15 extra multiple-choice questions for Immunology (12th Standard Zoology, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
During inflammation, the active migration of white blood cells (leucocytes) out of the blood vessels and into the surrounding damaged tissue is known as:
- A. Phagocytosis
- B. Opsonisation
- C. DiapedesisCorrect
- D. Karyotyping
Explanation. Diapedesis is the active movement of leucocytes out of the blood vessels and into the surrounding damaged tissue in response to inflammatory chemical signals like histamine and prostaglandins.
Q2
Which of the following cells are densely packed in the outer cortex of a lobule in the mammalian thymus gland?
- A. Mature thymocytes
- B. Plasma cells
- C. Immature T cellsCorrect
- D. Follicular dendritic cells
Explanation. The outer cortex of the thymus lobule is densely packed with immature T-lymphocytes (thymocytes) undergoing maturation, whereas the medulla contains mature, sparsely populated thymocytes.
Q3
In a mammalian lymph node, the paracortex zone is located beneath the cortex and is richly populated by which of the following immune cells?
- A. B lymphocytes and plasma cells
- B. T lymphocytes and interdigitating dendritic cellsCorrect
- C. Macrophages and follicular dendritic cells
- D. Erythrocytes and blood platelets
Explanation. The lymph node is divided into zones: the cortex is rich in B cells, the paracortex contains mainly T cells and interdigitating dendritic cells, and the medulla has antibody-secreting plasma cells.
Q4
Non-immunogenic substances that cannot elicit an immune response on their own but are capable of reacting with the products of a specific immune response are called:
- A. Adjuvants
- B. HaptensCorrect
- C. Epitopes
- D. Paratopes
Explanation. Haptens are small, non-immunogenic molecules that can only elicit an immune response when coupled with a larger carrier protein, though they can independently bind to antibodies.
Q5
Substances that can be added to an antigen or a vaccine formulation to enhance and boost the host's overall immune response are known as:
- A. Opsonins
- B. AdjuvantsCorrect
- C. Haptens
- D. Precipitins
Explanation. Adjuvants are substances formulated within vaccines to augment and strengthen the body's immune reaction toward the targeted antigen.
Q6
An antibody monomer is represented by the formula H2L2. What is the approximate molecular weight of a single immunoglobulin light (L) chain?
- A. 100,000 Da
- B. 50,000 Da
- C. 25,000 DaCorrect
- D. 10,000 Da
Explanation. An immunoglobulin molecule consists of two heavy chains of about 50,000 Da each and two light chains of about 25,000 Da each, bound together by disulfide bridges.
Q7
In serological reactions, when a soluble antigen reacts with its specific antibody to form a visible insoluble aggregate, the reaction is termed a:
- A. Agglutination reaction
- B. Opsonisation reaction
- C. Precipitin reactionCorrect
- D. Neutralization reaction
Explanation. Precipitation occurs when soluble antigens cross-link with specific antibodies to form visible insoluble complexes, while agglutination involves particulate antigens like whole bacterial cells.
Q8
Who is credited with the discovery and development of vaccines against rabies, anthrax, and cholera in the year 1885?
- A. Dr. Edward Jenner
- B. Louis PasteurCorrect
- C. Calmette and Guerin
- D. Dr. Albert Sabin
Explanation. Louis Pasteur pioneered the development of vaccines for rabies, anthrax, and cholera using weakened pathogens in the late nineteenth century.
Q9
Second-generation vaccines contain pure surface antigens of the pathogen to ensure safety and uniform quality. Which of the following is an example of a second-generation vaccine?
- A. MMR vaccine
- B. Hepatitis B vaccineCorrect
- C. DPT vaccine
- D. DNA vaccine
Explanation. Second-generation vaccines contain purified recombinant surface antigens of the pathogen rather than whole killed or weakened organisms, with the Hepatitis B vaccine being a prime example.
Q10
Under the electron microscope, the spherical Human Immunodeficiency Virus (HIV) particle has an approximate diameter of:
- A. 50-70 nm
- B. 100-120 nmCorrect
- C. 200-220 nm
- D. 300-320 nm
Explanation. Human Immunodeficiency Virus is a spherical retrovirus with an outer lipoprotein envelope measuring approximately 100 to 120 nanometers in diameter.
Q11
Upon entering the human body, HIV replicates its RNA genome into DNA within which of the following cell types, which subsequently acts as a "HIV factory"?
- A. Helper T lymphocytes
- B. MacrophagesCorrect
- C. B lymphocytes
- D. Plasma cells
Explanation. After infection, HIV replicates within macrophages to produce new viral particles, turning these cells into long-lived factories before progressively depleting the helper T-lymphocytes.
Q12
Autoimmune diseases in humans can be organ-specific or systemic. Which of the following is classified as a non-organ-specific (systemic) autoimmune disorder?
- A. Hashimoto's thyroiditis
- B. Graves' disease
- C. Rheumatoid arthritisCorrect
- D. Addison's disease
Explanation. Rheumatoid arthritis is a systemic autoimmune disorder that targets joints and tissues throughout the body, whereas Graves' and Addison's diseases are localized to specific endocrine organs.
Q13
What is the regulatory property of normal cells that inhibits their uncontrolled growth when they make contact with neighboring cells, which is notably absent in cancer cells?
- A. Metastasis
- B. Contact inhibitionCorrect
- C. Somatic mutation
- D. Immunological surveillance
Explanation. Contact inhibition is a regulatory mechanism that stops cellular proliferation when cells touch each other. The loss of this property leads to unchecked division and tumor formation.
Q14
Immunological memory is established after primary antigen exposure. In which of the following sites does the secondary immune response primarily appear?
- A. Spleen
- B. Lymph nodes
- C. Bone marrowCorrect
- D. Thymus gland
Explanation. While primary immune responses occur mostly in lymph nodes and the spleen, the secondary response is predominantly mounted in the bone marrow, where memory cells reside.
Q15
Who is historically credited with preparing the first vaccine against smallpox in the year 1796?
- A. Dr. Edward JennerCorrect
- B. Louis Pasteur
- C. Calmette and Guerin
- D. Dr. Jonas Salk
Explanation. Dr. Edward Jenner successfully developed the first vaccine in 1796 by using cowpox virus to immunize individuals against smallpox.
