The structure labeled x most likely represents

The propositions are :
(1) an antibody 
(2) an enzyme 
(3) a receptor molecule 
(4) a hormone

The right answer is an enzyme because it has catalytic activity. It transforms a substrate which is the starch to product(s) which are dextran and maltose

It is not an antibody because it does not have catalytic activity as a major role.
It is not a receptor molecule, because they cannot transforms molecules and forms products
It is not a hormone because it does not have a catalytic activity

Suspension typei