This is false. Organisms may play several important roles in an ecosystem. Consider for example and ocean shore environment occupied by a particular species of crab. The crabs are scavengers and eat any organic matter they encounter. They therefore play an important role in the cycling of nutrients in the ecosystem. The crabs are however also an important source of food for a range of other species occupying the same habitat, including octopi, certain fishes and sea otters. Therefore, the crabs are an important part of the food web in the ecosystem. Many species similarly occupy multiple important roles in an ecosystem.
        
             
        
        
        
Explanation:
I hope the diagram will help remember A always pairs with T and C always pairs with G. u can also remember as Apple Tree and Car Garage. :)
 
        
             
        
        
        
Answer:
Because of the fact that Snails cannot survive in nasty water.
Explanation: