Which one of the following is the site for active ribosomal $RNA$ synthesis?

The nuclear envelope consists of two parallel membranes with a space between them called the perinuclear space,which is about:

Identify $X$ in the given diagram of a chromosome.

Which scientist discovered the nucleus?

Robert Brown is well known for the discovery of . . . . . . .

Some chromosomes have non-staining secondary constrictions at a constant location. This gives the appearance of a small fragment called the ......