EXERCISE XXXVIII. 

 FOOD MATERIALS STORED BY PLANTS. 



Supplies for a Laboratory Section of Twelve. Starch; twelve test tubes; iodine solution (first dissolve a 

 little iodine in alcohol and then dilute with water); corn; wheat; beans; peas; potato; oatmeal; raisins; apple; 

 twelve reagent bottles filled with nitric acid; twelve reagent bottles filled with ammonia; glucose; cane sugar; 

 Fehling's solution; olive oil; English walnuts; twelve tin spoons; filter paper; a little carbon in the form of 

 charcoal. 



Part A. Starch. . 



1. Place a very little starch in a test tube. Add a few drops of iodine solution. Observe 

 any change in color. Substances which show a similar change in color when treated with 

 iodine will be found to contain starch. As a rule the intensity of color is proportional to the 

 amount of starch present. 



2. Cut a cross section of a kernel of corn a little nearer the point than the middle. 

 Treat with iodine solution, (a) Observe any change in color, (b) From the variation in 

 intensity of color, infer what portion of the kernel contains the most starch. 



3. Test wheat, oatmeal, potato, apple, raisins, peas, and beans for starch. Record the 

 result of each test. 



Part B. Protein. 



4. All proteids are turned yellow by nitric acid. To intensify the yellow color, rinse the 

 substance with water and add ammonia. 



Cut a cross section of a kernel of corn a little nearer the tip than the middle. Place the 

 parts in a test tube. Add a little nitric acid. Let stand for a few moments and then drain 

 the acid into the waste jar. Rinse with water and moisten with ammonia. Variation in 

 intensity of color indicates variation in the amount of protein present in the different parts of 

 the kernel. Observe which parts of the kernel contain the greatest amount of protein. 



5. Test wheat, oatmeal, potato, apple and beans, for protein. Record the result of each 

 test. 



Part C. Sugars. 



6. (a) To a small amount of glucose in a test tube add an inch of water and then a 

 few drops of Fehling's solution. Bring the solution to a boiling temperature. Observe any 

 change in color. A change in color shows the presence of grape sugar. (b) Test cane 

 sugar as you have glucose. Record the results of the test. Glucose is a sugar commonly 

 stored by plants. 



7. Test the following for glucose: Potato, apple, raisins, and beans. Record the result 

 of each test. 



Part D. Fat. 



8. Place a drop of olive oil on a piece of clean white paper, (a) Observe the appear- 

 ance of the paper, (b) Recall the source of olive oil. 



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