You've probably heard the saying, ''You are what you eat.'' of course you don't become a cow when you eat a hamburger, but you do draw your energy from the energy in the food you consume. All organisms are linked together by the food chain, which illustrates the transfer of energy from one organism to another. a bird gains strength from devouring a frog, which may have eaten a fly, which may have eaten rotten fruit. Science writers Alvin and Virginia...