Hormonal coordination

5. Homeostasis and Response

The second way of sending information around the body. Instead of electrical impulses along neurones, chemical messengers travel in the blood - slower to act, but their effects last much longer.

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221 questions9 subtopicsFoundation and Higher1 required practical

What hormonal coordination covers

Every subtopic below has its own questions, mark schemes and notes.

4.5.3.1The endocrine system

The second way of sending information around the body. Instead of electrical impulses along neurones, chemical messengers travel in the blood - slower to act, but their effects last much longer.

4.5.3.2Controlling blood glucose

The pancreas keeps blood glucose steady using two hormones that pull in opposite directions: insulin brings it down, glucagon brings it back up. Diabetes is what happens when that control fails.

4.5.3.3Water and nitrogen balance

The kidneys clean the blood by filtering everything small out of it and then taking back only what the body needs. What is left becomes urine.

4.5.3.4Hormones in reproduction

Four hormones run the menstrual cycle between them: two from the pituitary that act on the ovary, and two from the ovary that act on the uterus lining and back on the pituitary.

4.5.3.5Contraception

Contraception works either by using hormones to stop eggs maturing and being released, or by physically keeping the sperm and the egg apart. Exam questions usually ask you to weigh methods against each other, not just name them.

4.5.3.6Treating infertility

Higher Tier only. Understanding what FSH and LH do naturally is what makes it possible to use them artificially to help someone become pregnant.

4.5.3.7Adrenaline, thyroxine and negative feedback

Higher Tier only. Two more hormones: one for emergencies, one for the everyday running speed of the body. Thyroxine is the classic example of negative feedback keeping a level steady.

4.5.4.1Plant hormones and tropisms

Plants grow in useful directions because auxin does not spread evenly. The same uneven distribution bends a shoot one way and a root the other, because the two organs respond to auxin in opposite ways.

4.5.4.2Using plant hormones

Higher Tier only. Three hormones, several jobs each. The trick is keeping straight which hormone does what: auxins for weeds and roots, gibberellins for flowering, fruit size and germination, ethene for ripening.

Key terms

The definitions examiners expect, in the wording that earns the mark.

Hormone — A chemical made by a gland and carried in the blood to a target organ, where it produces an effect.

Endocrine gland — A gland that secretes hormones directly into the blood rather than along a duct.

Target organ — The organ whose cells respond to a particular hormone.

Insulin — The hormone from the pancreas that lowers blood glucose by moving it into cells and storing it as glycogen.

Glucagon — The hormone from the pancreas that raises blood glucose by converting stored glycogen back into glucose.

Glycogen — The insoluble storage carbohydrate held in the liver and muscles.

Filtration — The removal of small substances from the blood as it passes through the kidney.

Selective reabsorption — Taking useful substances such as glucose, some ions and water back into the blood after filtration.

Deamination — The breakdown of excess amino acids in the liver, producing ammonia.

ADH — Anti-diuretic hormone, released by the pituitary gland; it makes the kidney tubules reabsorb more water.

Ovulation — The release of an egg from an ovary, at about day 14 of the cycle.

Follicle — The structure in the ovary in which an egg matures.

FSH — Follicle stimulating hormone, from the pituitary; it causes an egg to mature.

LH — Luteinising hormone, from the pituitary; it stimulates the release of the egg.

Barrier method — A non-hormonal method that physically stops sperm reaching an egg.

Spermicide — A substance that kills or disables sperm.

Sterilisation — A permanent surgical method: cutting or tying the fallopian tubes or the sperm ducts.

IVF — In vitro fertilisation: eggs are fertilised outside the body and the resulting embryos are transferred to the uterus.

Fertility drug — A drug containing FSH and LH, given to stimulate ovulation.

Adrenaline — The hormone from the adrenal glands that prepares the body for fight or flight.

Basal metabolic rate — The speed at which the body's chemical reactions happen while it is at rest.

TSH — Thyroid stimulating hormone, released by the pituitary gland to make the thyroid release thyroxine.

Negative feedback — A control system in which a change away from normal triggers a response that reverses it.

Auxin — The plant hormone that controls growth near the tips of shoots and roots by stimulating cell elongation.

Phototropism — The growth of a plant in response to light.

Gravitropism — The growth of a plant in response to gravity; also called geotropism.

Cell elongation — Existing cells getting longer, which is how auxin causes growth.

Selective weedkiller — A weedkiller containing auxins that kills broad-leaved plants but not narrow-leaved grasses and cereals.

Rooting powder — A powder containing auxins that makes a cutting grow roots quickly.

Dormancy — When a seed will not germinate until it has been through certain conditions, such as cold or dryness.

Where marks get lost

The mistakes that come up again and again in this topic.

The blood carries a hormone everywhere. What makes it specific is that only the target organ's cells can respond - not that the blood delivers it to one place.
If a response is fast and short, call it nervous. If it lasts a while afterwards, call it hormonal.
A question asking you to identify a gland on a diagram is a recall mark. Learn the six positions.
Glycogen is a store; glucagon is a hormone. Handwriting that leaves the examiner guessing gets no mark.
Type 1 is a supply problem, Type 2 is a response problem. Saying Type 2 patients 'make no insulin' is wrong.
Percentage change is always divided by the value you started with.
The liver makes urea; the kidney removes it. Swapping the two is the most common error in this section.
The brain detects the change, but the pituitary gland releases the ADH.
For dialysis, always explain movement in terms of a concentration gradient and diffusion - that is where the marks are.
Oestrogen makes the lining grow; progesterone maintains it. The two get swapped constantly.
Oestrogen does opposite things to FSH and LH - inhibits one, stimulates the other.
FSH matures the egg, LH releases it. Both come from the pituitary.
Explaining how oestrogen prevents pregnancy needs the FSH step. 'It stops ovulation' on its own is worth little.
Only condoms protect against sexually transmitted diseases.
'Evaluate' means give both sides and then a judgement, weighing effectiveness, side effects, convenience and how permanent the method is.
Keep the IVF sequence in order: hormones, collect and fertilise, grow, transfer.
One or two embryos are transferred - enough to improve the chance of pregnancy without making a risky multiple birth likely.
Ethical questions here are not answerable by science alone, and exam answers are expected to say so.
The trigger for adrenaline release is nervous, but the response itself is hormonal - which is why the effects outlast the fright.
A high thyroxine level inhibits TSH, not thyroxine itself. Name the right hormone at each step.
Low thyroxine means a slow metabolism: tired, gaining weight, feeling cold. High thyroxine is the opposite.
Auxin makes cells elongate, not divide, when it causes growth near the tip.
Auxin ends up on the same side in both shoot and root - the difference is that it promotes growth in one and inhibits it in the other.
In the practical, a control variable only scores if you say how it is kept the same.
Gibberellin grows the fruit bigger; ethene ripens it afterwards. They are different stages.
For weedkillers, the broad-leaved versus narrow-leaved distinction is the mark, not just 'it kills weeds'.
Widespread weedkiller use reduces biodiversity - the specification links the two directly.

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