water into oxygen and carbohydrate molecules, such as glucose. Glucose is stored in the plant as a starch and is combined with other carbohydrate molecules to form cellulose, the basic structural material of a plant.

Consumers are organisms that must consume other organisms to gain energy. Herbivores are consumers that consume producers, while carnivores consume other consumers and omnivores consume both producers and other consumers. Energy is transferred through a food web as one member of an ecosystem consumes another. Consumers break down the carbohydrates of the organisms they eat to get the energy they need to live and grow by using a chemical reaction called cellular respiration.
In cellular respiration, carbohydrates react with oxygen to form carbon dioxide, water, and energy in the form of ATP. To gain the carbohydrates, animals must eat other organisms. To gain oxygen, animals must breath. The energy released during cellular respiration helps animals move, grow, reproduce, maintain body temperature, and perform many other necessary functions.
Note: Producers are the only organisms capable of carrying out photosynthesis. However, both producers and consumers carry out cellular respiration. In producers, photosynthesis only takes place during the daytime, because that is when sunlight is available. Respiration takes place during the day and night. As long as the process of photosynthesis exceeds the process of respiration, the producer will thrive and grow.
In every ecosystem, energy is transferred in a chain from the sun to producers, primary consumers, and then secondary consumers and tertiary consumers. These are the four trophic levels that exist in every ecosystem. The transfer of energy up the levels continues until the producers and consumers die. The energy from dead organisms, both producers and consumers, is then passed along the food web by decomposers.
Note: Herbivores or omnivores can serve as the primary consumer in a food chain if they are consuming a producer. Carnivores and omnivores can serve as secondary or tertiary consumers depending on what they are consuming and where that puts them on the food chain.