Interpret inherited-response survival models
Calculate genotype contributions before judging population outcomes.
Exam scope and assessment notes
Extended only (Supplement) · 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
- Recall DNA, inherited characteristics, nuclei and the distinction between growth and reproduction.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
How many of eighty P plants survive at twenty-five percent?
What you will learn
- Use the original population denominators
- Separate variation from its reproductive origin
Interpret inherited-response survival models
Invented P survival 25%, Q 75%: uniform 80 P → 20 survivors; mixed 40 P + 40 Q → 40. Survival 25% versus 50%; difference 25 percentage points, relative increase 100%. Original teaching model.
| Group | Starting P | Starting Q | Survivors |
|---|---|---|---|
| Uniform P | 80 | 0 | 20 |
| Mixed P/Q | 40 | 40 | 40 |
| Feature | Meaning |
|---|---|
| Uniform | 80 P; 20 survivors |
| Mixed | 40 P and 40 Q; 40 survivors |
| Comparison | 25 percentage points; 100% relative increase |
| Limit | Stipulated responses; origin unspecified |
Use the original population denominators
The invented model compares eighty plants of genotype P with a mixed group containing forty P and forty Q. Under one specified stress, twenty-five percent of P and seventy-five percent of Q survive. The uniform group contains one supplied genotype, while the mixed group has two. Its origin must be stated separately; diversity alone is not a complete reproductive history.
The uniform group has 80 × 0.25 = 20 survivors. The mixed group has 40 × 0.25 = 10 P survivors and 40 × 0.75 = 30 Q survivors, giving forty. Both groups started with eighty, so survival is twenty-five percent versus fifty percent, a difference of twenty-five percentage points. Use each starting total, not the survivor count, as the survival denominator.
Separate variation from its reproductive origin
The relative increase from the uniform group survival fraction is (50 − 25)/25 × 100 = 100 percent, distinct from twenty-five percentage points. State the comparison requested. In this model, Q gives an advantage because its response to this particular stress is better. A different stress or equal response fractions could remove or reverse the advantage.
These are stipulated teaching outcomes, not measured field results proving a reproductive mode caused survival. The record does not establish how the mixed group arose or that all future stresses have the same response pattern. A useful discussion connects the possible benefit of inherited variation to the supplied stress while keeping population origin and experimental evidence separate.
Pause and explain
Does the mixed-group label prove how it reproduced?
Worked example
Under the stipulated stress, forty Q plants survive at seventy-five percent. Find survivors.
Show the worked solution
- Use the initial Q count.
- Forty times 0.75 is thirty.
Answer Thirty Q survivors.
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.
Calculate survivors in the uniform P and mixed P/Q groups.
Give me a hint
Calculate each genotype contribution.
Compare my reasoning
- Uniform: 80×0.25 = 20.
- Mixed: 40×0.25 + 40×0.75 = 40.
Uniform P: 20 survivors. Mixed P/Q: 40 survivors.
Look for these in your work
- Use supplied fractions
- Add both mixed contributions
Find survival percentages, their percentage-point difference and the relative increase from uniform survival.
Give me a hint
Use initial totals of eighty and the 25% baseline.
Compare my reasoning
- 20/80 = 25%; 40/80 = 50%.
- Difference 25 percentage points; 25/25×100 = 100%.
Survival 25% versus 50%; difference 25 percentage points; relative increase 100% from the uniform fraction.
Look for these in your work
- Use starting denominators
- Distinguish points from relative percent
Does this model prove a sexual origin and better survival under every future stress?
Give me a hint
Origin and other stress responses are not supplied.
Compare my reasoning
- The reproductive history is unspecified.
- The advantage depends on Q’s stipulated response here.
No. Mixed-group origin is unspecified, and the advantage is specific to the supplied stress responses; it is not proof of universal superiority.
Look for these in your work
- State missing origin evidence
- Qualify the stress-specific result
Common mistakes
- Dividing by survivors to find a survival fraction.
- Equating a mixed genotype group with a proved sexual history.
What can you explain now?
Does the mixed-group label prove how it reproduced?
Compare with the explanation
No; origin needs separate evidence
Diversity and reproductive history differ.
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Make it stick
Calculate genotype contributions, then qualify the survival and origin conclusions.
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.