Test: Nucleus And Chromosomes - NEET MCQ

The nucleus as a cell organelle was first described by Robert Brown as early as 1831.

Later the material of the nucleus stained by the basic dyes was given the name chromatin by Flemming.

You may recall that the interphase nucleus has a loose and indistinct network of nucleoprotein fibres called chromatin.

Electron microscopy has revealed that the nuclear envelope, which consists of two parallel membranes with a space between (10 to 50 nm) called the perinuclear space.

These nuclear pores are the passages through which movement of RNA and protein molecules takes place in both directions between the nucleus and the cytoplasm.

Some mature cells even lack nucleus, e.g., erythrocytes of many mammals and sieve tube cells of vascular plants.

It is a site for active ribosomal RNA synthesis. Larger and more numerous nucleoli are present in cells actively carrying out protein synthesis.

Chromatin contains DNA and some basic proteins called histones, some non-histone proteins and also RNA.

The metacentric chromosome has middle centromere forming two equal arms of the chromosome.

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