Stimuli, both internal and external, are detected and lead to a response Flashcards

1
Q

Stimulus

A

Detectable change in the internal/external environment of an organism that leads to a response

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2
Q

Receptor

A

Detects stimulus, specific to one type of stimulus

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3
Q

Coordinator

A

Formulates a suitable response to a stimulus e.g nervous system/hormonal system

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4
Q

Effector

A

Produces a response to a stimulus e.g. muscles/glands

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5
Q

Reflex arc order

A

Stimulus → receptor → sensory neurone → coordinator (CNS/relay neurone) → motor neurone → effector → response

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6
Q

Reflex arc importance

A

Rapid (short pathway) because only 3 neurones and few synapses (synaptic transmission is slow)

Autonomic as it doesn’t involve passage to the brain - does not have to be learnt

Protects from harmful stimuli e.g. escape from predator/prevents damage to body tissues

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7
Q

Taxes

A

Directional responses by simple mobile organisms who move towards a favourable stimulus (positive taxis) or away from an unfavourable one (negative taxis)

e.g. woodlice show a tactic response to light. Move away from light → keeps concealed under stones during day away from predators, and in damp conditions which reduces water loss → improves chances of survival

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8
Q

Kineses

A

Non-directional responses by simple mobile organisms who change the speed of movement or the rate of direction change, in response to a non-directional stimulus
e.g. woodlice show a kinetic response to humidity

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9
Q

Positive and negative tropism in flowering plants

A

Tropism is the growth of a plant in response to a directional stimulus

Positive tropism is growth towards a stimulus

Negative response is growth away from the stimulus

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10
Q

Growth factors in flowering plants

A

A plant’s responses to external stimuli involves growth factors/hormone-like growth substances

Growth factors move from growing regions e.g. shoot tips/leaves where they are produced, to other tissues, where they regulate growth in response to directional stimuli e.g. auxins (such as IAA)

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11
Q

Indoleacetic acid (IAA)

A

Auxin

In roots, IAA inhibits cell elongation

In shoots, IAA promotes cell elongation

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12
Q

How IAA results in phototropism in shoots

A

Cells in tip of shoot produce IAA which is transported down the shoot (evenly initially)

IAA concentration increases on the shaded side and promotes cell elongation

Shoot bends towards light

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13
Q

How IAA results in gravitropism in roots

A

Cells in tip of root produce IAA which is transported down the root (evenly initially)

IAA concentration increases on the lower side of the root and inhibits cell elongation

Root curves downwards towards gravity

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14
Q

How does the Pacinian corpuscle function

A

In its normal state, the neurone Pacinian corpuscle has a resting potential as the stretch-mediated sodium channels of the neurone membrane are too narrow to allow sodium ions to pass along them.

Mechanical stimulus e.g. pressure deforms lamellae and stretch-mediated sodium ion channel

The sodium ion channels open and sodium ions diffuse into the sensory neurone

Greater pressure causes more channels to open and more sodium ions to enter, causes depolarisation which leads to a generator potential

If generator potential reaches threshold it triggers an action potential (nerve impulse)

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15
Q

What does the Pacinian corpuscle illustrate

A

Receptors respond only to specific stimuli – only responds to mechanical pressure

Stimulation of a receptor leads to the establishment of a generator potential. When threshold is reached, action potential sent, all-or-nothing principle.

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16
Q

Rod cells

A

Rod-shaped

Greater number than cone cells

More at the periphery of the retina, absent in fovea

One type of rod containing one pigment

Rods connected in groups to one bipolar cell/ganglion cell/neurone

Very sensitive to light (see in dim light)

Low visual acuity

Black & white (monochromatic) vision

17
Q

Cone cells

A

Cone-shaped

Fewer numbers than rod cells

Concentrated at the fovea, fewer at the periphery of the retina

3 types of cones containing different optical pigments

One cone joins one neurone

Less sensitive to light (require bright light)

High visual acuity

Colour (trichromatic) vision

18
Q

Differences in sensitivity to light in rod and cone cells

A

Rods are more sensitive to light

Rods connected in groups to one bipolar cell/ganglion cell/neurone (retinal convergence)

Spatial summation

Stimulation of each individual-cell alone is sub-threshold/insufficient but cells connected in groups means threshold more likely met/ exceeded to generate action potential

Cones are less sensitive to light/need higher intensity light

One cone joins to one neurone

No spatial summation

19
Q

Differences in visual acuity in rod and cone cells

A

Cones give higher visual acuity

One cone joins to one neurone

If 2 adjacent cone cells are stimulated, brain receives 2 separate impulses (information)

It can distinguish between 2 separate sources of light

Rods give lower visual acuity
Rods connected in groups to one bipolar cell/ganglion cell/neurone (retinal convergence)

Spatial summation

Many neurones only generate one impulse/ action potential, regardless of how many neurones stimulated

It can’t distinguish between separate sources of light

20
Q

Differences in sensitivity to colour in rod and cone cells

A

Cones allow colour vision

3 types of cones with different optical pigments that absorb different wavelengths/red/green/blue

Stimulation of different combinations/ proportions of cones gives a range of colour perception

Rods allow monochromatic vision since there is only one type of cone/pigment

21
Q

Myogenic stimulation of the heart and transmission of a subsequent wave of electrical activity.

A

Cardiac muscle is myogenic i.e. it can contract/relax without receiving electrical impulses from nerves

22
Q

Myogenic stimulation of the heart and transmission of a subsequent wave of electrical activity.

The role of the SAN in the bundle of His

A

Sinoatrial node (SAN) acts as a pacemaker and sends out regular waves of electrical activity across both atria

Causing right/left atria to contract simultaneously

(A layer of non-conductive tissue prevents wave crossing directly to ventricles)

23
Q

Myogenic stimulation of the heart and transmission of a subsequent wave of electrical activity.

The role of the AVN and Purkyne tissue in the bundle of His

A

Waves of electrical activity reaches the atrioventricular node (AVN) which delays impulse, allowing atria to fully contract and empty

AVN passes wave of electrical activity to bundle of His which conducts waves between ventricles to the apex of the heart, where the bundle branches into smaller fibres of Purkyne tissue

Ventricles contract simultaneously, from the bottom up

24
Q

Role and location of baroreceptors (pressure receptors) and the roles of the autonomic nervous system and effectors in controlling heart rate

A

Baroreceptors located in aorta and carotid arteries

Baroreceptors stimulated by high/low blood pressure

Low BP → more frequent impulses to medulla/cardiovascular control centre → more frequent impulses sent to SAN along sympathetic neurones → more frequent impulses sent from SAN → cardiac muscle contracts more frequently so heart rate increases

High BP → more frequent impulses to medulla/cardiovascular control centre → more frequent impulses sent to SAN along parasympathetic neurones → less frequent impulses sent from SAN → cardiac muscle contracts less frequently so heart rate decreases

25
Q

Role and location of chemoreceptors and the roles of the autonomic nervous system and effectors in controlling heart rate

A

Chemoreceptors located in aorta, carotid arteries and medulla

Chemoreceptors stimulated by blood pH/CO2 concentration/oxygen concentration (related to exercise)

High blood CO2 concentration/low pH/low blood O2 → more frequent impulses to medulla/cardiovascular control centre → more frequent impulses sent to SAN along sympathetic neurones → more frequent impulses sent from SAN → cardiac muscle contracts more frequently so heart rate increases

Low blood CO2 concentration/high pH/high blood O2 → more frequent impulses to medulla/ cardiovascular control centre → more frequent impulses sent to SAN along parasympathetic neurones → less frequent impulses sent from SAN → cardiac muscle contracts less frequently so heart rate decreases

26
Q

Sensory neurones

A

Transmit nerve impulses from a receptor to an intermediate or motor neurone

One dendron that carries the impulse towards the cell body and one axon that carries it away from the cell body

27
Q

Motor neurones

A

Transmit nerve impulses from an intermediate or sensory neurone to an effector such as a gland or a tissue

Long axon

Short dendrites

28
Q

Intermediate (relay) neurone

A

Transmit electrical impulses between sensory neurones and motor neurones