44 



WHAT IS BEIXG ALIVE? 



..root- hairs 



In what ways are the circulations of a plant and an animal alike ? tained 

 In what ways do they differ? 



Food taking. It is not so easy to prove at this time that all living 

 things take food. We know animals will die without a food 



supply. We also 

 know that some 

 plants, like molds 

 or mildews, grow 

 on food substances. 

 But green plants 

 live in soil appar- 

 ently without food 

 if they have a niod- 

 1 Xs & erate water supply. 

 This is possible be- 

 cause green plants 

 make organic food 

 substances out of 

 the materials ob- 

 from the 

 soil, of water, and 

 a part of the air. Both plants and animals use organic food sub- 

 stances in exactly the same way, that is, they get energy out of 

 them to do work, and they build up their bodily material out of 

 the food they use. 



Respiration. Respiration is the process by which oxygen is 

 supplied to the body and carbon dioxide is removed. As a result 

 food is oxidized and energy is released. The processes are the 

 same in both plants and animals as will be shown in detail later. 

 Plants release enough energy to force then way through the 

 compact earth: animals release their energy in the activity we 

 associate with running, swimming, flying, etc. 



Nutrition. The foods of plants and animals must be made 

 liquid so that they may pass freely to various parts of the organism 

 to be used there. In order to do this they must be digested, or 

 changed to a form that will enable it to be taken in by the smallest 

 units of body structure, the cells. The way this is done will form 

 the basis of an important problem later on in our course. Then 

 these foods must be absorbed or taken into the organs of circulation. 



