To interpret hormone-cycle data, follow describe, calculate, explain: say what the values do, use numbers from the table, and link the change to what the hormone does in the body. The data in exam questions come from an idealised cycle, so the goal is biological understanding, never a prediction about one person.
This lesson sits inside human reproduction and development and builds on the structures in the diagram lesson.
What is the model cycle?
In a model 28-day cycle, the uterus lining thickens, an egg is released from an ovary (ovulation) near the middle, and the lining breaks down if no embryo implants. Oestrogen is made by the ovary and helps rebuild the lining. Progesterone is made after ovulation and maintains the lining.
When both hormones fall near the end, the lining breaks down and the cycle restarts. Pregnancy changes this pattern, because the lining must be kept.
Worked example
The data below are invented for teaching and are not from a real person or study.
| Day | Oestrogen (arbitrary units) | Progesterone (arbitrary units) |
|---|---|---|
| 1 | 10 | 1 |
| 7 | 30 | 1 |
| 13 | 90 | 2 |
| 14 | 60 | 3 |
| 21 | 50 | 40 |
| 26 | 15 | 10 |
| 28 | 10 | 2 |
Question: (a) On which day is oestrogen highest? (b) Calculate the percentage increase in oestrogen from day 7 to day 13. (c) Explain why progesterone is high on day 21.
(a) Read down the oestrogen column: the highest value is 90, on day 13.
(b) Step 1. Difference: 90 − 30 = 60 units. Step 2. Divide by the starting value: 60 ÷ 30 = 2. Step 3. Multiply by 100: 200% increase. Check: 30 × 3 = 90, so the value tripled, which is a rise of 200%.
(c) Progesterone is made after ovulation, and it maintains the thickened lining of the uterus. On day 21 the lining is being kept ready in case an embryo implants, so the level is high.
How do you write a good data answer?
- Quote numbers with units from the table, not just “it goes up”.
- Name the turning points, such as the peak day.
- Give the biological reason using the hormone’s role.
- Say “in this model” when generalising, because the data are idealised.
The mistake to watch for
Mistaken answer: “On day 14 the graph shows this person is fertile, so she will ovulate on day 14.”
This treats an idealised example as a measurement of an individual. A model graph shows the typical pattern of hormone roles, not a rule for any one person. Real cycles vary in length and timing.
The correction is to describe what the model shows, for example “in the model, oestrogen peaks just before ovulation”, and to leave personal questions to a doctor.
A second slip is forgetting units or giving a difference when the question asks for a percentage. Always read the command word.
Check yourself
Use the table above.
1. State the highest progesterone value and the day it occurs.
Show answer
40 arbitrary units on day 21.
2. Calculate the decrease in oestrogen from day 13 to day 28.
Show answer
90 − 10 = 80 arbitrary units decrease.
3. Suggest what happens to the uterus lining after day 26 if no embryo implants, and link it to the data.
Show answer
Both oestrogen and progesterone fall (oestrogen 15 to 10, progesterone 10 to 2), so the lining is no longer maintained and breaks down, which is menstruation.
Where this leads next
Next, see how genes and surroundings shape development in inherited and environmental influences. Then practise the routine on new data in the mixed practice set. The mistake log and retest queue can help you record any calculation slips.
If graph questions still feel like guesswork, our teachers can work through fresh data with you in online one-to-one Biology tuition.