The term "virion" is used for

$T. O.$ Diener discovered a new infectious agent that was smaller than viruses and has the following characteristics:
$(i)$ It causes potato spindle tuber disease.
$(ii)$ It has free $RNA$.
$(iii)$ The molecular weight of $RNA$ is low.
Identify the infectious agent.

The structure present in nature which exhibits characteristics of both living and non-living organisms is:

Sometimes when a virus attacks a bacterium,neither the virus multiplies nor the bacterium dies. This phenomenon is called as

In which plant is the microorganism shown in the given figure found?

In the majority of lichens,there is an association of: