Vaccines introduce small amounts of dead viruses or harmful cells into the body in order to teach the body how to effectively fight said virus/cell
 
        
             
        
        
        
Black squirrels have a survival advantage over gray squirrels
 
        
             
        
        
        
I’m going to say for the first one it’s a
        
             
        
        
        
That would be Biochemistry. as that is th study of chemical changes and processes in living organisms