Answer:
React on cell surfaces, catalyze reactions.
 
        
             
        
        
        
Answer:
The dog breeder to check for all the details that meets her requirement of dogs. 
Explanation:
 A dog breeding is the practice of mating dogs. In the context, it is given that a dog breeder wants to purchase a male dog of three year old for her business and she founds an advertisement on the net about a purebred males that costs $700. Now before buying this purebred male dog, the dog breeder should first of all check whether the seller who is selling online is a licence breeder or not. 
The dog breeder should also check whether the dog is a purebred or not and should also find out the actual age of the dog. The health of the dog should be checked by an professional vet before buying the dog.
 
        
             
        
        
        
This can be identified as a population. In a population, the organisms are the same species and they have to live in the same area. For example, the population of cities are the head count of the species of human in that one area.