The nucleolus is formed by . . . . . . .

The structure of the nuclear membrane facilitates:

Match the parts of the chromosome given in Column $I$ with their explanation in Column $II$:

Column $I$ (Chromosome)	Column $II$ (Explanation)
$1$. Centromere	$a$. Disc-shaped plate where spindle fibres get attached during cell division.
$2$. Secondary constriction	$b$. Long unbranched slender highly coiled $DNA$.
$3$. Kinetochore	$c$. Place where $2$ chromatids are joined together.
$4$. Chromatonema	$d$. Nucleolus gets organised at this place.

Choose the correct answer from the following options.

$A$ chromosome having a sub-terminal centromere is called:

In the given figure,what does $B$ represent?

During cell division,to which part of the chromosome do the spindle fibers attach?