A Level H1 Biology Human Physiology Quiz

Answer Key - A-Level Biology H1 Quiz (Human Physiology)

1. Role of phagocytes: To engulf and digest pathogens/foreign particles via phagocytosis. [1]

2. Antigen presentation:

   • Phagocyte/Dendritic cell engulfs pathogen and digests it. [1]
   • Fragments of the pathogen's antigen are displayed on the cell surface using MHC molecules. [1]
   • This allows T-lymphocytes with complementary receptors to recognize the antigen. [1]

3. Primary vs Secondary Response:

   • Primary: Slower response (lag phase) as B-cells must be activated and proliferate; lower antibody concentration. [1.5]
   • Secondary: Faster response due to presence of memory cells; significantly higher antibody concentration. [1.5]

4. Antigen:

   • Definition: A molecule (usually a protein or polysaccharide) that triggers an immune response. [1]
   • Location: On the surface of the pathogen (e.g., viral envelope or bacterial cell wall). [1]

5. B-lymphocytes:

   • B-cells are activated by antigens (and cytokines from T-cells). [1]
   • They differentiate into plasma cells. [1]
   • Plasma cells secrete large quantities of soluble antibodies specific to the antigen. [1]

6. Vaccination:

   • Introduction of weakened/killed pathogens or antigens into the body. [1]
   • Triggers a primary immune response without causing disease. [1]
   • Leads to the production of memory B-cells and T-cells. [1]
   • Upon subsequent exposure to the real pathogen, a rapid secondary response occurs, neutralizing the pathogen before symptoms appear. [1]

7. IgG vs IgA:

   • IgG: Found in blood/tissue fluid; provides systemic immunity and can cross the placenta. [1]
   • IgA: Found in secretions (saliva, mucus, breast milk); provides mucosal immunity. [1]

8. Long-term immunity:

   • Production of long-lived memory cells during the first infection. [1]
   • These cells "remember" the specific antigen. [1]
   • They allow for a rapid and massive production of antibodies upon re-infection. [1]

9. Neutralization:

   • Antibodies bind to the active site or surface of the toxin. [1]
   • This prevents the toxin from binding to its target receptor on the host cell, rendering it harmless. [1]

10. Helper T-cells:

    • Recognize antigens presented by APCs. [1]
    • Secrete cytokines/interleukins. [1]
    • These chemicals activate B-cells to produce antibodies and Cytotoxic T-cells to kill infected cells. [1]

11. Tuberculosis:

    • Pathogen: Bacterium (Mycobacterium tuberculosis). [1]
    • Characteristic: Acid-fast cell wall / slow growing / aerobic. [1]

12. Antibiotics vs Viruses:

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

13. Water-borne transmission:

    • Route: Ingestion of contaminated water (fecal-oral route). [1]
    • Prevention: Water filtration, chlorination, or boiling water. [1]

14. Viral entry:

    • Viral surface proteins (ligands) bind to specific complementary receptors on the host cell membrane. [1]
    • This triggers endocytosis or direct fusion of the viral envelope with the membrane. [1]
    • The viral genome is then released into the cytoplasm. [1]

15. Antimicrobial resistance:

    • Overuse/misuse of antibiotics leads to natural selection. [1]
    • Bacteria with resistance mutations survive and reproduce. [1]
    • This results in "superbugs" that cannot be killed by standard drugs. [1]
    • Treatment requires more expensive, toxic, or rare "last-resort" antibiotics. [1]

16. Location: Mitochondrial matrix. [1]

17. Oxygen in ETC:

    • Oxygen acts as the final electron acceptor. [1]
    • It combines with electrons and protons to form water. [1]
    • Without oxygen, the ETC stops, NADH/FADH2 cannot be oxidized, and ATP synthesis via chemiosmosis ceases. [1]

18. NADH/FADH2:

    • They act as electron carriers. [1]
    • They transport high-energy electrons from glycolysis/Krebs cycle to the electron transport chain. [1]

19. Lactic acid:

    • During intense exercise, oxygen supply is insufficient (hypoxia). [1]
    • Pyruvate is converted to lactate to regenerate $\text{NAD}^+$. [1]
    • This allows glycolysis to continue producing a small amount of ATP in the absence of oxygen. [1]

20. ATP Yield:

    • Aerobic: High yield (approx. 30-32 ATP per glucose). [1]
    • Anaerobic: Low yield (net 2 ATP per glucose). [1]