Answer:
For a household pet, a bearded dragon is better because of its durability and its ability to form bonds with people over time. 
Explanation:
Bearded dragons also look cooler,, im more partial to moniter lizards myself but bearded dragons are awesome reptiles. Im not sure if that was what you were asking though :,)
 
        
                    
             
        
        
        
Mitochondria should be the answer 
        
                    
             
        
        
        
Cardiac Muscle, reason its called Cardiac attack when you have that sort of " Heart Attack "
        
                    
             
        
        
        
The deeper down you get, the colder the water is