Plants are often called producers because of their ability to make their own food from the sun's energy. When scientists discuss energy, they often refer to the Laws of Thermodynamics. The First Law of Thermodynamics states that energy can neither be created or destroyed. The Second Law states that energy is constantly converted from high quality to low quality. High quality energy is capable of performing a large amount of work, while low quality energy is capable of performing less work.
Scientists know that energy always changes from high to low quality when work is performed.
During the change, some energy is lost in the form of heat, which cannot do work. The amount of e nergy lost as heat is often as high as 90 percent of the total energy involved. Putting all this together in an example, if 1,000,000 units of solar energy were to reach Earth, one percent or 10,000 units, would be available for plants to use. Of these 10,000 units, plants would lose 90 percent, or 9,000 units, as heat. If an animal then ate the plants, it would only receive 1,000 units of energy.