Exam questions · Biology
The Nervous System
- 42 exam questions
- 142 marks
- 63 quick checks
Sensory Receptors and Neurones
Just this lesson-
1 Name [2 marks]
Name the two types of effector in the human body.
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Model answer
Muscles and glands.
Mark scheme
- Muscle — 1 mark
- Gland — 1 mark
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2 State [2 marks]
State what is meant by the term stimulus, and give one example.
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Model answer
A stimulus is a change in the environment that can be detected by a receptor. An example is a bright light, a loud sound or a hot object.
Mark scheme
- A change in the environment detected by a receptor — 1 mark
- A suitable example — 1 mark
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3 Complete [4 marks]
The path taken by an impulse when a person steps on a pin is shown below, with the missing words replaced by letters. Stimulus, then A, then sensory neurone, then B, then motor neurone, then C, then response. Name the parts A, B and C.
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Model answer
A is a receptor (pain receptor). B is the central nervous system (the spinal cord or brain), with a relay neurone. C is an effector (a muscle).
Mark scheme
- A: receptor — 1 mark
- B: central nervous system / spinal cord — 1 mark
- C: effector — 1 mark
- Muscle given as the example of an effector — 1 mark
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4 Describe [3 marks]
Describe the function of a motor neurone.
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Model answer
A motor neurone carries electrical impulses from the central nervous system, which is the brain or spinal cord, to an effector. The effector is a muscle or a gland, which then carries out the response.
Mark scheme
- Carries impulses / electrical signals — 1 mark
- From the central nervous system — 1 mark
- To an effector (muscle or gland) — 1 mark
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5 Explain [4 marks]
Explain how the structure of a motor neurone is adapted to its function.
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Model answer
A motor neurone has a very long axon, so it can carry impulses over a long distance, for example from the spinal cord to a muscle in the foot. The axon is covered with a myelin sheath, which insulates it and makes the impulse travel much faster. At the end it has branched axon terminals, which let it connect to the muscle fibres.
Mark scheme
- Long axon — 1 mark
- Carries impulses over long distances — 1 mark
- Myelin sheath insulates / speeds up impulses — 1 mark
- Branched ends connect to the effector or other neurones — 1 mark
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6 Compare [6 marks]
Compare the structure and function of a sensory neurone, a relay neurone and a motor neurone.
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Model answer
A sensory neurone carries impulses from a receptor, such as one in the skin, to the central nervous system. It has a long dendron, and the cell body lies to one side. A relay neurone lies wholly inside the CNS and passes impulses from the sensory neurone to the motor neurone. It is short and has many branches so that it can connect to several neurones. A motor neurone carries impulses from the CNS to an effector, which is a muscle or a gland. It has a long axon with a myelin sheath, and its cell body is in the CNS.
Mark scheme
- Sensory neurone carries impulses from receptor to CNS — 1 mark
- Feature of a sensory neurone, such as a long dendron — 1 mark
- Relay neurone is inside the CNS — 1 mark
- Relay neurone passes impulses from sensory to motor neurone — 1 mark
- Motor neurone carries impulses from CNS to an effector — 1 mark
- Feature of a motor neurone, such as a long axon or myelin sheath — 1 mark
Quick check
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1
What is the name for a change in the environment that can be detected?
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B: A stimulus
A change in the environment that a receptor can detect is called a stimulus.
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2
Which two organs make up the central nervous system?
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C: Brain and spinal cord
The central nervous system is the brain and the spinal cord.
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3
Which of these is an effector?
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A: A muscle
Muscles and glands are effectors because they carry out the response.
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4
Which type of neurone carries impulses from the CNS to a muscle?
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D: Motor neurone
Motor neurones carry impulses away from the central nervous system to an effector.
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5
Where is a relay neurone found?
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B: In the brain or spinal cord
Relay neurones are inside the CNS, where they connect sensory and motor neurones.
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6
What is the function of the myelin sheath?
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C: To insulate the neurone and speed up the impulse
Myelin is a fatty layer that insulates the neurone and makes impulses travel faster.
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7
Which sequence shows the correct route of an impulse in a nervous response?
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A: Receptor, sensory neurone, CNS, motor neurone, effector
The impulse passes from a receptor along a sensory neurone to the CNS, and then along a motor neurone to an effector.
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8
Which part of a neurone carries the impulse away from the cell body?
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D: The axon
The axon carries impulses away from the cell body. The dendron carries them towards it.
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9
In multiple sclerosis the myelin sheath is damaged. What effect does this have?
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B: Impulses travel more slowly or are lost
Without the insulating myelin, impulses travel more slowly or are lost, so messages in the nervous system are delayed.
Synapses and Neurotransmitters
Just this lesson-
1 State [1 mark]
State what a synapse is.
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Model answer
A junction between two neurones, with a tiny gap between them.
Mark scheme
- Junction / gap between two neurones — 1 mark
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2 Name [2 marks]
Name the chemical that carries a message across a synapse, and name the process by which it crosses the gap.
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Model answer
The chemical is a neurotransmitter. It crosses the gap by diffusion.
Mark scheme
- Neurotransmitter — 1 mark
- Diffusion — 1 mark
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3 Describe [3 marks]
Describe what happens to the neurotransmitter after it crosses the synaptic gap.
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Model answer
The neurotransmitter binds to receptor molecules on the membrane of the next neurone. This makes the next neurone produce an electrical impulse. The neurotransmitter is then broken down or taken back up.
Mark scheme
- Binds to receptors on the next neurone — 1 mark
- A new impulse is started — 1 mark
- It is broken down or reabsorbed — 1 mark
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4 Calculate [2 marks]
An impulse takes 0.02 s to travel 2 m along a neurone. Calculate the speed of the impulse. Give the unit.
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Model answer
Speed = 2 ÷ 0.02 = 100 m/s.
Mark scheme
- 2 divided by 0.02 — 1 mark
- 100 m/s — 1 mark
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5 Explain [3 marks]
Explain why impulses can only pass in one direction across a synapse.
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Model answer
Only the first neurone has vesicles that contain neurotransmitter, so it is the only one that can release the chemical into the gap. Only the second neurone has receptor molecules for the neurotransmitter on its membrane. This means the signal can pass from the first neurone to the second but not the other way.
Mark scheme
- Vesicles are only in the first neurone — 1 mark
- Receptors are only on the second neurone — 1 mark
- So the chemical signal can only go one way — 1 mark
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6 Explain [6 marks]
Explain how an electrical impulse in one neurone causes an electrical impulse in the next neurone.
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Model answer
When the electrical impulse reaches the end of the first neurone, it causes vesicles to release a neurotransmitter into the synaptic gap. The neurotransmitter diffuses across the gap, which is very narrow. It binds to specific receptor molecules on the membrane of the second neurone. This binding causes the second neurone to produce an electrical impulse. The neurotransmitter is then broken down or taken back up, so that the second neurone is not stimulated all the time.
Mark scheme
- Impulse arrives at the end of the first neurone — 1 mark
- Neurotransmitter released from vesicles — 1 mark
- It diffuses across the synaptic gap — 1 mark
- It binds to receptors on the next neurone — 1 mark
- A new impulse starts in the second neurone — 1 mark
- The neurotransmitter is broken down or reabsorbed — 1 mark
Quick check
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1
What is the name of the gap between two neurones?
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A: A synapse
The gap between neurones is called the synaptic gap, and the junction is a synapse.
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2
What crosses the synaptic gap?
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C: A neurotransmitter
A chemical called a neurotransmitter crosses the gap. The electrical impulse does not.
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3
How does a neurotransmitter move across the synaptic gap?
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B: Diffusion
Neurotransmitter molecules move by diffusion from a region of high concentration to a region of low concentration.
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4
Where are neurotransmitters stored?
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D: In vesicles
They are stored in vesicles in the end of the first neurone, ready to be released.
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5
What do neurotransmitters bind to on the next neurone?
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A: Receptor molecules
They fit into receptor molecules on the membrane of the next neurone, like a key into a lock.
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6
Why do impulses only cross a synapse in one direction?
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C: Vesicles are on one side and receptors on the other
Vesicles are found on one side of the gap and receptors only on the other, so the chemical can only act one way.
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7
An impulse travels 0.6 m in 0.006 s. What is its speed?
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D: 100 m/s
Speed is distance divided by time: \(0.6 \div 0.006 = 100\) m/s.
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8
Why does the end of the first neurone contain many mitochondria?
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B: To release energy for making and releasing neurotransmitter
Making and releasing neurotransmitter needs energy, which mitochondria release by respiration.
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9
A poison blocks the receptor molecules at a synapse. What will happen?
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C: The message will not be passed to the next neurone
If the neurotransmitter cannot bind to the receptors, no new impulse starts in the next cell, so the message is not passed on.
Reflex Arcs and Reaction Times
Just this lesson-
1 State [1 mark]
State what is meant by a reflex action.
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Model answer
A fast, automatic response that does not involve conscious thought.
Mark scheme
- Fast and automatic without thinking — 1 mark
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2 Name [3 marks]
Name the three types of neurone in a reflex arc, in the order that the impulse passes through them.
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Model answer
Sensory neurone, then relay neurone, then motor neurone.
Mark scheme
- Sensory — 1 mark
- Relay — 1 mark
- Motor, in the correct order — 1 mark
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3 Describe [3 marks]
A person touches a hot object and moves their hand away. Describe what the receptor and the effector do in this reflex.
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Model answer
The receptor in the skin detects the heat and starts an electrical impulse, which goes to the sensory neurone. The effector, a muscle in the arm, receives the impulse from the motor neurone and contracts to pull the hand away.
Mark scheme
- Receptor detects the stimulus and starts an impulse — 1 mark
- Effector is a muscle — 1 mark
- It contracts to move the hand away — 1 mark
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4 Explain [3 marks]
Explain why a reflex action is faster than a voluntary action.
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Model answer
In a reflex there are only a few neurones and synapses, so the impulse passes along a short pathway. The impulse travels through the spinal cord and does not have to be processed by the conscious part of the brain. This means there is less delay before the muscle responds.
Mark scheme
- Short pathway / few neurones — 1 mark
- Few synapses, so little delay — 1 mark
- No conscious thought or decision — 1 mark
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5 Calculate [3 marks]
A student catches a ruler five times in a reaction-time test, at 12 cm, 15 cm, 18 cm, 14 cm and 16 cm. Calculate the mean distance. Explain why the student repeated the test.
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Model answer
The total is 12 + 15 + 18 + 14 + 16 = 75 cm, so the mean is 75 divided by 5, which is 15 cm. The test was repeated so that a mean could be calculated, which reduces the effect of random errors and makes the result more reliable.
Mark scheme
- Total of 75 cm — 1 mark
- Mean of 15 cm — 1 mark
- Repeating makes the mean more reliable — 1 mark
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6 Evaluate [6 marks]
A student investigates the effect of caffeine on reaction time using the ruler drop test. Describe how the investigation could be done, and evaluate the method.
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Model answer
The student measures the distance the ruler falls before it is caught, before and after drinking a caffeinated drink. A longer distance means a slower reaction. The variables to control are the same person, the same hand, the same ruler and the same starting position, and the test is repeated and a mean calculated. The method is simple and uses cheap equipment. However, the person dropping the ruler might drop it at different speeds or give clues, and the participant gets better with practice, which can affect the results. Using a computer reaction test would be more precise.
Mark scheme
- Independent variable: caffeine; dependent variable: distance caught — 1 mark
- Describes repeated tests and a mean — 1 mark
- Controls at least two variables — 1 mark
- A strength, such as simple or cheap — 1 mark
- A weakness, such as human error or practice effect — 1 mark
- An improvement, such as a computer test — 1 mark
Quick check
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1
Which of these is an example of a reflex action?
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C: Pulling a hand away from a hot object
Pulling a hand away from something hot is automatic and does not involve conscious thought.
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2
What is the order of the parts in a reflex arc?
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A: Receptor, sensory neurone, relay neurone, motor neurone, effector
The impulse passes from the receptor through sensory, relay and motor neurones to an effector.
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3
Where is the relay neurone in a withdrawal reflex?
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B: In the spinal cord
The relay neurone is in the spinal cord, part of the central nervous system.
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4
Why are reflex actions so fast?
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D: The pathway is short and involves no thinking
The pathway is short, with few synapses and no conscious thought.
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5
What type of effector is used in a withdrawal reflex?
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A: A muscle
A muscle contracts to pull the hand away.
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6
What is the role of the pupil reflex?
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C: To protect the retina from too much light
The pupil gets smaller in bright light so that too much light does not damage the retina.
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7
In the ruler drop test, what does a longer distance mean?
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B: A slower reaction time
A ruler that falls further before being caught shows that the person took longer to react.
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8
A student does the ruler drop test five times and gets 10, 12, 11, 12 and 15 cm. What is the mean distance?
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D: 12 cm
The total is 60 cm, and 60 ÷ 5 = 12 cm.
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9
Why does a person feel pain after their hand has moved away from a hot pan?
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C: The impulse reaches the brain after the reflex has already happened
The reflex pathway goes through the spinal cord, so the muscle responds first. The impulse reaches the brain a moment later, and that is when the pain is felt.
The Brain
Just this lesson-
1 Name [3 marks]
Name the three main regions of the brain that you have studied.
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Model answer
The cerebral hemispheres, the cerebellum and the medulla oblongata.
Mark scheme
- Cerebral hemispheres — 1 mark
- Cerebellum — 1 mark
- Medulla oblongata — 1 mark
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2 State [2 marks]
State two functions of the cerebral hemispheres.
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Model answer
Any two from: consciousness, intelligence, memory, language, voluntary movement.
Mark scheme
- First function — 1 mark
- Second function — 1 mark
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3 State [2 marks]
The medulla oblongata controls unconscious activities. Give two examples.
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Model answer
The heart rate and the breathing rate.
Mark scheme
- Heart rate — 1 mark
- Breathing rate — 1 mark
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4 Explain [3 marks]
A person has a head injury and afterwards cannot walk in a straight line, and their movements are shaky. Explain which part of the brain has probably been damaged.
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Model answer
The cerebellum has probably been damaged. This region coordinates movement and keeps the body balanced, so damage to it leads to poor balance and uncoordinated, shaky movements.
Mark scheme
- Cerebellum — 1 mark
- It coordinates movement — 1 mark
- It maintains balance — 1 mark
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5 Explain [4 marks]
Explain why the cerebral cortex is folded, and why this is an advantage.
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Model answer
The cerebral cortex is folded into ridges and grooves. This gives it a larger surface area than a smooth surface would have. A bigger surface area means more neurones can fit into the skull, which allows more complex thinking, memory and language.
Mark scheme
- It is folded in ridges and grooves — 1 mark
- This increases the surface area — 1 mark
- More neurones fit inside the skull — 1 mark
- Allows more complex functions — 1 mark
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6 Describe [6 marks]
Describe the structure and the functions of the three main regions of the brain.
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Model answer
The cerebral hemispheres are the two large, folded halves at the top and front of the brain. They control consciousness, intelligence, memory, language and voluntary movement. The cerebellum is a smaller region at the back below the hemispheres, and it coordinates movement and balance. The medulla oblongata is at the base of the brain and joins it to the spinal cord. It controls unconscious activities such as the heart rate and breathing rate.
Mark scheme
- Hemispheres: large, folded, top and front — 1 mark
- Hemispheres: consciousness, memory, language etc. — 1 mark
- Cerebellum: at the back, below hemispheres — 1 mark
- Cerebellum: coordination and balance — 1 mark
- Medulla: base of the brain, joins the spinal cord — 1 mark
- Medulla: heart rate and breathing rate — 1 mark
Quick check
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1
Which part of the brain controls the breathing rate?
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C: Medulla oblongata
The medulla oblongata controls unconscious activities such as breathing and heart rate.
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2
Which part of the brain coordinates movement and balance?
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A: Cerebellum
The cerebellum coordinates movement and keeps the body balanced.
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3
Which part of the brain is used for memory and language?
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D: Cerebral hemispheres
The cerebral hemispheres are responsible for conscious thought, memory and language.
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4
Why is the cerebral cortex folded?
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B: To increase its surface area
The folds increase the surface area, so more neurones fit into the skull.
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5
Which part of the brain joins the brain to the spinal cord?
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C: Medulla oblongata
The medulla oblongata is at the base of the brain and links it to the spinal cord.
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6
A stroke damages the area of a person's brain that controls speech. Which region has been damaged?
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A: The cerebral hemispheres
Language is controlled by the cerebral hemispheres.
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7
What did the case of Phineas Gage show?
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D: That different parts of the brain have different functions
His change in personality after damage to the front of his brain suggested that different regions have different functions.
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8
Which activity is controlled mainly by the cerebellum?
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B: Riding a bike
Riding a bike needs balance and coordinated movement, which the cerebellum controls.
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9
A person's heart rate stays normal while they are asleep, even though they are unconscious. Which part of the brain explains this?
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C: Medulla oblongata
The medulla oblongata controls the heart rate automatically, without conscious thought.
Scanning and Treating the Brain (Higher tier)
Just this lesson-
1 State [2 marks]
State one difference between the information given by a CT scan and by a PET scan.
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Model answer
A CT scan shows the structure of the brain, whereas a PET scan shows its function, which means which areas are active.
Mark scheme
- CT shows structure — 1 mark
- PET shows function / activity — 1 mark
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2 Explain [3 marks]
Explain why it is difficult for doctors to investigate the brain tissue inside the skull.
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Model answer
The brain is protected by the skull, so it is difficult to reach. It is made of soft, delicate tissue, so surgery to take a sample could damage it. The neurones are tiny and work together, so looking at the tissue does not show which parts are active.
Mark scheme
- Inside the skull / inaccessible — 1 mark
- Delicate tissue easily damaged — 1 mark
- Cannot see which areas are active — 1 mark
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3 Describe [3 marks]
Describe how a PET scan is used to find which parts of the brain are active.
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Model answer
The patient is injected with glucose that contains a radioactive tracer. The active parts of the brain use more glucose, so more tracer collects in them. Detectors around the head pick up the radiation, and a computer turns it into an image in which the active areas show up brightly.
Mark scheme
- Radioactive tracer injected — 1 mark
- Active areas use more glucose and take up more tracer — 1 mark
- Detectors build an image showing the active areas — 1 mark
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4 Explain [4 marks]
A patient has headaches and slurred speech. Explain how a CT scan and a PET scan could each help the doctors.
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Model answer
A CT scan could show the structure of the brain, for example a tumour or a bleed that is pressing on the area. A PET scan could show the function, so the doctors could see whether the area that controls speech is less active than normal, or whether a tumour is growing fast. Used together, they give a more complete picture.
Mark scheme
- CT shows the structure, such as a tumour — 1 mark
- A tumour or bleed can explain the symptoms — 1 mark
- PET shows the activity of the area — 1 mark
- Together they give a fuller picture — 1 mark
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5 Explain [4 marks]
Explain why spinal injuries and brain tumours are difficult to treat.
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Model answer
Neurones in the brain and spinal cord do not regenerate well, so after a spinal injury the damage is permanent and the patient is paralysed below the injury. Brain tumours are difficult to remove because the tissue is delicate and the tumour may be near vital areas, so healthy tissue can be damaged. Many drugs also cannot cross from the blood into the brain.
Mark scheme
- Neurones do not regenerate — 1 mark
- Spinal injury causes paralysis — 1 mark
- Delicate brain tissue, close to vital areas — 1 mark
- Drugs cannot always reach the brain — 1 mark
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6 Evaluate [6 marks]
Evaluate the use of CT and PET scans to investigate the brain.
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Model answer
Both scans let doctors see inside the head without surgery, which is much safer than opening the skull. A CT scan is quick and gives a detailed picture of the structure, so it is useful in emergencies and for finding tumours and bleeds, but it cannot show activity and uses X-rays. A PET scan shows which areas of the brain are active, so it can show how the brain works and how a disease changes it, but the picture is less detailed, it is expensive and the patient receives a radioactive tracer. Using both gives the most complete information, and the benefit of an accurate diagnosis usually outweighs the small risk from radiation.
Mark scheme
- Avoids the risk of surgery — 1 mark
- CT: shows structure, fast — 1 mark
- CT: limitation (only structure, X-rays) — 1 mark
- PET: shows function — 1 mark
- PET: limitation (radioactive, expensive, less detail) — 1 mark
- A reasoned conclusion — 1 mark
Quick check
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1
Which scan uses X-rays to show the structure of the brain?
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A: CT scan
A CT scan uses X-rays from many angles to build an image of the brain's structure.
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2
Which scan shows which parts of the brain are active?
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B: PET scan
A PET scan shows activity, because active neurones take up more of the radioactive glucose.
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3
What is injected into a patient before a PET scan?
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C: A radioactive tracer
A radioactive tracer, usually a form of glucose, is injected and collects in the active areas of the brain.
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4
Why does the tracer collect in the active parts of the brain?
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D: Active neurones use more glucose
Active neurones respire faster and use more glucose, so more of the tracer is taken up.
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5
Why is it difficult to study brain tissue directly?
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B: It is inside the skull and easily damaged
The brain is protected by the skull and is delicate, so reaching it carries a risk of damage.
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6
What is the main problem with treating a spinal injury?
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A: Neurones do not regenerate
Neurones in the spinal cord do not regenerate well, so the damage is usually permanent.
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7
Why is it difficult to remove a brain tumour?
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C: It may be next to vital areas and healthy tissue can be damaged
Surgeons must avoid damaging healthy tissue and vital areas near the tumour.
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8
Which statement about CT scans is correct?
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D: They show the structure of the brain
A CT scan shows structure, so it can show a tumour or a bleed, but not which areas are active.
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9
A doctor wants to know whether the speech area of a patient's brain is working normally. Which scan is best?
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B: PET scan
A PET scan shows the function, which means how active an area is, so it can show whether the speech area is working normally.
The Eye
Just this lesson-
1 Name [3 marks]
Name the part of the eye that (a) refracts light as it enters, (b) controls the amount of light entering, and (c) contains the light receptors.
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Model answer
(a) The cornea. (b) The iris. (c) The retina.
Mark scheme
- Cornea — 1 mark
- Iris — 1 mark
- Retina — 1 mark
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2 Describe [3 marks]
Describe the pathway taken by light from an object to the brain.
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Model answer
The light is refracted by the cornea and passes through the pupil. The lens focuses it onto the retina, where light receptors turn it into impulses. The impulses are carried to the brain by the optic nerve.
Mark scheme
- Refracted by the cornea and lens, focused on the retina — 1 mark
- Receptors detect it and form impulses — 1 mark
- Optic nerve carries them to the brain — 1 mark
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3 Explain [3 marks]
Explain why the pupil gets smaller when a person goes from a dim room into bright sunlight.
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Model answer
Circular muscles in the iris contract and radial muscles relax, so the pupil gets smaller. This reduces the amount of light entering the eye. It protects the retina from being damaged by too much light.
Mark scheme
- Circular muscles contract, radial relax — 1 mark
- Less light enters the eye — 1 mark
- Protects the retina — 1 mark
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4 Compare [4 marks]
Compare rod cells and cone cells.
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Model answer
Rod cells work in dim light, but they cannot detect colour, so they give a black and white image. Cone cells need bright light and detect colour, and there are three types for red, green and blue light. There are more rods than cones, and the cones are concentrated in the centre of the retina.
Mark scheme
- Rods work in dim light — 1 mark
- Rods do not detect colour — 1 mark
- Cones work in bright light — 1 mark
- Cones detect colour (three types) — 1 mark
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5 Explain [4 marks]
Explain how the shape of the lens changes when a person looks from a distant object to a near object.
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Model answer
The ciliary muscles contract, so the suspensory ligaments become slack. The lens is then no longer pulled flat, so it becomes thicker and more curved. This increases the amount that it bends the light, so the near object is focused on the retina.
Mark scheme
- Ciliary muscles contract — 1 mark
- Suspensory ligaments slacken — 1 mark
- Lens becomes thicker / more curved — 1 mark
- Light is bent more so it focuses on the retina — 1 mark
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6 Explain [6 marks]
Explain how the structure of the eye allows a person to see a clear image in both bright and dim light.
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Model answer
In bright light, the circular muscles of the iris contract, making the pupil smaller. This limits the light entering and protects the retina. The cone cells work in bright light and detect colour, giving a sharp, detailed image. In dim light, the radial muscles contract and make the pupil larger, so more light enters the eye. The rod cells are very sensitive and work in dim light, so the person can still see, although only in black and white. The lens and cornea focus the light on the retina in both cases.
Mark scheme
- Pupil smaller in bright light, using the iris muscles — 1 mark
- Protects the retina — 1 mark
- Cones work in bright light and detect colour — 1 mark
- Pupil larger in dim light — 1 mark
- Rods work in dim light — 1 mark
- Cornea and lens focus the light on the retina — 1 mark
Quick check
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1
Which part of the eye bends light most as it enters?
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C: The cornea
The cornea does most of the refraction of light as it enters the eye.
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2
Which part of the eye contains the light receptors?
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B: The retina
The retina contains rod and cone cells, which detect light.
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3
What controls the amount of light that enters the eye?
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D: The iris
The iris changes the size of the pupil, which controls how much light enters.
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4
What happens to the pupil in bright light?
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A: It gets smaller
The pupil gets smaller, to stop too much light reaching the retina.
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5
Which cells detect colour?
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B: Cone cells
Cone cells detect colour, and there are three types, sensitive to red, green and blue.
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6
Why can we only see in black and white in very dim light?
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C: Only the rod cells work
In very dim light only the rod cells work, and rods cannot detect colour.
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7
What carries impulses from the retina to the brain?
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A: The optic nerve
The optic nerve is a bundle of sensory neurones that links the retina with the brain.
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8
To look at a near object, what happens to the lens?
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D: It becomes thicker and more curved
The lens becomes thicker and more curved, because the ciliary muscles contract and the ligaments slacken.
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9
Which muscles contract to make the pupil larger in dim light?
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B: Radial muscles
The radial muscles contract to pull the iris open and make the pupil larger. The circular muscles relax.
Eye Defects and Their Correction
Just this lesson-
1 State [2 marks]
State what a person who is short-sighted can see clearly and what they cannot.
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Model answer
They can see near objects clearly but not distant objects.
Mark scheme
- Near objects are clear — 1 mark
- Distant objects are blurred — 1 mark
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2 Name [2 marks]
Name the type of lens used to correct (a) short sight and (b) long sight.
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Model answer
(a) A concave lens. (b) A convex lens.
Mark scheme
- Concave for short sight — 1 mark
- Convex for long sight — 1 mark
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3 Describe [3 marks]
Describe what happens to light in the eye of a person with long sight.
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Model answer
The eyeball is too short, or the lens too weak, so the light is not bent enough. It would be focused behind the retina. The image on the retina is therefore blurred.
Mark scheme
- Light not bent enough — 1 mark
- Focused behind the retina — 1 mark
- Image blurred — 1 mark
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4 Explain [3 marks]
Explain how a cataract affects vision and how it can be treated.
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Model answer
A cataract is a cloudy lens, which stops light passing through properly, so vision is blurred or misty. It can be treated by an operation to replace the cloudy lens with a clear artificial lens.
Mark scheme
- The lens becomes cloudy — 1 mark
- Light cannot pass properly so vision is blurred — 1 mark
- Replaced with an artificial lens — 1 mark
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5 Explain [4 marks]
Explain how a concave lens corrects short sight.
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Model answer
In a short-sighted eye the light from a distant object is focused in front of the retina. A concave lens spreads the light rays out slightly before they enter the eye. The lens of the eye then focuses them further back, so that they meet on the retina and the image is sharp.
Mark scheme
- Light is focused in front of the retina — 1 mark
- A concave lens spreads the rays out — 1 mark
- The eye's lens focuses them further back — 1 mark
- On the retina, giving a sharp image — 1 mark
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6 Explain [6 marks]
Explain why colour blindness is more common in men than in women, and describe the effects of colour blindness and how it is diagnosed.
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Model answer
Colour blindness is caused by missing or faulty cone cells, so a person cannot tell some colours apart, most often red and green. The genes for these cone cells are carried on the X chromosome. A man has only one X chromosome, so one faulty gene makes him colour blind, whereas a woman has two, so a working gene on the other X usually hides the fault. It can be diagnosed with Ishihara plates, which hide numbers in coloured dots. There is no cure, but tinted lenses can help some people.
Mark scheme
- Missing or faulty cone cells — 1 mark
- Cannot tell some colours (red and green) apart — 1 mark
- Gene is on the X chromosome — 1 mark
- Men have one X, so one faulty gene has an effect — 1 mark
- Diagnosed using coloured plates — 1 mark
- No cure / tinted lenses help — 1 mark
Quick check
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1
A person cannot see distant objects clearly but can see near objects. What is the defect?
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B: Short-sightedness
This is short-sightedness (myopia). Distant objects are blurred because light is focused in front of the retina.
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2
Where is the light focused in a long-sighted eye?
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C: Behind the retina
In long sight the light would be focused behind the retina, so the image is blurred.
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3
Which lens corrects short sight?
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A: Concave
A concave lens spreads light rays out so the eye can focus them on the retina.
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4
Which lens corrects long sight?
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D: Convex
A convex lens brings light rays together, so the eye can focus them on the retina.
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5
What is a cataract?
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B: A cloudy lens
A cataract is a clouding of the lens, which makes vision misty or blurred.
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6
How are cataracts treated?
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C: By replacing the lens
The cloudy lens is removed and replaced by a clear artificial lens.
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7
What causes red-green colour blindness?
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A: Missing or faulty cone cells
One or more types of cone cell are missing or do not work properly.
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8
Which of these can cause short sight?
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D: An eyeball that is too long
If the eyeball is too long, light focuses before it reaches the retina.
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9
Many older people need reading glasses. Which is the most likely reason?
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B: Their lens becomes stiffer and cannot thicken
The lens becomes stiffer with age and cannot get thicker to focus on near objects, so reading glasses with convex lenses help.