Four steps that occur during the primary immune response to a pathogen are listed.
P B-lymphocytes divide by mitosis.
Q T-helper cells interact with macrophages that have digested pathogens.
R Plasma cells secrete antibodies.
S T-helper cells activate other lymphocytes.
These steps can be arranged in the sequence in which they occur.
Which step occurs third in the sequence?
▶️ Answer/Explanation
Ans: A
The sequence is: Q (macrophage interaction) → S (T-cell activation) → P (B-cell mitosis) → R (antibody secretion). Thus, the third step is P (A).
Which row is correct?
▶️ Answer/Explanation
Ans: A
T-lymphocytes (e.g., cytotoxic T-cells) phagocytose infected cells, while B-lymphocytes differentiate into plasma cells to secrete antibodies. Thus, the correct row is A.
Why is passive immunity effective for only a short time?
▶️ Answer/Explanation
Ans: A
Passive immunity involves receiving pre-made antibodies which aren’t produced by the body. These antibodies have a limited lifespan (typically weeks to months) before being broken down, unlike active immunity where memory cells provide long-term protection.
A bacterial pathogen produces a protein that acts as a toxin. This toxin is harmful to humans.
Scientists are developing monoclonal antibodies that can be used to detect the presence of the toxin in the body so that early treatment can be given.
Which statements describe steps in the development of these monoclonal antibodies?
- The toxin protein is injected into a mouse and triggers mitosis of specific B-lymphocytes.
- Antibodies are collected from the spleen of the mouse and fused with myeloma cells.
- A hybridoma cell produces many antibodies with a variety of different variable regions.
▶️ Answer/Explanation
Ans: B
Statement 1 is correct as injecting the toxin triggers B-lymphocyte production. Statement 2 is incorrect because B-lymphocytes (not antibodies) are fused with myeloma cells. Statement 3 is wrong as hybridomas produce identical antibodies. Thus, only statement 1 is correct.