Ch 3 · Hormones · IGCSE Biology 0610
Topic 3 of 5 in Coordination and Response — IGCSE Biology 0610 — 48 lessons.
Introduction
The nervous system is not the body's only way of sending messages. A second system uses hormones, chemical messengers released into the blood, to coordinate processes such as growth, reproduction, blood glucose control and the response to danger. Hormones act more slowly than nerve impulses but their effects last far longer. This lesson gives the Cambridge definition of a hormone, locates the main endocrine glands, examines adrenaline in detail and, at Extended level, compares the two coordination systems.
Key ideas — What a hormone is
A hormone is a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs. Every phrase matters:
🧑🏫 Teacher's explanation
Imagine a city where the mayor (the brain) cannot shout orders to every citizen individually. Instead, the mayor sends a sealed letter (a hormone) into the main water supply (the blood). The letter travels to every house, but only the houses with a specific lock (receptor) on the door can open it. This is how hormones work: they are chemical messengers, not electrical signals like the nervous system. They are slow to arrive but their effect lasts a long time, unlike the quick, short-lived electrical impulses of nerves.
📖 Definitions
🔍 Worked example — Easy
Define a hormone in your own words, ensuring you include the three key components of the Cambridge definition.
🔍 Worked example — Standard
Explain why a hormone traveling through the blood does not affect every cell in the body, even though it passes by them.
🔍 Worked example — Exam-style
Compare the speed of action and duration of effect of a hormone (like adrenaline) with a nerve impulse. Explain why the hormonal response is slower but longer-lasting.
⚠️ Common errors
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🎯 Exam question
Key ideas — The main endocrine glands
You must identify these glands on a diagram of the human body:
🧑🏫 Teacher's explanation
Think of the endocrine system as the body's long-distance postal service. While the nervous system is like a fast courier delivering urgent messages via electrical wires (nerves), hormones are like letters sent through the bloodstream. They travel everywhere, but only the specific organs with the right 'address' (receptors) open and read them. This ensures that a signal from the brain or a gland can precisely change the activity of a distant target, like the liver or muscles, without affecting every other cell in the body.
📖 Definitions
🔍 Worked example — Easy
Identify the endocrine gland located on top of each kidney and name the hormone it secretes.
🔍 Worked example — Standard
A student is startled by a loud noise. Describe the immediate physiological changes caused by adrenaline and explain why these changes are beneficial in this situation.
🔍 Worked example — Exam-style
Compare the nervous system and the hormonal system in terms of speed of action and duration of effect. Use the example of a hand touching a hot surface versus the action of adrenaline.
⚠️ Common errors
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🎯 Exam question
(b) Explain why the hormonal response to stress lasts longer than the nervous response. (2 marks) [5 marks]
Key ideas — Adrenaline: the fight or flight hormone
Adrenaline is the hormone secreted in fight or flight situations: moments of fear, stress or excitement when the body may need to act quickly. Its effects prepare the body for vigorous action:
🧑🏫 Teacher's explanation
Imagine you are walking through a dark park and suddenly hear a loud crash behind you. Your heart starts pounding, your breathing gets faster, and your eyes widen to see better. This is not a conscious decision; it is your body preparing for action. This rapid preparation is driven by adrenaline, a chemical messenger that tells your organs to get ready for vigorous activity.
📖 Definitions
🔍 Worked example — Easy
Define the term hormone and identify the gland that secretes adrenaline.
🔍 Worked example — Standard
Describe the effects of adrenaline on the body and explain how these changes prepare the body for vigorous action.
🔍 Worked example — Exam-style
A student is sitting a difficult examination and feels nervous. Explain the role of the brain and the adrenal glands in the release of adrenaline in this situation.
⚠️ Common errors
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🎯 Exam question
(b) Describe two effects of adrenaline on the body and explain how these changes prepare the body for vigorous action. (4 marks) (c) Explain the role of the brain in the release of adrenaline during a stressful situation. (2 marks) [8 marks]
Key ideas — Nervous versus hormonal control
🧑🏫 Teacher's explanation
Imagine your body has two communication networks. The nervous system is like a high-speed fibre-optic internet connection: it sends electrical signals along specific wires (neurones) to a single device (muscle or gland) instantly. It is fast and precise, but the connection drops as soon as the signal stops. Hormonal control is like sending a broadcast radio signal or a text message to a group chat: a chemical (hormone) is released into the blood and travels everywhere, but only specific organs with the right 'receivers' (target organs) respond. This is slower to start but keeps working for a long time.
📖 Definitions
🔍 Worked example — Easy
Define a hormone and state one feature that distinguishes hormonal control from nervous control in terms of the medium of transmission.
🔍 Worked example — Standard
A student is chased by a dog. Describe the effects of adrenaline on the student's body and explain why these changes are useful in this situation.
🔍 Worked example — Exam-style
Compare nervous and hormonal control in terms of speed of action and duration of effect. Explain why nervous control is suitable for withdrawing a hand from a hot surface, while hormonal control is suitable for regulating blood glucose levels.
⚠️ Common errors
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🎯 Exam question
Worked example
🔍 Worked example — Easy
Identify the endocrine gland that secretes adrenaline and name one other endocrine gland shown in a standard human anatomy diagram.
🔍 Worked example — Standard
Describe the three main physiological effects of adrenaline on the body and explain the purpose of these changes.
🔍 Worked example — Exam-style
Compare nervous and hormonal control in terms of speed of action and duration of effect. Use the example of a student giving a speech.
⚠️ Common errors
Common mistakes
Practice
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