3.2.4 Cell recognition and immunity Exam questions

Question 1

What is an antigen? (1 mark)

Answer 1

An antigen is a molecule, often a protein or polysaccharide, that triggers an immune response by being recognized as foreign by the immune system. (1 mark)

Question 2

What types of cells or particles can act as pathogens? (1 mark)

Answer 2

Bacteria, viruses, fungi, and protozoa. (1 mark)

Question 3

How do antigens enable the immune system to distinguish between self and non-self cells? (2 marks)

Answer 3

Self cells have unique antigens that the immune system recognizes as “self,” while foreign cells or pathogens have non-self antigens that trigger an immune response. (2 marks)

Question 4

Describe the process of phagocytosis. (4 marks)

Answer 4

The phagocyte recognizes foreign antigens on the pathogen. (1 mark)

The pathogen is engulfed into a vesicle called a phagosome. (1 mark)

The phagosome fuses with a lysosome to form a phagolysosome. (1 mark)

Enzymes digest the pathogen, and the phagocyte presents the pathogen’s antigens on its surface. (1 mark)

Question 5

What is the role of lysosomes in phagocytosis? (1 mark)

Answer 5

Lysosomes contain hydrolytic enzymes that digest pathogens within the phagolysosome. (1 mark)

Question 6

What type of immune response is phagocytosis part of? (1 mark)

Answer 6

The non-specific immune response. (1 mark)

Question 7

What is the role of T-helper cells in the immune response? (3 marks)

Answer 7

T-helper cells release cytokines to:

Activate B cells to produce antibodies. (1 mark)

Stimulate cytotoxic T cells (TC cells). (1 mark)

Enhance the activity of phagocytes. (1 mark)

Question 8

What is the role of cytotoxic T cells (TC cells)? (2 marks)

Answer 8

Cytotoxic T cells destroy infected cells by releasing perforins, which create pores in the cell membrane, leading to lysis. (2 marks)

Question 9

What is clonal selection and expansion? (2 marks)

Answer 9

Clonal selection: The activation of a specific B or T cell that matches the antigen. (1 mark)

Clonal expansion: The mitotic division of the selected cell to produce a large population of identical cells. (1 mark)

Question 10

What is the role of plasma cells in the immune response? (1 mark)

Answer 10

Plasma cells are derived from B cells and secrete large quantities of specific antibodies. (1 mark)

Question 11

What are memory cells, and why are they important? (2 marks)

Answer 11

Memory cells are long-lived lymphocytes that remain after an infection and enable a faster, stronger secondary immune response upon re-exposure to the same antigen. (2 marks)

Question 12

What is the structure of an antibody? (4 marks)

Answer 12

An antibody consists of:

Two heavy chains and two light chains. (1 mark)

Variable regions (specific to antigens). (1 mark)

Constant regions (for effector functions). (1 mark)

Disulfide bonds holding the chains together. (1 mark)

Question 13

How do antibodies neutralize pathogens? (3 marks)

Answer 13

Agglutination: Clumping pathogens together for easier phagocytosis. (1 mark)

Neutralization: Blocking toxins or preventing pathogens from binding to cells. (1 mark)

Opsonization: Marking pathogens for destruction by phagocytes. (1 mark)

Question 14

What is a vaccine, and how does it work? (2 marks)

Answer 14

A vaccine contains antigens from a pathogen (weakened, inactivated, or subunit) that stimulate the production of memory cells without causing disease. (2 marks)

Question 15

What is herd immunity? (1 mark)

Answer 15

When a large proportion of the population is immune to a disease, reducing its spread and protecting individuals who are not immune. (1 mark)

Question 16

What are the differences between active and passive immunity? (2 marks)

Answer 16

Active immunity: Produced by the individual’s immune system (e.g., vaccination or infection). Long-lasting. (1 mark)

Passive immunity: Antibodies are transferred from an external source (e.g., maternal antibodies or injections). Short-term. (1 mark)

Question 17

What are monoclonal antibodies? (1 mark)

Answer 17

Identical antibodies produced by a single clone of B cells that are specific to one antigen. (1 mark)

Question 18

List two uses of monoclonal antibodies in medicine. (2 marks)

Answer 18

Targeted cancer therapy by delivering drugs to specific cells. (1 mark)

Diagnostic tests, such as pregnancy tests, to detect specific hormones or antigens. (1 mark)

Question 19

What is antigenic variability? (2 marks)

Answer 19

The ability of pathogens to change their surface antigens, making them harder for the immune system to recognize. (2 marks)

Question 20

Why does antigenic variability reduce vaccine effectiveness? (2 marks)

Answer 20

Vaccines become less effective because memory cells and antibodies cannot recognize new antigens on the pathogen. (2 marks)

Question 21

What is an autoimmune disease? (1 mark)

Answer 21

A condition where the immune system attacks the body’s own cells due to a failure in self-recognition (e.g., type 1 diabetes, rheumatoid arthritis). (1 mark)

Question 22

How do autoimmune diseases arise? (2 marks)

Answer 22

Self-antigens are mistakenly identified as foreign, triggering an immune response against the body’s own tissues. (2 marks)

Question 23

What is the ELISA test, and what is it used for? (2 marks)

Answer 23

The ELISA test (enzyme-linked immunosorbent assay) detects the presence of specific antigens or antibodies in a sample. (2 marks)

Question 24

Describe the steps of an ELISA test. (4 marks)

Answer 24

ntigen is bound to a surface. (1 mark)

Add a specific antibody linked to an enzyme. (1 mark)

Add a substrate for the enzyme, producing a color change if the antigen is present. (2 marks)

Question 25

What are controls in an ELISA test used for? (1 mark)

Answer 25

Controls ensure the results are valid by confirming the test detects the antigen-antibody interaction specifically. (1 mark)

Question 26

What does a graph of antibody concentration during primary and secondary responses show? (2 marks)

Answer 26

The secondary response is faster, stronger, and produces more antibodies due to memory cells. (2 marks)

Question 27

How can data from vaccination programs demonstrate effectiveness? (2 marks)

Answer 27

By comparing infection rates before and after vaccination, and analyzing the impact of herd immunity. (2 marks)

Question 28

What is HIV? (1 mark)

Answer 28

HIV (Human Immunodeficiency Virus) is a retrovirus that infects and destroys helper T cells, leading to a weakened immune system. (1 mark)

Question 29

Describe the structure of HIV. (4 marks)

Answer 29

Glycoproteins on the surface (e.g., gp120) that bind to receptors on helper T cells. (1 mark)\n
A capsid containing:\n
Two single strands of RNA. (1 mark)\n
Enzymes: Reverse transcriptase, integrase, and protease. (1 mark)

Question 30

How does HIV replicate inside helper T cells? (5 marks)

Answer 30

Attachment: HIV’s gp120 binds to CD4 receptors on helper T cells. (1 mark)\n
Fusion: The viral envelope fuses with the T cell membrane, allowing the RNA and enzymes to enter. (1 mark)\n
Reverse Transcription: Reverse transcriptase converts viral RNA into complementary DNA (cDNA). (1 mark)\n
Integration: cDNA is integrated into the host genome by integrase. (1 mark)\n
Protein Synthesis and Assembly: The host cell produces viral proteins and assembles new viruses, which bud off, destroying the host cell. (1 mark)

Question 31

What is AIDS? (1 mark)

Answer 31

AIDS (Acquired Immunodeficiency Syndrome) is the final stage of HIV infection, where the immune system is severely weakened due to a critical loss of helper T cells. (1 mark)

Question 32

What causes the symptoms of AIDS? (2 marks)

Answer 32

Fewer helper T cells result in:\n
Reduced activation of B cells and cytotoxic T cells. (1 mark)\n
Increased susceptibility to opportunistic infections and cancers. (1 mark)

Question 33

What are some examples of opportunistic infections in AIDS? (2 marks)

Answer 33

Tuberculosis (TB). (1 mark)\n
Pneumonia or fungal infections like candidiasis. (1 mark)

Question 34

What is the ELISA test, and how is it used for HIV detection? (4 marks)

Answer 34

HIV antigens are attached to a surface. (1 mark)\n
Add patient serum; HIV antibodies, if present, bind to the antigens. (1 mark)\n
Add a secondary antibody linked to an enzyme that binds to the HIV antibody. (1 mark)\n
Add substrate; a color change indicates the presence of HIV antibodies. (1 mark)

Question 35

What are the ethical issues surrounding HIV testing? (2 marks)

Answer 35

Ensuring confidentiality of test results. (1 mark)\n
Informed consent before testing. (1 mark)

Question 36

Why Are Antibiotics Ineffective Against Viruses? (2 marks)

Answer 36

Antibiotics target structures or metabolic processes unique to bacteria, such as cell walls or protein synthesis. Viruses lack these structures and rely on the host cell for replication. (2 marks)