Repair explanations of cycle hormones and pregnancy support
Explanation audit: check source, signal, target, feedback direction, event order and pregnancy condition. Relative classroom graphs support model reasoning rather than individual diagnosis.
Section B14.2 · Sexual reproduction in humans
Cross-referenced to the 2028–2029 0653 section using original teaching from the related single-science courses. A 0653-specific objective-by-objective and Core/Supplement review is in progress. Written practice is self-checked and does not demonstrate supervised laboratory competence or award an official Cambridge grade.
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
Which claim has a source error?
What you will learn
- Audit source signal target and feedback claims
- Use conditional evidence in a complete explanation
Original teaching model.
| Feature | Meaning |
|---|---|
| Sources | FSH/LH:pituitary; cycle steroids:ovary |
| Targets | Ovarian tissues and uterine lining |
| Conditions | Lower/moderate versus sustained high; pregnancy branch |
| Evidence | Invented relative levels and stipulated events |
Audit source signal target and feedback claims
To check a hormone explanation, first classify every named item. Pituitary, ovarian follicle, corpus luteum, placenta and uterine lining are structures; FSH, LH, oestrogen and progesterone are signals. FSH and LH have pituitary sources, while cycle oestrogen and progesterone have ovarian sources. Targets and responding tissues should not automatically be relabelled as the signal source.
Next check causal order. FSH stimulates follicle development and oestrogen production. Oestrogen rebuilds the lining and usually limits FSH; sustained high pre-ovulation oestrogen promotes the LH surge. LH triggers ovulation and supports corpus luteum. Progesterone from corpus luteum maintains lining and inhibits FSH/LH. A correct answer includes intermediates rather than turning every rise into immediate pregnancy.
Use conditional evidence in a complete explanation
Then check the branch condition. Without established pregnancy, corpus-luteum breakdown and declining oestrogen/progesterone lead to lining shedding and renewed cycle stimulation. With established pregnancy, hormonal support continues; early corpus-luteum contribution and later major placental production help maintain the lining. A single unconditional end-of-cycle statement cannot correctly describe both branches.
Finally check the evidence. Invented relative curves can illustrate timing, differences and average changes within a supplied model. They do not establish exact personal concentrations, unsampled peaks, nuclear fusion or pregnancy outcome. A repaired explanation should retain what the model supports while removing overclaims.
Sources for this lesson
Pause and explain
Which explanation correctly distinguishes cycle branches?
Worked example
Repair “the uterine lining secretes FSH to fuse nuclei”.
Show the worked solution
- Place FSH source at pituitary.
- Replace nuclear fusion with follicle-development stimulation.
Answer Pituitary FSH stimulates ovarian follicle development and oestrogen production; it does not itself fuse gamete nuclei.
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.
Repair “FSH from uterus releases an egg immediately and progesterone always sheds lining”.
Give me a hint
Fix source, named effect and lining role.
Compare my reasoning
- Name pituitary FSH promoting follicle development/oestrogen.
- Name LH release trigger and progesterone maintenance.
Pituitary FSH stimulates follicle development and oestrogen production; LH surge triggers ovulation; progesterone supports maintenance of the prepared lining.
Look for these in your work
- Repair all three claims
- Include the release intermediary
Give paired end-of-cycle explanations with and without established pregnancy.
Give me a hint
Make the branch condition explicit.
Compare my reasoning
- Without: corpus-luteum breakdown, support decline, shedding.
- With: continuing hormones and changing ovarian/placental sources.
Without established pregnancy, corpus luteum breaks down and oestrogen/progesterone fall before menstruation. In pregnancy support continues, with early corpus luteum and later major placental production maintaining lining.
Look for these in your work
- Explain both branches
- Name changing sources
A relative graph has sampled LH maximum day 13 and stipulated ovulation day 14. State a supported sequence and two unsupported claims.
Give me a hint
Separate model events from individual conclusions.
Compare my reasoning
- State LH maximum precedes model release.
- Reject exact personal concentrations and proven fertilisation.
The sampled LH maximum precedes the stipulated model ovulation. The graph does not establish personal hormone concentrations or prove sperm–egg nuclear fusion.
Look for these in your work
- Give the supported order
- Name both limits
Common mistakes
- Check category, source, order and condition.
- Model patterns do not prove individual outcomes.
What can you explain now?
Which explanation correctly distinguishes cycle branches?
Compare with the explanation
Support falls without established pregnancy but continues in pregnancy
It retains the conditional source and lining relationship.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain audit source signal target and feedback claims and use conditional evidence in a complete explanation. 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.