THE BIOLOGICAL INTERRELATIONS OF 

 PLANTS AND ANIMALS 



PROBLEM XXII 



Some relations of fungi to man. 

 a. Conditions and Results of the Growth of Yeast 

 1. FOOD 



Method. Mix part of a cake of compressed yeast in a little 

 water to form a thin paste. 



Prepare five wide-mouthed bottles, labeling them 1 to 5. 

 In No. 1 put some yeast and water. 



In No. 2 put some yeast and some molasses or glucose. 

 Set the two bottles aside in a moderately warm place and ob- 

 serve after 24 hours. 



Observations. 1. What is the smell and taste of No. 1 ? 



2. What is the color in No. 1 ? 



3. What are the smell, taste, and color of No. 2 ? 

 Conclusions. 1. What evidence is there that the yeast is 



working in one of the bottles ? Which one ? 



2. What is one of the conditions necessary for the growth 

 of yeast ? 



2. TEMPERATURE 



Observations. 1. Pour some of the mixture from bottle No. 

 2 into bottles Nos. 3 and 4. Set No. 3 aside in a jar of cracked 

 ice or in a refrigerator. Result in a few hours ? 



2. Set No. 4 in a jar of boiling water, and heat it to boiling. 

 Set it aside to cool. Result ? 



Conclusion. Name some conditions of temperature harmful 

 to the growth of yeast. 



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