Test: Nucleus & Chromosomes - NEET MCQ

• Some cells such as the red blood cells or the erythrocytes of humans and the sieve tube cells of vascular plants lack a nucleus in their mature cells.
• Leukocytes, nerve cells and epithelial cells  possess a nucleus.

Topic in NCERT: Prokaryotic cells

Line in NCERT: "the prokaryotic cells lack such membrane bound organelles."

• 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.

• Nucleus Structure:




• The nucleus is a two-layered structure.


• It consists of an inner and outer nuclear membrane.


• The nuclear membrane is made up of two lipid bilayers.




• Functions of Nucleus:




• The nucleus houses the genetic material of the cell, including DNA and RNA.


• It is responsible for controlling the activities of the cell by regulating gene expression.


• The nucleus is involved in processes such as DNA replication, transcription, and mRNA processing.




• Importance of Nucleus:




• The nucleus is essential for the growth, development, and reproduction of the cell.


• It plays a crucial role in maintaining the integrity of genetic information.


• Any abnormalities in the nucleus can lead to various genetic disorders and diseases.

To determine which statement about the nucleus is incorrect, let's analyze each statement:

1. In plant cells, the nucleus lies towards the periphery due to the large nucleus that occupies almost the entire region of the cell:

   • This is incorrect. In plant cells, the nucleus is pushed towards the periphery not because of a large nucleus, but due to the presence of a large central vacuole that occupies most of the cell's interior.

2. Nucleus helps in reproduction and acts as the control centre of the cell:

   • This is correct. The nucleus contains genetic material and controls cell activities, including reproduction

3. Nucleoplasm condenses and groups together to form chromosomes:

   • This is correct. The nucleoplasm contains chromatin, which condenses and organizes into chromosomes during cell division.

4. Nucleus comprises of nuclear membrane, nuclear pores, nucleolus, nucleoplasm, and chromatin:
           This is correct. The nucleus includes all these components.

Therefore, the incorrect statement is:

1. In plant cells, the nucleus lies towards the periphery due to the large nucleus that occupies almost the entire region of the cell

Topic in NCERT: Nucleus

Line in NCERT: "the nucleus is enclosed by nuclear envelope, a double membrane structure with nuclear pores."

• Nuclear membrane is a double layered covering of nucleus which is separated by a perinuclear space.
• Nuclear pores allow the transfer of materials and disrupt the continuity of nuclear membrane.
• Nucleoplasm is also termed as “Karyolymph” and act as site for synthesis of DNA and RNA.
• Chromatin contains RNA, DNA, histone and non – histone proteins.

Topic in NCERT: Nucleus

Line in NCERT: "the nuclear matrix or the nucleoplasm contains nucleolus and chromatin."

• Chromosomes are rod shaped structures that condenses together when the cell is about divide.
• Chromosomes are composed of DNA, RNA and proteins which act as repository for inheritance.
• Kinetochores are disc like structures that are present on the sides of centromeres.
• In telocentric chromosomes, centromere is present in the end of the chromatids.

Topic in NCERT: Classification of chromosomes based on centromere position

Line in NCERT: "the centromere is situated close to its end forming one extremely short and one very long arm"

Chromatin is made of nucleoprotein. Chromatin is a complex of macromolecules found in cells, consisting of DNA, protein and RNA. The primary functions of chromatin are to pack DNA into a smaller volume to fit in the cell, to reinforce the DNA macromolecule to allow mitosis, to prevent DNA damage, and to control gene expression and DNA replication. The primary protein components of chromatin are histones that compact the DNA.

Topic in NCERT: Nucleus

Line in NCERT: "the interphase nucleus has a loose and indistinct network of nucleoprotein fibres called chromatin. chromatin contains dna and some basic proteins called histones, some non-histone proteins and also rna."