Suggestions for Laboratory Work to Precede Chapter Seven 



1. Make a thin paste by boiling a little starch in water. Test 

 a small portion of the paste with iodin. Test for sugar with Bene- 

 dict's solution l ; then add diastase solution (malt extract pur- 

 chased at the drug store may be used) to the starch paste ; after 

 it has stood in a warm place for some hours, test it again for starch 

 and .for sugar. What is meant by digestion of starch? What 

 enzyme brings this about? 



2. Test for starch a leaf from a green plant that has been in 

 sunlight by placing it (i) in boiling water for one minute, (2) in 

 hot alcohol until bleached, and (3) in an iodin solution. If starch 

 is present, put the plant in the dark, after cutting off one of its 

 leaves. Place the severed leaf in a covered dish containing moist 

 filter paper, and set the dish in the dark. On the following day 

 test the severed leaf for starch ; also test for starch a leaf freshly 

 cut from the plant that was placed in the dark. What do the 

 tests show regarding the movement of carbohydrate out of leaves ? 



3. Test seeds of corn, bean, and almond for starch, by placing a 

 drop of iodin solution on a freshly cut section of each seed. 



4. Test the same kinds of seeds for oil by scraping the seeds 

 and crushing the scrapings on a sheet of white paper. Oil makes 

 the paper translucent. Which contains the most oil ? 



5. Test the same kinds of seeds for protein by placing a drop of 

 nitric acid on a section of each seed. Nitric acid stains protein 

 yellow. 



6. If time permits, other organs of the plant may be tested 

 for food in the same way, and starch grains may be studied under 

 the microscope. Scrapings from potato, the root of the canna, 

 and various grains will furnish material for the study. 



1 Benedict's solution: Dissolve 173 gm. copper acetate and 100 gm. anhy- 

 drous sodium carbonate in 600 cc. of distilled water. Filter, and add water 

 until the total solution is 850 cc. Dissolve 17.3 gm. of copper sulfate in 100 cc. 

 of water and dilute to 150 cc. Then mix the two solutions, which together will 

 make a liter of Benedict's solution. It is ready for use immediately and keeps 

 indefinitely. To make a test for sugar, add 3 cc. of Benedict's solution to i cc. 

 of the solution to be tested, and boil. If sugar is present, a red or yellow pre- 

 cipitate will appear. 



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