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A2 Biology > Response To Stimuli > Flashcards

Response To Stimuli Flashcards

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1
Q

What is meant by a stimulus?

A

A detectable alteration in the internal/external environment that produces a change in an organism

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2
Q

What is a receptor?

A

A cell adapted to detect changes in the environment

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3
Q

What are the 3 main types of neurones?

A

Sensory neurones, motor neurones and relay/intermediate neurones

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4
Q

How is a plants response to stimuli different from an animal’s?

A

Their receptors produce chemicals whereas animal receptors send nerve impulses

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5
Q

What order of neurones follows after a stimulus has been detected by a receptor?

A

Sensory -> intermediate (CNS) -> motor

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6
Q

What direction do sensory and motor neurones travel in?

A

The sensory neurone travels from the receptor with the nerve impulse to the CNS and the intermediate neurone and the motor neurone travels from here to the effector, where a response will occur

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7
Q

What are the two main branches of the nervous system?

A

The peripheral nervous system and the central nervous system

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8
Q

What does the ANS branch off into?

A

Sympathetic and parasympathetic nervous system I.e. “Fight or flight” or “rest and digest”

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9
Q

What does the PNS branch off into?

A

Voluntary nervous system (somatic) and autonomic nervous system

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10
Q

What is meant by a taxis?

A

A response whose direction is determined by the direction of the stimulus

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11
Q

What is an example of taxis with algae?

A

They move towards light (positive photo taxis) to maximise light energy for photosynthesis to manufacture their food

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12
Q

What is meant by a kinesis?

A

A form of response in which the organism does not move towards/away from a stimulus, but instead the more unpleasant the stimulus the more rapidly it moves and changes direction, resulting in an increase in random movements

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13
Q

What is meant by a tropism?

A

A growth movement of part of a plant in response to a directional stimulus e.g. Light

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14
Q

What is an example of tropism in plants?

A

Plant shoots growing towards light (positive phototropism) and plant roots growing away from light (negative phototropism)

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15
Q

What is an effector?

A

An organ that responds to stimulation by a nerve impulse resulting in a change or response e.g. Muscle contraction

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16
Q

What are the main sequence of events after a stimulus has been detected?

A

Stimulus -> receptor -> coordinator -> effector -> response

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17
Q

What is the pacinian corpuscle and where are they found?

A

Receptor that responds to changes in mechanical pressure only and occur deep in the skin and are most abundant on fingers, soles of feet and external genitalia

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18
Q

What is meant by a generator potential?

A

Depolarisation of the membrane of a receptor cell as a result of a stimulus

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19
Q

What are transducer cells?

A

Cells that convert a non-electrical signal e.g. light into a nervous signal and vice versa

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20
Q

What are the main features of the stretch-mediated sodium channel in the plasma membrane of the sensory neurone in the pacinian corpulse?

A

Their permeability to sodium changes when they change shape e.g. when they are stretched. At resting state they are too narrow to allow sodium ions to pass along them (P.C has a resting potential). When pressure is applied, membrane around neurone is stretched causing the channel to widen which allows an influx of sodium ions to diffuse into the neurone, and the membrane becomes depolarised and a generator potential is produce, in turn creating an action potential that passes along the neurone and then to the CNS via other neurones.

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21
Q

Which part of the eye are the light receptor cells found?

A

The retina

22
Q

What two types of light receptors are found in the retina?

A

Rod and cone cells

23
Q

How do rod and cone cells act as transducers?

A

Covert light energy into the electrical energy of a nerve impulse

24
Q

What are rod cells responsible for?

A

Monochromatic vision (black and white) night vision, low light intensity

25
Q

How many rod cells share a single sensory neurone?

A

3

26
Q

What is meant by retinal convergence?

A

A number of rod cells attached to a single bipolar cell

27
Q

Why can rod cells respond to low light intensities?

A

A certain threshold value has to be exceeded before a generator potential is created in the bipolar cells, because of the retinal convergence there is a much greater chance that threshold will be exceeded than if only a single rod was attached to each bipolar cell. Rods allow us to see in low light levels, only in black and white however

28
Q

What pigment in rod cells has to be brown down and how much light is needed?

A

Rhodopsin and low-intensity light

29
Q

What is a consequence of many rod cells sharing a single bipolar neurone?

A

Light received by rod cells sharing the same neurone will only generate a single impulse regardless of how many of the neurones are stimulated

30
Q

Why do rod cells have low visual acuity?

A

Rods cannot distinguish between the separate sources of light that have stimulated them and so two dots close together will appear as a single blob. This is due to the fact how only one impulse is generated regardless of how many neurones are stimulated

31
Q

How many types of cone cells are there?

A

3, which each respond to a different wavelength of light

32
Q

How many cone cells are connected to one bipolar neurone?

A

1

33
Q

Why do cone cells only respond to high light intensity?

A

Because each cone has their own separate bipolar cell connected to a sensory neurone, this means that the stimulation of a number of cones cannot be combined to help exceed threshold and so create a generator potential

34
Q

What is the pigment found in cone cells and how much light is needed to break it down?

A

Iodopsin and high light intensity is needed for the breakdown and creation of a generator potential

35
Q

What are cone cells responsible for?

A

Coloured vision, day time

36
Q

Why are we unable to see colours at night?

A

Because cone cells respond to different wavelengths of light

37
Q

Where are rod cells mainly found?

A

More at the periphery of the retina and absent at the fovea

38
Q

Where are cone cells found?

A

More at the fovea and fewer at the periphery of the retina

39
Q

How and why can the brain distinguish between separate sources of light?

A

Each cone cell has its own connection to a single bipolar cell, meaning if two adjacent cone cells are stimulated, the brain receives two separate impulses. This means that two dots close together will appear as two separate dots ( higher resolution) and so cones have good visual acuity

40
Q

Out of rod and cone cells. which are found most in the human eye?

A

Rods (120 million)

41
Q

Where is light focused when it hits the eye?

A

On the part of the retina opposite the pupil (fovea) by the lens

42
Q

Which part of the eye receives the highest intensity of light, and which cells are found there and why?

A

Fovea and cone cells because they are responsible for colour vision and require higher light intensities in order for the iodopsin to be broken down in order to create a generator potential

43
Q

Which part of the eye receives the lowest intensity of light, and which cells are found there and why?

A

The peripheries of the retina, only rod cells are found as they are sensitive to low light intensities and are responsible for night time vision

44
Q

What are the basic steps after a stimulus is detected?

A 
##Stimulus above threshold
##Detected by receptors
##Changes its membrane potential
##Causes generator potential
##Action potential along sensory neurone
## Passes along to intermediate neurone in spinal chord (par of CNS)
##Impulse carried by motor neurone to effector
##Effector produces response
45
Q

How do the eyes of nocturnal animals differ from humans and why?

A

There eyes are bigger, have dilated pupils and their eyes glow up when light is shone at then. These adaptations increase the amount of light available at a night time and light is re-emitted back to the retina a second time, so the rods have a second chance to absorb the image/information, thus maximising light available.

46
Q

What is the retina of nocturnal animals composed of?

A

Almost entirely of rods, meaning they have virtually no colour vision. Despite being more sensitivee to light, the low number of cones means less visual acuity and so they must cope with unfocused images.

47
Q

What are the main causes of an after image?

A
  • Over stimulation of rods and cones means they lose sensitivity
  • After image remains until rhodopsin and iodopsin have returned to their resting configuration
48
Q

Are cones or rods responsible for after images?

A

If it is colourful then cones are, if black or white or colourless then rods are responsible

49
Q

What is meant by an after image?

A

An image that continues to appear in vision after the exposure of the original image has stopped

50
Q

What is the relationship between the amount of time spent looking at an object and the duration of an after image?

A

The longer the time spent looking, the longer the stimulation of rods and cones, therefore the more time needed for the pigments to recover after being broken down thus the longer the after image

A2 Biology (12 decks)

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