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Biology A-Level > Stimuli and Responses > Flashcards

Stimuli and Responses Flashcards

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1
Q

Define stimulus

A

Any change in the internal or external env

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2
Q

Why do animals and plants respond to changes in their env?

A
  • External : to inc chances of survival eg. avoid harmful env
  • Internal: to make sure conditions are optimum for metabolism
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3
Q

Define receptors

A
  • Detect specific stimuli
  • Can be cells/proteins on cell surface membranes
  • Loads of diff. types
  • Communicate w/ effector
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4
Q

Define effector

A
  • Cells that bring about a response to a stimulus, produce effect
  • Eg. Muscles + glands
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5
Q

Define nervous system

A

Complex network of cells called neurones

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6
Q

Sensory neurones

A

Transmit electrical impulses from receptor to CNS (brain + spinal cord)

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7
Q

Motor neurones

A

Transmit electrical impulses from CNS to effectors

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8
Q

Relay neurones

A

Transmit electrical impulses btw sensory neurones + motor neurones

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9
Q

Outline what happens when a stimulus is detected

A
  • Stimulus detected by receptor cells
  • Electrical impulse sent along sensory
  • At synapse, NT is sent
  • CNS processes info + sends impulse along motor
  • Impulse sent to effector
  • Response occurs
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10
Q

CNS

A

Made up of brain + spinal cord

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11
Q

Peripheral NS

A
  • Made up of neurones that connect CNS to rest of body
  • Has 2 systems: somatic NS + autonomic NS
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12
Q

Somatic NS

A

Controls conscious activities

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13
Q

Autonomic NS

A
  • Controls unconscious activities
  • 2 divisions: sympathetic NS + parasympathetic NS
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14
Q

Parasympathetic NS

A

Gets body ready for action - fight or flight

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15
Q

Sympathetic NS

A

Calms body down - rest and digest

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16
Q

Define reflex

A
  • Body responds to stimulus w/o conscious decision to respond
  • Protect body bc rapid
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17
Q

What is the reflex arc?

A
  • Stimulus
  • Receptor
  • Sensory
  • Relay
  • Motor
  • Effector
  • Response
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18
Q

Describe the nervous system communication

A
  • Localised: NT secreted directly to target cells
  • Short-lived: NT removed quickly
  • Rapid : electrical impulses are really fast
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19
Q

Give examples to how plants respond to changes in their env to inc their chances of survival

A
  • Sense direction of light + grow towards it to max light absorption for photosynthesis
  • Sense gravity, roots + shoots grow in right direction
  • Climbing plants: sense of touch, find things to climb + reach sunlight
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20
Q

Define tropism

A

Plant’s growth response to directional stimulus

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21
Q

How do plants respond to stimuli?

A

By regulating their growth

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22
Q

Positive tropism

A

Growth towards stimulus

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23
Q

Negative tropism

A

Growth away from stimulus

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24
Q

Phototropism

A
  • Growth of plant in response to light
  • Shoots: +ve phototropism - grow towards light
  • Roots: -ve phototropism - grow away from light
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25
Q

Gravitropism

A
  • Growth of plant in response to gravity
  • Shoots: -ve gravitropism - grow upwards
  • Roots: +ve gravitropism - grow downwards
26
Q

Growth factors

A
  • Hormone like-chemicals that speed up/slowdown plant growth eg. Indoleacetic acid (IAA)
  • Produced in growing regions (tips)
  • Shoots: stimulate growth by cell elongation - cell walls become loose + stretchy
  • Roots: inhibit growth
27
Q

How does IAA move around a plant?

A
  • Diffusion + AT (short distance)
  • Phloem (long distance)
28
Q

How does IAA respond to phototropism in the shoots and roots?

A
  • Moves to shaded area - uneven distrubution = uneven growth​
  • Shoots: cells elongate + bend towards light
  • Roots: inhibits growth so bends away from light
29
Q

How does IAA respond to gravitropism in the shoots and roots?

A
  • IAA moves underside - uneven distrubution = uneven growth
  • Shoots: cells elongate + grow upwards
  • Roots: growth inhibited so grow downwards
30
Q

How do mobile organisms respond to keep in favourable env?

A
  • Tactic response (taxes)
  • Kinetic response (kineses)
31
Q

Tactic response (taxes)

A

Organism move towards or away from directional stimulus eg. light

32
Q

Kinetic response (kineses)

A

Organisms’ movement is affected by non-directional stimulus eg. humidity

33
Q

Give one similarity and one difference between a taxis and a tropism (2)

A
  • Similarity: directional response to stimulus
  • Difference:
  • Taxi organism moves AND tropism growth response
  • Taxi occurs w/ animals AND tropism occurs in plants
34
Q

Outline what a choice chamber is

A

Container w/ diff compartments in which you can create diff environmental conditions

35
Q

Outline how you can use a choice chamber to investigate animal response to diff conditions

A
  • Light intensity: cover half of lid w/ black paper - one side of chamber will be dark. Put damp filter paper on both sides
  • Place woodlice on mesh + cover w/ lid
  • After 10mins record no. woodlice on each side - most will end up in dark side (tactic response to light)
  • Humidity: damp filter paper in one side + desiccating drying agent in other side
36
Q

What are pacinian corpuscles?

A
  • Mechanoreceptors - detect mechanical stimuli eg. pressure + vibrations
  • Found in skin
  • Contain sensory nerve ending which is wrapped in loads of layers of connective tissue called lamellae
37
Q

What happens when a pacinian corpuscle is stimulated?

A
  • Lamellae are deformed + press on sensory nerve ending
  • Causes sensory neurone’ cell membrane to stretch, deforming stretch mediated sodium ion channels
  • Channels open + sodium ions diffuse into cell, causing generator potential
  • If GP reaches threshold, triggers action potential
38
Q

How does light enter the eyes?

A

Through pupil

39
Q

The amount of light that enter the eyes is controlled by what?

A

Muscles of the iris

40
Q

What is the role of the retina?

A
  • Fovea, area in retina, contains photoreceptor cells - detect light
  • Nerve impulses are carried from retina to brain by optic nerve - bundle of neurones
41
Q

What is the role of the lens?

A

Focuses light rays onto retina

42
Q

What is the blind spot?

A
  • Where optic nerve leaves
  • No photoreceptor cells so not sensitive to light
43
Q

What happens when light enter the eye?

A
  • Hits photoreceptors + absorbed by light sensitive optical pigments
  • Light bleaches pigments, causing chemical change, altering membrane permeability to sodium ions
  • Generator potential created if threshold reached, nerve impulse sent along bipolar neurone
  • BP connects photoreceptors to optic nerve, takes impulse to brain
44
Q

What are the types of photoreceptors?

A
  • Rods
  • Cones
45
Q

What are the differences btw rods and cones?

A
  • R: found in peripheral part of retina, C: packed together in fovea
  • Different optical pigments so sensitive to diff wavelengths of light
  • R: black + white, C: colour (3 types of cones: red, green, + blue)
46
Q

Which photoreceptor is more sensitive to light?

A
  • Rods (work well in dim light) : many rods join 1 neurone, many weak GP combine to reach threshold + trigger AP
  • Cones less sensitive : 1 cone joins 1 neurone so takes more light to reach threshold
47
Q

Which photoreceptor has a higher visual acuity?

A
  • Cones : close together + 1 cone join 1 neurone so when light hits 2 cones, 2 AP go to brain so can distinguish 2 points as seperate points
  • Rods : many rods join same neurone, light from 2 close points can’t be told apart
48
Q

The heart is myogenic. What does this term mean?

A

Can contract + relax w/o recieving signals from nerves

49
Q

The heart rate controls + coordinates the regular contraction of the atria + ventricles. Describe how (5)

A
  • Sinoatrial node (SAN) acts as pacemaker
  • Sends wave of electrical activity to atria causing atrial contraction at same time
  • Non-conducting tissue
  • Transferred to atrioventricular node (AVN)
  • Delay at AVN ensure atria empty before ventricle contract
  • AVN sends electrical impulse to bundle of His/purkyne tissue
  • Causing ventricle to contract from base up
50
Q

What is the function of the non-conducting collagen tissue?

A

Prevents waves of electrical activity from being passed directly from atria to ventricle. Instead transferred to AVN

51
Q

Explain the importance of the slight delay at the AVN (2)

A
  • Allow ventricles to fill/atria to empty
  • Before ventricles contract
52
Q

Outline the function of the bundle of His

A
  • Group of muscle fibre
  • Conducts electrical activity btw ventricles to apex of heart
53
Q

Outline the function of the purkyne tissue

A
  • Bundle of His splits into finer muscle fibres in right + left ventricle wall
  • Carries electrical activity into muscular wall of right + left ventricle, causing them to contract at same time from bottom up
54
Q

What is the role of the medulla oblongata?

A

Unconsiously controls rate at which SAN generates electrical impulses causing cardiac muscle to contract

55
Q

Baroreceptors

A
  • Pressure receptors
  • In aorta + carotid arteries
  • Stimulated by high + low BP
56
Q

Chemoreceptors

A
  • Chemical receptors
  • In aorta, carotid arteries + medulla
  • Moniter O<strong>2</strong> , CO<strong>2</strong> + pH level in blood
57
Q

How does the heart respond to a high blood pressure?

A
  • Baroreceptors detect high BP
  • Electrical impulses sent to medulla, sends impulses along parasympathetic neurones. Secretes acetylcholine, binds receptors on SAN
  • Effector: cardiac muscles
  • HR slows to reduce BP
58
Q

How does the heart respond to a low blood pressure?

A
  • Baroreceptors detect low BP
  • Electrical impulses sent to medulla, sends impulses along sympathetic neurones. Secretes noradrenaline, binds to receptors on SAN
  • Effector: cardiac muscles
  • HR speeds up to inc BP
59
Q

How does the heart respond to high blood O2 , low CO2 or high pH level?

A
  • Chemoreceptors detect chem change
  • Impulse sent along medulla, sends impulses along parasympathetic neurones. Secrete acetylcholine, binds to receptors on SAN
  • Effector : cardiac muscle
  • HR dec
60
Q

How does the heart respond to low blood O2 , high CO2 or low pH level?

A
  • Chemoreceptors detect chem change
  • Impulse sent along medulla, sends impulses along sympathetic neurones. Secrete noradrenaline, binds to receptors on SAN
  • Effector : cardiac muscle
  • HR inc

Biology A-Level (10 decks)

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