Test: Nucleus & Chromosomes (May 20) - NEET MCQ

• The nuclear matrix or the nucleoplasm contains the nucleolus and chromatin.
• The nucleolus is the site for active ribosomal RNA or rRNA synthesis.
• The nucleolus is not bound by a membrane.

Topic in NCERT: Nucleolus

Line in NCERT: "the nucleoli are spherical structures present in the nucleoplasm. it is a site for active ribosomal rna synthesis."

• The nucleus contains the nucleolus which is not a membrane-bound organelle.
• The mitochondria, the endoplasmic reticulum, and lysosomes are present in the cytosol.
• They are membrane-bound organelles of the cell.

Topic in NCERT: Nucleolus

Line in NCERT: "the nucleoli are spherical structures present in the nucleoplasm. the content of nucleolus is continuous with the rest of the nucleoplasm as it is not a membrane bound structure."

• Every visible chromosome has two sister chromatids which are constricted together at a point known as the centromere.
• During mitosis, the spindle fibres attach to the chromosomes via the centromere.

Topic in NCERT: Chromosomes and chromatin

Line in NCERT: "every chromosome (visible only in dividing cells) essentially has a primary constriction or the centromere on the sides of which disc shaped structures called kinetochores are present."

Based on the position of the centromere, the chromosomes can be classified into four types. The metacentric chromosome has its centromere in the middle, thus forming two equal arms of the chromosome.

Topic in NCERT: Types of chromosomes based on the position of centromere

Line in NCERT: "the metacentric chromosome has middle centromere forming two equal arms of the chromosome."

Based on the position of the centromere, the chromosomes can be classified into four types. In telocentric chromosomes, the centromere is located at the proximal end or the tip of the chromosome.

Topic in NCERT: Types of chromosomes based on the position of centromere

Line in NCERT: "the telocentric chromosome has a terminal centromere."

• Some chromosomes have secondary constrictions which are non – staining, apart from the centromere.
• They give the appearance of a small fragment.
• This small fragment is known as a satellite.

Topic in NCERT: Satellite

Line in NCERT: "sometimes a few chromosomes have non-staining secondary constrictions at a constant location. this gives the appearance of a small fragment called the satellite."

Ribonucleic acid occurs in the nucleus and cytoplasm. The DNA molecules are transcribed inside the nucleus to form RNA. The RNA undergoes post-translational modification and forms different types of RNA which leave the nucleus by nuclear pore and undergo translation to form protein.

Topic in NCERT: Ribosomes

Line in NCERT: "ribosomes are composed of ribonucleic acid (rna) and proteins and are not surrounded by any membrane."

Discovery of Nucleus

• Robert Brown: Robert Brown, a Scottish botanist, discovered the cell nucleus in 1831 while studying orchids under a microscope. He observed a central structure within the cells which he named the nucleus.


• Significance: Brown's discovery of the nucleus was a crucial milestone in the field of cell biology as it provided insight into the organization and function of cells.


• Structure: The nucleus is a membrane-bound organelle found in eukaryotic cells and contains the cell's genetic material in the form of DNA. It plays a vital role in controlling cellular activities and gene expression.


• Function: The nucleus is responsible for regulating gene expression, DNA replication, and cell division. It acts as the control center of the cell, coordinating various cellular processes.

Topic in NCERT: Nucleus

Line in NCERT: "robert brown later discovered the nucleus."

• Some chromosomes have secondary constrictions which are non-staining, apart from the centromere.
• They give the appearance of a small fragment.
• This small fragment is known as a satellite.