CHAPTER 11 • HOW DO PLANTS AND ANIMALS BREATHE? 



1 Do plants breathe, as well as animals? 



2 What makes a fish die when it is taken out of water? 



3 What makes men drown where fish thrive? 



4 How do frogs breathe without a diaphragm? 



5 How do fish breathe? 



6 Have whales lungs, or do they breathe like fish ? 



7 How do the cells in the roots of water plants get oxygen ? 



8 How do animals in deep water breathe? 



9 How do clams breathe when they are buried in the sand ? 



The simplest plants and animals get their oxygen directly from the sur- 

 rounding air or water and discharge their carbon dioxide directly to the 

 surrounding medium by osmosis. Here respiration and oxidation are close 

 together in space and in time. But in more complex plants and in animals, 

 as in man, there is sometimes a considerable separation between the two 

 processes. 



The respiration of simple organisms, and the internal respiration carried 

 on by the cells of higher organisms, are very much alike, since the body cell 

 lives in a liquid medium, as does the ameba in the pond. But how do the 

 various complex plants and animals get oxygen and excrete carbon dioxide ? 

 Do all the organisms that live in water get their oxygen directly from the 

 water ? How do the innermost parts of large plants and animals get air ? 



How Do Cells Obtain Air? 



Gas Exchange of the Ceir Plants and animals consisting of single cells 

 absorb gases from the surrounding air or water by osmosis. And gases are 

 removed from such cells by osmosis, diffusing into the surrounding air or 

 water. 



In large, many-celled organisms air reaches the living cells either by 

 diffusing through special spaces, as in plants, or through special tubes, as 

 in insects (see page 16). Or it travels in a solution (blood) that reaches 

 all parts of the body (see page 186, and illustration, p. 202). In every case, 

 then, the protoplasm of the individual cell (1) gets its oxygen from its 

 immediate neighborhood, and (2) discharges its carbon dioxide and other 

 products of oxidation into its immediate surroundings. 



In the interior of a leaf air constantly circulates through the air-spaces 

 among the cells. Gas exchange between the various cells and the surround- 



^See Nos. 1, 2 and 3, p. 212. 

 201 



