QCE Biology — Unit 3
Immune Response — Flashcards & Quiz
QCE Biology Unit 3 asks you to describe how the immune system protects against pathogens and produces long-term memory. You need to distinguish the three lines of defence: physical/chemical barriers, the innate inflammatory response, and the adaptive response driven by B and T lymphocytes. The clonal selection model and the speed difference between primary and secondary responses are high-yield exam content.
Key Points
- First line: physical and chemical barriers — skin, mucus, stomach acid, tears, cilia.
- Second line (innate): inflammation, fever, phagocytosis, complement system, natural killer cells — fast but non-specific.
- Third line (adaptive): B lymphocytes produce antibodies, T lymphocytes coordinate and kill infected cells. Slow but specific and generates memory.
- Clonal selection: a specific B or T cell is activated by an antigen that matches its unique receptor, then proliferates into plasma/effector and memory cells.
- Primary response is slow (days) with modest antibody levels; secondary response is fast (hours) with much higher levels due to memory cells.
- Vaccination trains the adaptive system by exposing it to antigen without causing disease, generating memory cells for future encounters.
Common Mistakes to Avoid
- Confusing innate immunity (fast, non-specific) with adaptive (slow, specific, memory).
- Mixing up B cells (antibody-secreting) with T cells (cellular immunity).
- Claiming antibodies directly kill pathogens — they tag them for destruction by phagocytes or complement.
- Forgetting memory cells are the key difference between primary and secondary responses.
- Stating that natural killer cells are part of adaptive immunity — they're innate.
Exam Strategy
QCAA Unit 3 immune response questions usually give you a pathogen scenario (bacterial infection, viral outbreak) and ask you to describe the layered response. Structure: (1) first line (barriers), (2) second line (innate inflammation/phagocytosis), (3) third line (adaptive with B and T cells). Then add a graph or curve showing primary vs secondary response to demonstrate the memory effect. Naming specific cell types (helper T cells, cytotoxic T cells, plasma cells) separates strong from average responses.
Revision Tip
The three lines of defence and the primary-secondary response curve are recall-heavy — build a Revizi deck that asks you to name cells, functions, and the curve axes from memory.
Last updated: March 2026