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

This guide covers statements B3.2a to B3.2d of module B3.2 (Coordination and control: the endocrine system) in the OCR GCSE (9-1) Gateway Science Biology A (J247) specification, Version 4.0 (August 2026), for first assessment in 2018. Statements B3.2b and B3.2d are in bold in the specification, so they are tested in the Higher Tier papers only. They are labelled “Higher Tier only” below. B3.2a and B3.2c are for both tiers. Contraception, fertility treatment and plant hormones are separate statements (B3.2e onwards) and are not covered here.

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What this unit covers

Statement	What you must be able to do	Tier
B3.2a	Describe how hormones coordinate and control the body: chemical messengers, transport in the blood, endocrine glands, receptors	Both
B3.2b	Explain the roles of thyroxine and adrenaline; thyroxine as an example of negative feedback	Higher Tier only
B3.2c	Describe the roles of oestrogen, progesterone, FSH and testosterone in human reproduction, including control of the menstrual cycle	Both
B3.2d	Explain how FSH, LH, oestrogen and progesterone interact in the menstrual cycle, including analysing hormone-level data and graphs	Higher Tier only

The specification also lists two mathematical skills for this module: extracting and interpreting data from graphs, charts and tables, and translating information between numerical and graphical form. Both are practised in the worked examples.

B3.2a: Principles of hormonal control

A hormone is a chemical messenger. It is made in an endocrine gland, released straight into the blood and carried around the body. It only changes the cells that have the right receptor for it. Those cells are the target cells (together they make a target tissue or organ).

Three ideas carry most of the marks:

• Endocrine glands have no ducts. They secrete hormones directly into the blood. This is why the system is called the endocrine system.
• Transport in the blood. Every hormone reaches nearly every tissue, because the blood goes everywhere. See Scaling Up for how the circulatory system works.
• Receptors. A receptor on or in a cell fits one hormone. Cells without that receptor do not respond.

Gland	Hormone(s) in this unit	Main target
Pituitary gland (base of the brain)	FSH, LH	Ovaries
Thyroid (neck)	Thyroxine	Most body cells
Adrenal glands (above the kidneys)	Adrenaline	Heart, liver, muscles, others
Ovaries	Oestrogen, progesterone	Uterus lining, pituitary gland, body tissues
Testes	Testosterone	Male reproductive organs and body tissues

The thyroid and adrenal rows link to B3.2b, which is Higher Tier only. The pancreas is also an endocrine gland. Its hormones belong to the next module and are not needed here.

Hormonal control compared with nervous control

Feature	Nervous system	Endocrine system
Message carried by	Electrical impulses along neurones	Chemicals in the blood
Speed of response	Very fast	Slower
Length of effect	Short	Often longer lasting
Area affected	Specific, targeted	Can be widespread

Worked example 1: why does FSH act on the ovaries and not on a leg muscle?

FSH is released into the blood by the pituitary gland, so it reaches the ovaries and the leg muscle alike. Ovary cells have receptors that fit FSH, so they respond. Muscle cells have no FSH receptors, so nothing happens. A full answer needs both points: transport everywhere, response only where receptors exist.

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

Thyroxine

Thyroxine is made by the thyroid gland. It controls the body’s metabolic rate, which is the rate of the chemical reactions in cells. A higher thyroxine level means a higher metabolic rate. It also matters for normal growth and development. The thyroid needs iodine to make thyroxine, which is why diet matters.

Thyroxine is the specification’s example of a negative feedback system. In negative feedback, a change in a level triggers a response that pushes the level back the other way.

1. The level of thyroxine in the blood is monitored (by the brain and pituitary gland).
2. If the level falls below normal, more thyroxine is released by the thyroid.
3. If the level rises above normal, less thyroxine is released.
4. The level returns to the normal range and stays close to it.

Worked example 2: a thyroxine dip (data)

A volunteer takes a drug that briefly blocks the release of thyroxine. Blood thyroxine is measured in arbitrary units, and the drug wears off before hour 2.

Hour	0	2	4	6	8	10
Thyroxine (units)	100	68	78	88	96	100

(a) Percentage fall by hour 2: (68 - 100) / 100 x 100 = -32%, a fall of 32%.

(b) Average rate of recovery from hour 2 to hour 10: (100 - 68) / (10 - 2) = 32 / 8 = 4 units per hour.

(c) Explain the recovery. The low level is detected, so the thyroid is stimulated to release more thyroxine. This is negative feedback: the change (a fall) causes a response that reverses it. As the level nears 100 the rate of rise slows (5, 5, 4 and then 2 units per hour in successive two-hour steps), because the stimulus for more release gets weaker as the level returns to normal.

Adrenaline

Adrenaline is made by the adrenal glands. It is released in situations of fear, shock or excitement and prepares the body for “fight or flight”. It acts quickly and its effects are short lived. Its main effects are:

• Heart rate rises and the heart beats more strongly, so blood carries oxygen and glucose to the muscles faster.
• Breathing rate rises, so more oxygen enters the blood.
• Blood glucose rises because glucose is released from stores in the liver, giving the muscles more fuel for respiration.
• Blood is redirected towards the muscles.

Worked example 3: heart rate and adrenaline

A person’s resting heart rate is 72 beats per minute. During a sudden fright it rises to 126 beats per minute.

Increase = 126 - 72 = 54 beats per minute. Percentage increase = 54 / 72 x 100 = 75%.

Why this helps: the faster, stronger heartbeat delivers oxygen and glucose to muscle cells for aerobic respiration, releasing energy for running or fighting.

B3.2c: Hormones in human reproduction

At puberty, sex hormones from the gonads bring about the secondary sexual characteristics and make reproduction possible.

• Testosterone is the main male sex hormone. It is made in the testes. It brings about the changes of puberty in boys (such as the growth of facial and body hair and a deeper voice) and stimulates sperm production.
• Oestrogen is the main female sex hormone. It is made in the ovaries. It brings about the changes of puberty in girls (such as breast development) and helps to control the menstrual cycle.
• Progesterone is made in the ovaries after ovulation. It maintains the lining of the uterus.
• FSH (follicle stimulating hormone) is made in the pituitary gland. It causes an egg to ripen in its follicle, and it prompts the ovary to secrete oestrogen.

The menstrual cycle in outline

The menstrual cycle is a monthly series of changes in the ovary and the uterus, averaging 28 days. Day 1 is the first day of bleeding.

Days (approx.)	Event
1 to 5	Menstruation: the lining of the uterus breaks down and leaves the body
5 to 14	An egg matures in an ovary; the uterus lining is rebuilt and thickens
About 14	Ovulation: a mature egg is released from the ovary
15 to 28	The lining is maintained; if the egg is not fertilised, the lining breaks down and the cycle restarts

Individual cycles vary, so treat these day numbers as typical values only.

The specification notes that learners often confuse the time of conception with the state of the uterus lining. Ovulation happens when the lining is already thick. If a fertilised egg arrives, it can embed in this thick lining. In pregnancy the lining is kept, so there is no menstruation.

B3.2d: Interactions of FSH, LH, oestrogen and progesterone (Higher Tier only)

LH (luteinising hormone) is the fourth hormone in the cycle. It is made in the pituitary gland, and a sudden surge of LH causes ovulation.

The four hormones form a chain.

1. FSH rises early in the cycle. It matures an egg in a follicle and stimulates the ovary to make oestrogen.
2. Oestrogen rebuilds and thickens the uterus lining. As it rises it inhibits FSH, which stops further eggs maturing. A high oestrogen level also prompts a sudden release of LH from the pituitary gland.
3. LH surges and triggers ovulation.
4. After ovulation the empty follicle becomes a structure that makes progesterone. Progesterone maintains the thick lining and inhibits FSH and LH, so no new egg develops.
5. If there is no fertilisation, the empty follicle breaks down, and progesterone and oestrogen levels fall. The lining can no longer be maintained and breaks down (menstruation). With progesterone low, the inhibition on FSH is lifted and the next cycle begins.

Hormone	Made in	Main effect	Acts on
FSH	Pituitary	Egg matures; oestrogen made	Ovary
LH	Pituitary	Triggers ovulation	Ovary
Oestrogen	Ovary	Repairs and thickens lining; inhibits FSH; stimulates LH surge	Uterus, pituitary
Progesterone	Ovary (after ovulation)	Maintains lining; inhibits FSH and LH	Uterus, pituitary

Worked example 4: analysing hormone data

The table shows hormone levels (arbitrary units) across one cycle. It is illustrative data written for this guide.

Day	2	5	8	11	13	14	15	17	20	23	26	28
FSH	6	7	6	4	3	5	3	2	2	2	2	5
LH	3	3	4	5	9	30	6	3	3	3	3	3
Oestrogen	20	30	70	150	220	190	120	100	140	160	70	30
Progesterone	1	1	1	1	1	2	6	14	28	30	12	3

(a) Which day is ovulation most likely? LH peaks at 30 units on day 14, so ovulation is expected around day 14 (shortly after the surge).

(b) Percentage increase in oestrogen from day 5 to day 13. (220 - 30) / 30 x 100 = 633% (to 3 significant figures). Oestrogen rises by about seven and a third times.

(c) Link the FSH pattern to oestrogen. FSH falls from 7 units on day 5 to 3 on day 13 (a fall of 57%) while oestrogen climbs. This fits oestrogen inhibiting FSH.

(d) What happens after day 23? Progesterone falls from 30 to 12 units by day 26, a fall of 60%, and oestrogen falls from 160 to 70 (a fall of 56%). The lining can no longer be maintained, so menstruation is expected soon after day 28. FSH rising again (2 to 5) fits the loss of inhibition.

Turning a table into a graph (translating between forms)

To draw this table as a graph: put day on the x-axis (0 to 28, a linear scale, with an even step), put hormone level on the y-axis, and use one labelled line per hormone or four small graphs stacked so the days line up. To read a graph back into numbers, read the value on the y-axis at the exact day, and state units if given.

Common errors

• Saying hormones travel “in the nervous system” or “through glands”. They travel in the blood.
• Writing that negative feedback “makes more of the hormone”. It reverses the change, so a rise causes a fall and a fall causes a rise.
• Giving adrenaline’s job as “gives energy”. Say what it does: raises heart rate and releases glucose, so muscles get more oxygen and glucose.
• Mixing up the days: bleeding is the start of the cycle, not the end. The lining is thick at ovulation.
• Writing “FSH makes the egg” or “LH makes the egg”. FSH matures it; LH triggers its release.

Next steps

Condense with the revision notes, then test yourself with the practice questions. For exam technique see OCR GCSE Biology exam preparation, and check gaps with the free diagnostics.

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.