66 



PLANT GROWTH AND NUTRITION 



Problem 41 : To prove that organic substances are oxidized 

 within the human body. 



Materials. Wide-mouth bottle, glass tube, limewater. 



Method and Observations. Force the breath through a tube 

 into limewater. What happens? 



Conclusion. 1. What is one substance that comes from the 

 lungs ? 



2. How and where must this substance have been formed ? 



3. If oxidation takes place in the human body, and heat or 

 energy is released as a result of this oxidation, then something 

 must be oxidized within the human body when it does work. Your 

 answer will be helped by reference to the next problem. 



4. Burn several different substances as starch, sugar, bread, cake, 

 nuts, and meat in closed jars. Test contents of jars with lime- 

 water. What do you conclude was present in these substances? 

 How do you know? What other substance is given off when 

 these materials burn? Touch the jars. What does this suggest 

 with reference to energy released? 



Problem 42 : To prove that growing seeds oxidize food. 



Materials. Two Erlefimeyer flasks, rubber stopper, soaked 

 peas, blotting paper. 



Method 1. Put soaked blotting paper in 

 each of two flasks and place an equal number of 

 peas in each flask. Cork one flask only. 



Observations. Watch for evidences of growth 

 in each flask. Note carefully just what happened 

 to the peas in the closed flask ; in the open flask. 



Conclusion. Remembering what you have 

 learned in your previous experiments, how would 

 you account for what you see ? 



Method 2. Now- test the air in the closed 

 flask with limewater. (Or a bottle containing 

 limewater may be placed in the jar at the be- 

 ginning of the experiment. See accompanying 

 figure.) 



Observations. What happens? 



THE INCLOSED 

 BOTTLE CONTAINS 

 LIMEWATER. 



