Form 4 · Worked answers

Coordination and Response in Humans, worked answers

Fully worked answers for Coordination and Response in Humans, original structured and essay questions with mark-scheme keywords highlighted.

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How this topic is examined

Tracing the reflex arc from stimulus to response, naming each of the five parts in the correct order.
Comparing nervous and hormonal coordination in a table, covering speed, duration, and how the signal travels.
Matching a hormone to its gland and effect, including at least one example of negative feedback.
Explaining how a hormone disorder such as diabetes arises from too little insulin or reduced sensitivity to insulin.
Explaining how a nervous system disorder such as stroke or Parkinson's disease disrupts a normal action.
Interpreting or labelling a diagram of a neurone, a synapse, or the reflex arc.

Model answer structure

Read the command word and answer to the marks, one clear point per mark.
Define the key biological term precisely before you explain it.
Explain the process or reason in the correct sequence, using the right terms.
Where useful, add a labelled diagram or a worked example.
End with the link the question asks for (cause → effect, structure → function).

Fully worked answers

Trace the pathway of a reflex arc from a pin prick on a finger to the withdrawal of the hand, naming the five parts in order.

[6]

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A receptor in the skin of the finger detects the stimulus of the pin prick. A sensory neurone carries the impulse from the receptor towards the spinal cord. In the spinal cord, a relay neurone passes the impulse across to a motor neurone. The motor neurone carries the impulse away from the spinal cord to the effector. The effector, a muscle in the arm, contracts and pulls the hand away. The pathway is fast and automatic because it is processed in the spinal cord rather than by the brain.

receptor detects stimulussensory neurone to spinal cordrelay neuronemotor neurone to effectormuscle contractsprocessed in spinal cord

Compare nervous coordination and hormonal coordination, covering the type of signal, the speed and the duration.

[4]

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Nervous coordination uses electrical impulses carried along neurones, so it is very fast, precise and short-lived. Hormonal coordination uses chemical hormones carried in the blood, so it is slower to begin, more widespread and longer-lasting. A nerve impulse is targeted to one specific effector, while a hormone reaches all cells but only affects those with the matching receptor. The body uses nerves for quick responses and hormones for sustained changes such as growth.

electrical impulse vs chemical hormoneneurones vs bloodfast and short vs slow and longtargeted vs widespreadmatching receptor

Explain what happens at a synapse and why an impulse can only travel in one direction across it.

[4]

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A synapse is the small gap between the end of one neurone and the start of the next. When an impulse reaches the end of the first neurone, it triggers the release of a chemical neurotransmitter. The neurotransmitter diffuses across the gap and binds to receptors on the next neurone, starting a new impulse. Because the neurotransmitter is released only from the first neurone and the receptors are only on the next one, the impulse can cross in one direction only.

synapse is a gapneurotransmitter releaseddiffuses across the gapbinds to receptorsone direction only

A student is asked to match three hormones to their glands and effects. Name the gland that produces each hormone and state its effect: thyroxine, insulin and adrenaline.

[6]

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Thyroxine is produced by the thyroid gland and controls the metabolic rate of the body. Insulin is produced by the pancreas and lowers the blood glucose concentration by making cells take up glucose and the liver store it. Adrenaline is produced by the adrenal gland and prepares the body for a stressful or dangerous situation, for example by raising the heart rate. Each hormone travels in the blood but only affects cells with the matching receptor.

thyroxine thyroid metabolic rateinsulin pancreas lowers glucoseadrenaline adrenal glandprepares body for stressmatching receptor

Explain how negative feedback keeps the blood glucose concentration within the normal range after a meal and during fasting.

[5]

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After a meal the blood glucose concentration rises above normal. The pancreas detects this and releases insulin, which makes body cells take up more glucose and the liver store glucose as glycogen, so the concentration falls back towards normal. During fasting the blood glucose concentration falls below normal, so the pancreas releases glucagon, which makes the liver break down glycogen and release glucose into the blood, raising the concentration back towards normal. Insulin and glucagon are antagonistic, and this negative feedback holds the concentration within a narrow range.

glucose rises pancreas releases insulincells take up glucose liver stores glycogenglucose falls pancreas releases glucagonliver releases glucoseantagonistic negative feedback

Explain how diabetes mellitus arises and why it causes the blood glucose concentration to rise.

[4]

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Diabetes mellitus develops when the body produces too little insulin, or when the body cells stop responding normally to the insulin that is present. Insulin normally signals cells to take up glucose from the blood and the liver to store it as glycogen. When insulin is missing or ineffective, glucose is not taken up from the blood efficiently. As a result the blood glucose concentration rises above the normal range and stays high, which can damage blood vessels and organs over time.

too little insulin or poor responseinsulin signals cells to take up glucoseglucose not taken upblood glucose risesdamage over time

Explain how a stroke can impair a person's movement.

[4]

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A stroke occurs when the blood supply to part of the brain is interrupted, for example by a blocked blood vessel. The neurones in that region are starved of oxygen and glucose and begin to die. If the affected region is one that controls movement, the coordination of the muscles it controlled is lost or weakened. The person may therefore be unable to move part of the body normally, because the neurones that would send the impulses have been damaged.

blood supply to brain interruptedneurones starved of oxygenneurones dieregion controls movementcoordination lost

Distinguish between a voluntary action and an involuntary action, giving one example of each.

[3]

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A voluntary action is consciously decided and controlled by the brain, specifically the cerebrum, and can be started or stopped at will, for example picking up a pen. An involuntary action happens automatically without conscious control and usually protects or maintains the body, for example a reflex such as blinking or the beating of the heart. The key difference is that a voluntary action involves conscious choice, while an involuntary action does not.

voluntary conscious cerebrumcan be started or stopped at willinvoluntary automaticreflex or heartbeatno conscious control

Phrasing that earns marks

Nervous system: The nervous system is made up of the central nervous system, the brain and spinal cord, where most information is processed and decisions are made, and the peripheral nervous system, the network of nerves that carries electrical impulses between the central nervous system and every receptor and effector in the body.
Neurones: Sensory neurones carry impulses from a receptor towards the central nervous system, motor neurones carry impulses away from the central nervous system to an effector such as a muscle or gland, and relay neurones inside the brain or spinal cord connect the two, allowing impulses to be processed or redirected.
Synapse: A synapse is a tiny gap between the end of one neurone and the start of the next. When an impulse arrives, it triggers the release of a chemical neurotransmitter that diffuses across the gap and binds to receptors on the next neurone, generating a new impulse and ensuring signals travel in one direction only.
Reflex arc: A reflex arc is a fast, automatic, involuntary pathway that does not require conscious thought: a stimulus is detected by a receptor, carried by a sensory neurone to a relay neurone in the spinal cord, passed to a motor neurone, and finally reaches an effector, which responds within a fraction of a second.
Voluntary vs involuntary actions: A voluntary action, such as picking up a pen, is consciously decided and controlled by the brain, involves the cerebrum, and can be started, changed or stopped at will. An involuntary action, such as a reflex or the beating of the heart, happens automatically without conscious control and usually protects the body or maintains an internal process.
Endocrine system: The endocrine system is a collection of glands that release hormones directly into the bloodstream rather than through a duct. Each hormone travels throughout the body but only affects target cells that carry the matching receptor, producing effects that develop more slowly than a nerve impulse but often last for a much longer time.
Main hormones and glands: Four glands and their hormones are frequently examined: the pituitary gland releases growth hormone controlling body growth, the thyroid gland releases thyroxine controlling metabolic rate, the pancreas releases insulin and glucagon controlling blood glucose level, and the adrenal glands release adrenaline that prepares the body for a stressful or dangerous situation.
Negative feedback and homeostasis: Hormone levels are usually regulated by negative feedback: when a condition such as blood glucose level rises or falls away from normal, a gland releases a hormone that pushes it back towards normal, and once normal is restored the gland reduces hormone release again. This feedback loop is central to how the endocrine system maintains a stable internal environment.

Frequently asked questions

What is a reflex arc?

A reflex arc is the pathway of a reflex action: a receptor detects a stimulus, a sensory neurone carries the impulse to the spinal cord, a relay neurone passes it to a motor neurone, and the motor neurone triggers an effector (muscle or gland) to respond. It is fast and automatic because it does not wait for the brain to decide.

How is nervous coordination different from hormonal coordination?

Nervous coordination uses electrical impulses along neurones; it is very fast, precise and short-lasting. Hormonal coordination uses chemicals (hormones) carried in the blood; it is slower to start, more widespread and longer-lasting. The body uses both, nerves for quick responses and hormones for sustained changes such as growth.

What happens at a synapse?

A synapse is a small gap between two neurones. When an impulse reaches the end of the first neurone, it releases a chemical neurotransmitter that diffuses across the gap and triggers an impulse in the next neurone. This allows impulses to pass one way between neurones.