OCR GCSE Biology A: Named infections, STIs and plant disease defence and detection (J247) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover statements B6.3f to B6.3i of the OCR GCSE (9-1) Gateway Science Biology A (J247) specification, Version 4.0 (August 2026), for first assessment in 2018. Statement B6.3i is printed in bold, so questions on it are labelled Higher Tier only. Read the study guide and revision notes first if you need to. Other links: OCR GCSE Biology hub, printable checklist and free diagnostics.

Questions

1. State whether each disease is caused by a virus, a bacterium or a fungus. (a) Tobacco mosaic disease [1] (b) Barley powdery mildew [1] (c) Crown gall disease [1] (d) Chlamydia [1]

2. Athlete’s foot is a common fungal infection.

(a) Describe two signs of athlete’s foot. [2] (b) Suggest how a person could catch it at a swimming pool, and how this could be prevented. [2]

3. HIV is a sexually transmitted infection.

(a) State two ways, other than sexual contact, in which HIV can be passed on. [2] (b) Explain how HIV infection can lead to AIDS. [3] (c) A patient takes antiretroviral drugs. Explain why they can still pass on HIV. [1]

4. A clinic screened 2,150 people for chlamydia in a year. 172 tested positive.

(a) Calculate the percentage who tested positive. [2] (b) Explain why many people with chlamydia do not know they have it. [1] (c) State one possible long-term effect of untreated chlamydia. [1]

5. A tomato grower finds leaves with pale and dark green patches. The cause is tobacco mosaic virus.

(a) Explain why infected plants grow more slowly. [3] (b) Suggest two actions to stop the virus spreading to other plants. [2]

6. A farmer grows 9,000 barley plants. She chooses 30 plants at random and 6 show powdery mildew.

(a) Calculate an estimate of the number of infected plants. [3] (b) Explain why the plants were chosen at random. [1] (c) Give one change to the method that would improve the estimate. [1]

7. Describe how each of these defends a plant against pathogens. (a) the waxy cuticle [2] (b) the cell wall [1] (c) antimicrobial substances [2]

8. Researchers grew two types of a plant. Type X makes a low concentration of an antimicrobial chemical. Type Y makes a high concentration. Plants were exposed to the same fungal spores. The mean percentage of leaf area covered by fungus was 42% for type X and 11% for type Y.

(a) Calculate the percentage reduction in leaf area covered by fungus in type Y compared with type X. [2] (b) What conclusion can be drawn? [2] (c) Suggest one variable that must be kept the same in the investigation. [1]

9. Young trees were given different numbers of wounds on the stem and then exposed to Agrobacterium tumefaciens. The mean number of galls per tree was recorded.

Wounds per tree	0	1	2	3	4	5
Mean galls per tree	0	2	3	5	8	9

(a) Describe the relationship shown. [2] (b) Explain the relationship using how the bacterium infects a plant. [2] (c) Suggest two ways a nursery could reduce crown gall in its stock. [2]

10. (Higher Tier only) A laboratory tests plant samples for the DNA of a fungal pathogen. A positive control gives a band at 300 base pairs and a negative control gives no band. Sample P gives a band at 300 base pairs, sample Q gives no band and sample R gives a band at 180 base pairs.

(a) State what the results show for each sample. [3] (b) Describe how a test using antibodies could detect the pathogen. [2] (c) Explain one advantage of field diagnosis by observation and one advantage of laboratory testing. [2]

Answers

1. (a) virus [1] (b) fungus [1] (c) bacterium [1] (d) bacterium [1] [4] Examiner insight: Each part needs the pathogen type, not the name of a treatment; answers such as “bacteria” for powdery mildew gain nothing.

2. (a) Any two from: itchy skin [1]; red, flaky or cracked skin between the toes [1]. [2] (b) Spores picked up from damp floors or shared towels [1]; wear flip-flops or dry feet well and do not share towels [1]. [2] Examiner insight: “Suggest” questions need a link between the cause and the prevention, so name the route of infection as well as the measure.

3. (a) Any two from: sharing needles [1]; from mother to baby (in the womb, at birth or breast milk) [1]; infected blood (mark any two). [2] (b) HIV infects and destroys white blood cells (T helper lymphocytes) [1]; so the immune system is weakened [1]; the person then cannot fight other infections, which is AIDS [1]. [3] (c) Drugs reduce but do not remove the virus, so some remains in body fluids [1] [1] Examiner insight: Say that HIV is the virus and AIDS is the later stage; using the two words as if they mean the same thing is a common way to lose credit.

4. (a) 172 ÷ 2,150 [1] × 100 = 8.0% [1] [2] (b) Many infected people have no symptoms [1] [1] (c) Infertility, or damage to the reproductive system [1] [1] Examiner insight: Show the division as well as the final figure; and an answer to a stated number of significant figures should match the data given.

5. (a) Virus destroys chlorophyll in patches [1]; so less light is absorbed and less photosynthesis happens [1]; less glucose is made for growth [1]. [3] (b) Any two from: remove and destroy infected plants [1]; wash hands and tools between plants [1]; grow resistant varieties (mark any two). [2] Examiner insight: An explanation needs a chain: damage, then less photosynthesis, then less glucose; “it makes them weak” is too vague to credit.

6. (a) 6 ÷ 30 = 0.2 or 20% [1]; 0.2 × 9,000 [1]; = 1,800 plants [1] [3] (b) To avoid bias (for example choosing only plants at the field edge) [1] [1] (c) Use a larger sample, or repeat in several places and take a mean [1] [1] Examiner insight: Show the proportion first and then scale it up; a reason for random choice must mention bias, and “to be fair” alone is too vague.

7. (a) It is a waxy, waterproof layer [1]; forming a barrier microbes cannot easily cross, and water runs off it [1]. [2] (b) A tough cellulose layer that pathogens must break through to reach the cell [1] [1] (c) Chemicals that kill or stop the growth of bacteria and fungi [1]; they work if the pathogen gets past the physical barriers [1]. [2] Examiner insight: Describe the defence and how it prevents infection; naming the cuticle without saying it is a barrier does not complete the point.

8. (a) 42 − 11 = 31 [1]; 31 ÷ 42 × 100 = 73.8% [1] [2] (b) Type Y has much less fungus than type X [1]; so a higher concentration of the antimicrobial chemical gives better protection [1]. [2] (c) Number of spores, time of exposure, temperature, light or leaf size (any one) [1] [1] Examiner insight: A conclusion should refer to both variables in the data, and should say “suggests” if the study cannot prove cause.

9. (a) As the number of wounds increases, the number of galls increases [1]; a positive correlation [1]. [2] (b) The bacteria enter through wounds [1]; so more wounds give more entry points and more infections [1]. [2] (c) Any two from: avoid wounding plants [1]; clean tools [1]; buy healthy stock; destroy infected plants (mark any two). [2] Examiner insight: “Describe” asks only for the pattern, using figures if possible; save the biology for the “explain” part.

10. (a) P has a band matching the positive control, so it contains the pathogen DNA [1]; Q has no band, so no pathogen DNA was found [1]; R has a band of a different size, so it is not the same DNA [1]. [3] (b) Antibodies that bind a specific antigen from the pathogen are added to the sample [1]; a colour change or line shows the antigen is present [1]. [2] (c) Field: quick and cheap, no equipment needed [1]; lab: more specific, so it can confirm the exact pathogen [1]. [2] Examiner insight: Use the controls when interpreting a result; a conclusion that ignores them leaves out the reason the sample can be trusted.

Where marks are usually lost

• Naming the wrong pathogen type for the named plant diseases.
• Treating HIV and AIDS as the same thing.
• Saying antiretroviral drugs cure HIV.
• Saying the cuticle or cell wall kills pathogens.
• Writing “less growth” without the chain from damage to less photosynthesis.
• Leaving out the working in percentage calculations.
• Explaining a correlation without naming how the bacteria enter the plant.
• Ignoring the controls in a DNA test result.

Next steps

• Read the revision notes
• Reread the study guide
• Visit the OCR GCSE Biology hub and checklist
• Try all free 10-minute diagnostics
• Book a free trial class: /trial/

Official syllabus

OCR GCSE (9-1) Gateway Science Biology A (J247) specification, Version 4.0 (August 2026), first assessment 2018, published by OCR. Statements B6.3f to B6.3i; B6.3i is bold (Higher Tier only).