SEC G3 Combined Science Biology component K327/K328
B7: Infectious Diseases in Humans
Distinguish infectious disease, transmission, vaccination, antibiotics, and resistance through named examples.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Infectious-disease control follows a causal chain from pathogen and transmission route to symptoms, prevention, treatment limits, and resistance.
Disease classes and transmission
An infectious disease can spread between people; influenza and pneumococcal disease are examples. A non-infectious disease, such as type 2 diabetes or coronary heart disease, cannot spread between people. Infectious diseases are caused by pathogens including bacteria and viruses and may spread through body fluids, food, or water.
The structures of bacteria and viruses are not required here. Focus on the responsible pathogen type and how it moves between hosts.
Influenza and pneumococcal disease
Influenza is viral and commonly produces fever, cough, sore throat, fatigue, and body aches. Pneumococcal disease is bacterial and can produce fever, cough, chest pain, breathing difficulty, or more severe invasive disease.
Both pathogens can spread in respiratory droplets and secretions during close contact. Transmission can be reduced through appropriate vaccination, respiratory hygiene, hand hygiene, ventilation, avoiding close contact while ill, and safe handling of respiratory secretions.
Vaccines, antibiotics, and resistance
A vaccine contains an agent resembling a pathogen and prepares white blood cells to produce antibodies quickly when the pathogen later invades.
Antibiotics kill bacteria but do not work against viruses. Misuse and overuse increase selection for resistant bacteria, which survive, reproduce, and become more common.
Formulae and relationships
This chapter is assessed mainly through models, field patterns and explanations. Build the causal chain before adding any calculation.
Worked examples
Example 1: Why should antibiotics not be used to treat uncomplicated influenza?
- Influenza is caused by a virus.
- Antibiotics act against bacteria, not viruses.
- Unnecessary use also favours antibiotic-resistant bacteria.
Answer: They do not treat the viral cause and their misuse can accelerate resistance.
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Explain Disease classes and transmission with the named terms, evidence, and causal links kept distinct.
- Use Influenza and pneumococcal disease to interpret the evidence given and justify each conclusion.
- Apply Vaccines, antibiotics, and resistance to a new example, then check the conclusion against the information given.
Official outcome coverage
K327 B7: 7 mapped outcomes, references B7(a), B7(b), B7(c), B7(d), B7(e), B7(f), B7(g). Check the official K327 syllabus.
K328 B7: 7 mapped outcomes, references B7(a), B7(b), B7(c), B7(d), B7(e), B7(f), B7(g). Check the official K328 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Interpret transmission, vaccination or antibiotic-resistance data. Identify the pathogen type and transmission route, compare like groups, and do not infer that antibiotics treat a virus or that correlation alone proves a preventive effect.
Exam traps and retrieval check
Avoid these traps
- Calling every disease infectious.
- Claiming antibiotics kill viruses.
- Saying an individual bacterium deliberately becomes resistant because it needs to.
Check from memory
Which pathogen causes influenza?
Influenza virus.
What do vaccines prepare white blood cells to make?
Antibodies quickly after later exposure.
Why does antibiotic resistance spread?
Resistant bacteria survive selection and reproduce.
Official Combined Science scope
This shared Combined Biology owner serves both K327 and K328. Infectious and non-infectious disease, pathogens without pathogen structure, influenza, pneumococcal disease, vaccination, antibiotics, and resistance.