3.6.1.2 - RECEPTORS

Question 1

explain how applying pressure to the Pacinian corpuscle produces changes in membrane potential (3)

Answer 1

1. pressure causes membrane/lamellae to become stretched
2. sodium ion channels in membrane open and sodium ions move in
3. greater pressure more channels open/sodium ions enter

Question 2

the retina of an owl has a high density of rod cells.

explain how this enables an owl to hunt its prey at night (3)

do not refer to rhodopsin in your answer

Answer 2

1. high visual sensitivity (retinal convergence)
2. several rods connected to a single neurone/bipolar cell
3. enough neurotransmiter to overcome threshold OR spatial summation to reach threshold

Question 3

after staring at a purple square, a student saw a green afterimage. suggest why (3)

Answer 3

1. when staring at purple, red and blue cones are stimulated
2. red and blue cones become exhausted
3. afteriage is due to green cone cells working

Question 4

the fovea of the eye of an eagle has ahigh density of cones. an eagle focuses the image of its prey onto the fovea.

explain how the fovea enables an eagle to see its prey in detail (3)

Answer 4

1. high visual acuity
2. eachcone is connected to a single neurone (bipolar cell)
3. cones send separate sets of impulses to the brain/optic nerve

Question 5

explain what causes vision using the fovea: (2)

• to be in colour
• to have high visual acuity

Answer 5

1. 3 different types of cone cells that are different wavelengths/frequencies/colours
2. each receptor cell connects to a separate neurone

Question 6

cone cells give higher visual acuity than rod cells.
explain how (2)

Answer 6

1. each cone cell has a separate bipolar neurone
2. so no retinal convergence OR impulses from each coe are kept separate

Question 7

explain why it takes time for the rod cells to recover their sensitivity to light after moving into darkness (2)

Answer 7

1. rhodopsin bleached/broken down by light
2. time for resynthesis

Question 8

the blink reflex is caused by stimulation of receptors in the eye or eyelid.

suggest two types of stimuli these receptors might respond to (1)

Answer 8

any two from:
1. light
2. pressure
3. touch
4. temperature
5. chemicals
6. smell

Question 9

in humans resting blinking rate varies widely from 8 to 24 blinks per minute. this variation could result in the investigations into effect of stimulation on blink rate producing means that are not significantly different. explain why (2)

Answer 9

1. standard deviations
2. likely to overlap

Question 10

the blink reflex can be stopped by drugs which prevent the opening of sodium ion channel proteins in the axons of motor neurones.

suggest how these drugs affect the passage of nerve impulses along the axons (2)

Answer 10

1. no/low influx of sodium ions
2. so no depolarisation /action potential

Question 11

the blink reflex involves synapses. channel proteins on presynaptic neurones are involved in reflex responses. explain how (3)

Answer 11

1. allow calcium ions in
2. at the end of presynaptic neurone
3. causing release of neurotransmitter

Question 12

describe how a Pacinian corpuscle produces a generator potential when stimulated (3)

Answer 12

1. increased pressure deforms stretch-mediated sodium ion channels
2. sodium ion channels open and sodium ions flow in
3. depolarisation leads to generator potential

Question 13

nocturnal mammals are active at night. describe how the number and distribution of rods and cones across the retina would differ in a nocturnal mammal from the number and distribution in a human.

explain your answer (3)

Answer 13

1. more rods and fewer cones present
2. rods mainly at the fovea, not the periphery
3. rods have high sensitivity / show retinal convergence
4. rhodopsin is bleaches at low light intensities

Question 14

when a person looks directly at an object, its image is focused on the fovea.

when the image is focused on the fovea, the person sees the object in colour. explain why (3)

Answer 14

1. colour is detected by cone cells
2. fovea contains mainly cone cells
3. there are three types of cone cells, each are sensitive to different wavelengths - red, green or blue

Question 15

vision using the fovea has high visual acuity but low sensitivity to light compared with vision using other parts of the retina

explain why vision using the fovea has high visual acuity (1)

Answer 15

1. each cone in the fovea is connected to a separate neurone
2. whereas rods in the other parts of the retina share neurones

Question 16

vision using the fovea has high visual acuity but low sensitivity to light compared with vision using other parts of the retina

explain why vision using other parts of the retina has high sensitivity to light (3)

Answer 16

1. many rods in other parts of the retina
2. rod cells are very sensitive to light/work in low light
3. rods connected in groups to neurone summation
4. summation = if enough light above threshold hits any cells then get nerve impulses to brain