Answer:
Prions can be described as mis-folded proteins which infect the body. When found in an animals brain, they cause severe neurodegenerative diseases. Prions replicate by inducing benign proteins due to which they refold into abnormal shape. The mechanism has not fully been understood though.
Viroids can be described as the smallest infectious pathogens which infect the plants. The Viroid is made up of single stranded RN molecule. Voroids reproduce in the host cells by using their machinery.