Communicable diseases and pathogens – GCSE Biology exam questions with mark scheme

1Grade 1–33 marks

Name the type of pathogen that causes each disease.

(a) measles [1]

(b) Salmonella food poisoning [1]

(a) virus (allow viral)(1)
(b) bacterium / bacteria (allow bacterial)(1)
(c) protist (allow protoctist / protozoan; reject mosquito)(1)
Answer: (a) virus (b) bacterium (c) protist
Examiner tip: Malaria is caused by a protist, NOT by the mosquito — the mosquito is the vector.

2Grade 1–3Foundation4 marks

A farmer grows tomato plants in a greenhouse. Some of the plants are infected with tobacco mosaic virus (TMV).

(a) Describe how the leaves of a plant infected with TMV look different from the leaves of a healthy plant. [1]

(b) The infected tomato plants grow more slowly and produce fewer tomatoes than healthy plants.

Explain why. [3]

(a) mosaic pattern / patches of discolouration (on the leaves) (allow pale / yellow / light-green patches or mottled leaves; ignore spots; ignore 'leaves die')(1)
(b) less chlorophyll / fewer chloroplasts in the discoloured parts of the leaf (allow parts of the leaf cannot absorb light)(1)
(b) so less photosynthesis (takes place)(1)
(b) so less glucose / sugar produced (for respiration / to make new cells / proteins / for growth) (allow less food made; allow less energy released for growth; ignore 'no energy')(1)
Answer: (a) Mosaic pattern of discoloured patches. (b) Discoloured areas have less chlorophyll → less photosynthesis → less glucose for growth and making fruit.
Examiner tip: Don't stop at 'less photosynthesis' – the third mark needs the link to less glucose (food) for growth.

3Grade 1–3Foundation4 marks

(a) What is a pathogen? [1]

(b) The table shows three communicable diseases.

Complete the table. Choose answers from the box. Each answer may be used once, more than once or not at all.

by a vector

by droplets in the air

by sexual contact

by water splashes and wind

by eating contaminated food

Disease	How the disease is spread
gonorrhoea
measles
rose black spot

[3]

(a) a microorganism that causes (infectious / communicable) disease (allow bacterium / virus / fungus / protist that causes disease; 'causes disease' is essential; ignore 'germ' alone)(1)
(b) gonorrhoea – by sexual contact(1)
(b) measles – by droplets in the air(1)
(b) rose black spot – by water splashes and wind(1)
Answer: (a) A microorganism that causes disease. (b) gonorrhoea: sexual contact; measles: droplets in the air; rose black spot: water splashes and wind.
Examiner tip: A pathogen must be defined as something that causes disease – 'a microorganism' or 'a bacterium' on its own scores nothing.

4Grade 4–54 marks

Bacteria and viruses are both pathogens that can make people ill.

Explain how bacteria and viruses each cause the symptoms of disease once they are inside the body. [4]

bacteria produce (release) toxins / poisons (allow bacteria reproduce / multiply rapidly in the body if toxins are not mentioned)(1)
(the) toxins damage tissues / cells (and make us feel ill) (allow named example: Salmonella toxins cause fever, cramps, vomiting, diarrhoea)(1)
viruses (enter cells and) live / reproduce / replicate inside (body) cells (reject 'viruses reproduce by dividing')(1)
which damages / destroys / bursts the cells (reject 'viruses produce toxins' for this mark)(1)
Answer: Bacteria multiply rapidly and release toxins that damage tissues; viruses reproduce inside cells and damage or burst them.
Examiner tip: Toxins belong to bacteria – writing that viruses 'release toxins' loses the virus mark.

5Grade 4–55 marks

Salmonella bacteria live in the gut of many chickens. People can get food poisoning from eating chicken or eggs containing Salmonella.

The bar chart shows the number of reported cases of Salmonella food poisoning in people in one country. Vaccination of chickens against Salmonella began at the start of 2003.

(a) Calculate the percentage decrease in the number of reported cases between 2002 and 2010. [2]

(b) Explain why vaccinating chickens reduced the number of cases of Salmonella food poisoning in people. [2]

Suggest one reason why. [1]

(a) (15 000 − 6000) ÷ 15 000 (× 100) (allow 9000 ÷ 15 000)(1)
(a) 60 (%) (correct answer with no working scores 2 marks; allow ecf for 1 mark from one misread bar)(1)
(b) (vaccinated) chickens are immune / produce antibodies so are not infected with / do not carry Salmonella (allow fewer chickens infected)(1)
(b) so (fewer) chicken meat / eggs contain Salmonella / fewer people eat contaminated food (ignore 'kills the bacteria')(1)
(c) any one from: not all chickens are vaccinated / vaccine not 100% effective; food may be undercooked or prepared unhygienically / cross-contamination (e.g. raw chicken touching cooked food, unwashed hands); Salmonella from other foods or animals (e.g. imported chicken / eggs, pork, reptiles) (ignore 'people are not vaccinated')(1)
Answer: (a) 60% (b) Vaccinated chickens are not infected, so fewer chicken products carry Salmonella for people to eat. (c) e.g. undercooked or unhygienically prepared food.
Examiner tip: In (a) divide the decrease by the ORIGINAL (2002) value, not by the 2010 value.

6Grade 4–54 marks

Rose black spot is a disease of rose plants.

(a) What type of pathogen causes rose black spot? [1]

(b) A gardener notices that more of her rose plants become infected with black spot in a wet summer than in a dry summer.

Suggest why. [1]

(c) In autumn the gardener collects all the fallen leaves from under her infected roses and burns them. She also sprays the roses with a fungicide.

Explain how each of these actions reduces the spread of rose black spot. [2]

(a) fungus (allow fungal; reject bacterium / virus)(1)
(b) (spores / the fungus) are spread by water / rain splashes (from leaf to leaf / plant to plant) (allow fungus grows better in damp conditions)(1)
(c) burning leaves: destroys the fungus / spores on the infected leaves so they cannot spread (by wind / water) to other leaves / plants (allow 'removes the source of infection')(1)
(c) fungicide: kills the fungus (on the leaves) (reject 'kills bacteria'; ignore 'cures the plant' alone)(1)
Answer: (a) fungus (b) spores spread by water splashes (c) burning destroys infected leaves carrying spores; fungicide kills the fungus.
Examiner tip: Fungicides kill fungi – calling rose black spot a bacterium, or the spray an antibiotic, costs marks.

7Grade 6–75 marks

Malaria is common in two villages, A and B. In village B, every family was given insecticide-treated nets to sleep under. Village A was not given nets.

The table shows the number of people who had malaria in one year.

Village	Number of people living in the village	Number of people who had malaria
A (no nets)	2400	312
B (nets)	3100	155

(a) Village B had fewer cases of malaria per 1000 people than village A.

Calculate how many fewer cases per 1000 people there were in village B. [2]

(b) Explain how sleeping under a net reduces the chance of a person getting malaria. [2]

Give one reason why this conclusion may not be valid. [1]

(a) A: 312 ÷ 2400 × 1000 = 130 and B: 155 ÷ 3100 × 1000 = 50 (both values needed for this mark)(1)
(a) 80 (fewer cases per 1000) (correct answer with no working scores 2 marks)(1)
(b) mosquitoes are vectors / carry the (malaria) protist / pathogen (ignore 'mosquitoes carry the disease' alone if no reference to transfer)(1)
(b) the net stops mosquitoes biting (at night) so the protist is not passed into the blood (allow insecticide on the net kills mosquitoes)(1)
(c) any one from: other variables may differ between the villages, e.g. number of mosquitoes / amount of standing water / climate / access to medicines or other control methods; we do not know if everyone in B used the nets (correctly); only two villages / one year studied so results may not be repeatable (ignore 'different number of people' – rates already allow for this)(1)
Answer: (a) 130 − 50 = 80 fewer cases per 1000 (b) Mosquitoes are the vector; the net stops them biting, so the protist is not transferred into the blood. (c) e.g. village A may have more standing water / mosquitoes.
Examiner tip: In (c), 'village B has more people' is not a valid criticism – calculating per 1000 people already deals with that.

8Grade 8–9Higher5 marks

HIV is a virus. A person can be infected with HIV for many years before they develop AIDS.

(a) HIV can be passed from an infected mother to her baby through breast milk.

Suggest why. [1]

(b) People with AIDS often die from infections, such as tuberculosis, that most healthy people survive.

Explain why. [2]

Explain how taking antiretroviral drugs can stop HIV developing into AIDS. [2]

(a) HIV is spread by (exchange of) body fluids, and (breast) milk is a body fluid / contains the virus (allow virus can be in the milk)(1)
(b) HIV attacks / destroys (the body's) immune cells / white blood cells (allow lymphocytes; ignore 'attacks the immune system' alone)(1)
(b) so the body cannot fight / destroy other pathogens, e.g. fewer antibodies made / less phagocytosis, so the (tuberculosis) bacteria multiply (allow immune system badly damaged so pathogens are not destroyed)(1)
(c) the virus cannot reproduce inside (immune) cells so there is less virus / fewer new virus particles (in the body)(1)
(c) so fewer immune cells / white blood cells are destroyed and the immune system is not (badly) damaged (allow immune system still works; AIDS = late stage when the immune system is badly damaged; reject 'drugs kill the virus' / 'cure HIV')(1)
Answer: (a) Milk is a body fluid that can contain the virus. (b) HIV destroys immune cells, so other pathogens are not destroyed and multiply. (c) Less virus is made, so fewer immune cells are destroyed and the immune system is not badly damaged (AIDS is avoided).
Examiner tip: Antiretrovirals do not kill HIV or cure it – they stop it reproducing, which protects the immune cells.

9Grade 6–7Higher6 marks

Gonorrhoea is a disease caused by a bacterium.

(a) Give one symptom of gonorrhoea. [1]

Scientists tested samples of gonorrhoea bacteria from patients in one country to see if they were resistant to antibiotic R.

The graph shows the results.

(b) Calculate the mean increase per year in the percentage of samples resistant to antibiotic R between 2016 and 2022. [2]

(d) Health officials say that, as resistance increases, using condoms is becoming even more important for controlling the spread of gonorrhoea.

Explain why. [2]

(a) any one from: thick yellow / green discharge (from the vagina or penis); pain when urinating (allow burning feeling when urinating; ignore 'rash' / 'fever')(1)
(b) 32 − 8 = 24 and 24 ÷ 6 (allow correct readings of 32 and 8 from the graph)(1)
(b) 4 (% per year) (correct answer with no working scores 2 marks)(1)
(c) the rate (of increase) increases / resistance increases faster each period / the graph gets steeper (allow e.g. 'increased by 2% from 2012 to 2014 but by 10% from 2020 to 2022'; 'resistance increases' alone = 0)(1)
(d) gonorrhoea is spread by sexual contact and condoms are a barrier that stops the bacteria passing between partners (allow prevents contact with body fluids)(1)
(d) (resistant) infections cannot be cured / treated with antibiotics (such as R), so preventing infection is the main way to stop it spreading / infected people stay infectious for longer (allow 'antibiotics no longer work')(1)
Answer: (a) yellow/green discharge or pain urinating (b) 4% per year (c) the increase gets faster (graph steeper) (d) condoms stop the bacteria passing on during sex; resistant strains cannot be treated with antibiotics, so preventing infection matters more.
Examiner tip: For 'describe the rate' you must comment on how the steepness changes – just saying 'it goes up' scores nothing.

10Grade 6–76 marks

After severe flooding, many families in a town are moved into a large, crowded temporary camp. The water supply is unreliable and there are large pools of standing water nearby.

Doctors are worried about outbreaks of three communicable diseases in the camp:

measles
Salmonella food poisoning
malaria.

Explain how the spread of each of these diseases in the camp could be reduced.

Use your knowledge of how each disease is spread. [6]

Measles: virus spread by inhalation of droplets from sneezes and coughs; crowding makes spread easier(1)
Measles: isolate infected people (e.g. separate tent / area) so droplets cannot reach others(1)
Measles: vaccinate children / people who are not already vaccinated, so they become immune; vaccinating most people reduces spread (herd immunity)(1)
Salmonella: bacteria spread in undercooked food or food prepared in unhygienic conditions(1)
Salmonella: cook food (especially chicken / eggs) thoroughly to kill the bacteria; store food cool / covered(1)
Salmonella: hygiene – hand washing (with soap), clean / disinfect cooking surfaces and utensils, keep raw and cooked food apart, provide clean water(1)
Malaria: caused by a protist carried by mosquitoes, which are vectors; mosquitoes breed in standing water(1)
Malaria: drain / cover / spray standing water (or use insecticide) to stop mosquitoes breeding / kill the vector(1)
Malaria: sleep under (insecticide-treated) nets / use repellent so people are not bitten and the protist is not passed into the blood(1)
Malaria is not spread directly from person to person, so isolating patients is less useful than controlling the vector(1)

Level	Marks	What it looks like
Level 3	5–6	Explains control measures for all three diseases, and each measure is clearly linked to how that disease is spread (droplets, contaminated food, mosquito vector). Uses correct terms such as vector, isolation, vaccination and hygiene.
Level 2	3–4	Describes relevant control measures for at least two diseases with some links to how they are spread, OR lists measures for all three diseases with little explanation.
Level 1	1–2	Gives one or more simple, relevant control measures (e.g. 'wash hands', 'use nets') with little or no explanation, or describes how one disease is spread.
No marks	0	No relevant content.

Answer: Measles: isolate cases, vaccinate. Salmonella: cook food thoroughly, wash hands, clean surfaces, clean water. Malaria: remove standing water / insecticide to stop mosquito breeding, nets to prevent bites. Each linked to how the disease spreads.
Examiner tip: Top-level answers link every control method to HOW that disease spreads – a list of methods without reasons stays in Level 2.

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