"what is an antigen" "what macromolecules are the best antigens"

Antigens are molecular structures that trigger an immune response which later results in the production of antibodies. Macromolecules that are usually the best antigens have a lot of examples, however, they have four common characteristics: foreignness, size, complexity, and degradability. The more a macromolecule has these, the better it is as an antigen. 

It depends on the surface of the levels. the rougher the surface, the greater is the frictional force. for rougher surfaces, you would need to exert greater force to move the object. the concept is that, you must overcome the frictional force in order to bring the object into motion. this is the reason why we add lubricants to the joints so they could easily move. this answer was on