14 PLANT BIOLOGY 



4. What substance is left in the cooking spoon after the 



flame goes out? 



5. Name two chemical elements present in starch. 



6. Starch also contains oxygen. Name now the three chem- 



ical elements of which this nutrient is composed. 



20. To determine the chemical composition of sugar, 

 fat, and protein. Laboratory Study No. 7. (Optional.) 



1 . Test sugar in the same way as directed in Laboratory Study 

 No. 6, 1-5 (above). 



a. Describe each of the experiments, giving results and con- 



clusions. 



b. Sugar, like starch, has oxygen also in its composition. Name 



now all the chemical elements of which sugar is com- 



2. In a similar way test a fat (e.g. lard, or the fat of meat). 



a. State what you do, what you see, and what you conclude. 

 6. Fat, like starch and sugar, has oxygen in its composition, but 



in a different proportion. State, therefore, the three 



elements present in fat. 



3. (Demonstration.) Secure a vegetable protein (e.g. gluten) 



and test it as directed above. 



a. Describe your experiments and give your results and con- 

 clusions. 



6. Besides the two elements you have shown to be present, 

 protein also contains oxygen, nitrogen, sulphur, phos- 

 phorus, and often other elements. State, now, the 

 chemical elements of which this food substance is com- 

 posed. 



21. Summary. The carbohydrates, as we have learned 

 and as their name implies, are composed of the chemical ele- 

 ments carbon, hydrogen, and oxygen. The same three chemi- 

 cal elements are likewise present in fats and proteins, but in 

 different proportions. Proteins, however, in addition to the 

 carbon, hydrogen, and oxygen, contain at least three other 



