201. Which statement correctly describes pathogen specificity in acquired immunity?
ⓐ. The same response is produced against every foreign substance.
ⓑ. Different pathogens can trigger different specific immune responses.
ⓒ. Only bacteria can be recognized specifically by the immune system.
ⓓ. Specificity is absent unless a physical barrier is broken.
Correct Answer: Different pathogens can trigger different specific immune responses.
Explanation: Acquired immunity can distinguish between different antigens and respond accordingly. This means the body does not treat every invading pathogen in exactly the same way. The immune response is tailored to the particular antigen that triggered it. Such specificity is a major difference from innate defense.
202. Assertion (A): Secondary immune response is usually stronger than primary immune response.
Reason (R): The first exposure leads to formation of immunological memory.
ⓐ. Both A and R are true, but R is not the correct explanation of A.
ⓑ. A is true, but R is false.
ⓒ. A is false, but R is true.
ⓓ. Both A and R are true, and R is the correct explanation of A.
Correct Answer: Both A and R are true, and R is the correct explanation of A.
Explanation: The first encounter with an antigen leaves behind memory cells in the acquired immune system. These memory cells respond much more effectively when the same antigen appears again. That is why the secondary response is faster and stronger than the primary one. The reason directly explains the assertion.
203. Which comparison between primary and secondary immune responses is correct?
ⓐ. Primary response is slower and weaker, whereas secondary response is faster and stronger.
ⓑ. Primary response belongs to acquired immunity, whereas secondary response belongs to innate immunity.
ⓒ. Primary response is always antibody-free, whereas secondary response has only cells.
ⓓ. Primary response occurs only in childhood, whereas secondary response occurs only in adulthood.
Correct Answer: Primary response is slower and weaker, whereas secondary response is faster and stronger.
Explanation: Primary response occurs when the immune system meets an antigen for the first time, so it takes longer to build an effective defense. Secondary response occurs after memory has already been formed, making it quicker and more intense. Both responses belong to acquired immunity. The main difference lies in timing and strength.
204. Fill in the blank in the most accurate way:
On first exposure to an antigen, acquired immunity usually shows a relatively low-intensity ______.
ⓐ. barrier reaction
ⓑ. allergic attack
ⓒ. primary response
ⓓ. passive transfer
Correct Answer: primary response
Explanation: The first specific response of acquired immunity is called the primary response. It is relatively low in intensity because the immune system has not yet built memory against that antigen. Later exposure produces a stronger secondary response. This sequence is central to understanding immune memory.
205. Which lymphocytes are mainly responsible for producing antibodies?
ⓐ. Neutrophils
ⓑ. T-lymphocytes
ⓒ. B-lymphocytes
ⓓ. Macrophages
Correct Answer: B-lymphocytes
Explanation: B-lymphocytes are the cells that differentiate into antibody-producing cells in acquired immunity. Their products circulate in body fluids and help recognize and neutralize specific antigens. This makes them central to the humoral branch of immune defense. They are different from phagocytic cells and from T-lymphocytes, which have other roles.
206. Which statement best describes the role of T-lymphocytes?
ⓐ. They mediate cell-mediated immunity.
ⓑ. They secrete hydrochloric acid in the stomach.
ⓒ. They act as physical barriers on body surfaces.
ⓓ. They produce mucus in the respiratory tract.
Correct Answer: They mediate cell-mediated immunity.
Explanation: T-lymphocytes are key cells in the cell-mediated branch of acquired immunity. Instead of producing antibodies directly, they act through cellular responses against infected or abnormal cells. Some T cells also help coordinate other immune activities. Their role is therefore distinct from structural barriers and secretory cells.
207. Which immune branch mainly acts through antibodies present in body fluids?
ⓐ. Passive immunity
ⓑ. Innate immunity
ⓒ. Local immunity
ⓓ. Humoral immunity
Correct Answer: Humoral immunity
Explanation: Humoral immunity is the branch of acquired immunity that depends mainly on antibodies circulating in blood and other body fluids. These antibodies bind specifically to foreign antigens and help neutralize them. Because the action occurs through soluble molecules in fluids, the term “humoral” is used. This branch is closely associated with B-lymphocytes.
208. Which branch of acquired immunity is most directly associated with T-lymphocyte action against infected cells?
ⓐ. Passive immunity
ⓑ. Cell-mediated immunity
ⓒ. Humoral immunity
ⓓ. Innate immunity
Correct Answer: Cell-mediated immunity
Explanation: Cell-mediated immunity depends mainly on T-lymphocytes rather than on free antibodies. It is especially important when the immune system must deal with infected body cells or abnormal cells directly. This branch complements humoral immunity but works through a different mechanism. The main distinction lies in whether defense is antibody-based or cell-based.
209. Which statement about B-lymphocytes and T-lymphocytes is correct?
ⓐ. B-lymphocytes produce antibodies, whereas T-lymphocytes help mediate cellular responses.
ⓑ. B-lymphocytes form skin barriers, whereas T-lymphocytes secrete stomach acid.
ⓒ. B-lymphocytes cause fever, whereas T-lymphocytes produce mucus.
ⓓ. B-lymphocytes act only in innate immunity, whereas T-lymphocytes act only in passive immunity.
Correct Answer: B-lymphocytes produce antibodies, whereas T-lymphocytes help mediate cellular responses.
Explanation: B-lymphocytes and T-lymphocytes are both parts of acquired immunity, but they perform different jobs. B cells are associated with antibody production, while T cells are central to cell-mediated responses and immune coordination. Confusing these two functions leads to serious conceptual errors. Their roles are different but complementary.
210. The structure of a typical antibody molecule is represented as
ⓐ. HL
ⓑ. H2L
ⓒ. H3L2
ⓓ. H2L2
Correct Answer: H2L2
Explanation: A typical antibody molecule contains two identical heavy chains and two identical light chains. This arrangement is represented as H2L2. The notation shows the number and type of peptide chains in the molecule. It is a simple way to summarize antibody structure.
211. Fill in the blank in the most accurate way:
An antibody molecule consists of two ______ chains and two ______ chains.
ⓐ. lipid, peptide
ⓑ. heavy, light
ⓒ. DNA, RNA
ⓓ. alpha, beta
Correct Answer: heavy, light
Explanation: Antibodies are protein molecules built from four peptide chains. Two of these are heavy chains, and the other two are light chains. Their association gives the molecule its characteristic overall form. This structural pattern is the basis of the notation H2L2.
212. Which comparison between humoral immunity and cell-mediated immunity is correct?
ⓐ. Humoral immunity is innate, whereas cell-mediated immunity is acquired.
ⓑ. Humoral immunity acts mainly through skin barriers, whereas cell-mediated immunity acts through tears.
ⓒ. Humoral immunity is antibody-based, whereas cell-mediated immunity is mainly T-cell-based.
ⓓ. Humoral immunity depends on stomach acid, whereas cell-mediated immunity depends on mucus.
Correct Answer: Humoral immunity is antibody-based, whereas cell-mediated immunity is mainly T-cell-based.
Explanation: Both humoral and cell-mediated immunity belong to acquired immunity, but they operate differently. Humoral immunity works mainly through antibodies produced by B-lymphocytes, whereas cell-mediated immunity depends largely on T-lymphocytes. This distinction is one of the most important comparisons in immunology at this level. The difference lies in the main defensive tool used.
213. A patient forms a large amount of specific antibody in blood after exposure to an antigen. Which cells are most directly responsible for this response?
ⓐ. B-lymphocytes
ⓑ. Erythrocytes
ⓒ. Neutrophils
ⓓ. Platelets
Correct Answer: B-lymphocytes
Explanation: Specific antibodies in blood are produced by cells derived from B-lymphocytes. These antibodies belong to the humoral immune response and act against particular antigens. Red blood cells, platelets, and neutrophils have different functions and do not perform this specific antibody-producing role. The presence of antigen-specific antibody therefore points strongly to B-cell activity.
214. Which statement is most accurate about the relationship between T-lymphocytes and B-lymphocytes?
ⓐ. T-lymphocytes and B-lymphocytes both belong only to innate immunity.
ⓑ. T-lymphocytes may help B-lymphocytes, and they also mediate cell-mediated immunity.
ⓒ. B-lymphocytes destroy all pathogens physically before entry into the body.
ⓓ. T-lymphocytes are the main source of antibodies in humoral immunity.
Correct Answer: T-lymphocytes may help B-lymphocytes, and they also mediate cell-mediated immunity.
Explanation: T-lymphocytes are important not only because they mediate cell-mediated immunity, but also because some of them assist B-lymphocytes in mounting effective immune responses. This supportive role helps coordinate acquired immunity. B cells remain the main antibody-producing cells. The two lymphocyte types therefore interact rather than functioning in complete isolation.
215. Assertion (A): Antibodies are central to humoral immunity.
Reason (R): Humoral immunity mainly depends on B-lymphocyte-mediated production of specific antibodies.
ⓐ. Both A and R are true, but R is not the correct explanation of A.
ⓑ. A is true, but R is false.
ⓒ. Both A and R are true, and R is the correct explanation of A.
ⓓ. A is false, but R is true.
Correct Answer: Both A and R are true, and R is the correct explanation of A.
Explanation: Humoral immunity works mainly through antibodies present in body fluids. These antibodies are produced by B-lymphocytes in response to specific antigens. Because antibody action is the core feature of this branch, the reason directly explains the assertion. This is why B cells are strongly linked with humoral responses.
216. Which statement about antibodies is correct?
ⓐ. They are non-specific barriers present from birth.
ⓑ. They are signaling cytokines released by virus-infected cells.
ⓒ. They are structural coverings that block pathogen entry.
ⓓ. They are specific immune molecules associated with B-lymphocyte response.
Correct Answer: They are specific immune molecules associated with B-lymphocyte response.
Explanation: Antibodies are antigen-specific molecules produced as part of acquired immunity. They are associated with B-lymphocyte activity and form the main tools of humoral defense. This makes them very different from innate barriers such as skin or cytokines such as interferons. Specificity is one of their defining characteristics.
217. A person can form specific antibodies normally, but has a serious defect in T-lymphocyte function. Which branch of acquired immunity will be most directly affected?
ⓐ. Cell-mediated immunity
ⓑ. Physical barrier immunity
ⓒ. Passive immunity
ⓓ. Physiological barrier immunity
Correct Answer: Cell-mediated immunity
Explanation: T-lymphocytes are central to cell-mediated immunity. They help attack infected or abnormal cells and coordinate cellular immune responses. Although some T cells also support B-cell function, their most direct association is with the cell-mediated branch. A defect in T cells therefore weakens this branch most clearly.
218. Which immune branch would be most directly weakened if B-lymphocytes failed to function properly?
ⓐ. Innate immunity
ⓑ. Humoral immunity
ⓒ. Cytokine barrier
ⓓ. Physical barrier immunity
Correct Answer: Humoral immunity
Explanation: B-lymphocytes are the main source of antibody production in acquired immunity. Since humoral immunity depends primarily on antibodies present in body fluids, defective B-cell function reduces this branch directly. Innate barriers such as skin and mucus are not dependent on B cells. The strongest effect is therefore on humoral defense.
219. Fill in the blank in the most accurate way:
The notation H2L2 for an antibody means that the molecule contains two heavy chains and two ______ chains.
ⓐ. peptide
ⓑ. alpha
ⓒ. light
ⓓ. gamma
Correct Answer: light
Explanation: The antibody molecule is built from four peptide chains in total. Two of these are heavy chains and the other two are light chains. This arrangement is summarized by the notation H2L2. The symbol does not refer to chain color, location, or antigen type.
220. Which statement best distinguishes active immunity from passive immunity?
ⓐ. Active immunity is non-specific, whereas passive immunity is always pathogen-specific.
ⓑ. Active immunity is present only at birth, whereas passive immunity develops later.
ⓒ. Active immunity involves ready-made antibodies, whereas passive immunity involves memory cells only.
ⓓ. Active immunity develops when the body produces its own antibodies, whereas passive immunity is due to transfer of preformed antibodies.
Correct Answer: Active immunity develops when the body produces its own antibodies, whereas passive immunity is due to transfer of preformed antibodies.
Explanation: Active immunity arises when the immune system of the person is stimulated to make its own defense response. Passive immunity, in contrast, is obtained by directly receiving antibodies formed elsewhere. This makes passive protection faster, but usually less lasting. The difference depends on the source of the antibodies.
