Why are some substances biodegradable and some non-biodegradable?

Explanation

The micro-organisms like bacteria and other decomposer organisms (called swaprophytes ) present in out environment are 'specific' in their action . They break down the nature substances or products made from naturel substances (like dead remains of plants and animals, and their waste products, paper, etc.) but do not break down men-made substances such as plastics, metals and glass objects, etc. So , it is due to the property of decomposer organisms of being specific in their action that some waste substances are biodegradable whereas some are non-biodegradable.