CHAPTER XXIV 



RESPIRATION 



And tis my faith that every flower 

 Enjoys the air it breathes. 



— Wordsworth. 



It has been pointed out that the chief use of certain kinds of 

 foods (fats and carbohydrates) is to supply energy for the proc- 

 esses which go on within the organism. During photosynthesis 

 and the various other syntheses which take place within the plant, 

 potential energy is stored in the molecules of material built up. 

 This energy, which is derived from the sun, is of use only when 

 it is changed over into kinetic energy, or the energy of motion. 

 To do work, energy must be supplied, and the only way in which 

 this is done in living organisms is by releasing the potential energy 

 of the food molecules in the katabolic process known as respiration. 



Respiration and Breathing. — This release of energy goes on 

 in the cells of the body and is not associated with any particular 

 set of organs. Since it is ordinarily accompanied by the addition 

 of oxygen, the gaseous exchange between the lungs of animals 

 and the outer air, by which oxygen is brought in and carbon diox- 

 ide released, is sometimes, but erroneously, spoken of as respira- 

 tion. This is breathing and is different from respiration, which 

 takes place in the tissues. Breathing is an accompaniment of 

 respiration in animals which have such special organs as the lungs, 

 and is an aid in this exchange of gases, but the real respiration is 

 the oxidative process, which occurs in the cells of the body where 

 the energy is released. Plants consequently never breathe. It 

 has been suggested, in order to avoid confusion, that the term 

 energesis be used for the energy-releasing process; but if the word 

 respiration is properly understood and used, the need for a new 

 term disappears. 



Respiration in Plants and Animals. — Respiration in plants and 

 animals is essentially the same. In a charged storage battery, 

 the potential energy is of no value until a circuit is completed and 

 the energy is permitted to become kinetic. In a power dam the 

 stored water is of no use until it can fall and by its motion do work. 



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