OCR GCSE Biology A: Endocrine system, thyroxine, adrenaline and menstrual cycle (J247) – Revision Notes

These notes condense statements B3.2a to B3.2d of module B3.2 in the OCR GCSE (9-1) Gateway Science Biology A (J247) specification, Version 4.0 (August 2026), for first assessment in 2018. B3.2b and B3.2d are in bold in the specification, so they are Higher Tier only and are labelled. For the full explanations and worked data examples, read the study guide. Test yourself with the practice questions. Course pages: OCR GCSE Biology hub | checklist | free diagnostics.

B3.2a: Hormonal control (both tiers)

• Hormone: a chemical messenger made in an endocrine gland and released directly into the blood.
• Carried in the blood plasma to all parts of the body.
• Only target cells respond, because only they have receptors that fit that hormone.
• Endocrine glands have no ducts.

Gland	Hormone
Pituitary	FSH, LH
Thyroid	Thyroxine
Adrenal	Adrenaline
Ovary	Oestrogen, progesterone
Testis	Testosterone

The thyroid and adrenal rows link to B3.2b, which is Higher Tier only.

Nervous	Hormonal
Electrical impulses	Chemicals in the blood
Fast	Slower
Short-lived	Longer-lasting
Specific area	Can be widespread

Model answer pattern: “released into the blood, so it reaches all tissues; only cells with receptors respond.”

B3.2b: Thyroxine and adrenaline (Higher Tier only)

Thyroxine

• Made by the thyroid gland (needs iodine).
• Controls metabolic rate: more thyroxine, faster reactions in cells.
• Example of negative feedback.

Negative feedback in steps:

1. Level of thyroxine in the blood is detected.
2. Level too low: more thyroxine released.
3. Level too high: less thyroxine released.
4. Level returns to the normal range.

Change	Response	Result
Thyroxine falls	More released	Level rises
Thyroxine rises	Less released	Level falls

Key phrase: the response reverses the change.

Adrenaline

• Made by the adrenal glands, released in fear, shock or excitement.
• Prepares the body for “fight or flight”.
• Effects: faster heart rate and stronger beat, faster breathing, glucose released from the liver into the blood, more blood to muscles.
• Net result: muscles receive more oxygen and glucose for respiration.

Small worked reminder. Heart rate rises from 80 to 140 beats per minute. Increase = 60. Percentage increase = 60 / 80 x 100 = 75%.

B3.2c: Hormones in reproduction (both tiers)

Hormone	Made in	Role
Testosterone	Testes	Male puberty changes; stimulates sperm production
Oestrogen	Ovaries	Female puberty changes; helps control the cycle; thickens the uterus lining
FSH	Pituitary	Egg matures in the ovary; ovary makes oestrogen
Progesterone	Ovaries (after ovulation)	Maintains the uterus lining

The cycle in outline

Days (typical)	Event
1 to 5	Menstruation (lining leaves the body)
5 to 14	Egg matures; lining rebuilds
About 14	Ovulation
15 to 28	Lining maintained; if no fertilised egg arrives, lining breaks down

• Day 1 is the first day of bleeding.
• The lining is already thick when the egg is released, so a fertilised egg can embed.
• In pregnancy the lining is kept and there is no menstruation.

B3.2d: Interactions of the four hormones (Higher Tier only)

LH is named only in this statement. Learn the chain.

1. FSH matures an egg and stimulates oestrogen production.
2. Oestrogen thickens the lining, inhibits FSH and stimulates an LH surge.
3. LH surge triggers ovulation.
4. Empty follicle makes progesterone: keeps the lining thick, inhibits FSH and LH.
5. No fertilisation: progesterone and oestrogen fall, the lining breaks down, FSH is released from inhibition and the next cycle starts.

Reading hormone graphs: method

1. Name the axes and units (days; arbitrary units).
2. Find the peak: LH peak is at ovulation; progesterone peak is in the second half.
3. Read values at exact days, using a ruler if needed.
4. For a percentage change: (new - old) / old x 100.
5. Link two hormones with a cause and effect: “as oestrogen rises, FSH falls”.
6. Use data in the answer: quote the number and the day.

Small worked reminder. Oestrogen is 40 units on day 6 and 160 units on day 12. Change = 120. Percentage increase = 120 / 40 x 100 = 300%.

Worked reminder: explain a hormone graph (Higher Tier only)

A table gives LH as 4 units on day 11 and 33 units on day 14, with progesterone at 2 units on day 14 and 24 units on day 21.

• LH rises from 4 to 33 units in three days. This surge triggers ovulation, so ovulation is expected at about day 14.
• Progesterone is still low on day 14 and then rises to 24 units by day 21. It is made after ovulation, so a rise after the LH peak fits an empty follicle making progesterone.
• A high progesterone level in the second half of the cycle keeps the lining thick, which prepares the uterus for a fertilised egg.

A strong answer names the hormone, quotes the day and the value, and says what the change causes.

Worked reminder: table to graph

Given days 2, 6 and 10 with FSH 7, 6 and 4 units: draw day on the x-axis with an even scale, units on the y-axis, plot the three points and join them. Label the axis with the unit and give the line a key if there is more than one hormone. To go back from a graph to numbers, read across from the line to the y-axis at the exact day.

Phrases worth learning word for word

• “A hormone is a chemical messenger secreted by an endocrine gland directly into the blood.”
• “Only target cells have receptors for that hormone.”
• “This is negative feedback because the change causes a response that reverses it.”
• “Adrenaline increases heart rate, so more oxygen and glucose reach the muscles for respiration.”
• “FSH causes an egg to mature; LH causes ovulation.”
• “Oestrogen thickens the lining; progesterone maintains it.”
• “Falling progesterone means the lining breaks down.”

Command words in this topic

Command word	What to do
State / name	Give the fact or term only
Describe	Say what happens, in order, using the data if there is any
Explain	Give a reason: because, so, which causes
Calculate	Show the working and give the unit or percentage sign
Compare	Give a similarity or a difference in the same feature for both items

Must-know distinctions

Pair	Difference
FSH and LH	FSH matures the egg; LH triggers ovulation
Oestrogen and progesterone	Oestrogen rebuilds and thickens the lining; progesterone maintains it
Hormonal and nervous	Blood-borne and slower, versus impulses and fast
Negative feedback and just “a response”	The response must reverse the original change
Adrenaline and thyroxine	Adrenaline: short-term, emergencies. Thyroxine: metabolic rate, set by feedback

Quick self-test

1. State what is meant by a target cell.
2. Name the gland that makes thyroxine.
3. State two effects of adrenaline on the body.
4. Name the hormone that triggers ovulation.
5. A person’s thyroxine level is 60 units, then drops to 45 units. Calculate the percentage fall.
6. Explain what happens to thyroxine release when blood thyroxine rises above normal.
7. Name two hormones made in the ovary.
8. State the job of progesterone in the second half of the cycle.
9. Explain why the uterus lining is thick at ovulation.
10. Explain what causes menstruation to begin.
11. Give one similarity and one difference between testosterone and oestrogen.

Answers

1. A cell with receptors for a particular hormone, so it responds to that hormone.
2. The thyroid gland.
3. Any two: heart rate rises; breathing rate rises; glucose released from the liver; more blood sent to muscles.
4. LH (luteinising hormone), in a surge.
5. (60 - 45) / 60 x 100 = 25% fall.
6. Less thyroxine is released, so the level falls back to normal (negative feedback).
7. Oestrogen and progesterone.
8. It maintains the thick lining of the uterus (and inhibits FSH and LH).
9. Oestrogen has been rebuilding it since the end of menstruation; FSH has stimulated oestrogen production.
10. Progesterone (and oestrogen) fall after the empty follicle breaks down, so the lining cannot be maintained.
11. Similarity: both are sex hormones that bring about the changes of puberty. Difference: testosterone is made in the testes and stimulates sperm production; oestrogen is made in the ovaries and helps control the menstrual cycle.

Questions 2, 3, 4, 5, 6 and 10 draw on Higher Tier only content (B3.2b and B3.2d).

Where marks are usually lost

• Writing that hormones travel through nerves or tubes instead of the blood.
• Forgetting the receptor idea when asked why only some cells respond.
• Describing negative feedback without saying the response reverses the change.
• Saying adrenaline “gives energy” rather than naming a specific effect and its benefit.
• Mixing up FSH (matures the egg) and LH (triggers ovulation).
• Saying progesterone or oestrogen “causes” bleeding when the point is that their fall lets the lining break down.
• Starting percentage-change calculations from the wrong value (divide by the original).
• Quoting a graph value without the day or the unit, or reading the wrong curve.
• Describing a hormone graph without using any numbers from it.

Official syllabus

OCR GCSE (9-1) Gateway Science Biology A (J247), specification Version 4.0 (August 2026), for first assessment in 2018, published by OCR. Module B3.2, statements B3.2a to B3.2d.