A Level H1 Biology Human Physiology Quiz

Answer Key - A-Level Biology H1 Quiz: Human Physiology

Note: This content is syllabus-aligned and generated based on inferred patterns.

Section A: Innate and Adaptive Immunity

1. Role of skin/mucous membranes (1m): Act as a physical/chemical barrier to prevent the entry of pathogens into the body.

2. Phagocytosis process (3m):

   • Recognition/binding of the pathogen by receptors on the macrophage surface (1).
   • Engulfment of the pathogen to form a phagosome (1).
   • Fusion of lysosomes with the phagosome, where hydrolytic enzymes digest the pathogen (1).

3. Primary vs Secondary Response (3m):

   • Time: Primary response has a longer lag phase/takes longer to produce antibodies; secondary is much faster (1).
   • Concentration: Secondary response produces a significantly higher concentration of antibodies (1).
   • Duration: Secondary response antibodies persist for a longer period (1).

4. Antigen and Specificity (3m):

   • Antigen: A foreign molecule (usually a protein/polysaccharide) that triggers an immune response (1).
   • Specificity: Antibodies have a variable region/binding site (1) that is complementary in shape to a specific antigen (1).

5. Helper T-cells and B-cells (3m):

   • Helper T-cells recognize antigens presented by APCs (1).
   • They release cytokines/interleukins (1).
   • These cytokines activate B-cells that have already bound the specific antigen, stimulating them to divide (1).

6. Clonal Expansion (3m):

   • An activated B-cell or T-cell undergoes rapid mitosis (1).
   • This produces a large population of identical clones (1).
   • This ensures there are enough effector cells (e.g., plasma cells) to neutralize the high number of pathogens present (1).

7. Plasma vs Memory Cells (2m):

   • Plasma cells: Short-lived; secrete large quantities of soluble antibodies (1).
   • Memory cells: Long-lived; remain in the body to provide a rapid response upon re-exposure to the same antigen (1).

8. Antibody Neutralization (2m):

   • Antibodies bind to the surface antigens of the virus/toxin (1).
   • This physically blocks the pathogen from binding to host cell receptors, preventing entry (1).

9. Vaccination Protection (3m):

   • Vaccination introduces a weakened/inactive pathogen to trigger a primary response (1).
   • This leads to the production of memory B and T cells (1).
   • Upon actual infection, these memory cells trigger a rapid, high-concentration secondary response that eliminates the pathogen before symptoms appear (1).

10. Cytotoxic T-cells vs Antibodies (4m):

    • Antibodies: Target extracellular pathogens; act by neutralization or opsonization (1).
    • Cytotoxic T-cells: Target intracellular pathogens (infected host cells) (1).
    • Mechanism: T-cells release perforins/granzymes to induce apoptosis in the infected cell (1).
    • Comparison: Antibodies cannot enter cells, whereas T-cells identify and destroy the "factory" producing the virus (1).

Section B: Infectious Diseases and Pathogens

11. Pathogen Definition (2m):

    • Definition: A biological agent that causes disease in its host (1).
    • Examples: Virus (e.g., Influenza/HIV) and Bacteria (e.g., Mycobacterium tuberculosis) (1).

12. Antibiotics vs Viruses (3m):

    • Antibiotics target bacterial structures/processes (e.g., cell wall synthesis, 70S ribosomes) (1).
    • Viruses lack these structures (no cell wall, use host machinery) (1).
    • Therefore, antibiotics have no target to act upon in viruses (1).

13. Viral Replication (4m):

    • Attachment: Virus binds to specific receptors on the host cell membrane (1).
    • Entry: Virus enters the cell via endocytosis or fusion (1).
    • Replication: Viral genome is released; host enzymes (RNA/DNA polymerase) are hijacked to replicate viral nucleic acids and synthesize viral proteins (1).
    • Assembly/Release: New virions are assembled and released via lysis or budding (1).

14. Vectors (3m):

    • Definition: An organism (usually an arthropod) that transmits a pathogen from one host to another (1).
    • Example: Anopheles mosquito (1).
    • Mechanism: Transmits Plasmodium (malaria parasite) from an infected person to a healthy person during a blood meal (1).

15. Antibiotic Resistance (4m):

    • Variation exists in the bacterial population due to mutation (1).
    • Antibiotics act as a selection pressure, killing susceptible bacteria (1).
    • Resistant bacteria survive and reproduce (selection for the resistance allele) (1).
    • Over time, the frequency of the resistance gene increases in the population (1).

Section C: Integrated Physiology and Application

16. Inflammatory Response (3m):

    • Histamines are released, causing vasodilation (increased blood flow $\rightarrow$ redness) (1).
    • Increased capillary permeability allows plasma and phagocytes to enter the tissue (swelling) (1).
    • This concentrates immune cells at the site of infection to neutralize pathogens quickly (1).

17. MHC Molecules (3m):

    • MHC I molecules are present on all nucleated cells and present fragments of internal proteins (1).
    • If a cell is infected, it presents viral antigens on MHC I (1).
    • T-cell receptors (TCRs) recognize the specific antigen-MHC complex, triggering the T-cell to destroy the infected cell (1).

18. Autoimmune Disorders (4m):

    • Normally, the immune system is "tolerant" of self-antigens (1).
    • In autoimmune disorders, the system fails to distinguish between self and non-self (1).
    • B-cells/T-cells are activated against the body's own healthy tissues (1).
    • This leads to the production of auto-antibodies or T-cell attacks that damage organs (1).

19. Active vs Passive Vaccines (4m):

    • Active: Introduces antigens; stimulates the body to produce its own antibodies and memory cells (1). Example: MMR vaccine for long-term immunity (1).
    • Passive: Introduces pre-formed antibodies from another source (1). Example: Anti-tetanus serum for immediate protection during acute exposure (1).

20. Window Period (4m):

    • The window period is the time between initial infection and the production of detectable antibodies (1).
    • During this time, the primary immune response is still occurring (lag phase) (1).
    • An antibody test will return a "false negative" because antibody levels are below the detection threshold (1).
    • This is significant because the individual is infectious but believes they are negative (1).