The centromere may also be called as:

The factory of ribosomes in the cell is ........

Match the following columns regarding chromosome types based on the position of the centromere:

Column-$I$	Column-$II$
$P$. Metacentric	$I$. One arm shorter and one arm longer
$Q$. Sub-metacentric	$II$. One arm extremely short and one arm extremely long
$R$. Acrocentric	$III$. Terminal centromere
$S$. Telocentric	$IV$. Middle centromere forming two equal arms

$S$ - Statement: $RNA$ and protein molecules move between the nucleoplasm and the cytoplasm.
$R$ - Reason: Nuclear pores are present at several locations in the nuclear envelope of the nucleus.

Some chromosomes have non-staining secondary constrictions at a constant location. What are these small fragments called?

$A$ chromosome with an extremely short and a very long arm is called . . . . . . .