Cambridge numbers all of this as a single section, 10.1; the split into 10.1–10.5 on this site is mine, for teaching. The content is identical. Topic 10 has fewer facts in it than any other topic you have done, and it produces more wrong answers per fact than any of them, because two words that differ by three letters mean opposite things. An antigen is on the pathogen. An antibody is made by your lymphocyte. A vaccine contains antigens, never antibodies. Passive immunity is the fast one and the one with no memory cells. The cholera toxin moves chloride ions, and the water follows by osmosis on its own. Twelve traps, six walkthroughs, six lookalike pairs, a concept map and ten full practice questions below — every one aimed at a place where a confident, fluent sentence earns nothing.
Twelve traps that cost marks on Topic 10 challenge papers. Every one is an answer that sounds right and that mark schemes refuse.
Six challenge-level questions worked through in the order you should actually think about them. Try each part before revealing the next step.
Do not merge them. The second response is faster (measurable antibody within 4 days against 8 days), larger (peak 96 against peak 11, roughly nine times higher) and it lasts longer (still 74 at day 70, whereas the first had fallen to 2 by day 38). Quote at least two pairs of figures — describing with data is very often a mark on its own.
The first exposure produced antibodies and memory cells. On the second exposure the memory cells recognise the same antigen immediately, so there is almost no lag, and antibodies are produced faster and in much greater quantity. That single cause explains all three differences, which is why a three-mark explain question is not asking for three different reasons.
Antigen Y has a different shape, so the memory cells for X cannot recognise it. The response to Y will be a primary response — slow, small, several days of lag — even though it is happening at the same moment as a vigorous secondary response to X in the same bloodstream. Two entirely different curves, in one person, at one time.
If your answer to a describe question contains the word lymphocyte, you have answered the wrong question; if your answer to an explain question contains only numbers, you have done the same in reverse. Read the command word, then choose your vocabulary from it.
Group 2 shows what happens without the vaccine, so 174 out of 200 gives you the baseline the vaccine must beat — without it, 6 out of 200 means nothing. It also controls for the injection itself, since the mice were injected with salt solution rather than left alone. Group 3 shows that the vaccine does not itself cause the disease, which is the whole claim behind the word weakened.
Group 4 received ready-made antibodies from another individual, which is the definition of passive immunity. Protection was immediate — only 11 fell ill on the same day, better even than the vaccine group. Three months later 168 fell ill, because the antibodies had been broken down and no memory cells were produced, so nothing replaced them.
Memory cells are produced by lymphocytes stimulated by an antigen. Group 4 received only antibodies; no antigen entered until the exposure, by which time the borrowed antibodies were destroying the bacteria before the mouse’s own lymphocytes had much to respond to. The comparison with group 1, whose protection was still working, is the point of the whole experiment.
Mice are a different species, so their immune response and the dose that protects them may differ from a human’s. The mice were also all exposed under controlled laboratory conditions to one measured dose, which is not how people meet a pathogen. Notice that “only 200 mice” is a weak answer here — 200 is a decent sample, and the difference between 6 and 174 is enormous.
84 units at birth, with no rise before it, means these antibodies were not made by this baby. They came from another individual — the mother — which is the definition of passive immunity. The two routes named by the syllabus are across the placenta before birth and in breast milk afterwards.
Antibodies are proteins and are gradually broken down. That alone is not the answer; the answer is why nothing replaces them. No memory cells were produced, because no antigen ever entered the baby — only finished antibodies did — so the baby’s lymphocytes were never stimulated and produce none of their own.
The vaccine supplied antigens, which stimulated the baby’s own lymphocytes to produce antibodies — this is active immunity — and, crucially, memory cells. The memory cells persist, so the concentration is maintained at 39 a year later, and a later encounter with real measles would produce a fast, large secondary response.
Between the passive protection running out and the vaccination taking effect, the baby is genuinely unprotected. That is exactly the argument for why vaccination programmes start early and why they matter most where a disease is common — and it is a two-mark suggest question waiting to be asked.
Change = 62.0 − 55.4 = 6.6 kg. Original = 62.0, the mass before the illness, not 55.4. So 6.6 ÷ 62.0 × 100 = 10.6 %. Show the working: the method mark is awarded separately from the value, and dividing by the final mass would give 11.9 %, which is a wrong answer with no working to rescue it.
The bacterium releases a toxin; the toxin causes the cells lining the small intestine to secrete chloride ions into the gut; the gut contents therefore have a lower water potential than the blood and cells; so water moves in by osmosis, through partially permeable membranes, from higher to lower water potential. Four links, four marks, and no link may be skipped.
Chloride is at 104 mmol per dm³ in the fluid against 100 in plasma, and sodium is at 128, so the patient has lost ions in a concentration similar to or higher than that of the blood. Over 11.4 dm³ that is an enormous quantity of ions. Replacing the volume with pure water would leave the plasma too dilute, so the drink must contain ions as well.
A very strong answer adds the consequence: if the plasma became too dilute, its water potential would rise relative to the cells, and water would move into the body cells by osmosis. You are being rewarded for using Topic 3 twice in one question, in opposite directions.
41 ÷ 2 = 20.5 times. Check the direction before writing: the river group has the larger rate, so the answer must be greater than 1. Ratios inverted by accident are one of the commonest single-mark losses in data questions.
This is cholera: a bacterium transmitted in contaminated water. Saying so early is worth doing, because everything that follows then has a name. The sewage outflow upstream of the collection point is the source — the bacterium leaves an infected person in the faeces and re-enters someone else in the drinking water.
River users take water directly downstream of untreated sewage, so their exposure is highest at 41. Piped treated water contains no pathogens, so 2 per 1000 is near-background. The well at 18 is the interesting one: it is covered, so it is not receiving sewage directly, but it is not treated either and can be contaminated by seepage, by dirty containers or by hands. A good answer says why the middle group is in the middle.
All three groups used the same market, yet their case rates differ twenty-fold. So the market cannot explain the pattern, and closing it would not end the outbreak. Be fair to the councillor, though: food washed in river water could still spread the bacterium, so hygienic food preparation is worth doing — it is simply not the main route. Conclude clearly: treat the sewage and the water supply first.
(i) A bat bite: the animal is the intermediate, so this is indirect transmission by an animal. (ii) The sap: contaminated food or drink, so indirect. (iii) Contact with a patient’s saliva: a body fluid passing with nothing in between, so direct. Do not be distracted by which route sounds most dangerous; the classification depends only on whether there was an intermediate.
The molecules on the surface of the virus are its antigens, and they have specific shapes. Lymphocytes are stimulated by them and produce antibodies with a complementary shape, which bind to the antigens; the virus is then destroyed directly or marked for destruction by phagocytes. Memory cells are also produced, giving long-term immunity to anyone who recovers.
Do not reach for a vaccine — the stem says there is not one. The measures must close the routes given: do not drink raw sap, or cover the collecting pots so bats cannot reach them (closing the contaminated-food route), and use gloves and wash hands when caring for a patient (closing the direct body-fluid route). Each measure must be paired with the route it closes; a bare list of measures scores badly.
You have never met this disease and you did not need to. Read the stem for the transmission route, classify it, then take the matching measure from the syllabus list of five. Every applied question in Topic 10 is built this way, which is why 10.1 is worth far more attention than its length suggests.
Six pairs that look almost identical and have different answers. The distinction is where the marks live.
Click each node to see how the sub-topics connect into one story: an organism, a journey, a shape, and a memory.
Six real student answers. Find the fault before you reveal it.
Ten Cambridge-style challenge questions. Write your answer first, then reveal the model answer and the examiner’s notes.