EXERCISE 108 



The exchange of material between an organism and its environment, in nutrition, in respiration, and 

 in excretion, takes place through the general body surface or through special surfaces. In many organisms 

 the total amount of metabolism therefore depends directly upon the total amount of surface that can be 

 exposed. 



Problem. Does not the amount Of surface of a body vary directly with the size of the body ? 



What to use. A number of cubical blocks of the same size, wooden or clay. 



What to do. Since the blocks are all the same size, we may count the edge of a block as the unit 

 of length (for example, i inch, i centimeter), one face of a cube as the unit of area (for example, 

 I square inch, i square centimeter), and so on. Build up sets of blocks having one, two, three, die. 

 inches as a base, with the same width and height, and note the total amount of exposed surface each 

 such cubical pile has. The cubical measure may be taken as proportional to the mass or weight of the 

 body represented by such a pile. Note the relation between the surface of a cube and its mass. 



Record. In the table enter the observed or calculated surface and the volume of mass for a cube 

 of each dimension. 



Questions. 1. What effect upon its volume has the doubling of the dimensions of an object? 



2. What effect upon its surface has the doubling of the dimensions of an object ? 



3. Does the ratio of surface to volume remain constant ? Why ? 



4. How would you arrange eight blocks to get the largest amount of surface exposed ? 



5. How would you arrange eight blocks to get the smallest amount of surface exposed ? 



6. What is the effect of growth upon the relative amount of absorbing surface ? 



7. What kinds of organisms are capable of indefinite growth ? 



8. What are some of the ways in which the structure of an absorbing or discharging surface makes 

 for a large area ? 



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