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Biology A-Level > stimulus + receptors > Flashcards

stimulus + receptors Flashcards

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1
Q

what is a stimulus?

A

change in the internal or external
environment, such as light, temperature etc..

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2
Q

differences between electrical impulse response vs hormone response

A

impulse:
specific to one target cell only
as it releases neurotransmitter directly onto it, producing a response that is usually rapid, short-lived and localised.
hormone:
bind to complementary binding sites of protein receptors on target cells and produce responses that are usually slow, long-lasting and widespread.

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3
Q

what is a tropism?

A

a directional growth response of a PLANT to a stimulus.

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4
Q

describe production of IAA in shoot tips vs root tips in response to light + gravity

A

shoot tips:
1. IAA is produced in the shoot tip + diffuses to the lower/shaded side of the
shoot, increasing its concentration.
2. Stimulates cell elongation so cells on lower/shaded side elongate more than the cells on the light side.
3. Causes directional growth towards light and away from gravity (upwards) for photosynthesis- positive phototropism, negative gravitropism
root tips:
1. IAA is produced in the root tip + diffuses towards shaded side, increasing
its concentration.
2. Inhibits cell elongation so the cells on shaded side elongate less than the cells on the upper side/ light side.
3. Causes directional growth away from light and towards
gravity (downwards)- negative phototropism, positive phototropism

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5
Q

interpret the data

A
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6
Q

interpret the data

A
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7
Q

interpret the data

A
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8
Q

interpret the data

A
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9
Q

what is kinesis?

A

Non-directional movement to a stimulus. It involves increasing/decreasing random movements,
including speed of movement and the rate at which it changes direction.

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10
Q

give example of kinesis

A

Woodlice move faster when the humidity is low and change direction less (less non-directional
random movements).
Woodlice move slower when the humidity is high and change direction more (more non-directional random movements). Woodlice are more likely to stay in favourable conditions (high
humidity)

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11
Q

what is a taxis?

A

directional movement to a stimulus

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12
Q

give example of taxis

A

Earthworms move away from light- negative phototaxis
* More chance of survival as move into soil
o More likely to find food/ mate
o More likely to avoid predators
o Less likely to dehydrate

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13
Q

which 2 divisions is the nervous system controlled?

A
  1. CNS (Central Nervous System)– the brain and the spinal cord
  2. Peripheral nervous system- nerves that originate from brain or spinal cord that cover the rest of the
    body
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14
Q

which 2 divisions can the peripheral nervous system be divided into?

A
  • Voluntary nervous system- which is under voluntary control (conscious).
  • Autonomic nervous system- it is involuntary (subconscious control).
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15
Q

what is a reflex?

A

rapid, involuntary response to a stimulus.

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16
Q

chain of events in a reflex arc

A

stimulus-receptor-sensory neurone-intermediate neurone-motor neurone-effector-response

17
Q

why are reflex actions important?

A
  • Rapid – due to short pathway and only 3 synapses (slowest part of nerve impulse)
  • Inate - Do not have to be learned, (effective from birth)
  • Prevent damage to tissues.
  • Help escape from predators
  • Have a role in homeostasis (maintaining internal conditions)
  • Involuntary / automatic – don’t require brain, but impulses are sent to the brain which can override
    reflex if necessary
  • Allows food / mates / suitable conditions to be found
18
Q

stimulus of receptors leads to what

A

a generator potential

19
Q

where are pacinian corpuscles found?

A

mainly in skin

20
Q

draw a pacinian corpuscle

A
21
Q

how do pacinian corpuscles cause a generator potential

A
  • Pressure on the skin causes the lamellae to become deformed+ stretch mediated sodium ion channels open in the membrane of the sensory neurone.
  • Sodium ions diffuse into the axon, causing depolarisation forming a generator potential.
  • The greater the pressure on the pacinian corpuscle the more sodium ion channels open, the more sodium ions diffuse in and the larger the depolarisation.
  • If the generator potential reaches threshold, action potentials are created and nerve impulses pass along the sensory neurone membrane.
  • The frequency of impulses relates to the intensity of the stimulus – the greater the pressure (stimulus) the more frequent impulses
22
Q

describe rods in the retina

A
  • found mainly at the periphery (less at the fovea).
  • they do not allow colour vision
  • contains the pigment rhodopsin (cannot distinguish different wavelengths of light)
  • higher sensitivity to light (stimulated in low light
    intensities)
  • have low visual acuity, this means the image has a
    poor resolution.
23
Q

describe cones in the retina

A
  • present mainly in the fovea (where the lens focuses the light)
  • Contains the pigment iodopsin
  • they allow colour vision as there are 3 different types of cone cell, each with an iodopsin which responds to different wavelengths of light. Blue sensitive, green sensitive and red sensitive cone cells.
  • Lower sensitivity to light (only stimulated in high light
    intensities)
  • they have high visual acuity with a higher resolution.
24
Q

how do rod/cones detect light

A

Light causes the pigment (rhodopsin or iodopsin) to break down (bleach) causing depolarisation and a generator potential. If the
generator potential reaches threshold, action potentials are transmitted to the brain forming an image.

25
Q

why do rods have low visual acuity + high sensitivity

A

Low visual acuity as several rods are synapsed to a single bipolar cell (retinal convergence). Therefore only a single set of action potentials are sent to the brain and the brain
cannot distinguish between the separate light sources from the separate rods.
* Higher sensitivity because of this arrangement. In low light intensities, the stimulation of several rods results in more neurotransmitter being released to reach threshold
at the single connected bipolar neurone. This is an example of spatial summation where the
generator potentials have been combined.

26
Q

why do cones have high visual acuity + low sensitivity

A

high visual acuity as one cone is synapsed to one bipolar neurone so separate sets of action potentials are sent to the brain from each cone cell so the brain can distinguish between the separate light sources.
Low sensitivity to light because at low light intensities not enough
neurotransmitter is released from the single cone cell to reach threshold in the single bipolar cell. High acuity can only be achieved at high light intensities

27
Q

the cardiac muscle is myogenic, what does that mean?

A

contraction of the heartbeat is initiated within the
heart muscle cells (myocytes) themselves.

28
Q

describe electrical coordination of heart contraction

A

The contraction starts in the Sino-Atrial node in the wall of the right atrium, sending out a wave of action potentials over the atria, causing the atria to contract simultaneously.
The electrical wave is prevented from passing to the ventricles by non-conducting tissue in the wall of the heart between the atria and ventricles.
At the atrioventricular node (AVN) there’s delay, to give time for the atria to empty and the ventricles to
fill, sending out electrical impulses down the Bundle of His and up the Purkynje fibres, causing the ventricles to contract from the apex (base) upwards.
(It is important the heart contracts from the base up, so that the blood is forced out through the arteries at the top.)

29
Q

what are the 2 branches of the autonomic nervous system?

A
  1. sympathetic- stimulates effectors + speeds up heart rate
  2. parasympathetic- inhibits effectors + slows down heart rate
    The two branches are antagonistic- they have opposing effects.
30
Q

heart rate is controlled by the medulla oblongata in the brain with 2 parts, what are they?

A
  • Acceleratory centre
    o Linked to SAN by the sympathetic nervous system
  • Inhibitory centre.
    o Linked to the SAN by the parasympathetic nervous system
31
Q

how do chemoreceptors work?

A
  1. if CO2 rises blood pH falls, detected by chemoreceptors in aorta and carotid arteries
    * impulses sent to cardiac centre in medulla
    * more frequent impulses from medulla down sympathetic nerve to SAN
    * more frequent impulses from SAN across atria
    * Heart rate increases
  2. if CO2 falls blood pH rises, detected by chemoreceptors in aorta and carotid arteries
    * impulses sent to cardiac centre in medulla
    * more frequent impulses from medulla down parasympathetic nerve to SAN
    * Decreases frequency of impulses from SAN across atria.
    * Heart rate decreases.
32
Q

how do pressure receptors work?

A
  1. blood pressure rises, detected by pressure receptors in aorta and carotid arteries
    * impulses sent to cardiac centre in medulla
    * More frequent impulses from medulla to SAN via parasympathetic nerve to SAN
    * Decreased frequency of impulses from SAN across atria.
    * Heart rate decreases
  2. blood pressure falls, detected by pressure receptors in aorta + carotid arteries.
    * impulses sent to cardiac centre in medulla
    * More frequent impulses from medulla via sympathetic nerve to SAN
    * Increases frequency of impulses from SAN across atria
    * Heart rate increases

Biology A-Level (17 decks)

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