UNIT IV. OUR FOOD SUPPLY 



Eating is one of our most important activities. Our 

 bodies are in some respects like machines. We need 

 a supply of energy to keep going; parts of our body 

 must be repaired from time to time and new parts 

 must be built. Our bodies differ from machines in 

 that the human body can repair and strengthen its 

 own parts while machines must be rebuilt and re- 

 paired by a mechanic. 



Nearly everyone knows that food makes these 

 things possible, but do you know that foods vary 

 greatly in their ability to furnish energy and materials 

 for growth and repair? Chemists analyze foods and 

 find that there are different constituents 1 in them and 

 that the percentages of the different food nutrients 2 

 in foods vary tremendously. In fact, some foods may 

 be entirely lacking in one or more of the food nutri- 

 ents. 



We also know that the foods we eat should be 

 selected carefully. In order to have healthy bodies we 

 must have not only enough food but also the proper 



1 Constituent, a necessary or essential part. 

 'Nutrients, substances which furnish food to the body. 



amounts of the various food nutrients. When both of 

 these conditions are satisfied our diet is properly bal- 

 anced. 



In this unit you will learn about how our food is 

 produced, of what it is composed, what the use of 

 each kind of food is, how much of each kind of food 

 we should eat, how to prepare and preserve food, and 

 finally how food is digested and assimilated by our 

 bodies. This knowledge will help you live happy and 

 healthful lives. 



What do you already know about food? Write the 

 answers in your notebook. 



1. Why do all living things need food? 



2. Why do you eat different kinds of food? 



3. Where do the foods used by the people in your 

 community come from? 



4. Why are many foods cooked before we eat them ? 



5. What causes foods to spoil? 



6. How do we keep foods from spoiling? 



7. Why is milk considered a nearly perfect food? 



8. How does your body digest and assimilate food? 



9. How is milk pasteurized? 



TOPIC 1. MAN'S NEED OF FOOD 



SUGGESTED PROBLEMS AND QUESTIONS 



1. Why must we eat food? 



2. How do we grow? 



3. Why do we need energy? 



4. What are the sources of our food? 



5. How do plants manufacture food? 



6. What are the factors that control our food 

 supply ? 



SUGGESTIONS AND HELPS FOR STUDY 



1. Carefully study the problems listed above and 

 see if they are questions which you have wondered 

 about or are interested in. 



2. To answer problem 5 write a paragraph explain- 

 ing the process of food manufacture in plants. Com- 

 pare food manufacture in plants with a commercial 

 manufacturing process. 



3. The following words may be used in this topic. 

 If they are new to you, study them carefully and use 

 them as often as possible. 



osmosis the process by which roots of plants take in 



water. 

 photosynthesis the process by which food is made in 



plants. Photo means light. Synthesis means building 



up. 

 chlorophyll the green-colored material in leaves. 



EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 HELP ANSWER THE PROBLEM QUESTIONS 1 



Activity 49. Where do our foods come from? 



In your notebook list all the different foods that you 

 have eaten for several days. In list 1 name the foods that 

 were obtained from animals. In list 2 name the foods that 

 were obtained from plants. In list 3 name foods which 

 came from neither plants nor animals. 



Activity 50. What parts of plants and animals do we 

 eat? 



In your notebook make lists to show the parts of the 

 plants and animals from which the foods listed in Activity 

 49 came. For the plant foods list whether it was from root, 

 stem, leaf, flower, fruit, or grain. For the animal foods 

 list whether it is muscle, fat, muscle and fat, or the entire 

 animal such as an oyster. 



Experiment 51. What is osmo- 

 sis? 



Secure a carrot or a sweet po- 

 tato. Set up a carrot or sweet po- 

 tato osmometer as shown in Fig- 

 ure 117. The rubber stopper must 

 fit into the carrot closely. Fill the 

 cavity in the carrot with strong 

 sugar solution. Seal the stopper to 

 the carrot with wax. Place in a 

 jar of water. Allow the osmom- 

 eter to stand for twenty- four 

 hours and observe what happens. 



In your notebook state the in- 

 ferences which you draw from 

 this experiment. 



Glass Tube 



FIG. 117 

 CARROT OSMOMETER 



1 See workbook, p. 29. 



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