Answer:
Proteins serve many functions within an organism, such as mammals. Proteins are used to grow and repair tissues. ... Proteins also form hormones, which transport chemical messages between tissues and organs. Proteins are also important building blocks of bone, carilage, muscle, skin, and blood. 
Link: 
https://www.enotes.com/homework-help/outline-role-proteins-life-mammals-547196
 
        
             
        
        
        
A sex-linked trait is a trait that is carried by the X chromosomes in females but it is not expressed(the phenotype). Females are only carriers because they have two copies of the X chromosome [one of them carries the trait and the other does not]. Males who inherit one copy of the X chromosome often get the trait (because the trait is in either one copy or the other of the X chromosome) and express it while their Y chromosome would became recessive. Thus, only males express sex-linked traits such as hemophilia or color blindness
        
             
        
        
        
The Nucleus is sort of like the "brain" of a cell.
        
                    
             
        
        
        
Answer:
Integumentary is least connected to the Digestive system