Infection and Response
Infection and response is the GCSE biology topic covering how communicable diseases are caused and spread by pathogens (bacteria, viruses, fungi and protists), how the body defends itself against them, and how vaccines and new medicines are developed and tested. Example diseases studied include measles, salmonella, malaria and rose black spot.
Method
- Learn the four types of pathogen (bacteria, viruses, fungi, protists), one named disease example of each, and how each is spread (for example, droplet infection, direct contact, contaminated water or food, or a vector such as a mosquito).
- Learn the body's non-specific defences against pathogens entering the body: the skin as a physical and chemical barrier, hairs and mucus in the nose, and mucus and cilia in the trachea and bronchi.
- Learn how white blood cells respond to infection in three ways: phagocytes engulf and digest pathogens, lymphocytes produce antibodies specific to the antigens on a pathogen's surface, and some white blood cells produce antitoxins to neutralise toxins.
- Explain how vaccination works: a small, safe dose of dead or inactive pathogen (containing antigens) is introduced, causing white blood cells to produce antibodies and memory cells without the person becoming ill, so the response is faster if the same pathogen is met again.
- Learn the stages of drug testing: preclinical testing on cells, tissues and sometimes animals checks toxicity and efficacy, then clinical trials use very low doses on healthy volunteers before testing on patients, often using a placebo and a double-blind design.
- For the antibiotic required practical, learn the aseptic techniques used (for example, sterilising the inoculating loop, working near a Bunsen flame, taping the lid of the Petri dish) and how to compare antibiotics using the area of the clear zone of inhibition.
Worked example
A student tests the effectiveness of an antibiotic by measuring the diameter of the clear zone (zone of inhibition) around a paper disc soaked in the antibiotic, on an agar plate covered in bacteria. The mean diameter of the clear zone is 18 mm. Calculate the area of the clear zone, to 3 significant figures. (area of a circle = pi x r^2)
- Find the radius: radius = diameter / 2 = 18 / 2 = 9 mm.
- Write down the formula: area = pi x r^2.
- Substitute the radius: area = pi x 9^2 = pi x 81.
- Calculate: pi x 81 = 254.469...
- Round to 3 significant figures: 254 mm^2.
- Final answer: the area of the clear zone is 254 mm^2.
Practice questions
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Q1Which type of pathogen causes athlete's foot, a fungal skin infection?Show answer
Answer: A fungus.
Q2State one way that pathogens can be spread from person to person.Show answer
Answer: Direct contact (also accept: through the air/droplet infection, contaminated water, or contaminated food).
Q3Name the vector that spreads the protist pathogen that causes malaria.Show answer
Answer: The mosquito.
Q4Describe how phagocytes destroy pathogens in the body.Show answer
Answer: A phagocyte engulfs the pathogen, then digests/destroys it.
Q5A student measures the mean diameter of a zone of inhibition as 12 mm. Calculate its radius.Show answer
Answer: 6 mm (12 / 2)
Q6Explain why a small number of healthy volunteers are given a very low dose of a new drug in the first stage of a clinical trial.Show answer
Answer: To check the drug is safe (not toxic) and to identify any side effects before testing higher doses or testing on patients.
Exam-style questions
Written in the style of a GCSE Science exam paper, with a full mark scheme.
Describe three ways that the human body's non-specific defences prevent pathogens from entering the body.
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Explain how vaccinating a large proportion of a population against a disease such as measles can also protect the small number of people who have not been vaccinated.
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A student compared two antibiotics, C and D, using the zone of inhibition method. Antibiotic C produced a mean clear zone diameter of 24 mm. Antibiotic D produced a mean clear zone diameter of 10 mm, giving an area of 78.5 mm^2. (a) Calculate the area of the clear zone for Antibiotic C, to 3 significant figures. (area of a circle = pi x r^2) (b) Use both areas to determine which antibiotic was more effective, explaining your reasoning.
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Free printable worksheet
Want more practice on paper? Download the infection and response worksheet pack - 15 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 3 of GCSE Biology Workbook, the whole course as one free printable PDF.
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