They mainly target airway epithelial cells
        
             
        
        
        
Answer:
6==. During spermatogenesis, four sperm result from each primary spermatocyte, which divides into two haploid secondary spermatocytes; these cells will go through a second meiotic division to produce four spermatids
 
        
             
        
        
        
People who are lactose intolerant are unable to digest lactose, the sugar commonly found in dairy, because their bodies don't make the enzyme lactase. 
Lactase works by breaking down lactose into a simpler sugar that can be used by the body. Without it, lactose is not absorbed by the body & remains in the waste where gut bacteria metabolize it & cause the bloating, gas & other similar discomforts experienced by the lactose intolerant. 
Hope that helps!
In truth, though, it is the non-lactose intolerant people that are the mutants. Not the other way around. Most wild animals don't consume milk after they have been weaned & it's just something humans developed to accommodate their diet.
        
                    
             
        
        
        
Answer:
carrying capacity (carrying capacity is the total population size that a particular environment can comfortably support with little increase or decrease over a relatively long period of time) given the food, habitat, water e.t.c. that is available in the environment.