Chemical Change and Energy 333 



day take jJiis leaf from the plant and heat it in a beaker of 

 alcohol until the green coloring matter is removed from the 

 leaf. Then place the leaf in a glass of water that contains 

 iodine. The iodine will color the leaf dark where the cells 

 contain starch. (See Experiment 115, page 373.) Is starch 

 formed where the light does not reach the leaf ? 



No plant can make food except with the help of light. 

 The part of the plant that can put carbon dioxid and 

 water together is the green stuff or chlorophyll, and this 

 can work only when light is shining on it. So all plants 

 would die without light. 



But if all plants should die, all animals would die 

 also, for animals cannot make food out of carbon dioxid 

 and water, as they do not have the chlorophyll that 

 puts these things together. A lion does not live on 

 leaves, it is true, but he lives on deer and other animals 

 that do live on leaves and plants. If the plants died, 

 all plant-eating animals would die. Then there would 

 be nothing for the flesh-eating animals to eat except 

 each other, and in time no animals would be left in the 

 world. The same thing would happen to the fish. 

 And man, of course, could no longer exist. The food 

 supply of the world depends on the fact that light can 

 start chemical change. 



Oxygen released in the manufacture of plant food. Be- 

 sides in one way or another giving us all of our food, 

 plants, helped by light, also give us most of the free 

 oxygen that we breathe. We and all animals get the 

 energy by which we live by combining oxygen with 

 the hydrogen of our food (forming water) and by com- 

 bining oxygen with the carbon in our food (forming 



