Adaptive immunity, antibodies and memory
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Question
What does 'specific' (adaptive) immunity mean?
Answer
Immunity that targets **one particular pathogen**, recognised by its **antigen** — unlike the non-specific skin and phagocytes.
Question
Define an antigen.
Answer
A molecule (usually on a pathogen's surface) that the immune system **recognises as foreign** and responds to.
Question
Which white blood cells carry out the adaptive response?
Answer
**Lymphocytes** — mainly **B-cells** and **T-cells**.
Question
What is the main function of a helper T-cell?
Answer
To **activate other immune cells**, especially the **B-cells** — it does **not** make antibodies itself.
Question
Which cells actually make antibodies?
Answer
**B-cells** (which become **plasma cells**) once they have been activated.
Question
What event triggers antibody production?
Answer
A **lymphocyte detecting the antigen** of an invading pathogen.
Question
Describe the shape of an antibody and what its tips do.
Answer
An antibody is a **Y-shaped protein**; the **tips of its arms** are **antigen-binding sites** (the variable region) that fit one antigen.
Question
Why does one antibody bind only one pathogen?
Answer
Its binding sites are a **specific shape, complementary to one antigen** — like a key that fits only one lock.
Question
What is a memory cell?
Answer
A **long-lived lymphocyte** kept after an infection, giving a **faster, stronger** response if the same pathogen returns.
Question
Why is the secondary response faster and larger than the primary?
Answer
**Memory cells** from the first exposure recognise the antigen **immediately**, so antibodies are made **faster and in greater amounts**.
Question
Compare the primary and secondary response on a graph.
Answer
Primary: a **slow, late, low** curve. Secondary: a **fast, early, much higher** curve.
Question
If a person's blood shows no antibodies before vaccination, what can you conclude?
Answer
They have had **no prior exposure** to that antigen — no previous infection or vaccination against it.
Question
Which defences are non-specific (innate)?
Answer
The **skin** barrier and **phagocytes** (phagocytosis) — they attack any pathogen the same way, with no memory.
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Topic 3.7 hub
Defence against infectious disease
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