Final answer:
Prions are infectious agents that cause progressive brain disorders, while viroids are single-stranded RNA pathogens that infect plants.
Step-by-step explanation:
Prions are infectious agents consisting of protein but no DNA or RNA. They produce their deadly effects by duplicating their shapes and accumulating in tissues, causing progressive brain disorders such as mad cow disease and Creutzfeldt-Jakob disease. On the other hand, viroids are single-stranded RNA pathogens that infect plants. They reproduce only within a host cell and have a severe impact on the agriculture industry.