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ECOLOGY 



Part II 



Fig. 5.10. With every high tide the tide pools and surrounding rocks are flooded 

 with water carrying milHons of little plants and animals that are fit for food. During 

 low tide the pool dwellers are busy consuming the meal. They are attached and 

 slow moving protozoans, bryozoans, barnacles, tunicates, and many mollusks often 

 along with a few crabs, starfishes, brittle stars, and sea urchins. (Courtesy, the 

 American Museum of Natural History.) 



Chemical Conditions 



Plants and animals are continually taking materials from their environments 

 and making them into their own bodies. Certain substances and conditions 

 must be present around them. Whether in arctic or tropic regions, in water or 

 on land, these essentials are: sufficient energy from the sun for the plants to 

 synthesize food, enough oxygen for respiration, enough water, the chemical 

 elements which take part in protoplasmic activities, and certain physical con- 

 ditions, such as temperature and pressure. 



