Homeostasis, the nervous system and reflexes (RP7) – GCSE Biology exam questions with mark scheme

1Grade 1–3Foundation4 marks

A student touches a hot pan and quickly pulls her hand away. This is a reflex action.

(a) Name the type of neurone that carries impulses from the receptor in the skin to the spinal cord. [1]

(b) Name the effector in this reflex. [1]

(c) Information passes from one neurone to the next across a gap. Name this gap and describe how the impulse crosses it. [2]

(a) sensory (neurone)(1)
(b) muscle (in the arm)
allow named arm muscle eg biceps; do not accept 'hand' or 'arm' alone(1)
(c) synapse(1)
(c) chemical released / chemical diffuses across the gap (and stimulates the next neurone)
allow neurotransmitter(1)
Answer: (a) Sensory neurone (b) Muscle (c) Synapse; a chemical diffuses across the gap.
Examiner tip: 'Electrical impulse jumps across the gap' gets no credit – the signal crosses a synapse as a chemical.

2Grade 4–55 marks

A student carried out an investigation to see if drinking coffee affects her reaction time. She used the ruler-drop test: her partner dropped a ruler and the student caught it as quickly as possible.

The table shows the distance the ruler fell before the student caught it, before she drank any coffee.

Trial	1	2	3	4	5
Distance in cm	12	14	13	25	11

(a) Identify the anomalous result. [1]

(b) Calculate the mean distance. Do not include the anomalous result. [2]

(a) 25 (cm) / trial 4(1)
(b) (12 + 14 + 13 + 11) ÷ 4(1)
(b) 12.5 (cm)
correct answer with no working scores 2(1)
(c) any one from: same hand used to catch; same ruler; same starting position of hand/fingers on the ruler (eg thumb level with 0 cm); same person dropping the ruler; same height the ruler is dropped from; same volume/strength of coffee (or same mass of caffeine); same time between drinking coffee and testing; same time of day / same level of tiredness; no warning given before the drop; same surroundings / no distractions
allow no other caffeine / energy drinks before the test(1)
(c) a second variable from the list
ignore 'same amount of time' unqualified; ignore 'same person' unqualified(1)
Answer: (a) 25 cm (b) 12.5 cm (c) e.g. same hand used to catch; same starting position of fingers on the ruler.
Examiner tip: Including the anomaly (mean = 15 cm) is the commonest way to lose the calculation mark.

3Grade 1–3Foundation5 marks

The human body uses control systems to keep its internal conditions stable. This is called homeostasis.

(a) Complete the sentence. Choose the answer from the box.

maximum optimum changing minimum

Homeostasis is the regulation of the internal conditions of a cell or organism to maintain __________ conditions for function. [1]

(b) Give two internal conditions in the human body that are controlled by homeostasis. [2]

Part of control system		Example
Receptor		A muscle in the arm
Coordination centre		Light-sensitive cells in the eye
Effector		The brain

(a) optimum(1)
(b) any one from: blood glucose concentration; body temperature; water level (in the body)
allow blood sugar level; allow amount of water in the blood / water balance
allow ion / salt concentration (in the blood)
ignore 'heart rate', 'oxygen', 'pH' (not on this specification)(1)
(b) a second condition from the list(1)
(c) all three lines correct = 2 marks: receptor → light-sensitive cells in the eye; coordination centre → the brain; effector → a muscle in the arm(1)
(c) one or two lines correct = 1 mark
more than one line drawn from a part of the control system: that line scores 0(1)
Answer: (a) optimum (b) any two of: blood glucose concentration, body temperature, water level (allow ion concentration) (c) receptor → light-sensitive cells in the eye; coordination centre → brain; effector → muscle in the arm
Examiner tip: Effectors are muscles or glands, not 'the arm' or 'the brain' – the brain (or spinal cord, or pancreas) is the coordination centre.

4Grade 4–55 marks

The diagram shows the reflex arc involved when a person pulls their finger away from a sharp object.

P, Q and R are neurones. X is part of the central nervous system.

(a) Name the neurones labelled Q and R. [2]

(b) Name the part of the central nervous system labelled X. [1]

(a) Q: relay (neurone)
allow intermediate / connector neurone(1)
(a) R: motor (neurone)
do not accept 'motion' / 'movement' neurone(1)
(b) spinal cord
do not accept 'spine' / 'backbone' / 'CNS' alone(1)
(c) the conscious (part of the) brain is not involved
allow no thinking / no (conscious) decision needed
do not accept 'the brain is not involved' unless qualified by conscious / thinking(1)
(c) short pathway / impulse only travels to the spinal cord and back
allow few neurones / few synapses involved
allow (electrical) impulses travel quickly along neurones(1)
Answer: (a) Q relay neurone, R motor neurone (b) spinal cord (c) no conscious thought / decision by the brain is needed and the pathway (via the spinal cord) is short with few synapses.
Examiner tip: 'It doesn't go to the brain' is not enough – say it bypasses the conscious part of the brain, so no decision is made.

5Grade 4–55 marks

A cyclist sees a traffic light change to red. She squeezes the brake levers with her hands.

(a) Complete the flow chart to show the pathway for this response. [2]

stimulus → receptor → A __________ → CNS → B __________ → effector → response

(b) Identify the stimulus in this response. [1]

(d) Squeezing the brakes is not a reflex action. Give one reason why. [1]

(a) A: sensory neurone
allow sensory nerve(1)
(a) B: motor neurone
allow motor nerve
both answers correct but reversed scores 0(1)
(b) (the traffic light changing to) red light
allow light / change in colour of the light
do not accept 'traffic light' or 'the eye' alone(1)
(c) eye
allow retina(1)
(d) any one from: (she has to) make a (conscious) decision / think about it; it is a learned response; it involves the conscious (part of the) brain; it is not automatic
ignore 'it is slow' unqualified(1)
Answer: (a) A sensory neurone, B motor neurone (b) the light turning red (c) the eye (d) it involves a conscious decision made by the brain (it is learned, not automatic).
Examiner tip: The stimulus is the change in the environment (the red light), not the receptor that detects it – students often write 'the eye' for both.

6Grade 6–7Higher6 marks

A student investigated whether people react more slowly with their non-dominant hand (the hand they do not write with).

She used the ruler-drop test. She recorded the distance the ruler fell before it was caught. She converted the mean distance into a reaction time using the equation:

$$\text{reaction time in s} = \sqrt{\frac{\text{distance in cm}}{490}}$$

The table shows her results.

Hand used	Mean distance in cm	Reaction time in s
Dominant	15.4	0.177
Non-dominant	21.0	X

(a) Calculate reaction time X. Give your answer to 2 significant figures. [2]

(b) Calculate the percentage increase in reaction time from the dominant hand to the non-dominant hand. Use the value 0.207 s for the non-dominant hand. [2]

(c) In her first plan, the student was going to do all 10 trials with her dominant hand first, then all 10 trials with her non-dominant hand.

Explain why it would be better to alternate between the two hands. [2]

(a) $\sqrt{21.0 \div 490}$ or $\sqrt{0.04286}$ or 0.207(1)
(a) 0.21 (s)
correct answer with no working scores 2
0.207 with no rounding scores 1(1)
(b) $\dfrac{0.207 - 0.177}{0.177} \times 100$ or $\dfrac{0.030}{0.177} \times 100$(1)
(b) 16.9 (%)
allow 16.8 – 17 (%)
correct answer with no working scores 2
allow 18.6 / 19 (%) if 0.21 used
do not accept 36.4 % (percentage increase in distance)(1)
(c) reaction time improves with practice / the person gets used to the test
allow the person may get tired / bored during later trials(1)
(c) so (if all dominant-hand trials were done first) the non-dominant hand would have an unfair advantage / results would not be a fair comparison
allow alternating means any practice (or tiredness) effect is spread equally between both hands
allow order would become a second (independent / confounding) variable(1)
Answer: (a) 0.21 s (b) 16.9 % (allow 17 %) (c) Reaction time improves with practice (or tiredness builds up), so doing one hand first would give the other hand an advantage; alternating spreads this effect equally so the comparison is fair.
Examiner tip: In (b) the percentage must be calculated from the reaction times, not the distances – using 15.4 cm and 21.0 cm gives 36.4 %, which scores 0.

7Grade 6–77 marks

A student used a computer program to measure his reaction time. He pressed a key as soon as a shape appeared on the screen. He did the test 10 times in a row.

The graph shows his results.

(a) Describe the pattern shown by the graph. [2]

(b) Use the graph to calculate the percentage decrease in reaction time between attempt 1 and attempt 10. Give your answer to 3 significant figures. [2]

(d) Give one advantage of using the computer program rather than the ruler-drop test to measure reaction time. [1]

(e) The student now wants to compare the reaction times of different people in his class.

Use the graph to suggest how he should carry out the test on each person so that the comparison is valid. [1]

(a) reaction time decreases (as attempt number increases)
allow gets faster / quicker(1)
(a) then levels off / stays the same (at 270 ms) from attempt 8
allow levels off from attempt 7 or 8 / after about 7 attempts
allow the decrease gets smaller with each attempt(1)
(b) $\dfrac{420 - 270}{420} \times 100$ or $\dfrac{150}{420} \times 100$(1)
(b) 35.7 (%)
correct answer with no working scores 2
allow 1 mark for 35.71… or 36 (%) not given to 3 s.f.(1)
(c) practice / he learned what to expect / he got used to the test
allow he became better at anticipating when the shape would appear
ignore 'his brain got faster'(1)
(d) any one from: measures the time directly (no conversion needed); more precise / measures to the nearest millisecond; no (human) error from a partner dropping the ruler; the person cannot see a hand movement that warns them; the timing is the same each trial (eg random delay controlled by computer)
ignore 'more accurate' unqualified / 'easier'(1)
(e) give each person (several / at least 7 or 8) practice attempts before recording results
allow use only the results after the reaction time has levelled off / use the mean of the last few attempts for each person
allow give everyone the same number of attempts (and compare the same attempts)(1)
Answer: (a) Reaction time decreases, then levels off at 270 ms from about attempt 8 (b) 35.7 % (c) practice – he learned the task (d) e.g. measures time directly to the nearest ms with no human error from dropping (e) let each person practise (about 8 attempts) first and use only results once times have levelled off.
Examiner tip: Describing a pattern needs both the trend and where it changes – 'it goes down' alone scores only 1 of the 2 marks.

8Grade 8–9Higher6 marks

A student wants to find out whether listening to loud music affects how quickly a person reacts.

Plan an investigation to find out whether listening to loud music through headphones affects reaction time.

Your plan should give valid results. You may use the ruler-drop test in your answer. [6]

independent variable: music played through headphones vs no music (or several volumes, measured with a sound-level meter / app)(1)
dependent variable: the distance the ruler falls before it is caught (or the reaction time)(1)
person holds thumb and forefinger level with the 0 cm mark (a set distance apart); partner holds the ruler vertically above, then drops it without warning(1)
read the distance at the top of the thumb / where the ruler is caught(1)
convert the distance to a reaction time using a conversion table or equation(1)
control: same person catching; same person dropping; same hand (dominant hand); same ruler; same starting position of the fingers(1)
control: same music track / same type of music; same headphones; same time of day / not tired; no caffeine before the test; random interval before the drop(1)
repeat (eg 5–10 times) for each condition and calculate a mean; identify and remove anomalies(1)
give practice trials first, or alternate the conditions, so improvement with practice does not bias the results(1)
rest between trials / test several people to make the results more representative(1)
compare the mean reaction times (with and without music) to reach a conclusion(1)

Level	Marks	What it looks like
Level 3	5–6	A coherent, logically ordered method that could be followed to give valid results. Includes how the ruler is dropped and caught and how the result is measured, the independent variable (music vs no music), at least two relevant control variables, and repeats with a mean calculated.
Level 2	3–4	A method that could be followed to produce results but has gaps or steps out of order. The independent and dependent variables are clear, and at least one control variable or repeat is given.
Level 1	1–2	Simple, unlinked statements about the investigation, eg 'drop a ruler with and without music'. Not enough detail to obtain valid results.
No relevant content	0	Nothing worthy of credit.

Answer: A full answer describes a ruler-drop method: music through headphones vs no music as the independent variable, distance fallen (converted to reaction time) as the dependent variable, several named control variables, practice trials or alternating conditions, at least 5 repeats per condition with a mean calculated, then the means compared.
Examiner tip: Name the variables you will keep the same specifically (same catching hand, same finger start position) – 'keep everything else the same' scores nothing.

9Grade 6–75 marks

Doctors test the nervous system by touching the skin of a patient's hand with a sharp pin. Normally the patient feels the pin and their hand moves away.

Patient A has damage to nerves in the arm. Patient A can feel the pin, but their hand does not move.

(a) Explain why Patient A can feel the pin but the hand does not move. [3]

Patient B has a spinal cord injury in the upper neck, above the point where the nerves from the arms join the spinal cord. When the pin touches Patient B's hand, the hand moves away, but Patient B cannot feel the pin.

(b) Explain why Patient B's hand moves away even though Patient B does not feel the pin. [2]

(a) receptors and sensory neurones are working / undamaged(1)
(a) so impulses (still) reach the brain / CNS (so the patient is aware of the pin)(1)
(a) motor neurones are damaged so impulses cannot reach the muscle / effector
allow 'so the muscle does not contract'
allow signals / messages for impulses(1)
(b) the reflex arc passes through the spinal cord (below the injury) / does not need the brain
allow sensory → relay → motor neurone pathway is still intact(1)
(b) impulses cannot travel (up the spinal cord) to the brain, so the patient is not aware of the stimulus
allow the conscious part of the brain does not receive the impulse(1)
Answer: (a) The receptors and sensory neurones work, so impulses reach the brain; the motor neurones are damaged so impulses cannot reach the muscle (effector), so it does not contract. (b) The reflex arc only goes through the spinal cord below the injury, so the hand still withdraws, but impulses cannot pass up the cord to the brain, so there is no awareness of the pin.
Examiner tip: Feeling something needs impulses to reach the brain; a reflex only needs the spinal cord – link each observation to the part of the pathway that is or is not working.

10Grade 8–9Higher7 marks

When a finger touches something sharp, a reflex makes the arm muscle contract.

In one person:

the sensory neurone from the fingertip to the spinal cord is 0.90 m long
the motor neurone from the spinal cord to the arm muscle is 0.85 m long
the relay neurone is so short that its length can be ignored
impulses travel along these neurones at 75 m/s.

(a) Calculate the time taken for impulses to travel along the sensory and motor neurones. Give your answer in milliseconds (ms).

Use the equation: time = distance ÷ speed [3]

(b) The measured time between the pin touching the finger and the arm muscle starting to contract was 31 ms.

Suggest why this is longer than your answer to part (a). [2]

Explain why this response takes longer than the reflex. [2]

(a) total distance = 0.90 + 0.85 = 1.75 (m)(1)
(a) time = 1.75 ÷ 75 = 0.0233 (s)
allow 0.023 (s)(1)
(a) 23 (ms)
allow 23.3 (ms)
correct answer with no working scores 3
allow 1 mark for 12 (ms) or 11.3 (ms) (one neurone only) and 2 marks for 0.023 s not converted(1)
(b) impulse has to cross synapses (between the neurones) / there are (at least) two synapses(1)
(b) crossing a synapse is slower because a chemical has to diffuse across the gap
allow time for the receptor to detect the stimulus / produce an impulse(1)
(c) impulses have to travel to the brain (and back) / a longer pathway with more neurones and synapses(1)
(c) a (conscious) decision has to be made (by the brain)
allow the brain has to process the information(1)
Answer: (a) 1.75 m ÷ 75 m/s = 0.0233 s = 23 ms (b) Time is needed to cross the (two) synapses, where a chemical must diffuse across the gap (and for the receptor to respond). (c) Impulses must travel to the brain along a longer pathway with more synapses, and the brain has to make a conscious decision.
Examiner tip: Add both neurone lengths before dividing, and convert seconds to milliseconds (×1000) – 0.023 s left unconverted loses the final mark.

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