GCSE Biology Topic 3: Infection and Response MCQs – 30 Practice Questions with Answers (AQA 8461)
Free practice for AQA GCSE Biology 8461 on communicable diseases, human defences, vaccination, antibiotics, drug development, monoclonal antibodies and plant disease, with a short explanation after every question.
Pathogens and Communicable Diseases
Q1. Which four groups of microorganisms can act as pathogens in animals and plants?
- (A) Viruses, bacteria, algae and mosses
- (B) Viruses, bacteria, protists and fungi
- (C) Bacteria, fungi, ferns and protists
- (D) Viruses, yeasts, mosses and bacteria
Show Answer
Answer: B – Pathogens may be viruses, bacteria, protists or fungi, and they can spread by direct contact, by water or by air.
Q2. How does a virus cause damage once it has infected a host?
- (A) It releases toxins into the soil around the host in most ordinary cells
- (B) It blocks the host’s stomata with fungal spores
- (C) It lives and reproduces inside host cells, damaging them
- (D) It eats red blood cells from outside the body
Show Answer
Answer: C – Viruses reproduce inside living host cells, and that reproduction damages the cells they occupy.
Q3. Measles spreads when an infected person coughs or sneezes near others. Which route of spread is this?
- (A) Spread by a mosquito vector
- (B) Spread through contaminated soil
- (C) Spread by inhaling droplets from coughs and sneezes
- (D) Spread through sexual contact
Show Answer
Answer: C – The measles virus travels in droplets released by coughs and sneezes, and other people become infected by inhaling those droplets.
Q4. A tomato plant shows a mosaic pattern of discolouration on its leaves and grows poorly. Which pathogen best fits these symptoms?
- (A) Salmonella bacteria from contaminated food in a typical living organism
- (B) The protist that causes malaria
- (C) Tobacco mosaic virus, which reduces photosynthesis in the leaves
- (D) A fungus causing rose black spot
Show Answer
Answer: C – Tobacco mosaic virus gives a distinctive mosaic discolouration on leaves, cutting photosynthesis and slowing the plant’s growth.
Q5. Salmonella food poisoning is often linked to food prepared in unhygienic conditions. Which symptoms are caused by the bacteria and their toxins?
- (A) Fever, abdominal cramps, vomiting and diarrhoea
- (B) A red skin rash and a high fever only
- (C) Recurrent episodes of fever spread by mosquitoes
- (D) Purple spots on leaves that turn yellow and drop
Show Answer
Answer: A – Salmonella bacteria ingested in food secrete toxins that damage tissues, producing fever, cramps, vomiting and diarrhoea.
Q6. Gonorrhoea was once easily treated with penicillin, but many resistant strains have now appeared. How is its spread controlled today?
- (A) By treatment with antibiotics and by barrier methods such as condoms
- (B) By using mosquito nets and draining breeding sites for the organism described
- (C) By removing affected leaves and spraying fungicide
- (D) By vaccinating poultry against the bacterium
Show Answer
Answer: A – Gonorrhoea spreads by sexual contact, so its spread is controlled by antibiotic treatment and by barrier contraception.
Q7. Rose black spot weakens a rose plant. How does the disease reduce the plant’s growth?
- (A) It blocks water uptake by the roots completely
- (B) It stops the plant producing seeds
- (C) Spotted leaves turn yellow and drop early, so less photosynthesis takes place
- (D) It causes the stem to grow extra thorns
Show Answer
Answer: C – Purple or black spots on leaves lead to yellowing and early leaf drop, which reduces the leaf area available for photosynthesis.
Q8. Malaria causes recurrent fever and can be fatal. Which organism spreads the protist that causes it?
- (A) An aphid feeding on plant sap
- (B) A fungus releasing spores in the wind
- (C) A bacterium living in contaminated water
- (D) A mosquito acting as a vector
Show Answer
Answer: D – The malarial protist has a life cycle that includes the mosquito, which carries it between people when it bites.
Q9. Which two measures help control the spread of malaria in a community?
- (A) Preventing mosquitoes from breeding and using nets to avoid bites
- (B) Spraying fungicide and removing spotted leaves over a short period of time
- (C) Vaccinating poultry and improving food hygiene
- (D) Taking painkillers and drinking more water
Show Answer
Answer: A – Controlling malaria means targeting its vector: stopping mosquitoes breeding and protecting people from bites with nets.
Human Defences and Vaccination
Q10. Which part of the body acts as a non-specific barrier that physically blocks pathogens from entering?
- (A) The liver, which converts lactic acid to glucose
- (B) The bone marrow, which makes blood cells
- (C) The skin, which covers the body surface
- (D) The pancreas, which releases enzymes
Show Answer
Answer: C – The skin is a non-specific defence: its unbroken surface forms a physical barrier that pathogens cannot easily cross.
Q11. Mucus in the nose, trachea and bronchi traps particles from inhaled air. What happens to the trapped pathogens next?
- (A) They are digested by stomach acid immediately at ordinary temperatures in a normal healthy cell
- (B) They are moved out of the airways by tiny hair-like structures and swallowed or expelled
- (C) They are absorbed directly into the blood
- (D) They are turned into antibodies on the spot
Show Answer
Answer: B – Mucus traps inhaled pathogens, and the lining of the airways moves the mucus away so the pathogens do not reach the lungs.
Q12. Stomach acid is a non-specific defence. How does it protect the body?
- (A) It produces antibodies against every pathogen
- (B) It kills many pathogens swallowed with food or drink
- (C) It stores white blood cells until they are needed
- (D) It blocks blood vessels to stop infection spreading
Show Answer
Answer: B – The strongly acidic conditions in the stomach destroy many of the pathogens that are swallowed before they can establish an infection.
Q13. A white blood cell engulfs a bacterium and digests it. What is this defence process called?
- (A) Vaccination
- (B) Translocation
- (C) Fermentation
- (D) Phagocytosis
Show Answer
Answer: D – Phagocytosis is the process by which white blood cells engulf and digest pathogens that have entered the body.
Q14. Some bacteria release toxins that damage tissues. How do white blood cells counter these toxins?
- (A) They produce extra red blood cells to dilute the toxins
- (B) They produce antitoxins that neutralise the toxins
- (C) They close the stomata to block toxin entry
- (D) They convert toxins into sugars for respiration
Show Answer
Answer: B – Alongside phagocytosis and antibody production, white blood cells produce antitoxins that counter the poisons released by bacteria.
Q15. A vaccine contains small quantities of dead or inactive forms of a pathogen. What response does it trigger in the body?
- (A) Red blood cells begin to carry the pathogen
- (B) White blood cells produce antibodies against that pathogen
- (C) The skin thickens to block future infections
- (D) Platelets clot around the pathogen permanently when conditions stay suitable
Show Answer
Answer: B – Vaccination stimulates white blood cells to make antibodies, so if the same pathogen returns, the response is fast enough to prevent illness.
Antibiotics, Drug Development and Monoclonal Antibodies
Q16. A patient has a viral throat infection and asks for antibiotics. Why would antibiotics not cure this infection?
- (A) Antibiotics kill bacteria, but they cannot kill viruses living inside host cells
- (B) Antibiotics only work on fungal infections
- (C) Antibiotics are painkillers that mask symptoms only in a typical living organism during normal activity
- (D) Antibiotics destroy the patient’s own antibodies
Show Answer
Answer: A – Antibiotics such as penicillin cure bacterial disease by killing bacteria, but they cannot kill viral pathogens, which reproduce inside host cells.
Q17. Why is the rise of antibiotic-resistant bacteria a serious concern?
- (A) Resistant bacteria can no longer cause disease
- (B) Resistant bacteria are killed by painkillers instead
- (C) Resistant strains survive antibiotic treatment, so bacterial infections become harder to cure
- (D) Resistant bacteria stop producing toxins entirely
Show Answer
Answer: C – When bacteria evolve resistance, the antibiotics that once cured their infections no longer kill them, leaving fewer effective treatments.
Q18. A headache medicine relieves pain but does not remove the pathogen causing an infection. Which statement describes such a medicine?
- (A) It is an antibiotic that kills bacteria
- (B) It is a vaccine that prevents future infection
- (C) It is a monoclonal antibody that targets one antigen for the organism described
- (D) It is a painkiller that treats symptoms without killing pathogens
Show Answer
Answer: D – Painkillers and similar medicines treat the symptoms of disease but do not kill the pathogens causing it.
Q19. Which traditional source gave medicine its first important antibiotic?
- (A) The foxglove plant, source of the heart drug digitalis under the conditions given
- (B) The Penicillium mould, source of penicillin discovered by Alexander Fleming
- (C) The willow tree, source of aspirin
- (D) The rose plant, source of fungicides
Show Answer
Answer: B – Penicillin was discovered by Alexander Fleming from the Penicillium mould, while digitalis came from foxgloves and aspirin from willow.
Q20. Before a new drug is given to people, it is tested in the laboratory on cells, tissues and live animals. What is this stage called?
- (A) Preclinical testing
- (B) Clinical testing
- (C) Peer review
- (D) Double blind testing
Show Answer
Answer: A – Preclinical testing happens in the laboratory using cells, tissues and animals, checking toxicity, efficacy and dose before human trials begin.
Q21. In a double blind clinical trial, neither the patients nor the doctors know who receives the real drug and who receives a placebo. Why is this design used?
- (A) To prevent expectations from biasing the reported effects
- (B) To hide the results from peer reviewers
- (C) To reduce the dose given to every patient
- (D) To test the drug on animals instead of people
Show Answer
Answer: A – Keeping both groups unaware removes bias from expectations, so any difference between the drug and placebo groups reflects the drug itself.
Q22. A hybridoma cell is formed by combining a mouse lymphocyte with a tumour cell. What two abilities does the hybridoma gain?
- (A) It can photosynthesise and fix nitrogen
- (B) It can produce toxins and resist antibiotics in a healthy organism
- (C) It can engulf bacteria and form blood clots
- (D) It can divide repeatedly and make one specific antibody
Show Answer
Answer: D – The lymphocyte contributes antibody production and the tumour cell contributes the ability to divide, so cloned hybridomas yield large amounts of one identical antibody.
Q23. Monoclonal antibodies are used in pregnancy tests. How does the test work in general terms?
- (A) The antibody binds to one specific target molecule, showing whether it is present
- (B) The antibody kills all bacteria in the sample
- (C) The antibody digests the sample by phagocytosis at ordinary temperatures in a normal healthy cell
- (D) The antibody vaccinates the person being tested
Show Answer
Answer: A – Because each monoclonal antibody is specific to one binding site on one antigen, it can detect whether a particular molecule is present in a sample.
Q24. In cancer treatment, a monoclonal antibody can be joined to a toxic drug. Why is this targeted approach useful?
- (A) It delivers the drug to cancer cells without harming as many healthy cells
- (B) It vaccinates the patient against all future cancers
- (C) It replaces the need for any diagnosis
- (D) It makes the cancer cells photosynthesise
Show Answer
Answer: A – The antibody guides its attached substance to the cancer cells it recognises, so healthy cells elsewhere in the body are harmed less.
Plant Disease and Defences
Q25. A gardener notices stunted growth and yellow patches on a plant’s leaves. Which deficiency could explain the yellowing, and why?
- (A) Nitrate deficiency, because nitrates are needed for chlorophyll under normal conditions
- (B) Magnesium deficiency, because magnesium is needed to make chlorophyll
- (C) Nitrate deficiency, because nitrates form the waxy cuticle
- (D) Magnesium deficiency, because magnesium builds cell walls
Show Answer
Answer: B – Magnesium ions are needed to make chlorophyll, so a shortage causes chlorosis, the yellowing of leaves, while nitrate shortage mainly stunts growth because protein synthesis slows.
Q26. A plant shows stunted growth but its leaves stay green. Which ion shortage fits best?
- (A) Magnesium, because it is needed for protein synthesis in most ordinary cells when conditions stay suitable
- (B) Calcium, because it makes chlorophyll
- (C) Potassium, because it forms the cell wall
- (D) Nitrate, because nitrate ions are needed for protein synthesis and therefore growth
Show Answer
Answer: D – Nitrate ions are used to build amino acids and proteins, so without enough nitrate a plant cannot grow normally even though its chlorophyll remains.
Q27. Which feature is a physical defence that helps a leaf resist invasion by microorganisms?
- (A) Antibacterial chemicals produced inside leaf cells
- (B) Poisons that deter herbivores from eating the leaf
- (C) A tough waxy cuticle covering the leaf surface
- (D) Leaves that droop or curl when touched
Show Answer
Answer: C – The tough waxy cuticle is a physical barrier on the leaf surface, while antibacterial chemicals are chemical defences and drooping leaves are mechanical adaptations.
Q28. Bark on a tree trunk falls off in layers. How does this help defend the tree?
- (A) It exposes fresh wood for photosynthesis
- (B) It sheds layers of dead cells that may carry microorganisms
- (C) It opens the stomata wider for gas exchange
- (D) It releases antibacterial chemicals into the soil
Show Answer
Answer: B – Layers of dead cells around stems fall off, carrying any microorganisms on them away from the living tissues beneath.
Q29. A plant disease is suspected but the pathogen is unknown. Which identification method uses antibodies to test the plant?
- (A) Checking a gardening manual for matching symptoms during normal activity
- (B) Taking the plant to a laboratory for examination
- (C) Counting aphids on the leaves
- (D) Using a testing kit that contains monoclonal antibodies
Show Answer
Answer: D – Testing kits containing monoclonal antibodies can identify a plant pathogen, alongside reference manuals and laboratory identification.
Q30. Aphids feed on a plant and spread disease between plants. Which category of plant problem do aphids belong to?
- (A) A viral pathogen living inside leaf cells for the organism described
- (B) A fungal pathogen spread by wind
- (C) An ion deficiency caused by poor soil
- (D) An insect pest that damages plants and can carry pathogens
Show Answer
Answer: D – Plants can be damaged by insects as well as by pathogens, and aphids are named in the specification as insects that affect plants.
Work through any questions you missed again, then revise those areas before moving on to the next topic.