CELL RESPIRATION 



405 



As the table shows, there is a loss of nearly 5 per cent of oxygen, 

 and a corresponding gain in carbon dioxide and water vapor, in 

 expired air. There are also some organic waste substances in 

 expired air which are not shown in the table. 



Cell respiration. It has been shown, in the case of very simple 

 animals, such as the Paramecium, that when oxidation of food 

 takes place in the cell, energy will result. In man the oxygen 

 taken into the lungs 

 is not used there, 

 but is carried by 

 the blood to all 

 parts of the body 

 where work is done. 

 Cell activity de- 

 mands food and 

 oxygen. 



When oxidation 

 of food takes place 

 in the cell, energy is 



released for cell work and certain wastes are formed. The waste, 

 carbon dioxide, is given off to the blood when any food containing 

 carbon is burned. When proteins are burned, other wastes con- 

 taining nitrogen are formed. These must be passed off from the 

 cells, as they are poisons. This is done by the lymph and the 

 blood, which take the waste materials to points where they may be 

 excreted or passed out of the body. Water, another waste product, 

 is excreted by the skin and kidneys. 



Explain this diagram. 



Self-Testing Exercise 



An (1) of oxygen and (2) (3) takes place 



in the blood as it passes through the (4) (5) of 



the lungs. Air entering the lungs has about (6) per cent 



more (7) than expired air. Respiration takes place in th& 



. . .' (8) of the body. As a result of cell activity after (9) 



and (10) are taken into the cell (IP (12), 



(13) and (14) wastes are given off. 



h. bio — 27 



