The introductory passage describes ways that virophages use megavirus-producing factories in amoeba to reproduce because they are unable to do so independently. compare characteristics of viruses and virophages by dragging the characteristics into the correct bin to indicate whether each is a characteristic of virophages only, viruses only, both, or neither.

The virophages require a bigger virus to double themselves known as the host-virus. They are devoid of the genes for proteins required to double themselves and are always smaller in comparison to archaea and bacteria. On the other hand, in viruses, the genetic information can be in the form of RNA or DNA.  

Both the virophages and viruses possess a protein capsid enveloping their nucleic acid. Both the forms do not belong to any of the three domains, and they cannot replicate on their own. Neither the virophages nor the viruses produce energy via mitochondria.  

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.