Launching your learning experience…
Detailed notes on Diseases and Immunity for Cambridge IGCSE Biology, covering key concepts, explanations, examples, and exam-focused revision points.
How the body's immune system attacks pathogens that get past the barriers — and how vaccines hijack this system to prevent disease.
Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).
Phagocyte detects → engulfs → digests pathogen. Non-specific — works on any pathogen.
Step 1. Pathogen enters the body and releases chemicals (or its presence is detected by other immune signals).
Step 2. Phagocytes (a type of WBC) MIGRATE to the site.
Step 3. Phagocyte recognises the pathogen as foreign and EXTENDS its membrane around it.
Step 4. Pathogen is fully ENGULFED into a vesicle inside the cell.
Step 5. LYSOSOMES (full of enzymes) fuse with the vesicle. Enzymes DIGEST the pathogen.
Step 6. Some pathogen fragments are displayed on the phagocyte surface — alerts lymphocytes.
Why this is non-specific. Phagocytes don't 'know' the pathogen — they just detect anything that's foreign. Works on viruses, bacteria, dead cells, etc.
Worked qualitative. Why is pus yellow-white?
Cambridge tip. Memorise the two-stage process: ENGULF → DIGEST. Don't say phagocytes 'fight' or 'attack' — those are too vague.
Lymphocytes make Y-shaped proteins that lock onto one specific antigen.
Antigens. Markers (proteins or other molecules) on the SURFACE of a pathogen. Each pathogen has its own unique antigens — like a barcode.
Lymphocytes. White blood cells with receptors that match ONE specific antigen. The body has millions of different lymphocytes, each waiting to find its match.
The response:
What antibodies do:
Specificity.
Worked qualitative. Why does a cold last about a week?
Cambridge tip. Cambridge marks 'specific antibody' for each antigen. Don't say antibodies 'fight germs' generally — link each antibody to ONE antigen.
Vaccines train the immune system to respond fast to specific antigens — without making you sick.
The principle. Show the immune system the antigens of a pathogen WITHOUT actually infecting you.
What vaccines contain.
What happens after a vaccine:
On future exposure:
Boosters.
Herd immunity.
Worked qualitative. Why does vaccination wipe out diseases like smallpox?
Cambridge tip. When asked HOW a vaccine works, your answer MUST mention MEMORY CELLS. Without memory cells, the long-term immunity wouldn't exist.
Active = you make your own antibodies. Passive = you receive someone else's.
Active immunity.
Passive immunity.
Comparison.
| Feature | Active | Passive |
|---|---|---|
| Source of antibodies | Self-made | Received |
| Speed | Slow (1-2 weeks) | Immediate |
| Duration | Long (years/life) | Short (weeks/months) |
| Memory cells | Yes | No |
Worked qualitative. Why are babies often immune to diseases their mothers have had?
Cambridge tip. Cambridge often gives a scenario asking "is this active or passive?" The trick: ask "did the person make their own antibodies?". If yes → active. If received → passive.
Verbatim phrases and definitions Cambridge mark schemes credit.
Immunity appears every Paper 4 (8-12 marks). Common formats: phagocytosis steps, antibody action, vaccine mechanism, active vs passive. Examiner reports flag students forgetting memory cells in vaccine answers, and saying antibodies 'kill' pathogens directly.
Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (10.2-10.3); 0610/42 Oct/Nov 2024 — Q9 (immunity); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on immunity, written exactly the way a tutor would explain them at the board.
Question
Describe how a phagocyte destroys a pathogen.
Step-by-step solution
Step 1
The phagocyte (a white blood cell) moves towards the pathogen.
Step 2
It changes shape and engulfs the pathogen, taking it inside the cell.
Step 3
Enzymes inside the phagocyte then digest and destroy the pathogen.
Answer
The phagocyte engulfs the pathogen and digests it with enzymes (phagocytosis).
Question
State the difference between active and passive immunity, giving an example of each.
Step-by-step solution
Step 1
Active immunity is gained when the body makes its own antibodies in response to an antigen — for example after an infection, or after vaccination.
Step 2
Passive immunity is gained when antibodies made by another organism are received — for example a baby receiving antibodies from its mother across the placenta or in breast milk.
Step 3
Active immunity is long-lasting (memory cells are made); passive immunity is short-lived (no memory cells).
Answer
Active: the body makes its own antibodies (from infection or vaccination); long-lasting. Passive: antibodies received from another (e.g. mother to baby); short-lived.
Examiner tip
The key difference is who makes the antibodies — your own body (active) or another organism (passive).
Question
Explain how lymphocytes respond to a pathogen using antibodies.
Step-by-step solution
Step 1
Each pathogen carries antigens (markers) on its surface, and a lymphocyte with a complementary shape recognises them.
Step 2
That lymphocyte divides rapidly to make many copies of itself.
Step 3
These cells produce large amounts of antibody — proteins with a shape specific to that antigen.
Step 4
The antibodies bind to the pathogens, clumping them together and marking them so phagocytes destroy them (some also neutralise toxins). Some lymphocytes remain as memory cells.
Answer
A lymphocyte recognises the antigen, divides, and produces specific antibodies that clump and mark the pathogens for destruction. Memory cells remain for the future.
Question
Explain why an antibody made against one pathogen does not work against a different pathogen.
Step-by-step solution
Step 1
Each pathogen has its own antigens with a particular shape on its surface.
Step 2
An antibody has a shape that is complementary to one specific antigen, so it fits that antigen like a key in a lock.
Step 3
A different pathogen has different antigens with a different shape.
Step 4
The first antibody does not fit the new antigen, so it cannot bind to it — the body must make a different, specific antibody for each pathogen.
Answer
Antibodies have a shape complementary to one specific antigen. A different pathogen has differently-shaped antigens that the antibody cannot fit, so a new antibody is needed.
Examiner tip
The complementary shape (lock-and-key) of antibody and antigen is the key idea for specificity.
Question
Explain how a vaccine makes a person immune to a disease.
Step-by-step solution
Step 1
A vaccine contains a weakened or dead pathogen, or its antigens, which cannot cause the disease.
Step 2
The antigens are recognised by lymphocytes, which divide and produce antibodies against them.
Step 3
Some of these lymphocytes remain in the blood as memory cells.
Step 4
If the real pathogen later enters the body, the memory cells produce the correct antibodies very quickly and in large amounts, destroying the pathogen before it can cause illness — so the person is immune.
Answer
A vaccine introduces harmless antigens; lymphocytes make antibodies and memory cells. On real infection, the memory cells respond quickly, destroying the pathogen before symptoms develop — giving immunity.
Examiner tip
'Memory cells' and the fast secondary response are the marking points. Vaccines PREVENT, not cure.
Question
A graph shows that the second time a person meets a pathogen, antibodies are produced faster and in much greater amounts than the first time. Explain why.
Step-by-step solution
Step 1
On the first exposure, only a few lymphocytes can recognise the new antigen, so it takes time for them to divide and produce antibodies — the response is slow and small (the primary response).
Step 2
After this, some lymphocytes remain as memory cells.
Step 3
On the second exposure, these memory cells recognise the antigen immediately and divide quickly.
Step 4
So antibodies are produced much faster and in far greater amounts (the secondary response), destroying the pathogen before it causes illness — the person is immune.
Answer
The first response is slow and small because few lymphocytes match the antigen, but memory cells remain. On the second exposure these respond at once, so antibodies are made faster and in greater amounts — giving immunity.
Examiner tip
Compare the two responses (slow/small vs fast/large) and explain the difference using memory cells.
High-scoring sample answers for immunity on the Cambridge IGCSE 0610 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
State what is meant by an antigen. (1 mark)
Model answer
An antigen is a molecule (often a protein) on the surface of a pathogen that the immune system recognises as foreign.
Why this scores
One mark for 'a marker/protein on a pathogen recognised by the immune system'.
State two ways in which antibodies help to destroy pathogens. (2 marks)
Model answer
Antibodies can clump the pathogens together (agglutination) so phagocytes can engulf them more easily, and they can mark the pathogens for destruction by phagocytes. (Neutralising the toxins they release is also accepted.)
Why this scores
Any two of: clump/agglutinate; mark for phagocytes; neutralise toxins.
Describe how a phagocyte destroys a pathogen (phagocytosis). (3 marks)
Model answer
The phagocyte moves towards the pathogen and engulfs it, taking it inside the cell. Enzymes within the phagocyte then digest and destroy the pathogen.
Why this scores
Three marks: moves towards/recognises pathogen; engulfs it; digests it with enzymes.
Explain how vaccination gives a person immunity to a disease. (4 marks)
Model answer
A vaccine contains weakened or dead pathogens, or their antigens, which cannot cause the disease. These antigens are recognised by lymphocytes, which divide and produce antibodies. Some lymphocytes remain as memory cells. If the real pathogen later enters the body, the memory cells respond quickly, producing antibodies fast and destroying the pathogen before it causes illness.
Why this scores
Four marks: vaccine contains weakened pathogen/antigens; lymphocytes make antibodies; memory cells produced/remain; fast response on real infection.
Explain how lymphocytes respond when a pathogen carrying a new antigen enters the body. (5 marks)
Model answer
A lymphocyte that has a shape complementary to the antigen on the pathogen recognises it and binds to it. This lymphocyte then divides rapidly to produce many identical cells. These cells produce large numbers of antibodies that are specific to that antigen. The antibodies attach to the pathogens, clumping them together and marking them so that phagocytes can engulf and destroy them (and neutralising any toxins). Some of the lymphocytes remain in the body as memory cells, ready to respond quickly if the same pathogen returns.
Why this scores
Five marks: specific lymphocyte recognises the antigen; divides/clones; produces specific antibodies; antibodies clump/mark pathogens for destruction; memory cells remain.
Explain why the body's response to a pathogen is faster and larger the second time it is infected with the same pathogen, and why this makes the person immune. (6 marks)
Model answer
When the pathogen enters for the first time, only a few lymphocytes have the right shape to recognise its antigen, so they must first divide before they can produce antibodies. This makes the first (primary) response slow, and only a small amount of antibody is made — so the person may become ill. After this response, some of the lymphocytes remain in the blood as long-lived memory cells. When the same pathogen enters again, these memory cells recognise the antigen immediately and divide very quickly, producing the correct antibodies much faster and in much greater amounts (the secondary response). The pathogen is therefore destroyed before it can multiply enough to cause illness, so the person does not become ill — they are immune. This is why a vaccine, which causes memory cells to be made without causing the disease, can give long-lasting protection.
Why this scores
Up to 6 marks: first exposure — few matching lymphocytes, slow/small response; memory cells produced and remain; second exposure — memory cells recognise antigen at once; faster and larger antibody production; pathogen destroyed before illness; person is immune.
Definitions to memorise and the exact keywords mark schemes credit for immunity answers — sharpened from recent examiner reports for the 2026 0610 sitting.
A molecule (often a protein) on the surface of a pathogen that the immune system recognises as foreign. Each pathogen has its own antigens.
A protein produced by lymphocytes that binds specifically to one antigen — clumping pathogens, marking them for destruction, or neutralising their toxins.
A preparation containing weakened or dead pathogen (or its antigens) used to trigger an immune response and create immunity.
A long-lived lymphocyte made after an immune response. It triggers a faster, larger response if the same pathogen returns.
Immunity gained when the body makes its own antibodies — from infection (natural) or vaccination (artificial). Long-lasting because memory cells are made.
Immunity gained from antibodies made by another organism — e.g. across the placenta or in breast milk. Short-lasting; no memory cells.
The traps other students keep falling into on immunity questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.
Why it happens
Vaccines protect against diseases.
How to avoid it
Vaccines PREVENT disease; they do not cure it. They are given BEFORE infection to prime the immune system.
Why it happens
They are seen as the 'killer molecule'.
How to avoid it
Antibodies mark/clump pathogens or neutralise toxins; phagocytes then destroy them. Antibodies usually do not kill directly.
Why it happens
The injection is quick.
How to avoid it
It takes time (days to weeks) for the body to make enough antibodies and memory cells; some vaccines need booster doses.
The things students keep getting wrong in this sub-topic, answered.