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GCSE · Biology

B5a The Nervous System and Reflexes

AQA 8464 · Calculator allowed · about 100 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Reacting to the World Around You

Original text written for Revision Library.

Every moment, the nervous system processes information from the world around you, from the warmth of a mug of tea to the sound of a bicycle bell. Receptors detect these stimuli and convert them into electrical impulses that pass along neurones, across synapses, and on to effectors that produce a response. Most of the time this happens under conscious control, but some situations, such as touching something dangerously hot, need an immediate reaction. For these, the body relies on reflex actions: fast, automatic and protective pathways that do not wait for the brain to consciously process what has happened. This worksheet covers how the nervous system is organised into the CNS and PNS, how reflex arcs and synapses allow rapid communication between neurones, how reaction time is investigated in the required practical, and how the brain and eye detect and respond to information from the surroundings.

Homeostasis keeps the internal conditions of the body within narrow limits, despite changes inside and outside the body.

(a)Define the term 'homeostasis'.(1)

(b)Negative feedback is the general mechanism that keeps a condition close to its normal level. Describe, in general terms, what happens when a condition rises above its normal level in a system controlled by negative feedback.(2)

(Total for Question 1 is 3 marks)

The nervous system allows the body to detect changes (stimuli) in its surroundings and to coordinate a rapid response.

(a)Name the two organs that together make up the central nervous system (CNS).(2)

(b)State the general function of the peripheral nervous system (PNS).(1)

(c)An effector is a muscle or a gland. Give one example of an effector, other than a muscle.(1)

(Total for Question 2 is 4 marks)

Table 1 describes three types of neurone found in the nervous system, labelled P, Q and R.

Neurone	Description
P	Carries impulses from receptors to the CNS
Q	Found inside the CNS; connects sensory neurones to motor neurones
R	Carries impulses from the CNS to effectors

(a)Identify neurones P, Q and R as sensory, relay or motor neurones.(3)

(b)State where in the body relay neurones (neurone Q) are mainly found.(1)

(Total for Question 3 is 4 marks)

Figure 1 shows the pathway of a reflex action. Priya is ironing a school shirt and accidentally touches the hot iron with her fingertip. Her hand pulls away from the iron before she consciously feels any pain.

Figure 1: stimulus -> receptor -> ___ -> ___ -> ___ -> effector -> response

Figure (to be drawn): Figure 1: reflex arc flow diagram - boxes reading stimulus, receptor, [blank], [blank], [blank], effector, response, joined by arrows, for students to complete

(a)Complete Figure 1 by writing the three missing stages of the pathway, in order.(3)

(b)Name the effector involved when Priya's hand is pulled away from the iron.(1)

(c)Explain why this reflex action happens before Priya consciously feels pain.(2)

(Total for Question 4 is 6 marks)

Reflex actions are one type of response the nervous system can produce; voluntary (conscious) actions are another.

(a)Suggest why it is important for survival that Priya's hand-withdrawal response in Question 4 is a reflex rather than a voluntary action.(1)

(b)State one example of a voluntary response Priya might make after touching the iron, other than the reflex withdrawal, and explain how the neural pathway for this response differs from the reflex pathway.(2)

(Total for Question 5 is 3 marks)

Figure 2 shows a synapse: the gap between the end of one neurone and the start of the next.

Figure (to be drawn): Figure 2: synapse diagram showing the end of the presynaptic neurone, the synaptic gap, and the membrane of the postsynaptic neurone, with unlabelled vesicles and receptor molecules shown

(a)Define the term 'synapse'.(1)

(b)Describe how an electrical impulse in one neurone is transmitted across the synapse shown in Figure 2, to trigger an impulse in the next neurone.(4)

(Total for Question 6 is 5 marks)

Impulses can only cross a synapse in one direction: from the neurone that releases the neurotransmitter to the neurone that receives it.

(a)Explain why impulses can only cross a synapse in one direction.(2)

(b)Suggest why one-way transmission at synapses is important for a coordinated reflex response.(1)

(Total for Question 7 is 3 marks)

Required practical: Kwame investigates his own reaction time using the ruler-drop method, with his partner Freya recording the results.

(a)Describe how Kwame and Freya could carry out this practical to measure Kwame's reaction time using a 30 cm ruler.(4)

(b)Identify one variable, other than the person catching the ruler, that should be kept the same each time to make this a fair test.(1)

(c)Explain why Kwame should repeat the test several times and calculate a mean falling distance.(1)

(Total for Question 8 is 6 marks)

Kwame and Freya convert the falling distance into a reaction time using the equation d = 0.5 * g * t², where d is the distance fallen in metres, g = 9.8 m/s², and t is the reaction time in seconds.

(a)On Kwame's first attempt, the ruler fell a distance of 24.5 cm before he caught it. Rearrange the equation to make t the subject, then calculate Kwame's reaction time. Give your answer to 3 significant figures.(3)

(b)On a second attempt, the ruler fell only 12.25 cm before Kwame caught it. State which of the two attempts shows the faster reaction time, and explain your answer.(1)

(Total for Question 9 is 4 marks)

Olamide investigates the effect of caffeine dose on her own mean reaction time, using a computer-based reaction time test. Figure 3 shows her results as a line graph, with the data also given in Table 2.

Table 2
Caffeine dose (mg): 0, 40, 80, 120, 160
Mean reaction time (ms): 220, 205, 190, 178, 188

Figure (to be drawn): Figure 3: line graph of mean reaction time (y-axis, ms, scale 150-230) against caffeine dose (x-axis, mg, scale 0-160), plotting the five points from Table 2 joined by a curve, with the point at 160 mg visibly breaking the downward trend

(a)Describe the pattern shown by the data for caffeine doses between 0 mg and 120 mg.(2)

(b)One result does not fit this pattern. Identify this result and suggest an explanation for it.(2)

(c)Calculate the percentage decrease in mean reaction time from 0 mg to 120 mg of caffeine. Give your answer to 3 significant figures.(2)

(Total for Question 10 is 6 marks)

A teacher suggests that a computer-based reaction time test may give more valid results than the ruler-drop method used by Kwame and Freya.

(a)Suggest one reason why a computer-based test might give more valid results than the ruler-drop method.(2)

(b)Suggest one way the ruler-drop method could be made more reliable.(2)

(Total for Question 11 is 4 marks)

Table 3 lists three main regions of the brain.

Brain region	Main function
Cerebrum (cerebral cortex)	?
Cerebellum	?
Medulla oblongata	?

(a)Complete Table 3 to give the main function of each brain region.(3)

(b)Explain why it can be difficult for surgeons to safely repair damage inside the brain.(2)

(Total for Question 12 is 5 marks)

Higher tier only. In addition to studying patients with brain damage, scientists use other techniques to map regions of the brain to their functions.

(a)Name two techniques, other than studying patients with brain damage, that can be used to investigate brain function.(2)

(b)Suggest why electrically stimulating a region of a patient's brain during surgery does not cause the patient pain.(1)

(Total for Question 13 is 3 marks)

Figure 4 shows a cross-section of the human eye with five structures labelled A to E, which are described below.
A: refracts most of the light entering the eye
B: contains muscles that control the diameter of the pupil
C: changes shape to fine-focus light onto the retina
D: contains the light receptor cells (rods and cones)
E: carries electrical impulses from the eye to the brain

Figure (to be drawn): Figure 4: cross-section of the human eye with structures labelled A to E by pointer lines, with no text labels, for students to complete from the descriptions given

(a)Name structures A to E.(5)

(b)State the function of the pupil.(1)

(Total for Question 14 is 6 marks)

Higher tier only. The diameter of the pupil is controlled by two sets of antagonistic muscles in the iris: circular muscles and radial muscles.

(a)Explain how these muscles act together in bright light to protect the retina from damage.(2)

(b)Predict what happens to these two muscles, and to the pupil, in dim light.(2)

(Total for Question 15 is 4 marks)

Higher tier only. Accommodation allows the eye to focus on objects at different distances by changing the shape of the lens.

(a)Describe how the ciliary muscles, suspensory ligaments and lens change when the eye focuses on a near object.(3)

(b)Explain why a thicker, more curved lens is needed to focus on a near object rather than a distant one.(1)

(Total for Question 16 is 4 marks)

Higher tier only. Glasses (spectacles) can correct common problems with how the eye focuses light: myopia (short-sightedness) and hyperopia (long-sightedness).

(a)State the type of lens (concave or convex) used in glasses to correct hyperopia (long-sightedness).(1)

(b)Olusegun has myopia, so he cannot focus clearly on distant objects. Explain, in terms of the shape of the eyeball or the lens, why this happens.(2)

(c)State one structural cause of hyperopia (long-sightedness).(1)

(d)Explain how a convex lens corrects hyperopia.(1)

(Total for Question 17 is 5 marks)

Aoife steps barefoot onto a drawing pin that has been left point-up on the carpet. Her foot lifts away from the pin before she consciously feels any pain. Explain, in as much detail as you can, how the structures of the nervous system work together to produce this reflex response, and why this reflex response is more effective than a voluntary response would be in this situation.

(Total for Question 18 is 6 marks)

A student measures their own reaction time five times using a computer-based reaction time test. Table 4 shows the results.

Table 4
Attempt: 1, 2, 3, 4, 5
Reaction time (s): 0.28, 0.25, 0.51, 0.24, 0.27

(a)Identify the anomalous result in Table 4.(1)

(b)Calculate the mean reaction time, excluding the anomalous result. Give your answer to 3 significant figures.(3)

(Total for Question 19 is 4 marks)

Chidinma and Tom want to find out whether listening to loud music affects reaction time. Chidinma tests her own reaction time in a silent room in the morning. Tom tests his own reaction time while listening to loud music in the afternoon. They compare Chidinma's result directly with Tom's result and conclude that loud music slows reaction time.

(a)Evaluate this investigation, giving three reasons why the conclusion may not be valid.(3)

(b)Suggest one improvement to the design of this investigation.(1)

(Total for Question 20 is 4 marks)

Mark scheme · B5a The Nervous System and Reflexes

Question 1

(a) B1 the regulation/maintenance of a stable internal environment in the body, despite changes inside and outside the body, oe (e.g. to maintain the conditions needed for enzymes and cells to function normally)
(a) Answer: The maintenance of a stable internal environment in the body, despite internal and external changes.
(b) B1 the rise is detected (by receptors), which triggers a response that counteracts the change and brings the condition back down towards normal, oe
(b) B1 once the condition returns to its normal level, the corrective response is reduced/switched off, keeping the condition within narrow limits around a set point, oe
(b) Answer: The rise is detected and a response is triggered to counteract it, lowering the condition back towards normal; once normal, the response is switched off.

Question 2

(a) B1 brain
(a) B1 spinal cord
(a) Answer: Brain and spinal cord.
(b) B1 carries (electrical) nerve impulses between the CNS and the rest of the body (receptors and effectors), oe
(b) Answer: It carries nerve impulses between the CNS and the receptors and effectors in the rest of the body.
(c) B1 any named gland, e.g. a salivary gland, sweat gland or the pancreas (accept any gland that secretes a substance)
(c) Answer: A gland, e.g. a salivary gland or a sweat gland.

Question 3

(a) B1 P: sensory neurone
(a) B1 Q: relay neurone
(a) B1 R: motor neurone
(a) Answer: P: sensory neurone. Q: relay neurone. R: motor neurone.
(b) B1 in the CNS (the brain and/or spinal cord), oe
(b) Answer: In the central nervous system (brain and spinal cord).

Question 4

(a) B1 sensory neurone
(a) B1 relay neurone
(a) B1 motor neurone (must be in this order for all 3 marks)
(a) Answer: Sensory neurone, relay neurone, motor neurone (in that order).
(b) B1 a muscle (in the arm), oe
(b) Answer: A muscle in the arm.
(c) B1 the impulse is relayed via the spinal cord, rather than being processed by the brain first, oe
(c) B1 this shorter, more direct pathway (with fewer synapses) means the muscle is made to contract more quickly than if the brain had to process the information and decide on a response, oe
(c) Answer: The impulse is relayed through the spinal cord rather than being processed by the brain first; this shorter, more direct pathway means the muscle contracts before the brain registers pain.

Question 5

(a) B1 a reflex is much faster than a voluntary response, which reduces the time the hand is in contact with the hot iron and so reduces the harm/injury caused, oe
(a) Answer: Being a reflex makes the response much faster than a voluntary one, reducing the time in contact with the hot iron and therefore reducing injury.
(b) B1 example: e.g. she consciously runs her fingertip under cold water, fetches a burn dressing, or tells someone she has burnt herself, oe (any sensible voluntary action)
(b) B1 this pathway involves impulses travelling to the brain, where they are consciously processed and a decision is made, before impulses are sent back out to the effector, unlike the reflex, oe
(b) Answer: E.g. she consciously runs her finger under cold water; unlike the reflex, this involves impulses reaching the brain, where they are processed and a decision is consciously made, before a response is sent to the effector.

Question 6

(a) B1 the junction/gap between two neurones, oe
(a) Answer: The gap (junction) between two neurones.
(b) B1 the electrical impulse reaches the end of the first (presynaptic) neurone, oe
(b) B1 this triggers the release of a chemical called a neurotransmitter (e.g. into the synaptic gap), oe
(b) B1 the neurotransmitter diffuses across the gap/cleft, oe
(b) B1 the neurotransmitter binds to (complementary) receptor molecules on the membrane of the second (postsynaptic) neurone, which triggers a new electrical impulse in that neurone, oe
(b) Answer: The impulse reaches the end of the first neurone and triggers release of a neurotransmitter, which diffuses across the gap and binds to receptor molecules on the next neurone, triggering a new impulse there.

Question 7

(a) B1 the neurotransmitter is only released from (vesicles at the end of) the first (presynaptic) neurone, oe
(a) B1 the (complementary) receptor molecules for the neurotransmitter are only found on the membrane of the second (postsynaptic) neurone, so an impulse cannot be triggered in the reverse direction, oe
(a) Answer: Neurotransmitter is only released from the first neurone, and the receptor molecules it binds to are only found on the second neurone, so transmission cannot happen in reverse.
(b) B1 it ensures nerve impulses travel in the correct sequence along the reflex arc, from receptor to sensory neurone to relay neurone to motor neurone to effector, producing an appropriate, coordinated response, oe
(b) Answer: It ensures impulses travel in the correct sequence through the reflex arc (receptor to effector), so the response produced is appropriate and coordinated.

Question 8

(a) B1 Freya holds the ruler vertically so that the 0 cm mark is level with the top of Kwame's open finger and thumb, without the ruler touching them, oe
(a) B1 Freya releases the ruler without warning, at a random moment, oe
(a) B1 Kwame catches the ruler between his finger and thumb as quickly as he can, oe
(a) B1 the distance the ruler fell is read from the scale at the point where it is caught, and recorded (in cm), oe
(a) Answer: Freya holds the ruler vertically at the 0 cm mark level with Kwame's fingers, releases it without warning, and Kwame catches it as fast as possible; the distance it fell is read from the ruler's scale and recorded.
(b) B1 any one of: the same ruler/ruler length used each time; the same person (Freya) releasing the ruler; the same starting position of the ruler; no warning given before release each time, oe
(b) Answer: E.g. the same ruler is used every time (or: the same person releases it, or: no warning is given before release).
(c) B1 a single result could be an anomaly (e.g. Kwame anticipated the drop, or was briefly distracted), so repeating and finding a mean reduces the effect of random variation and gives a more reliable value for his reaction time, oe
(c) Answer: A single result could be anomalous (e.g. due to anticipation or distraction); repeating and finding a mean reduces the effect of this random variation, giving a more reliable reaction time.

Question 9

(a) M1 correctly rearranges to t = √2*d/g, oe
(a) M1 converts 24.5 cm to 0.245 m and substitutes correctly: t = √(2*0.245)/9.8, oe
(a) A1 0.224 s awrt cao
(a) Answer: 0.224 s
(b) B1 the second attempt (12.25 cm) shows the faster reaction time, because a shorter falling distance means less time passed before the ruler was caught, oe (accept a correctly recalculated time, ft from a candidate's own value in part (a), used to make a consistent comparison)
(b) Answer: The second attempt (12.25 cm) is faster, as the ruler fell a shorter distance, so less time passed before it was caught.

Question 10

(a) B1 as caffeine dose increases from 0 mg to 120 mg, mean reaction time decreases, oe
(a) B1 correct data quoted to support this, e.g. from 220 ms at 0 mg to 178 ms at 120 mg, oe
(a) Answer: As caffeine dose increases from 0 mg to 120 mg, mean reaction time decreases, from 220 ms to 178 ms.
(b) B1 the result at 160 mg (188 ms) is anomalous, since reaction time increases here instead of continuing to fall, oe
(b) B1 sensible explanation, e.g. too high a dose of caffeine may cause overstimulation/jitteriness/anxiety, which can slow reaction time; OR this could be a random measurement error, oe
(b) Answer: The 160 mg result (188 ms) is anomalous; a high caffeine dose may cause overstimulation/jitteriness that slows reaction time, rather than continuing to improve it.
(c) M1 correct method: (220 - 178)/220*100, oe
(c) A1 19.1% awrt cao
(c) Answer: 19.1% decrease.

Question 11

(a) B1 a computer test measures reaction time directly, in milliseconds, without relying on a calculation that assumes the ruler falls freely under gravity, oe
(a) B1 it removes possible human error in reading the ruler's scale or in releasing/catching the ruler consistently, oe
(a) Answer: A computer test measures reaction time directly and precisely, without a calculation based on free fall, and removes human error in releasing or reading the ruler.
(b) B1 increase the number of repeats for Kwame (e.g. from a few drops to at least ten) and calculate a mean, discarding any clear anomalies, oe
(b) B1 OR test a larger sample of different people to check whether the same pattern of results is seen across the wider population, oe (any two distinct, valid suggestions)
(b) Answer: E.g. increase the number of repeats and calculate a mean, discarding anomalies; or test a larger sample of people to see if the pattern holds more widely.

Question 12

(a) B1 cerebrum (cerebral cortex): controls complex behaviour, conscious thought, memory, personality, language and intelligence, oe
(a) B1 cerebellum: controls muscular coordination, balance and posture (fine control of movement), oe
(a) B1 medulla oblongata: controls unconscious/involuntary activities, e.g. heart rate and breathing rate, oe
(a) Answer: Cerebrum: complex behaviour, conscious thought, memory and language. Cerebellum: muscular coordination and balance. Medulla oblongata: unconscious activities such as heart rate and breathing rate.
(b) B1 the brain contains billions of interconnected neurones controlling many different functions packed into a small space, so damaging healthy tissue during surgery could cause loss of an unrelated function, oe
(b) B1 the brain is soft/delicate tissue enclosed within the skull, making it difficult to access without a high risk of causing further damage, oe
(b) Answer: The brain is extremely complex, with many functions controlled in a small space, so surgery risks damaging healthy tissue; it is also delicate and enclosed by the skull, making safe access difficult.

Question 13

(a) B1 any one of: MRI scanning (or CT/PET scanning), producing a detailed image of brain structure or activity
(a) B1 a second, different technique: electrically stimulating an exposed region of the brain during surgery and observing the patient's response
(a) Answer: E.g. MRI (or CT/PET) scanning, and electrically stimulating an exposed region of the brain during surgery.
(b) B1 brain tissue itself contains no pain receptors, oe
(b) Answer: Brain tissue has no pain receptors.

Question 14

(a) B1 A: cornea
(a) B1 B: iris
(a) B1 C: lens
(a) B1 D: retina
(a) B1 E: optic nerve
(a) Answer: A: cornea. B: iris. C: lens. D: retina. E: optic nerve.
(b) B1 the hole in the centre of the iris through which light passes/enters the eye, oe
(b) Answer: It is the opening through which light enters the eye.

Question 15

(a) B1 the circular muscles contract and the radial muscles relax, oe
(a) B1 this causes the pupil to constrict (get smaller), reducing the amount of light entering the eye and reaching the retina, oe
(a) Answer: The circular muscles contract while the radial muscles relax, making the pupil constrict, which reduces the amount of light reaching the retina.
(b) B1 the radial muscles contract and the circular muscles relax, oe
(b) B1 causing the pupil to dilate (get bigger), allowing more light to enter the eye, oe
(b) Answer: The radial muscles contract and the circular muscles relax, causing the pupil to dilate and let more light enter the eye.

Question 16

(a) B1 the ciliary muscles contract, oe
(a) B1 the suspensory ligaments loosen/slacken, oe
(a) B1 the lens becomes thicker/more rounded (more curved), oe
(a) Answer: The ciliary muscles contract, the suspensory ligaments slacken, and the lens becomes thicker and more curved.
(b) B1 light rays from a near object are diverging more strongly (spreading out more) as they reach the eye, so a more curved lens is needed to refract them more strongly, bringing them to a focus on the retina, oe
(b) Answer: Light from a near object diverges more strongly, so a more curved lens is needed to refract it more strongly and focus it on the retina.

Question 17

(a) B1 convex (converging) lens
(a) Answer: A convex (converging) lens.
(b) B1 the eyeball is too long, or the lens is too curved/refracts light too strongly, oe
(b) B1 so light from a distant object is focused in front of the retina, rather than on it, oe
(b) Answer: The eyeball is too long (or the lens too curved), so light from distant objects focuses in front of the retina instead of on it.
(c) B1 the eyeball is too short, or the lens does not refract light strongly enough (is too thin/flat), oe
(c) Answer: The eyeball is too short (or the lens does not refract light strongly enough).
(d) B1 a convex lens refracts light rays more strongly (causes them to converge) before they enter the eye, moving the point of focus forward onto the retina instead of behind it, oe
(d) Answer: A convex lens refracts light more strongly before it enters the eye, moving the focus point forward onto the retina.

Question 18

Level 1 (1-2): Simple, isolated statements are made, for example naming one or two structures (e.g. receptor, effector) or simply stating that reflexes are fast, with little linking of ideas and no clear logical sequence.
Level 2 (3-4): A description of most stages of the reflex arc pathway in a broadly logical order, with some reference to synapses, and some explanation of why the response is fast, but the answer may lack full detail on synaptic transmission or the comparison with a voluntary response.
Level 3 (5-6): A detailed, logically sequenced explanation of the full reflex arc pathway (receptor, sensory neurone, relay neurone, motor neurone, effector), including the role of synapses (neurotransmitter release, diffusion and binding to receptors), together with a clear explanation of why bypassing conscious processing in the brain makes the response faster, linked to the survival benefit of minimising harm from the drawing pin.
Indicative content:
- A (pain/pressure) receptor in the skin of Aoife's foot detects the stimulus, the sharp point of the drawing pin
- An electrical impulse passes along a sensory neurone to the spinal cord
- At a synapse, the impulse triggers release of a neurotransmitter, which diffuses across the gap and binds to receptors on a relay neurone, generating a new impulse
- The impulse passes along the relay neurone (in the spinal cord) and, at another synapse, triggers an impulse in a motor neurone
- The motor neurone carries the impulse to an effector: a muscle in the leg or foot
- The muscle contracts, lifting the foot away from the pin, the response
- This pathway does not involve conscious processing in the brain, unlike a voluntary response, which would require impulses to travel to the cerebral cortex, be processed, and a decision sent back to the muscle
- Because the reflex pathway is shorter and involves fewer synapses than a pathway via the brain, the response happens automatically and much faster
- This is more effective for survival because it minimises the time the foot is in contact with the pin, reducing the injury caused

Question 19

(a) B1 0.51 s (attempt 3) cao
(a) Answer: 0.51 s (attempt 3).
(b) M1 excludes the anomalous result identified in (a) from the calculation (allow ft from candidate's own answer to (a))
(b) dM1 correct sum of the remaining four readings: 0.28 + 0.25 + 0.24 + 0.27 = 1.04 (s), dependent on M1
(b) A1 0.260 s awrt cao
(b) Answer: 0.260 s.

Question 20

(a) B1 different people were tested in each condition, so any difference could be due to natural variation between Chidinma and Tom rather than the music, oe
(a) B1 the time of day also differed between the two tests (morning vs afternoon), which is an uncontrolled variable that could itself affect reaction time, oe
(a) B1 only one reading was taken for each condition, so no mean can be calculated and any anomalous reading cannot be identified, oe (any three distinct, valid criticisms)
(a) Answer: Different people were compared (natural variation, not music, could explain the difference); time of day also differed (an uncontrolled variable); and only one reading was taken for each condition, so no mean or anomaly check was possible.
(b) B1 test the same person in both conditions (with and without music), at the same time of day, repeating each test several times to calculate a mean, oe (any one improvement addressing a flaw identified in (a))
(b) Answer: Test the same person in both conditions, at the same time of day, with several repeats to calculate a mean for each condition.

The Nervous System and Reflexes - Worksheets, Questions and Revision