OxfordAQA International GCSE Biology: Nervous system, reflexes and animal behaviour (9201) – Revision Notes

These notes condense sections 3.4.1 and 3.4.6 of the OxfordAQA International GCSE Biology (9201) specification, Version 5.2, for exams May/June 2018 onwards. The qualification is untiered. For full explanations read the study guide. Then try the practice questions. Course pages: the OxfordAQA IGCSE Biology hub, the checklist and the free 10-minute diagnostics.

Key terms

Term	Meaning
Stimulus	A change in the surroundings
Receptor	A cell that detects a stimulus
Neurone	A nerve cell that carries impulses
Impulse	The electrical signal in a neurone
CNS	Central nervous system: brain and spinal cord
Coordinator	Part of the CNS that processes information and sends instructions
Effector	A muscle or a gland
Synapse	Junction between two neurones where a chemical is released
Reflex	An automatic, rapid response, often involving sensory, relay and motor neurones

3.4.1 The human nervous system

Main points

• The nervous system lets humans react to surroundings and coordinate behaviour.
• Receptors send impulses along neurones to the CNS. The brain coordinates the response.
• Reflexes are automatic and rapid and often protect the body.

The reflex arc in order

Step	What happens
1	Stimulus detected by a receptor
2	Impulses pass along a sensory neurone to the CNS
3	Chemical released at the synapse to the relay neurone, which sends an impulse
4	Chemical released at the synapse to the motor neurone, which sends impulses
5	Motor neurone carries impulses to the effector
6	Muscle contracts or gland secretes

Neurones at a glance

Type	Direction	Located
Sensory	Receptor to CNS	Mostly outside the CNS
Relay	Between sensory and motor	Inside the CNS
Motor	CNS to effector	Mostly outside the CNS

Effectors

Effector	Response
Muscle	Contracts
Gland	Releases (secretes) chemical substances

Method: analysing any behaviour

1. Name the stimulus (the change).
2. Name the receptor that detects it (by organ or cell type).
3. Name the coordinator (CNS: brain or spinal cord).
4. Name the effector (muscle or gland).
5. State the response (contracts, secretes, moves).

Worked reminder: a bright light shone in the eye makes the pupil narrower. Stimulus: bright light. Receptor: light receptors in the eye. Coordinator: the CNS. Effector: muscle in the iris. Response: the pupil narrows.

Another: the smell of food makes the mouth water. Effector: salivary gland. Response: saliva is secreted.

Must-know distinctions

• Impulse (electrical, along a neurone) versus chemical (crosses the synapse).
• Muscle (contracts) versus gland (secretes).
• Sensory (towards the CNS) versus motor (away from the CNS).
• Reflex (automatic, fast) versus voluntary action (conscious, slower).

Speed check

Time = distance / speed. A 0.9 m pathway at 60 m/s takes 0.9 / 60 = 0.015 s, which is 15 ms. Fewer neurones and synapses means a quicker response.

3.4.6 Behaviour

Courtship and mating

• Finding and selecting a suitable mate is part of sexual reproduction.
• Courtship behaviour can advertise the quality of an individual.
• Mating strategies: a mate for life, several mates over a lifetime, a mate for a breeding season, several mates over one breeding season.

Strategy	Example	Possible advantage
Mate for life	Albatrosses	Both parents work as a pair to rear young
Several mates over a lifetime	Birds with a new partner in later years	Chance to choose again if a partner is lost
Mate for a breeding season	Emperor penguins	Both parents share care for one cycle
Several mates in a season	Male red deer	More offspring carrying his genes

Parental care

• Special behaviours for rearing young: feeding, guarding, warming, nest building.
• Benefits: more offspring survive, and more parental genes are passed on by the offspring.
• Risks to parents: energy used, no time to feed, injury from predators, easier for predators to find, less energy for later broods.

Worked reminder: 26 of 40 guarded eggs survive, which is 65 %. 2 of 40 unguarded eggs survive, which is 5.0 %.

Types of behaviour

Type	Key idea	Example
Innate	Inborn, not learned	Hatchling sea turtles heading to the sea
Imprinting	Early attachment to the first moving object seen	Goslings following a parent
Habituation	Learning to ignore a repeated harmless stimulus	Pigeons and traffic
Classical conditioning	Link between a neutral stimulus and a natural stimulus	Dog salivating to a bell
Operant conditioning	Trial and error, with reward or punishment	Rat pressing a lever for food

Classical conditioning is the same as “classic conditioning” in the specification.

Training animals

Animal	Method	Result
Sniffer dog	Reward when the target scent is found	The dog repeats the search and indicates the scent
Police horse	Repeated safe exposure to crowds, flags and noise, with rewards for calm	The horse stops reacting to the stimuli

Communication signals

Signal	Example	Strength	Limit
Sound	Bird song, alarm calls	Carries far, works in the dark	Can attract predators
Chemical	Ant trails, scent marking	Lasts after the animal leaves	Slow to change
Visual	Peacock tail display, posture	Quick and clear	Needs light and line of sight

Worked reminder (habituation): a snail withdrawn for 42 s on tap 1 and 4 s on tap 20 shows a (42 - 4) / 42 x 100 = 90.5 % decrease.

Model short answers to learn

Why is a reflex action quick? It is automatic, so there is no time spent on conscious decision-making. The pathway often has only three neurones and two synapses, and the response does not wait for conscious thought.

Why is a reflex useful? It protects the body from harm, for example by pulling a hand away from a sharp object before serious damage occurs.

Describe what happens at a synapse. Impulses reach the end of one neurone. A chemical is released. It crosses the gap and causes an impulse in the next neurone.

Why do some animals use courtship? It lets an animal advertise its quality to a possible mate and lets the other animal judge it before mating. Two animals of the same species find each other and are ready to mate together.

Explain how parental care helps the parent’s genes survive. The offspring are fed, kept warm and protected, so more of them survive to adulthood. When they breed they pass on copies of the parent’s genes.

Explain how a sniffer dog is trained. The handler rewards the dog with food or a toy when it finds the target scent. The dog links finding the scent with the reward and repeats the behaviour. This is operant conditioning.

Explain why a police horse is exposed to crowds and flags during training. The horse learns that the stimuli are harmless. It stops showing a fear response (habituation) and stays calm on duty. Rewarding calm behaviour adds operant conditioning.

Compare sound and chemical signals. Sound reaches a distant animal quickly and works at night, but it stops when the animal stops calling. A chemical signal stays in the environment after the animal has left, but it changes slowly and is not easy to direct.

Worked data reminders

Situation	Working	Answer
Percentage survival, 18 of 30	18 / 30 x 100	60 %
Percentage decrease, 42 s to 4 s	(42 - 4) / 42 x 100	90.5 %
Saliva drops after 15 pairings compared with 5 pairings (11 and 2)	11 / 2	5.5 times as many
Reflex path 1.2 m at 60 m/s	1.2 / 60	0.020 s (20 ms)

Show the working line in calculations, then the answer with its unit.

Quick self-test

1. What is the CNS made of?
2. Which type of neurone carries impulses from a receptor to the CNS?
3. Where is the relay neurone located?
4. What crosses a synapse?
5. Name the two kinds of effector and what each does.
6. Give the order: stimulus, response, coordinator, receptor, effector.
7. A reflex pathway is 0.6 m long and impulses travel at 60 m/s. How long does the impulse take to travel it?
8. Give two risks of parental care to a parent.
9. Which type of behaviour is learned by linking a neutral stimulus with a natural one?
10. A horse stops reacting to a flag after repeated safe exposure. What is this called?
11. Name three types of signal used in animal communication.
12. In a fish nest, 18 of 30 guarded eggs hatch and survive. What is the percentage?

Answers

1. The brain and spinal cord.
2. A sensory neurone.
3. Inside the CNS.
4. A chemical (released from one neurone, causing an impulse in the next).
5. Muscle (contracts) and gland (secretes).
6. Stimulus, receptor, coordinator, effector, response.
7. 0.6 / 60 = 0.010 s (10 ms).
8. Any two from: uses up energy reserves; cannot feed while guarding; injury or death from predators; attracts predators to the nest; less energy for later breeding.
9. Classical conditioning.
10. Habituation.
11. Sound, chemical, visual.
12. 18 / 30 x 100 = 60 %.

Where marks are usually lost

• Writing “message” or “nerve” instead of “impulse” and “neurone”.
• Saying a muscle secretes or a gland contracts.
• Putting the relay neurone outside the CNS.
• Missing the chemical at the synapse, or saying an electrical impulse jumps across it.
• Giving only one risk of parental care when two are asked for.
• Describing imprinting without the early, short period.
• Confusing habituation with conditioning.
• Naming a signal type without saying what it is used for in the example.
• Leaving out units in a speed or time calculation.

Official syllabus

OxfordAQA International GCSE Biology (9201), Version 5.2, for exams May/June 2018 onwards, published by OxfordAQA: sections 3.4.1 and 3.4.6.