<h2>a) is the correct option </h2>
Explanation:
The extracellular domain of the transmembrane receptor protein acts as binding site for primary messenger molecule whereas the transmembrane domain holds the receptor within membrane and the cytosolic domain has intrinsic tyrosine kinase activity, all these helps in proper cell signaling 
If because of any mutation there is change in shape of the extracellular domain then that molecule that normally binds to the receptor protein will no longer attach hence cellular response will be deactivated 
 
        
        
        
Answer:
c. none of the subjects to show signs and symptoms of a cholesterol deficiency during the entire study.
Explanation:
this is because the blood cholesterol is from two sources. Nearly 80% of the cholesterol the body needs  are made by the liver and intestine.certain small amounts are also produced in the adrenal glands and the reproductive organs.The remaining fragment amounts comes from the diets. 
Therefore even if these subjects  were fed with diet without cholesterol, it will not have any significant effects on the body cholesterol composition. Therefore no symptoms of its deficiency will be observed.
Generally it biosynthesis is regulated by the amount of cholesterol present in the blood.
 
        
             
        
        
        
Cell walls, which are found in plant cells, maintain cell shape. Some animal cells dont need to maintain shape. Such as muscle cells, they are constantly moving.