Immunity & Disease is a core part of A-Level Biology. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
Active immunityBody makes its own antibodies — slow but long-lasting
Passive immunityAntibodies received from another source — fast but short-lived
VaccineDose of antigen (dead/attenuated/subunit) triggering active immunity
Herd immunitySufficient vaccinated proportion stops pathogen circulating
Antibiotic resistanceBacteria with resistance allele survive antibiotic; selected
MRSAMethicillin-resistant Staphylococcus aureus — example of resistant strain
Helper T cell (Th)Binds antigen-presenting cells; releases cytokines to activate B and Tc cells
Cytotoxic T cell (Tc)Kills infected body cells by releasing perforin
B cellLymphocyte that displays antibodies; clonal selection on antigen binding
Plasma cellActivated B cell that secretes thousands of antibodies per second
Memory cellLong-lived clone that responds rapidly to repeat infection
AntibodyY-shaped protein with variable regions specific to one antigen
PathogenDisease-causing organism (bacterium, virus, fungus, protist)
AntigenMolecule on a cell that triggers an immune response
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
How do vaccines protect you from a disease?✗ Vaccines kill the pathogen if it ever enters the body. ✓ They expose your immune system to a harmless form of the pathogen so memory cells form, allowing rapid response if exposed later.
Why is the secondary immune response to a pathogen faster and stronger than the primary?✗ The pathogen becomes weaker after the primary exposure, so the body has an easier job. ✓ Memory cells generated during the primary response can rapidly proliferate and produce large amounts of specific antibody on re-exposure.
What is actually transferred to the body when you get a vaccine?✗ Vaccines inject ready-made antibodies directly into the bloodstream. ✓ Antigens (often from weakened, dead, or fragmented pathogens) that train the immune system to make memory cells.
How do bacteria become resistant to an antibiotic?✗ They learn to resist ✓ Random mutations conferring resistance are selected for
What is the main role of B-cells compared to T-cells?✗ B-cells and T-cells both produce antibodies in equal amounts. ✓ B-cells produce antibodies (humoral response); T-cells coordinate the immune response and kill infected cells (cell-mediated response).
Practise Immunity & Disease — free games
Test yourself with these quick revision games for this topic:
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