Distinguish transmissible disease from other illness
Use movement of a pathogen between hosts to explain transmissibility.
Exam scope and assessment notes
Core and Extended · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Distinguish pathogens from symptoms.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is a host in this context?
What you will learn
- Transmission needs a pathogen route
- Distinguish shared risks from spread
Transmission needs a pathogen route
A transmissible disease is one in which a pathogen can pass from one host to another. A host supports the pathogen; an infected host can become a source for another host, directly or through an intermediate route. The condition is transmissible because the disease-causing agent can move, not because two people have similar symptoms.
In a supplied chain, infected host A contaminates an object and host B later acquires the pathogen from it. The indirect route still connects hosts. A disease need not spread by ordinary touch to be transmissible; the appropriate route may involve fluids, contaminated food, an animal or air.
Distinguish shared risks from spread
An inherited disorder does not become transmissible merely because several family members have it. Nor does a shared exposure to non-biological smoke mean a pathogen passed between people. Describe the cause and the route separately before deciding whether a case fits the biological definition.
Passing a pathogen does not guarantee every exposed host develops the same illness. Exposure amount, barriers and immune responses can affect outcomes. When evidence is limited, state what it supports: similar illness after a shared event can suggest a common source, but alone does not prove direct host-to-host transmission.
Pause and explain
What defines a transmissible disease?
Worked example
Two learners inherit the same non-infectious condition. Does its presence in both establish transmissibility?
Show the worked solution
- Ask whether a pathogen moved between hosts.
- The supplied cause is inheritance.
Answer No; shared inheritance is not passage of a pathogen between hosts.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Host A passes a supplied pathogen to host B through a contaminated cup. Is the disease transmissible?
Give me a hint
An intermediate object does not remove the host connection.
Compare my reasoning
- The pathogen leaves A.
- It reaches B through the cup.
Yes; the pathogen can pass between hosts indirectly through the cup.
Look for these in your work
- Identify both hosts
- Keep the intermediate route
Compare transmissible disease with a supplied illness caused only by a non-infectious chemical exposure.
Give me a hint
State the causal difference.
Compare my reasoning
- The first includes a disease-causing agent that can pass between hosts.
- The second supplied cause is not a pathogen.
The transmissible disease involves passage of a pathogen; the chemical illness described does not.
Look for these in your work
- Use pathogen passage
- Avoid comparison based only on symptoms
Three people become ill after a shared meal. Does that prove one directly infected the other two?
Give me a hint
Consider a shared source.
Compare my reasoning
- All may have acquired a pathogen from the meal.
- Timing and symptoms alone do not identify a direct route.
No; a common contaminated source is possible and direct person-to-person transmission is not proved.
Look for these in your work
- Give an alternative route
- Retain the evidence limit
Common mistakes
- Equating any shared illness with transmission.
- Assuming transmissible means only direct touch.
What can you explain now?
What defines a transmissible disease?
Compare with the explanation
Its pathogen can pass between hosts
This is the defining mechanism.
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Make it stick
Draw a transmissible chain and contrast it with an inherited condition.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.