756 General and Applied Biology 



appear, so that the interfaces are also constantly changing. This con- 

 stant change in surface tension at these interfaces is closely related with 

 many of the phenomena of living protoplasm. 



Energy 



Energy may be defined as the ability to produce change or do work. 

 Energy, which may be in the form of electromagnetic waves, is the unit 

 of the universe because the various types of matter are thought to be 

 merely different forms of energy. The power to do work or produce 

 change is a property of living protoplasm. Energy, which is involved in 

 all changes constantly taking place in living protoplasm, is ordinarily 

 measured by the amount of work or change performed. A great variety 

 of energies are known, the following being the more common: electrical, 

 chemical, radiant, mechanical, and heat. Energies may be divided into 

 potential and kinetic. Potential energy is the stored energy possessed by 

 a substance because of its position or condition. Coal and wood before 

 they are burned possess potential energy. Carbohydrates before they are 

 digested also possess potential energy. Kinetic energy is action energy, 

 or energy possessed by virtue of motion. Kinetic energy may become 

 potential, and potential energy may become kinetic. Energy required to 

 form a molecule of substance becomes inactive potential energy when 

 stored in that molecule, but it is converted into active kinetic energy 

 when the molecule is broken down. Energy cannot be created anew or 

 decreased, but, when a quantity of a certain type disappears, an exactly 

 equal quantity appears in some other forms. 



All chemical reactions involve changes in energy distribution. Certain 

 chemical reactions require some form of energy, usually heat, while others 

 release energy in some form. When a sugar is built, energy is required; 

 when it is catabolized, energy is released. The construction and cata- 

 bolizing of other foods reveal a similar phenomenon. Both types of 

 reactions, those which require and those which release energy, occur in 

 living protoplasm. Much of the energy for heat production, muscular 

 action, and similar activities is the result of oxidizing foods containing 

 potential energies. Energy is used in joining chemical compounds to- 

 gether, and chemical energy is produced by the transformation of foods 

 containing these chemical compounds. The living protoplasm of both 

 animals and plants is composed of compounds so arranged as constantly 

 to transform potential to kinetic or other energies. This constant trans- 

 formation of energy requires a constant supply of potential energy in 

 order to exhibit the continual changes and perform work. The ultimate 



