Human Defences, Vaccination and Drug Development
The body defends itself against pathogens in two stages: non-specific defences, such as the skin, mucus and stomach acid, work against anything, while white blood cells respond specifically once a pathogen gets through, by phagocytosis, by producing antibodies that lock onto its antigens, and by producing antitoxins. Vaccination uses this system deliberately, introducing a small quantity of dead or inactive pathogen so that a real infection is destroyed rapidly before a person becomes ill.
Before you start
Make sure you're comfortable with these topics first:
Method
- Separate the two lines of defence in your answer: name the non-specific barriers first (skin, nose, trachea and bronchi with mucus and cilia, stomach acid), then the specific immune response by white blood cells.
- Learn the three white blood cell actions with the right verbs: phagocytosis is engulfing and digesting the pathogen; antibody production is specific to the antigens on that pathogen and causes pathogens to clump together and be destroyed; antitoxins neutralise the toxins produced by bacteria.
- Explain vaccination as a sequence, because the marks are for the order: a small quantity of dead or inactive pathogen is introduced, white blood cells produce antibodies specific to its antigens, and if the same pathogen enters later the antibodies are produced far more quickly and in greater quantity, so the pathogen is destroyed before symptoms develop.
- Explain herd immunity when a question mentions a whole population: if a large enough proportion is vaccinated, the pathogen cannot spread easily, so unvaccinated people, including those too young or too ill to be vaccinated, are also protected.
- Keep antibiotics and painkillers apart, since the distinction is a very common exam question: antibiotics kill bacteria inside the body and cure the disease; painkillers treat the symptoms only and do not kill pathogens. Antibiotics do not work against viruses.
- Learn the drug testing sequence with what each stage checks: preclinical testing on cells, tissues and live animals (toxicity and efficacy), then clinical trials on healthy volunteers at very low doses (safety and dosage), then on patients (efficacy and optimum dose), using double blind trials with a placebo, where neither the patient nor the doctor knows who receives the drug, so expectation cannot bias the result.
Worked example
In a clinical trial, 400 patients receive a new drug and 400 receive a placebo. 320 of the treated patients improve, and 120 of the placebo group improve. Calculate the percentage improvement in each group and explain why the placebo group is needed.
- Treated group: (320 / 400) x 100 = 80 percent improved.
- Placebo group: (120 / 400) x 100 = 30 percent improved.
- Find the difference attributable to the drug: 80 - 30 = 50 percentage points.
- Explain the placebo group: some patients improve anyway, through the natural course of the illness or the placebo effect, so without a control group the drug would appear to help 80 percent of patients.
- State the design point: the trial should be double blind, so that neither the patient nor the doctor assessing them knows who received the drug, preventing expectation from biasing the results.
- Final answer: 80 percent against 30 percent, a difference of 50 percentage points, which is the improvement that can be attributed to the drug itself.
Practice questions
Try each question, then tap to reveal the answer.
Q1Name three non-specific defences of the human body.Show answer
Answer: Any three of: the skin as a barrier, hairs and mucus in the nose, mucus and cilia in the trachea and bronchi, hydrochloric acid in the stomach.
Q2Describe phagocytosis.Show answer
Answer: A white blood cell engulfs the pathogen and digests it using enzymes.
Q3What is an antigen?Show answer
Answer: A protein on the surface of a pathogen that the immune system recognises as foreign, and to which a specific antibody binds.
Q4Why does a vaccinated person not usually become ill when they meet the pathogen?Show answer
Answer: White blood cells that have met the antigen before produce the correct antibodies quickly and in large amounts, destroying the pathogen before it can reproduce enough to cause symptoms.
Q5State the difference between an antibiotic and a painkiller.Show answer
Answer: An antibiotic kills bacteria inside the body and cures the disease; a painkiller relieves symptoms only and does not kill the pathogen.
Q6What is tested during preclinical testing?Show answer
Answer: Toxicity, efficacy and dose, using cells, tissues and live animals before the drug is given to any person.
Q7Explain what is meant by a double blind trial.Show answer
Answer: Neither the patient nor the doctor knows whether the patient is receiving the drug or the placebo, so neither party's expectations can bias the assessment of the results.
Exam-style questions
Written in the style of a GCSE Science exam paper, with a full mark scheme.
Explain how vaccination protects a person from a disease.
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Explain why the overuse of antibiotics has led to strains of bacteria that antibiotics cannot treat.
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A pharmaceutical company has developed a new drug from a compound found in a plant. Describe the stages the drug must pass through before doctors can prescribe it, and explain the purpose of each stage.
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See real GCSE Science past-paper questions, with official mark schemes →
Free printable worksheet
Want more practice on paper? Download the human defences, vaccination and drug development worksheet pack - 14 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 18 of GCSE Biology Workbook, the whole course as one free printable PDF.
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