Lesson 8.2.1

8.2.1 Rod cells, rhodopsin and action potentials in the retina Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 8

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 8.2.1, Rod cells, rhodopsin and action potentials in the retina: 20 multiple choice questions for the Pearson Edexcel Biology A (Salters-Nuffield) (9BI0), Unit 8: Grey Matter, written with Revision Ninja.

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The 20 questions

  1. Which light-sensitive pigment is found in rod cells?

    • Haemoglobin, an oxygen-binding protein found in red blood cells and not in any light-sensitive cell
    • Myoglobin, an oxygen-storing protein found in muscle tissue and used to supply oxygen during activity
    • Chlorophyll, a pigment found in the chloroplasts of plant cells and used to absorb light for photosynthesis
    • Rhodopsin, a light-sensitive pigment found in rod cells and used for vision in dim light

  2. What are the two components that make up rhodopsin?

    • Actin and myosin, the contractile proteins that slide past each other in skeletal muscle fibres
    • Opsin and retinal, a protein combined with a light-absorbing molecule derived from vitamin A
    • Keratin and collagen, which are structural proteins found in skin, hair and connective tissue
    • Glucose and fructose, two simple sugars that combine to form sucrose used as a transport sugar in plants

  3. What happens to retinal when rhodopsin absorbs a photon of light?

    • It changes shape, from the cis to the trans form, and the rhodopsin is bleached
    • It is pumped out of the rod cell by an active transport pump that works against a concentration gradient
    • It is hydrolysed into glucose, which is then used to power the rod cell during the light response
    • It is broken into two sodium ions, which then pass through open channels into the rod cell

  4. In the dark, what is the state of sodium ion channels in the outer segment of a rod cell?

    • Closed, so that no sodium ions can enter the outer segment of the rod cell in darkness
    • Open, allowing sodium ions to flow in, which keeps the rod depolarised in the dark
    • Blocked by calcium ions, which prevent the channels from opening until light is absorbed by rhodopsin
    • Broken down by light, which removes the channels from the membrane in the dark state

  5. What happens to the rod cell membrane potential in the light?

    • It becomes depolarised, because the influx of sodium ions increases when light is absorbed
    • It remains unchanged, since the photoreceptor responds to light by changing only the shape of its pigment
    • It rises above +40 mV, which is the typical peak value reached during a neuronal action potential
    • It becomes hyperpolarised because sodium channels close, reducing the influx of positive ions

  6. What is the effect of hyperpolarisation of a rod cell on its neurotransmitter release?

    • Neurotransmitter release increases, which stimulates the bipolar cell more strongly in the light
    • Neurotransmitter release stops permanently, which removes all signalling from the rod for the rest of its life
    • Neurotransmitter release decreases, which reduces the signal sent to the bipolar cell
    • Release is unaffected, since neurotransmitter is released at a constant rate regardless of membrane potential

  7. Why do rod cells provide vision in dim light but not colour vision?

    • They detect only ultraviolet light, which is invisible to the human eye and so cannot produce colour perception
    • They have three types of photopigment, one for each colour, which allows them to detect the full range of colour
    • They are found only in the fovea, where the light is focused, so they are not spread across the retina
    • They have high sensitivity to light, but only a single type of photopigment, so they cannot distinguish wavelengths

  8. Which region of the retina has the highest density of cone cells but very few rods?

    • The optic disc, where the optic nerve leaves the eye and no photoreceptors are present at all
    • The sclera, the tough white outer layer of the eye which protects the eye from injury and damage
    • The fovea, a central region of high acuity that contains cones and almost no rods
    • The blind spot, which is the area where the blood vessels enter the eye at the back of the retina

  9. Why is the blind spot the region where there are no photoreceptors?

    • Because the lens blocks light from reaching the back of the eye in that particular part of the retina
    • Because rods are destroyed by blood vessels, which pass through the region and damage the cells
    • Because cones are found only in the centre of the eye and so the outer region has no photoreceptors at all
    • Because the optic nerve fibres leave the eye at the optic disc, so there is no room for receptors

  10. Which statement describes convergence of rod cells onto bipolar cells in the retina?

    • Rods connect directly to the brain without synapses, which makes the signal faster but less sensitive to light
    • One rod cell connects to many bipolar cells, which increases the spatial detail that the eye can resolve
    • Rods have no connection to any other neurone, so each rod sends its signal directly to the visual cortex
    • Many rod cells connect to one bipolar cell, which increases sensitivity in dim light but reduces acuity

  11. Which of the following is the best description of the sequence of events in a rod cell after light is absorbed?

    • Rhodopsin is synthesised, potassium channels open, and the rod depolarises in response to the new pigment
    • Rhodopsin bleaches, sodium channels close, the rod hyperpolarises, and neurotransmitter release falls
    • Sodium channels open, the rod depolarises, and neurotransmitter release rises in response to light
    • Retinal is stored in the nucleus, the rod remains unchanged, and neurotransmitter release is unaffected

  12. In the dark, a rod cell releases neurotransmitter at 10 units per second. In bright light the release falls to 2 units per second. What is the percentage decrease?

    • 80 per cent, found by taking the fall of 8 units as a share of the starting release of 10 units
    • 500 per cent, found by dividing the starting release of 10 units by the final release of 2 units
    • 8 per cent, found by taking the fall of 8 units as a share of 100 units of total release
    • 20 per cent, found by dividing the final release of 2 units by the starting release of 10 units

  13. Which statement best describes an action potential in the optic neurone?

    • It is generated by bipolar cell hyperpolarisation alone, which sends a signal down the optic nerve directly
    • It is generated by the blind spot, where the light is concentrated and triggers an impulse in the neurone
    • It is generated directly by light falling on the optic nerve, which is sensitive to light along its length
    • It is generated when a change in the bipolar or ganglion cell potential reaches threshold, producing an impulse along the optic nerve

  14. Why does a bright flash of light produce a brief and then fading response in rods?

    • Retinal is converted into opsin by the flash, which removes the light-absorbing molecule from the rod
    • Sodium channels stay permanently open, so the rod is constantly depolarised by the flash of light
    • Rhodopsin is bleached and must be regenerated before full sensitivity returns, so the response weakens
    • Rods stop being sensitive to all light for ever after a single flash of bright light is absorbed

  15. What is the role of cGMP in the rod cell's dark state?

    • It keeps cation channels open so sodium can enter, maintaining the depolarised dark state of the rod
    • It breaks down retinal, which removes the light-absorbing molecule from the rod in darkness
    • It transports rhodopsin out of the cell, which keeps the pigment from being bleached by ambient light
    • It closes sodium channels in the dark, which hyperpolarises the rod and stops neurotransmitter release

  16. A student says rods are always sensitive to light, so they respond equally in bright and dim light. Which evaluation is correct?

    • Incorrect, because rods saturate in bright light and respond less, so they are most useful in dim light
    • Incorrect, because rods do not respond to light at all, so they cannot contribute to any form of vision
    • Correct, because rods are only found in bright areas of the retina, which means they always work in full light
    • Correct, because rods have no photopigment and so are not affected by changes in light intensity at all

  17. Which feature of the retina improves vision in dim light compared with bright light?

    • Cone cells located only at the blind spot, which detect the faint light that reaches the back of the eye
    • Rod convergence, which pools many rod signals into one bipolar cell so that weak light is detectable
    • The absence of any bipolar cells, which allows the rods to send their signals directly to the brain
    • The lack of rhodopsin in all rods, which makes them more sensitive to the small amounts of light in dim conditions

  18. Which pair correctly matches a retinal component with its role?

    • Rhodopsin: the photopigment that absorbs light in rods, starting the change in membrane potential
    • Bipolar cell: the cell that absorbs light directly, sending the signal to the optic nerve without any synapse
    • Blind spot: the region where light is most strongly absorbed, which gives the eye its best sensitivity
    • Fovea: the region with most rods and no cones, which gives the best detail in dim light

  19. A researcher finds that a mutation prevents sodium channels from closing in response to light in rods. What is the likely consequence?

    • Rods would not hyperpolarise properly, so light would produce less change in neurotransmitter release
    • Rods would stop releasing any neurotransmitter in the dark, which would make the eye blind in the dark
    • Rods would be unaffected in all conditions, since the mutation only changes the shape of the sodium channel
    • Rods would become hyperpolarised in the light, so the signal to the brain would be strongly enhanced

  20. In darkness, rod cells release neurotransmitter continuously. Which change in the rod follows the absorption of a photon of light?

    • Rhodopsin becomes a sodium channel, so neurotransmitter release increases in the light
    • Sodium channels close, the membrane hyperpolarises, and neurotransmitter release falls
    • Calcium channels open in the nucleus, releasing more neurotransmitter into the synapse
    • Sodium channels open wider, depolarising the membrane further and increasing neurotransmitter release

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