138 BIOLOGY AND HUMAN LIFE 



2. Digestion of nutrients in the human body 



Starch changed into grape sugar 



SaHva (ptyaHn) ; pancreatic juice (amylopsin) 

 Protein changed into peptones and amino acids 



Stomach juices (pepsin; acts in acid) 



Pancreatic juices (trypsin ; acts in alkali) 

 Fat changed into glycerin and fat 



Pancreatic juice (steapsin) 

 Cane sugar changed into grape sugar 



Intestinal juice 



3. Absorption 



Villi of small intestine Lining of large intestine 



Transfer to blood stream 



4. Undigested refuse 



QUESTIONS 



1. Why cannot the cells of our body make use of the food as we 

 receive it from the kitchen ? 



2. What kind of nutrient is digested by the mouth juices ? 



3. Why should we chew food that is not digested by mouth juices ? 



4. What use does the body make of the saliva secreted as a result of 

 chewing gum if the saliva is thrown out ? if the saliva is swallowed ? 



5. How can we show that pepsin acts upon proteins but not' upon 

 starch or fat ? How can we show that pepsin acts in an acid solution but 

 not in an alkaline solution ? 



6. How can we show that saliva acts upon starch but not upon protein ? 



7. How can we show that crystalloids will pass through the wall of the 

 intestine but that colloids will not ? 



8. Why is it important to prevent accumulation of refuse in the large 

 intestine for a long period ? 



REFERENCE READINGS 



Bergen and Caldwell. Practical Botany, pp. 144-145. 

 OsTERHOUT, W. J. V. Experiments with Plants, pp. 155-178. 

 Densmore, H. D. General Botany, pp. 124-130. 

 Hough and Sedgwick. The Human Mechanism, pp. 99-134. 



