Answer:
Population of cactus like plants which grows in the hot and dry weather of deserts,begins the flow of energy in the desert food web. Because plants are the only producer of energy in every food web.
Explanation:
 
        
             
        
        
        
Pupil is the answer, it changes according to the light it recives
        
                    
             
        
        
        
D. It expands and contrasts
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Answer:
A population consists of all individuals of all species in one area