Biology Multiple Choice Questions on “Cell – Nucleus”.
1. Which scientist coined the term chromatin?
a) Robert Koch
b) Louis Pasteur
c) Robert Brown
d) Alexander Fleming
Answer: d
Clarification: Sir Alexander Fleming was a Scottish scientist, known for his work on microbiology and medicine. The material in the nucleus which he stained by basic dyes was coined by him as chromatin.
2. What is the space between the two membranes of the nuclear envelope known as?
a) Reticular space
b) Intra – membrane space
c) Perinuclear space
d) Somatic space
Answer: c
Clarification: Electron microscopy has revealed that the nuclear envelope consists of two parallel membranes with a space between them called the perinuclear space. It forms a barrier between the materials present inside the nucleus and that of the cytoplasm.
3. Which of these cells lack a nucleus?
a) Thrombocytes in humans
b) Lymphocytes of primates
c) Sieve tube cells of vascular plants
d) Epithelial cells
Answer: c
Clarification: 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 and thrombocytes possess a nucleus.
4. Which of these is an important constituent of the nuclear matrix?
a) Chromatin
b) Ribosomes
c) Mitochondria
d) Centrosomes
Answer: a
Clarification: The nuclear matrix or the nucleoplasm contains the nucleolus and chromatin. The nucleoli are spherical structures present in the nucleoplasm and the chromatin is present along with it.
5. What is the site of rRNA synthesis within a cell?
a) Chromatin
b) Nucleolus
c) Perinuclear space
d) Centrosomes
Answer: b
Clarification: 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.
6. Which of these organelles are not membrane bound?
a) Mitochondria
b) Endoplasmic reticulum
c) Nucleolus
d) Lysosome
Answer: c
Clarification: 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.
7. Which is the primary constriction for every visible chromosome?
a) Centromere
b) Ribosomes
c) Kinetochores
d) Histones
Answer: a
Clarification: 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.
8. Which form of chromosome has two equal arms?
a) Telocentric chromosome
b) Acrocentric chromosome
c) Sub – metacentric chromosome
d) Metacentric chromosome
Answer: d
Clarification: 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.
9. Which type of chromosome has its centromere at its tip?
a) Acrocentric chromosome
b) Telocentric chromosome
c) Sub – metacentric chromosome
d) Metacentric chromosome
Answer: b
Clarification: 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.
10. The nucleolus is the site of rRNA synthesis. True or false?
a) True
b) False
Answer: a
Clarification: The nucleus contains the nucleolus which is not a membrane-bound organelle. The nucleus also contains chromatin. The nucleolus is the site of active ribosomal RNA or rRNA synthesis.
11. Identify the structure.
a) Chromatin
b) DNA
c) Centromere
d) Kinetochore
Answer: d
Clarification: At the constriction between the arms of a chromosome lies disc shaped structures known as kinetochores. It is the site where spindle fibres attach during cell division to pull sister chromatids apart.
12. A few chromosomes have non-staining constrictions at a constant location. What are these constrictions called?
a) Cilia
b) Flagella
c) Satellite
d) Kinetochore
Answer: c
Clarification: 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.
13. Identify the structure.
a) Cilia
b) Flagella
c) Satellite
d) Kinetochore
Answer: c
Clarification: 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.
14. What are the disc shaped structures located on the sides of the centromere?
a) Kinetochores
b) Satellite cells
c) Flagella
d) Ribosomes
Answer: a
Clarification: Every chromosome has a primary constriction known as the centromere. The sides of the centromere contains disc shaped structures known as kinetochores.
15. What is the number of chromosomes present in an oocyte?
a) 46
b) 23
c) 21
d) 48
Answer: b
Clarification: A single human cell has approximately two metre long thread of DNA. This DNA is distributed among its forty-six (twenty-three pairs) chromosomes. Since, the oocyte is haploid, it contains 23 chromosomes.