Nucleus and Chromosomes Practice Questions
20 free Nucleus and Chromosomes practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Who first described the nucleus as a cell organelle in 1831?
- A Robert Hooke
- B Anton von Leeuwenhoek
- C Schleiden
- D Robert Brown
Correct answer: Robert Brown
Robert Brown was the first to discover and describe the nucleus as a distinct cell organelle in 1831. Later, Flemming gave the name 'chromatin' to the material of the nucleus stained by basic dyes.
The nuclear envelope consists of two parallel membranes with a space between them called the:
- A Perimitochondrial space
- B Intermembranous lumen
- C Nucleoplasm
- D Perinuclear space
Correct answer: Perinuclear space
The perinuclear space (10 to 50 nm) forms a barrier between the materials present inside the nucleus and that of the cytoplasm. The outer membrane usually remains continuous with the endoplasmic reticulum.
Nuclear pores are formed by the fusion of the two nuclear membranes. What is their primary function?
- A Synthesis of lipids and membrane proteins
- B Attachment of ribosomes
- C Passage of RNA and protein molecules
- D Storage of calcium ions
Correct answer: Passage of RNA and protein molecules
Nuclear pores act as passages through which movement of RNA and protein molecules takes place in both directions between the nucleus and the cytoplasm. They are essential for gene expression and protein regulation.
Which of the following mature cells lacks a nucleus?
- A Parenchyma cells
- B Companion cells of phloem tissue
- C Lymphocytes
- D Erythrocytes of most mammals
Correct answer: Erythrocytes of most mammals
Mature mammalian erythrocytes (RBCs) and sieve tube cells of vascular plants lack a nucleus. Despite the absence of a nucleus, these cells are considered 'living' for their functional lifespan.
The nucleoplasm contains which of the following structures?
- A Nucleolus and Chromatin
- B Mitochondria and Lysosomes
- C Centrioles and Vacuoles
- D Golgi apparatus and ER
Correct answer: Nucleolus and Chromatin
The nucleoplasm is the nuclear matrix that houses the nucleolus and chromatin. Chromatin is a network of nucleoprotein fibers that condenses into chromosomes during cell division.
Which statement best describes the nucleolus?
- A It is the site for active ribosomal RNA synthesis
- B It is a membrane-bound organelle
- C It is responsible for lipid storage and metabolism
- D It contains the primary genetic code
Correct answer: It is the site for active ribosomal RNA synthesis
The nucleolus is a non-membrane bound spherical structure within the nucleoplasm. It is the site for active rRNA synthesis; thus, cells active in protein synthesis have larger and more numerous nucleoli.
Chromatin contains DNA and some basic proteins called:
- A Histones
- B Albumins
- C Glutenins
- D Actins
Correct answer: Histones
Chromatin is composed of DNA, RNA, and proteins. The basic proteins are called histones, while some non-histone proteins are also present to help in structural organization.
Every chromosome essentially has a primary constriction called the:
- A Telomere
- B Satellite
- C Centromere
- D Kinetochore
Correct answer: Centromere
The centromere is the primary constriction where the two sister chromatids are held together. On the sides of the centromere, disc-shaped structures called kinetochores are present.
In which type of chromosome is the centromere situated in the middle, forming two equal arms?
- A Metacentric
- B Sub-metacentric
- C Acrocentric
- D Telocentric
Correct answer: Metacentric
A metacentric chromosome has a middle centromere, resulting in two equal arms. This gives the chromosome a 'V' shape during anaphase movement.
A sub-metacentric chromosome is characterized by having:
- A Centromere slightly away from the middle
- B Centromere at the very end
- C Centromere positioned to form two equal chromosome arms
- D Centromere very close to the end
Correct answer: Centromere slightly away from the middle
Sub-metacentric chromosomes have a centromere slightly away from the middle, resulting in one shorter arm (p-arm) and one longer arm (q-arm). This often appears 'L' shaped during division.
In an acrocentric chromosome, the centromere is located:
- A In the exact center
- B At the terminal end
- C Close to its end forming one extremely short arm
- D Located entirely outside the nuclear membrane boundary
Correct answer: Close to its end forming one extremely short arm
Acrocentric chromosomes have the centromere situated close to the end. This results in one 'extremely short' arm and one 'very long' arm.
Which chromosome type has a terminal centromere?
- A Telocentric
- B Metacentric
- C Acrocentric
- D Sub-metacentric
Correct answer: Telocentric
Telocentric chromosomes have the centromere at the proximal end (tip). Note that telocentric chromosomes are generally not found in humans.
What are 'Satellites' in the context of chromosomes?
- A Non-staining secondary constrictions at constant locations
- B Small fragments of RNA
- C Specialized proteins that bind directly to the centromere region
- D A type of extranuclear DNA
Correct answer: Non-staining secondary constrictions at constant locations
Some chromosomes have non-staining secondary constrictions at a constant location. This gives the appearance of a small fragment called a satellite (SAT-chromosome).
A single human cell has approximately how much DNA distributed among its 46 chromosomes?
- A 2 centimeters
- B 2 meters long
- C 2 millimeters
- D 20 micrometers
Correct answer: 2 meters long
The DNA thread in a single human cell is approximately 2 meters long. This massive length is highly condensed and packaged into the 23 pairs of chromosomes found in the nucleus.
Which of the following is the 'Master Organelle' that directs all cellular activities and contains genetic information?
- A Mitochondria
- B The nucleus
- C Ribosome
- D Chloroplast
Correct answer: The nucleus
The nucleus is considered the control center or master organelle of the cell. It contains the DNA (genetic blueprint) and regulates growth, metabolism, and reproduction.
During which phase of the cell cycle is the nucleus seen as a 'highly extended and elaborate nucleoprotein fiber' network called chromatin?
- A Prophase
- B Cytokinesis
- C Interphase
- D Anaphase
Correct answer: Interphase
During interphase (the non-dividing phase), the nucleus does not show distinct chromosomes but rather a diffuse network called chromatin. Distinct chromosomes are only visible during cell division phases.
The content of the nucleolus is continuous with the rest of the nucleoplasm because:
- A It is a liquid droplet
- B It is not membrane-bound
- C It is made of DNA only
- D It is attached to the nuclear pore
Correct answer: It is not membrane-bound
The nucleolus is not surrounded by a membrane. This lack of a boundary allows its contents to be continuous with the surrounding nucleoplasm, facilitating the movement of ribosomal components.
Kinetochores are important during cell division because they:
- A Synthesize DNA
- B Hold sister chromatids together
- C Anchor the spindle fibers
- D Form the nuclear envelope
Correct answer: Anchor the spindle fibers
Kinetochores are disc-shaped structures found at the centromere. They are the specific sites where spindle fibers attach to pull the chromosomes apart during mitosis or meiosis.
Cells that are actively involved in protein synthesis generally have:
- A No nucleolus
- B Small, indistinct nucleoli
- C Larger, more numerous nucleoli
- D More mitochondria than ribosomes
Correct answer: Larger, more numerous nucleoli
Because the nucleolus is the factory for rRNA and ribosome subunit assembly, cells requiring high protein production have prominent nucleoli to keep up with ribosomal demand.
The outer nuclear membrane is often studded with _______, similar to the Rough ER.
- A Lysosomes
- B Ribosomes
- C Centrosomes
- D Nucleoli
Correct answer: Ribosomes
The outer nuclear membrane is continuous with the Endoplasmic Reticulum and often bears ribosomes on its surface, participating in protein synthesis just like the RER.