CHAPTER 6 • WHAT IS THE RELATION OF FOOD TO LIFE? 



1 Must all living things have food ? 



2 Do all animals have mouths? 



3 How do plants get food? 



4 How is it that some animals eat animals and others eat plants ? 



5 Do any plants eat animals? 



6 Is the food of one organism suitable for other organisms ? 



7 Can we change the nature of an animal by feeding it different 



foods ? 



8 What do hibernating animals use for food? 



9 Do all people have to use the same foods ? 



10 What do different kinds of food do for a living thing ? 



We know that we must have food to keep alive, but the connection be- 

 tween feeding and keeping alive is not always clear. We assume that all 

 other organisms must also have food, although we do not recall ever seemg 

 a plant feed. Many of us think that feeding is the same as eating. Yet the 

 plants, and many species of animals too, have no mouths; and they must 

 somehow take food. Is the water that a plant soaks up through its roots 

 food for the plant ? Or is the fertilizer which we place in the ground ? 



Since it is the protoplasm in any organism that is alive, it may help to 

 think of food in its relation to the peculiarities and activities of protoplasm. 

 What has being alive to do with food ? What has food to do with being 

 alive ? 



How Does Food Act in Living Protoplasm? 



Chemical Needs From a dozen to twenty or more different chemical 

 elements are present in the tissues of various species of plants and animals 

 (see illustration opposite). Most of these elements are found in practically 

 all species. But that does not necessarily mean that they are all involved in 

 living. Nor does it mean that we or other species could live on a supply of 

 these elements. For protoplasm is an active process in which various mate- 

 rials are involved, not merely a collection of those materials. Indeed, if it 

 were possible to arrange such a collection of "elements" anywhere, no 

 plant or animal could live in it. We know that food is the source of these 

 elements in living bodies. But we have to ask how the various foods are 

 related to the doings of protoplasm. 



Protoplasm-Builders We may think of protoplasm as consisting basi- 

 cally of nitrogen-containing compounds called proteins, suspended in water, 

 along with various salts and other substances, some of them dissolved m the 

 water. The growth of protoplasm depends essentially on a supply of pro- 



96 



