Energy is the ability to rearrange a collection of matter. All organisms require chemical energy for growth, repair, physiological processes, regulation and reproduction. Energy exists in various forms. The study of energy through living systems begins with the cell and how energy is obtained and used.
All organisms require chemical energy for growth, repair, physiological processes, regulation and reproduction. Organisms can be classified by how they obtain this energy. Autotrophs such as plants use light energy to build energy–rich organic molecules and then use those organic molecules for fuel. In contrast, heterotrophs such as animals must obtain their chemical energy from food, which contains organic molecules synthesized by other organisms. The flow of energy through an animal–its bioenergetics–ultimately limits the animal's behavior, growth, and reproduction and determines how much food it needs. Studying an animal's bioenergetics tells us a great deal about the animal's adaptations.
Energy is the ability to rearrange a collection of matter. For example, we expend energy to read these pages, and our cells expend energy in transporting certain substances across membranes. Energy exists in various forms, and the work of life depends on the ability of cells to transform energy from one type into another. Energy can be associated with the relative motion of objects; this energy is called kinetic energy. Moving objects can perform work by imparting motion to other matter: For example, the contraction of leg muscles pushes bicycle pedals. An object not presently moving may still possess energy. Energy that is not kinetic is called potential energy.