124 



WHY DO SEEDS GERMINATE? 



released by the seeds. A familiar example of release of en- 

 ergy is seen in an engine. Coal is placed in the fire box and 

 lighted, and the lower door of the furnace is opened so as to 



y. .stopper 



equal number of £ eects im-s 

 A fi^d. B 



Why is the growth of seeds in flask B greater than 

 that in flask A ? 



make a draft of air which 

 will reach the coal. The 

 coal burns, heat is released, 

 causing the water in the 

 boiler to make steam, the 

 engine wheels to turn, 

 and work is accomplished. 

 Let us see what happens 

 from the chemical stand- 

 point. 



Coal is formed largely 

 from dead plants, which 

 were long ago pressed into 

 the present hard form of 

 coal. It contains a large amount of the chemical element carbon. 

 We have already observed one of the effects of the oxidation of 

 carbon as proved by the lime water test. Let us now apply this 

 test to the oxidation of food substances in our own bodies. 



Demonstration 8. To prove that food materials are oxidized by the 

 human body. Expel air from the lungs through a tube into a bottle 

 of lime water. Note what happens. As a control pass air from the 

 room through lime water. Explain your results. 



Oxidation in our bodies. In life the temperature of the body 

 (98.6° Fahrenheit) is due to oxidation within the cells. Food is 

 also oxidized within the human body to release energy for our 

 daily work. In fact, all living things, both plant and animal, 

 release energy as the result of oxidation of food within their cells. 



Self-Testing Exercise 



The presence of (1) (2) in large amounts in the air 



surrounding seeds growing in a closed jar indicates that they have 



(3) food within their bodies. The (4) of (5) 



in the body releases (6) to do work. When seeds grow they take 



in (7) and give off ........ (8) (9), 



