QCE Biology — Unit 2
Immune Response — Flashcards & Quiz
QCE Biology Unit 2 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 2 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.
Sample Flashcards
Q1: What is a pathogen, and what distinguishes the major groups?
A pathogen is an organism or agent that causes disease in a host. Bacteria are single-celled prokaryotes that can reproduce independently and are often treatable with antibiotics. Viruses are not cellular and must use a host cell to replicate, so antibiotics do not affect them. Fungi and protists are eukaryotes causing infections such as thrush and malaria, while prions are misfolded proteins that induce misfolding in others.
Q2: List the main modes of pathogen transmission.
Direct contact transmits pathogens between individuals by touch or bodily fluids. Droplet and airborne routes carry pathogens in exhaled droplets or suspended particles. Vehicle transmission occurs through contaminated food, water or objects. Vector transmission uses another organism, commonly an insect, to carry the pathogen between hosts. Vertical transmission passes a pathogen from parent to offspring before or during birth.
Q3: What makes up the first line of defence?
The first line is a set of non-specific barriers that prevent pathogens entering the body at all. It includes the physical barrier of intact skin, mucus that traps particles and cilia that sweep them away, and chemical defences such as stomach acid, lysozyme in tears and saliva, and sebum on the skin. Beneficial resident microorganisms also compete with incoming pathogens for space and nutrients.
Q4: What characterises the second line of defence?
The second line is the innate internal response, which acts against any pathogen that breaches the barriers without distinguishing between species. It includes inflammation, phagocytosis by cells such as macrophages and neutrophils, fever, the complement system of blood proteins, and natural killer cells that destroy infected body cells. It responds within minutes to hours but generates no lasting memory.
Q5: Describe the inflammatory response and its purpose.
Damaged cells and mast cells release chemical signals including histamine, which cause nearby arterioles to dilate and capillaries to become more permeable. Increased blood flow produces redness and heat, while fluid leaving the capillaries causes swelling and, with the chemicals released, pain. The purpose is to deliver phagocytes and defensive proteins to the site quickly and to restrict the spread of the pathogen.
Sample Quiz Questions
Q1: Antibiotics are effective against viral infections.
Answer: FALSE
Viruses are not cellular and lack the structures antibiotics target, so antibiotics have no effect on them. They act against bacteria.
Q2: Malaria is transmitted by a vector.
Answer: TRUE
Correct. It is carried between hosts by mosquitoes, which is why control focuses on removing breeding sites and preventing bites.
Q3: Stomach acid and lysozyme in tears are part of the first line of defence.
Answer: TRUE
Correct. The first line includes chemical as well as physical barriers, all acting to prevent pathogens entering the body.
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.
Related Concepts
Last updated: March 2026 · 20 flashcards · 20 quiz questions