Calculate a model progesterone change and explain its limits
Invented progesterone rises from 2 units on day 14 to 9 on day 22: rise 7 units, increase 350%, interval-average 0.875 units/day. These are relative teaching values and do not establish instantaneous rates or pregnancy.
Section 16.5 · Sex hormones in humans
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 endocrine glands, blood-borne hormones, ovaries, testes, uterine lining, ovulation and implantation.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is the relative increase from 2 to 9 units?
What you will learn
- Calculate difference relative change and average change
- Keep arithmetic separate from a clinical inference
Original teaching model.
| Feature | Meaning |
|---|---|
| Endpoints | Day 14:2; day 22:9 relative units |
| Absolute rise | 7 relative units |
| Relative increase | 350% |
| Interval average | 7 ÷8 =0.875 units/day |
Calculate difference relative change and average change
The invented progesterone series gives 2 relative units on model day 14 and 9 units on day 22. Subtracting the earlier level from the later level gives a rise of 7 units. Dividing the rise by the initial value gives 7 divided by 2, or 3.5, so the relative increase is 350%. This differs from saying the final value is 350% of the initial value; the final value is 450% of it.
The elapsed interval is 22 minus 14, or 8 days. Average change over the interval is 7 divided by 8, equal to 0.875 relative units per day. This is a secant or interval-average calculation, not evidence that the hormone increased at a constant rate every day. The model includes sparse samples and dashed visual joins, not continuous monitoring.
Keep arithmetic separate from a clinical inference
The rise after stipulated ovulation is consistent with increased progesterone production by the corpus luteum and support of the prepared uterine lining. Arithmetic identifies the size of change; biological reasoning identifies the source and function. Neither step should replace the other in an explanation, and a relative increase alone does not identify a tissue source without the supplied cycle context.
The units are invented relative levels, not concentrations from a medical test. They cannot be compared with personal health thresholds or used to diagnose pregnancy. A positive average change does not prove every intermediate change is positive, especially since other samples and later decline may differ. State the interval, unit and evidence limit with the numerical result.
Pause and explain
What is the average change over days 14 to 22?
Worked example
Find the difference from 2 to 9 relative units.
Show the worked solution
- Subtract 2 from 9.
- State rise with the model unit.
Answer A rise of 7 relative units.
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 the absolute rise and percentage increase from 2 to 9 units.
Give me a hint
Use the initial level as the percentage denominator.
Compare my reasoning
- Difference 9−2=7.
- Relative increase 7÷2×100.
Rise =7 relative units; percentage increase =350%.
Look for these in your work
- Give both quantities
- Use initial 2 as denominator
Calculate the interval-average change between days 14 and 22 and explain why it is not an instantaneous rate.
Give me a hint
Divide the rise by elapsed time.
Compare my reasoning
- Elapsed 22−14=8 days.
- Average 7÷8=0.875; sparse samples do not give every moment.
Average change =0.875 relative units/day over the 8-day interval; it does not establish the rate at each instant.
Look for these in your work
- Show elapsed interval
- State the rate limit
A learner uses the 350% rise to declare pregnancy and equal concentrations with oestrogen. Evaluate both claims.
Give me a hint
The series is invented and relative.
Compare my reasoning
- Reject diagnosis from teaching data.
- Reject cross-hormone concentration equality without matched units.
Neither claim follows: these relative teaching levels do not diagnose pregnancy or establish equal actual concentrations across different hormones.
Look for these in your work
- Reject both claims
- Keep the valid within-series arithmetic
Common mistakes
- 350% increase differs from 450% of initial.
- Average change does not establish a constant rate.
What can you explain now?
What is the average change over days 14 to 22?
Compare with the explanation
0.875 relative units per day
The rise 7 is divided by elapsed 8 days.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Explain calculate difference relative change and average change and keep arithmetic separate from a clinical inference. Follow the event arrows or graph labels before opening the solutions.
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.