In the given figure,what does the part labeled as $A$ represent?

They are smaller than virus.

Which of the following microbes is made up of protein only?

$A.$ The capsid of a virus is made up of many small units called capsomeres.
$R.$ Viruses exhibit active and living behavior in a virus-free state.

What acts as the phycobiont in the organism shown in the given figure?

Assertion $(A)$: Viruses are considered as a link between living and non-living things.
Reason $(R)$: Viruses are inactive and behave like non-living matter in a free state,whereas they show active and living behavior inside a host cell.