The polytene chromosomes were discovered for the first time in

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.

Which molecules are transported between the nucleoplasm and the cytoplasm through nuclear pores?

The structure present inside the nucleus responsible for ribosomal unit formation is

What are chromosomes with arms of equal length called?

The main components of chromosomes are.......