Hormone — the four-element definition
A hormone is a chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs. Four elements, usually one mark each: CHEMICAL → GLAND → BLOOD → TARGET ORGAN. The blood carries it everywhere, but only cells with the matching receptor respond, which is what makes the effect specific. After acting, hormones are broken down — mainly by the liver — so levels do not build up indefinitely.
Adrenaline — source, trigger, effects
Adrenaline is secreted by the adrenal glands (one above each kidney) in fear, stress, excitement or danger. Its effects: heart rate and force of contraction rise; breathing rate and depth increase; the bronchi dilate; the pupils dilate; blood vessels to the muscles dilate while those to the gut constrict; the liver converts glycogen to glucose. Together these deliver more oxygen and glucose to the muscles for aerobic respiration — the "fight or flight" response.
(Extended) Nervous vs hormonal control
Nervous control transmits electrical impulses along neurones (with a chemical neurotransmitter at each synapse); hormonal control sends a chemical in the blood. Nervous control is fast — a fraction of a second — but short-lived, stopping almost as soon as the stimulus stops, and usually acts on one specific effector. Hormonal control is slow (seconds to hours) but long-lasting, and can affect many target organs at once.
Drawn from real examiner reports.
Hormone ≠ "a chemical messenger"
"A chemical messenger" or "a substance released by the body" earns little credit. The mark scheme wants all four elements: a chemical substance, produced by a gland, carried by the blood (the transport route), altering a specific target organ (not "affecting the body"). Each element is normally worth a separate mark, so a vague one-line answer caps at 1.
Cambridge mark schemes consistently require the full four-element definition — vague definitions of precisely-defined terms recur across sittings (e.g. "species", s23 Paper 12 Q2).
Muscle vessels dilate, gut constrict
Under adrenaline the vessels supplying the muscles dilate, raising blood flow and delivering more oxygen and glucose for respiration. The vessels supplying the gut constrict, cutting blood flow because digestion is not a priority. Candidates routinely reverse the pair. Anchor it to the reason: blood is reallocated to the organs needed for immediate physical action.
Confusing the direction of dilation/constriction recurs across circulatory topics (e.g. artery/vein lumen size, s23 Paper 22 Q18); the same care applies to adrenaline.
Pupils and bronchi dilate, not constrict
Adrenaline widens — never narrows — these two. The pupils dilate, improving vision of the surroundings, and the bronchi dilate, so more air reaches the lungs. Writing that adrenaline constricts the pupils or the airways contradicts the whole purpose of the response, which is to prepare the body for rapid physical action.
One-sided nervous vs hormonal answers
(Extended) A "compare" question needs marking points on both sides. Stating that nervous control is fast and stopping there earns at most one mark; the answer must add that hormonal control is comparatively slow, and ideally contrast duration (short-lived vs long-lasting) and specificity (one effector vs many target organs).
Comparison answers left one-sided (nervous side only) recorded in w22 Paper 43 Q1c.
Hormone ≠ neurotransmitter
Both are chemicals, but a hormone travels in the blood from a gland to distant target organs, acting slowly and for a long time. A neurotransmitter crosses a synapse — the tiny gap between two neurones — acting locally and almost instantly. Describing hormonal transmission as "crossing a synapse" loses the transmission-route mark in a comparison.
Endocrine ≠ exocrine gland
Endocrine glands — such as the adrenal glands — have no duct: they secrete hormones straight into the blood. Exocrine glands, such as the salivary glands, release their product through a duct to where it is needed. Presence or absence of a duct is the distinguishing feature; writing "gland" alone does not show which type you mean.
One mark per definition element
Count the marks. A 3-mark "define hormone" question wants three of: chemical substance; produced by a gland; carried by the blood; alters the activity of a target organ. Write all four elements and you cannot drop a mark on a technicality.
Illustrate with adrenaline
Asked to illustrate hormonal control, use adrenaline: produced by the adrenal glands, carried in the blood, acting on the heart, lungs, pupils and blood vessels at once — a concrete example of one hormone reaching many target organs, slowly and for a sustained period.
Three rows: speed, duration, reach
Answer every nervous-vs-hormonal comparison from the same three rows — speed of action, duration of response, and method/area of transmission. One explicit both-sides sentence per row is a reliable full-mark structure.
Use comparative words
Write "faster/slower", "shorter/longer", "one specific effector/many target organs". Comparative wording proves you have compared; two separate descriptions sitting side by side often fail to earn the comparison marks.
Hormone: a chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more (specific) target organs. Hormones are eventually broken down (destroyed), mainly by the liver.
Gland: an organ that produces and secretes a substance. Endocrine glands (e.g. adrenal glands, pituitary gland, thyroid gland, pancreas, ovaries, testes) secrete hormones directly into the blood — they have no duct.
Target organ: the specific organ (or organs) whose activity is altered by a hormone. Only cells bearing the matching receptor respond to a given hormone, even though the hormone is carried everywhere in the blood.
Which gland secretes adrenaline, and in response to what?
(a) Define the term "hormone." [3]
(b) State the gland that secretes adrenaline. [1]
(c) State ONE situation that would trigger the release of adrenaline. [1]
