What is the difference between structural and functional proteins? and give a definition for both!

Functional proteins are a complex mixture of biologically active protein which help to support and maintain normal immune functions. Examples of functional proteins are immunoglobulins and avidin. 
Structural proteins are fibrous proteins which are part of the structures found in the living cells. Examples of structural proteins are keratin and collagen.
The major difference between these two types of protein is that structural proteins are used as structures while functional proteins perform specific active functions in the cells. Also, structural proteins are usually dominated by two dimensional structure while the functional proteins have three dimensional structures. 

Reduction in overall biodiversity