Kinetic energy is due to motion, and results in work. Work that results from the expenditure of energy can both store energy (as potential energy) and arrange or order matter without storing energy.
The expenditure and storage of energy is described by two laws of thermodynamics. The first law of thermodynamics called law of conservation of energy states that energy is neither created nor destroyed.
It may change forms, pass from one place to another, or act upon matter in various ways, but regardless of what transfers and transformations take place, no gain or loss in total energy occurs. Energy is simply transferred from one form or place to another.
When wood is burned the potential energy present in the molecules of wood equals the kinetic energy released, and heat is evolved to the surroundings. This is an exothermic reaction. In an endothermic reaction, energy from the surrounding may be paid into a reaction.
For example, in photosynthesis, the molecules of the products store more energy than the reactants. The extra energy is acquired from the sunlight, but even than there is no gain or loss in total energy.
Further, though the total amount of energy involved in any chemical reaction, such as burning wood, does not increase or decrease, much of the potential energy stored in the substance undergoing reaction is degraded during the reaction into a form incapable of doing any further work.
This energy ends up as heat serving to disorganize or randomly disperse the molecules involved, thus making them useless for further work. The measure of this relative disorder is named entropy.
The second law of thermodynamics states that whenever energy transformed from one kind to another, there is an increase in entropy and a decrease in the amount of useful energy. Thus, when coal is burned in a boiler to produce steam, some of the energy creates steam that performs work, by part of the energy is dispersed as heat to the surrounding air.
The same thing happens to energy in the ecosystem. As energy is transformed from one organism to another in the form of food, a large part of that energy is degraded as heat and as a net increase in the disorder of energy. The remainder is stored in living tissue.
Three sources of energy account for virtually all the work of the ecosystem: gravitation, internal forces within the earth and solar radiation. The last is very significant for ecosystem. The solar radiation which originates from sun is the source of energy for life and life is what sets the ecosystem apart from other natural systems.