Explain why a person who is infected with a pathogen may not show symptoms of disease immediately.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
1. After infection there is an incubation period before symptoms appear.
2. During this time the pathogen must multiply or reproduce inside the host.
3. Symptoms only arise once the pathogen load (or toxin amount) reaches a critical level.
4. The person can still spread the pathogen to others while asymptomatic and therefore be contagious.
2. During this time the pathogen must multiply or reproduce inside the host.
3. Symptoms only arise once the pathogen load (or toxin amount) reaches a critical level.
4. The person can still spread the pathogen to others while asymptomatic and therefore be contagious.
Examiner tips
- Use the word ‘incubation period’ to show understanding of timing. Mention pathogen multiplication or toxin production as the trigger for symptoms. Explain that symptoms appear only after a threshold is reached. Highlight that the individual can still transmit the disease during the incubation period.
Common mistakes
- Confusing incubation period with latent period. Forgetting to mention the role of pathogen load or toxin. Saying the person is not contagious during the incubation period. Using vague terms like ‘time delay’ instead of ‘incubation period’.
Mark scheme (4 marks)
- There is an incubation period after infection
- The pathogen must multiply / reproduce inside the body
- Symptoms only appear once the number of pathogens (or toxins produced) reaches a sufficient level
- During the incubation period the infected person can still spread the pathogen to others / is contagious without knowing
Key terms in this question
Related
- All Eduqas GCSE Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →