80 



OUR FOOD SUPPLY 



.5. Soil water and minerals enter plants through the . 



by a process called 



6. Food is manufactured by plants principally in the 



7. Green plants with the aid of sunlight manufacture food 

 from the raw materials , and is given off as a by- 

 product. This process is called . 



8. Can you suggest a method to prove that oxygen is 

 given off as a by-product of the process of photosynthesis? 



9. Suggest a method for testing the importance of sun- 

 light in the process of photosynthesis. 



10. Show how the process of osmosis might be of im- 

 portance in the absorption of food in the human body. 



11. On the basis of your knowledge of osmosis, predict 

 what would have to happen to such a food as cooked egg 

 before it could be absorbed into the blood stream. 



12. How would you prove by experiment that water vapor 

 is given off by green plants? 



13. Suggest a way of proving that water rises to the 

 leaves of a plant through the stem. 



14. What are the four most important factors which 

 control our food supply? 



TOPIC 2. IMPORTANCE OF A BALANCED DIET 



SUGGESTED PROBLEMS AND QUESTIONS 



1. How many classes of food substances are 

 there? 



2. What is the work of vitamins? How are vita- 

 mins classified and what is the principal func- 

 tion of each kind? 



3. How should we select our food? 



4. Why is milk sometimes called the perfect 

 food? 



5. How can we provide ourselves with pure 

 milk? 



SUGGESTIONS AND HELPS FOR STUDY 



1. Carefully read the problems listed above to be 

 sure that you understand them before you begin your 

 reading and investigation. 



2. Work out a balanced diet for three meals a day 

 for several consecutive days. 



3. Many of the general science textbooks give tables 

 or charts showing the percentages of the different 

 food nutrients in common foods and also the prin- 

 cipal vitamins found in each. Consult these tables and 

 charts freely. 



4. If the following words are new for you, study 

 them carefully until they become a part of your vo- 

 cabulary. 



nutrients substances which furnish food to the body. 



protein food material containing carbon, hydrogen, 

 oxygen, and nitrogen. Meat and eggs contain a large 

 amount of protein. 



elements substances, such as iron, gold, copper, oxy- 

 gen, which cannot be broken into anything simpler. 



carbohydrate group of compounds containing carbon, 

 oxygen, and hydrogen, as sugar and starch. 



vitamins regulative food substances necessary to life. 



bacteria tiny one-celled plants. 



EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 HELP ANSWER THE PROBLEM QUESTIONS 



Experiment 53. How do we test for starch in foods? 



Bring to class small quantities of the following foods: 

 white potato, sugar, lima beans. Dissolve a few crystals 



of iodine in alcohol to make a weak iodine solution. The 

 tincture of iodine, obtainable at the local drug store, may 

 be used. White potatoes have large amounts of starch in 

 them. Put a few drops of the iodine solution on the peeled 

 potatoes. 



In your notebook 1 record the results of your experiment, 

 answer the following questions, and complete the state- 

 ment. 



What color appears? If you put a few drops of iodine 

 solution on the sugar, what happens? 



Remove the outer shell of a lima bean and put a few 

 drops of iodine solution on the inside of the bean. Do 

 lima beans contain any starch? 



When a food containing starch is tested with an . . 



solution a color appears. 



Experiment 54. How do we test for sugar in foods? 



Obtain bottles of Benedict's solution. 2 Place a small 

 amount of Karo in a test tube. Add a small amount of water. 

 Heat gently until the Karo is mixed with the water. Now 

 pour into the test tube a small amount of Benedict's solu- 

 tion. Heat the mixture in the test tube to the boiling point. 

 Repeat this procedure with samples of various foods, such 

 as raisins, grapefruit, and prunes. Record the results in 

 your notebook. 3 



When the mixture of sugar solution and Benedict's solu- 

 tion was heated the color changed from . to This 



is a test for . 



Experiment 55. How do we test for proteins in foods? 



Put a small piece of raw meat into a test tube, add a 

 little water, and boil. Next add a little nitric acid (strong 

 solution). Drain the nitric acid from the tube and add cau- 

 tiously a small amount of ammonium hydroxide, a few drops 

 at a time. What color appears? This is the protein test. 



Repeat this test on samples of other foods. In your note- 

 book 4 record your results and complete the statement. 



Proteins in the presence of nitric acid and ammonium 

 hydroxide form a coloration. 



Experiment 56. How do we test for fats and oils in 

 foods? 



Put a piece of fat meat into a test tube, add ether, and 

 let it stand for awhile. As ether is very inflammable, it 

 should not be used near open flames. The ether will dissolve 

 the fats. Pour off the ether from the meat and evaporate. 



1 See workbook, p. 30. 



2 Directions for making Benedict's solution are in the teacher's 

 manual. 



1 See workbook, p. 30. 

 * See workbook, p. 30. 



