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school. “Paper 42” means Paper 4, variant 2.
Practice questions
Original questions written by HomiLabs in the style of the exam, with answers and mark schemes. They are not
Cambridge past paper questions and have not been reviewed by Cambridge. Try each one before opening the answer.
Q1Medicinal drugs & antibiotics · Core · Paper 1 style · 1 mark
(a)Which is the best definition of a drug?[1]
Show answer
(a) B any substance taken into the body that modifies or affects chemical reactions in the body
A drug is any substance taken into the body that modifies or affects chemical reactions in the body; this covers medicines and misused drugs. A is too narrow because it describes only antibiotics.
Q2Medicinal drugs & antibiotics · Core · Paper 1 style · 1 mark
(a)For which disease would a course of antibiotics NOT be effective?[1]
Show answer
(a) B influenza
Influenza is caused by a virus, and antibiotics do not affect viruses. Cholera, tuberculosis and typhoid are bacterial diseases, so the other options are treated with antibiotics.
Q3Medicinal drugs & antibiotics · Core · Paper 4 style · 5 marks
(a)Explain why the inoculating loop is heated in a Bunsen flame until it glows red before and after use.[1]
(b)Explain why the lid of the Petri dish is held with two short pieces of tape and not sealed all the way round.[2]
(c)Explain why plates in a school laboratory are incubated at 25 °C and not at 37 °C.[1]
(d)Explain why the plates must not be opened after incubation.[1]
Show answer
(a) To kill any microorganisms on it, so the plate is not contaminated (and no bacteria escape afterwards).
B1.
(b) Oxygen can still enter, so harmful anaerobic bacteria are not encouraged to grow; the lid cannot be opened accidentally.
B1 allows oxygen in / prevents anaerobic conditions; B1 lid stays shut.
(c) At 37 °C (body temperature) bacteria that cause disease in humans could grow.
B1.
(d) Large numbers of bacteria have grown, which could include harmful ones; opening would release them.
B1.
Q4Medicinal drugs & antibiotics · Core · Paper 2 style · 4 marks
(a)State what an antibiotic is.[1]
(b)A patient with a cold asks a doctor in Islamabad for antibiotics. The doctor refuses. Explain why.[2]
(c)Name the type of organism from which penicillin was first obtained.[1]
Show answer
(a) A drug (medicine) that kills bacteria or stops their growth.
B1.
(b) Colds are caused by viruses; antibiotics do not affect viruses (they work on structures / processes found in bacteria), so they would not help and would increase the risk of resistance.
B1 cold caused by virus; B1 antibiotics have no effect on viruses (or unnecessary use leads to resistance).
(c) a fungus (mould), Penicillium
B1.
Q5Medicinal drugs & antibiotics · Core · Paper 2 style · 5 marks
(a)Antibiotics can kill bacteria inside the human body without harming human cells. Suggest why.[1]
(b)State two examples of medicinal drugs other than antibiotics and what each is used for.[2]
(c)Explain why antibiotics should not be shared with a friend who has similar symptoms.[2]
Show answer
(a) They act on structures or processes found in bacterial cells but not in human cells, such as the bacterial cell wall.
B1.
(b) e.g. painkillers (paracetamol) to relieve pain / fever; insulin to treat diabetes. Any two medicinal drugs with a correct use.
B1 each drug with correct use.
(c) The friend's illness may be caused by a virus or a different bacterium; the dose may be wrong; incomplete courses for both encourage resistance.
B1 each for any two.
Q6Medicinal drugs & antibiotics · Core · Paper 2 style · 4 marks
(a)Poultry farms sometimes add small amounts of antibiotics to chicken feed to keep the birds healthy and growing quickly. Explain why this practice can be a risk to human health.[3]
(b)Suggest one alternative way the farmer could keep the chickens healthy.[1]
Show answer
(a) Constant low doses kill susceptible bacteria and select for resistant ones; resistant bacteria multiply in the chickens; they can pass to humans through meat or the environment, so human infections become harder to treat.
B1 selection for resistance; B1 resistant bacteria increase in the animals; B1 transfer to humans / antibiotics less effective for people.
(b) Vaccinate the birds; keep sheds clean; give birds more space; use antibiotics only to treat sick birds.
B1.
Q7Medicinal drugs & antibiotics · Core · Paper 2 style · 4 marks
(a)State what is meant by an antibiotic-resistant bacterium.[1]
(b)Give two reasons why antibiotic resistance is a serious problem for the world.[2]
(c)Suggest why some antibiotics are kept by doctors only for patients for whom other antibiotics have failed.[1]
Show answer
(a) A bacterium that is not killed (and keeps growing) when exposed to the antibiotic.
B1.
(b) Infections that were easy to treat may become untreatable; more people die / stay ill longer; surgery and cancer treatment become riskier; few new antibiotics are being discovered; more expensive treatments needed.
B1 each for any two.
(c) If used rarely, bacteria are less likely to become resistant to them, so they keep working.
B1.
Q8Medicinal drugs & antibiotics · Core · Paper 2 style · 4 marks
(a)Bilal has a painful tooth infection caused by bacteria. His dentist gives him paracetamol and an antibiotic. State the purpose of each drug.[2]
(b)Explain why the paracetamol alone would not cure the infection.[1]
(c)The dentist tells Bilal to take the antibiotic at regular times each day. Suggest why.[1]
Show answer
(a) Paracetamol: a painkiller that relieves the pain (a symptom). Antibiotic: kills the bacteria causing the infection (or stops their growth).
(b) It only reduces pain; it does not kill the bacteria.
B1.
(c) To keep the concentration of antibiotic in the blood high enough to kill the bacteria all the time.
B1.
Q9Medicinal drugs & antibiotics · Standard · Paper 1 style · 1 mark
(a)Paper discs soaked in four different antibiotics were placed on agar covered with the same bacteria. After incubation the diameters of the clear zones were:W: 8 mmX: 22 mmY: 15 mmZ: no clear zoneWhich antibiotic would be most useful against these bacteria?[1]
Show answer
(a) B X
The largest clear zone shows that the most bacteria were killed or stopped from growing, so X is most effective. Z had no clear zone; the bacteria are resistant to it.
Q10Medicinal drugs & antibiotics · Standard · Paper 1 style · 1 mark
(a)Which sequence describes how a population of bacteria becomes resistant to an antibiotic?[1]
Show answer
(a) B random mutation gives resistance → antibiotic kills non-resistant bacteria → resistant bacteria reproduce
Resistance arises by random mutation; the antibiotic acts as a selection pressure, so resistant bacteria survive and reproduce (natural selection). A is wrong because bacteria do not 'learn' resistance; it is genetic.
Q11Medicinal drugs & antibiotics · Standard · Paper 4 style · 8 marks
A student spread a harmless bacterium on a nutrient agar plate and placed five paper discs (6 mm diameter) on it. Four discs were soaked in different antibiotics and one in sterile water. After two days at 25 °C the diameters of the clear zones were measured.penicillin 26 mm; streptomycin 18 mm; tetracycline 30 mm; erythromycin 12 mm; sterile water: no clear zone beyond the disc.
(a)Calculate the area of the clear zone around each antibiotic disc in mm², using area = πr². Give each answer to the nearest whole number.[3]
(b)Rank the antibiotics from most to least effective against this bacterium.[1]
(c)Explain the purpose of the disc soaked in sterile water.[2]
(d)State two precautions the student should take to avoid contaminating the plate or himself.[2]
(c) It is a control; it shows that the clear zones are caused by the antibiotics and not by the paper disc or the water.
B1 control; B1 shows effect is due to antibiotic.
(d) Flame the forceps / loop; open the lid only slightly and briefly; tape the lid (do not seal fully) and do not open after incubation; wash hands; incubate at no more than 25 °C.
B1 each for any two.
Q12Medicinal drugs & antibiotics · Standard · Paper 2 style · 6 marks
(a)Explain how the use of an antibiotic can lead to a population of bacteria that is resistant to it.[4]
(b)Explain why bacteria can become resistant much faster than animals become adapted to a new condition.[2]
Show answer
(a) A random mutation makes some bacteria resistant; the antibiotic kills the non-resistant bacteria; the resistant bacteria survive and reproduce; the resistance gene is passed on so the proportion of resistant bacteria rises (natural selection).
B1 mutation / variation; B1 non-resistant killed; B1 resistant survive and reproduce; B1 allele / gene passed on, population becomes resistant.
(b) Bacteria reproduce very quickly (some divide every 20 minutes), so many generations occur in a short time; large populations mean more mutations.
B1 rapid reproduction / short generation time; B1 large numbers so more mutations.
Q13Medicinal drugs & antibiotics · Standard · Paper 2 style · 6 marks
(a)MRSA is a type of bacterium found in some hospitals. State what is unusual about MRSA.[1]
(b)Describe three ways in which doctors, hospitals and patients can reduce the development and spread of antibiotic-resistant bacteria.[3]
(c)Suggest why antibiotic resistance is a bigger danger in hospitals than in most homes.[2]
Show answer
(a) It is resistant to many (most commonly used) antibiotics.
B1.
(b) Only prescribe antibiotics when needed (not for viral infections); patients complete the course; use a range of different antibiotics; good hygiene such as hand washing and cleaning wards; isolate infected patients.
B1 each for any three.
(c) Many patients are ill or have weak immune systems; antibiotics are used a lot so resistant bacteria are selected; bacteria spread easily between patients.
B1 each for any two.
Q14Medicinal drugs & antibiotics · Standard · Paper 2 style · 6 marks
(a)A bacterium divides into two every 20 minutes. Starting with one bacterium, calculate how many there would be after 3 hours if none die.[2]
(b)In a patient's gut there are 5 × 10⁹ bacteria of one species. One in every 10 million of them carries a mutation for resistance to an antibiotic. Calculate the number of resistant bacteria.[2]
(c)Use your answers to explain why even a very rare mutation for resistance can quickly become a problem when the antibiotic is used.[2]
Show answer
(a) 512
M1 180 ÷ 20 = 9 divisions; A1 2⁹ = 512.
(b) 500
M1 5 × 10⁹ ÷ 1 × 10⁷; A1 500.
(c) There are already hundreds of resistant bacteria; when the antibiotic kills the others, these survive and, dividing every 20 minutes, soon form a large resistant population.
B1 some resistant cells are present in a large population; B1 they survive and multiply rapidly.
Q15Medicinal drugs & antibiotics · Standard · Paper 4 style · 6 marks
A student made garlic extract at 0 %, 25 %, 50 % and 100 % concentration and soaked 6 mm paper discs in each. The discs were placed on agar plates spread with bacteria. The diameter (in mm, including the disc) of the area with no bacterial growth was measured on three plates.0 %: 6, 6, 625 %: 9, 10, 850 %: 12, 13, 14100 %: 16, 18, 17
(a)Calculate the mean diameter for each concentration to 1 decimal place.[2]
(b)Describe the relationship shown by the results.[1]
(c)Explain why the 0 % result is 6 mm and not 0 mm.[1]
(d)Give two variables, other than those mentioned, that should be kept constant.[2]
Show answer
(a) 0 %: 6.0 mm, 25 %: 9.0 mm, 50 %: 13.0 mm, 100 %: 17.0 mm
A2 all four correct (A1 for two or three).
(b) As the concentration of garlic extract increases, the clear zone gets larger.
B1.
(c) 6 mm is the diameter of the paper disc itself; there was no clear zone around it.
B1.
(d) Volume of extract on each disc; time discs soaked; type and amount of bacteria spread; temperature and time of incubation; depth / type of agar.
B1 each for any two.
Q16Medicinal drugs & antibiotics · Standard · Paper 2 style · 6 marks
A patient took an antibiotic for a bacterial infection. The doctor said to take it for 7 days, but the patient felt better and stopped after day 3. The number of bacteria in samples taken from the patient (per cm³) was:day: 0, 1, 2, 3, 5, 7bacteria per cm³: 8000, 3000, 900, 200, 600, 2500
(a)Calculate the percentage decrease in bacteria between day 0 and day 3. Give your answer to 1 decimal place.[2]
(b)Explain the change in the number of bacteria after day 3.[3]
(c)Suggest what the doctor might do now, and why.[1]
Show answer
(a) 97.5 %
M1 (8000 − 200) ÷ 8000 × 100; A1 97.5.
(b) The patient stopped taking the antibiotic while some bacteria were still alive; these survivors were likely the most resistant ones; they reproduced, so numbers rose again.
B1 bacteria not all killed when course stopped; B1 survivors are more resistant; B1 they multiplied.
(c) Prescribe a different antibiotic, because the surviving bacteria may now be resistant to the first one.
B1.
Q17Medicinal drugs & antibiotics · Challenge · Paper 1 style · 1 mark
(a)[1]
Show answer
(a) B The bacteria that survive longest are the most resistant, and stopping early may let them multiply.
Stopping early leaves the most resistant bacteria alive; they can multiply and pass on resistance. C is wrong because antibodies are made against pathogens, not against antibiotics.
Q18Medicinal drugs & antibiotics · Challenge · Paper 4 style · 7 marks
The same antibiotic disc test was repeated on four plates.clear-zone diameter / mm: plate 1: 21; plate 2: 23; plate 3: 14; plate 4: 22
(a)Identify the anomalous result and calculate the mean clear-zone diameter without it. Give your answer to 1 decimal place.[2]
(b)Calculate the mean if the anomalous result were included, and explain why it should be left out.[2]
(c)Suggest two possible causes of the anomalous result.[2]
(d)Suggest why the zones were measured across two diameters at right angles and the values averaged.[1]
(b) 20.0 mm; it is far from the other values and probably due to an error, so including it would make the mean too low.
A1 80 ÷ 4 = 20.0; B1 reason.
(c) Disc not soaked for the same time / less antibiotic on it; disc not pressed flat on the agar; more bacteria spread on that plate; plate incubated at a different temperature; diameter measured wrongly.
B1 each for any two.
(d) The clear zones may not be perfect circles, so averaging two diameters gives a more accurate value.
B1.
Q19Medicinal drugs & antibiotics · Challenge · Paper 2 style · 7 marks
Samples of a gut bacterium were collected from patients in a large city. The percentage of samples that were resistant to one antibiotic was recorded.year: 2014, 2016, 2018, 2020, 2022, 2024resistant samples / %: 18, 23, 31, 38, 46, 52
(a)Describe the trend shown by the data.[2]
(b)Calculate the mean increase in percentage of resistant samples per year between 2014 and 2024.[2]
(c)Suggest two reasons for this trend.[2]
(d)Predict, with a reason, the percentage of resistant samples in 2026 if the trend continues.[1]
Show answer
(a) The percentage of resistant samples increased every time, from 18 % in 2014 to 52 % in 2024.
B1 increases throughout; B1 data quoted with units.
(b) 3.4 percentage points per year
M1 (52 − 18) ÷ 10; A1 3.4.
(c) Antibiotics bought without prescription / overused; patients not finishing courses; antibiotics used in animal feed; resistant bacteria spread through poor sanitation / contaminated water.
B1 each for any two.
(d) About 59 % (52 + 2 × 3.4 ≈ 59); accept 57–60 % with reference to the same rate of increase.
B1 value in range with reason.
Q20Medicinal drugs & antibiotics · Challenge · Paper 2 style · 6 marks
(a)A strain of typhoid bacteria that is resistant to most antibiotics has spread in some cities. Explain why this strain is dangerous.[2]
(b)Health workers vaccinated large numbers of children against typhoid. Explain how this helps to slow the spread of antibiotic resistance.[3]
(c)Typhoid spreads through contaminated food and water. Suggest one other measure, apart from vaccination, to reduce cases.[1]
Show answer
(a) Very few antibiotics can treat infected people, so the disease lasts longer and more people may die; the strain can spread to others.
B1 few / no effective antibiotics; B1 more severe illness / deaths / spread.
(b) Vaccinated children become immune so fewer get typhoid; fewer cases need antibiotics, so less selection pressure for resistance; fewer infected people means less spread of resistant bacteria.
B1 fewer infections; B1 fewer antibiotics used / less selection; B1 less transmission.
Q21Medicinal drugs & antibiotics · Challenge · Paper 4 style · 6 marks
Paper discs (6 mm diameter) were soaked in different concentrations of an antibiotic and placed on agar covered with bacteria.concentration / µg/cm³: 0, 1, 2, 4, 8, 16diameter of clear area including disc / mm: 6, 6, 9, 13, 17, 21
(a)State the lowest concentration of the antibiotic that had any effect on the bacteria. Explain your answer.[2]
(b)Describe the pattern in the results from 2 to 16 µg/cm³.[2]
(c)Predict the zone diameter for 32 µg/cm³ if the pattern continues.[1]
(d)Suggest why a doctor would want to know the lowest concentration that is effective.[1]
Show answer
(a) 2 µg/cm³; the zone is larger than the 6 mm disc only from 2 µg/cm³ upwards.
B1 2 µg/cm³; B1 reason (6 mm = disc only).
(b) Each time the concentration doubles, the zone diameter increases by about 4 mm.
B1 increases; B1 quantified (4 mm per doubling).
(c) about 25 mm
B1.
(d) So the dose given is high enough to kill the bacteria but not more than needed, reducing side effects and cost.
B1.
Q22Medicinal drugs & antibiotics · Challenge · Paper 4 style · 5 marks
(a)A clear zone has a diameter of 24 mm around a disc of diameter 6 mm. Calculate the area of agar where bacteria were killed, not counting the area under the disc. Give your answer in mm² to 1 decimal place.[3]
(b)Explain why the bacteria nearest the disc are killed while those further away are not.[2]
(b) The antibiotic diffuses out into the agar; its concentration falls with distance from the disc, so beyond a certain distance it is too dilute to kill bacteria.
B1 diffusion from disc; B1 concentration decreases with distance.
Q23Misused drugs (alcohol, heroin, nicotine, steroids) · Core · Paper 1 style · 1 mark
(a)Which describes heroin?[1]
Show answer
(a) B a depressant that slows the activity of the nervous system
Heroin is a powerful, addictive depressant drug that slows down the activity of the nervous system. C describes a stimulant, the opposite effect.
Q24Misused drugs (alcohol, heroin, nicotine, steroids) · Core · Paper 2 style · 5 marks
(a)Name the addictive drug in tobacco smoke.[1]
(b)State two effects of nicotine on the circulatory system.[2]
(c)Explain why many smokers find it very hard to give up smoking even when they know it is harmful.[2]
Show answer
(a) nicotine
B1.
(b) Increases heart rate; increases blood pressure; narrows blood vessels; makes blood more likely to clot.
B1 each for any two.
(c) Nicotine is addictive; stopping causes withdrawal symptoms such as cravings and irritability.
B1 addiction; B1 withdrawal symptoms.
Q25Misused drugs (alcohol, heroin, nicotine, steroids) · Standard · Paper 1 style · 1 mark
(a)Why are some athletes banned from competition after taking anabolic steroids?[1]
Show answer
(a) B Steroids increase muscle growth, giving an unfair advantage.
Anabolic steroids are hormone-like drugs that increase muscle mass and strength, which is unfair to other competitors (and has health risks). A describes painkillers, not steroids.
Q26Misused drugs (alcohol, heroin, nicotine, steroids) · Standard · Paper 2 style · 8 marks
In a road-safety study in Europe, volunteers did a computer test of reaction time after drinking different amounts of alcohol.units of alcohol: 0, 2, 4mean reaction time / s: 0.21, 0.27, 0.36
(a)Calculate the percentage increase in reaction time after 4 units of alcohol compared with none. Give your answer to 1 decimal place.[2]
(b)A car travels at 20 m/s. Calculate how much further it travels during the driver's reaction time after 4 units than after 0 units.[2]
(d) Liver damage (cirrhosis); brain damage; addiction; increased risk of heart disease / high blood pressure; social problems (loss of job, violence, family problems).
B1 each for any two.
Q27Misused drugs (alcohol, heroin, nicotine, steroids) · Standard · Paper 2 style · 7 marks
(a)Explain what is meant by addiction to a drug such as heroin.[2]
(b)Heroin affects the nervous system at synapses. Suggest why a heroin user needs larger and larger doses to get the same effect.[2]
(c)Explain why injecting heroin increases the risk of HIV infection.[2]
(d)Give one social problem linked to heroin addiction.[1]
Show answer
(a) The body becomes dependent on the drug so the person feels a strong need to keep taking it; stopping causes withdrawal symptoms.
B1 dependence / craving; B1 withdrawal symptoms when stopped.
(b) The body becomes tolerant: the synapses / receptors adapt to the drug, so the same dose has less effect and more is needed.
B1 tolerance; B1 nervous system / receptors adapt.
(c) Users may share needles; blood containing the virus from an infected person is passed directly into the next person's blood.
(c) Steroids are often used during training to build muscle and then stopped before competitions so they are not detected; random testing catches this.
B1 used in training / stopped before event; B1 random testing detects this.
Q30Misused drugs (alcohol, heroin, nicotine, steroids) · Challenge · Paper 2 style · 7 marks
In one country the legal limit for driving is 80 mg of alcohol per 100 cm³ of blood. The table (figures for this question) shows the relative risk of a crash compared with a driver with no alcohol.blood alcohol / mg per 100 cm³: 0, 50, 80, 100, 150relative risk of crash: 1, 2, 4, 7, 25
(a)Calculate how many times greater the risk of a crash is at 150 mg per 100 cm³ than at the legal limit of 80 mg per 100 cm³.[1]
(b)Describe how the risk changes as blood alcohol concentration increases.[2]
(c)Some countries have lowered their limit to 50 mg per 100 cm³. Use the data to argue for this change.[2]
(d)Explain why the risk of a crash increases.[2]
Show answer
(a) 6.25 times
A1 25 ÷ 4 = 6.25.
(b) The risk rises as blood alcohol rises; it rises slowly at first and then very steeply above about 100 mg per 100 cm³.
B1 risk increases; B1 increase is faster at higher concentrations (with data).
(c) At 50 mg the risk is 2 times, half the risk at 80 mg (4 times); lowering the limit could prevent many crashes.
B1 quotes data; B1 conclusion.
(d) Alcohol slows reaction time; it reduces judgement / self-control, so drivers take more risks.
B1 slower reactions; B1 poor judgement / more risk-taking.
Similar questions
Questions that test the same subtopic in different years, grouped so you can work on one skill at a time.
References only: find each question in its paper (official link where available, otherwise through your school).
