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Flashcards in Stimuli and Responses Deck (92)
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1

How do animals increase their chances of survival?

by responding to changes in their external environment, e.g. avoiding harmful environments that are too hot or too cold, and changes in their internal environment to ensure conditions are always optimal for their metabolism

2

How do plants increase their chances of survival?

by responding to changes in their environment

3

What is a stimulus?

any change in the internal or external environment

4

What are receptors?

cells or proteins on cell surface membranes that detect stimuli (loads of different types of receptors that detect different stimuli - are specific)

5

What are effectors?

cells that bring about a response to a stimulus, to produce an effect. (muscle cells and cells found in glands)

6

How do receptors communicate with effectors?

via the nervous system or hormonal system, or both

7

How does the nervous system send info?

as electrical impulses

8

What is the NS made up of?

a complex network of cells called neurones

9

What are the 3 main types of neurone?

sensory, motor, relay

10

What is the role of sensory neurones?

transmit electrical impulses from receptors to CNS - brain and spinal cord

11

What is the role of motor neurones?

transmit electrical impulses from CNS to effectors

12

What is the role of relay neurones?

transmit electrical impulses between sensory neurones and motor neurones

13

What are electrical impulses also called?

nerve impulses or action potentials

14

Describe process of a stimulus to response.

-stimulus is detected by receptor cells and electrical impulse is sent along sensory neurone
-when electrical impulse reaches end of neurone, neurotransmitters take info across to next neurone, which then send an electrical impulse
-CNS (coordinator) processes info and sends impulses along motor neurones to an effector

15

What is the CNS?

brains and spinal cord

16

What is the peripheral nervous system?

made up of neurones that connect CNS to rest of the body

17

2 systems of peripheral NS?

-somatic NS controls conscious activities
-autonomic NS controls unconscious activities e.g. digestion

18

2 divisions of autonomic NS?

-sympathetic NS gets body ready for action ('fight or flight' system)

-parasympathetic NS calms body down ('rest and digest' system)

19

What is a reflex?

body responds to stimulus without making a conscious decision to respond

20

How do reflexes help organisms protect the body?

they're rapid (don't spend time deciding how to respond so info travels really fast from receptors to effectors)

21

What is a reflex arc?

pathway of neurones linking receptors to effectors in a reflex

22

Describe the hand-withdrawal response to heat.

-thermoreceptors in skin detect heat stimulus
-sensory neurone carries impulse to relay neurone
-relay neurone connects to motor neurone
-motor neurone send impulse to effector (biceps muscle)
-muscle contracts to withdraw hand and stop it being damaged

23

How is it possible to override the reflex?

if there's a relay neurone involved in the simple reflex arc, then its possible to override reflex, e.g. brain could tell hand to withstand heat

24

Why is NS communication described as localised?

when electrical impulse reaches end of neurone, neurotransmitters are secreted directly onto target cells (e.g. muscle cells) - so nervous response is localised

25

Why is NS communication described as short-lived?

neurotransmitters are quickly removed once they've done their job - so response is short-lived

26

Why is NS communication described as rapid?

electrical impulses are really fast - so response is rapid (allows animals to react quickly to stimuli)

27

Polio is a virus that can cause damage to CNS. In severe cases, virus can damage motor neurones. Suggest and explain how this might lead to paralysis.

Motor neurones carry electrical impulses from CNS to effectors which then respond. Damage to motor neurones means the CNS can't communicate with effectors such as muscles, so muscles don't respond and are paralysed.

28

The knee-jerk is a reflex response. Suggest why the absence of this response could indicate some damage to a person's CNS.

Damage to the CNS could interrupt transmission of the reflex, preventing the reflex response from occurring.

29

Give 3 ways in which flowering plants respond to stimuli.

-they sense direction of light and grow towards it to maximise light absorption for photosynthesis
-they can sense gravity, so their roots and shoots grow in the right direction
-climbing plants have a sense of touch, so can find things to climb up and reach sunlight

30

What is a tropism?

the response of a plant to a directional stimulus

31

How do plants respond to stimuli?

by regulating their growth

32

What is a positive tropism?

growth towards stimulus

33

What is a negative tropism?

growth away from stimulus

34

What is phototropism?
-shoots?
-roots?

growth of a plant in response to light
-shoots are positively phototropic
-roots are negatively phototropic

35

What is gravitropism?
-shoots?
-roots?

growth of a plant in response to gravity
-shoots are negatively gravitropic
-roots are positively gravitropic

36

What are growth factors?

hormone-like chemicals that speed up or slow down plant growth

37

Where are growth factors produced?

growing regions of plant (shoot tips, leaves) and they move to where they're needed in other parts of the plant

38

What is the role of auxins in shoots?

stimulate growth of shoots by cell elongation (cell walls become loose and stretchy, so cells get longer)

39

What is the role of auxins in roots?

high concentrations of auxins inhibit root growth

40

What is IAA?

Indoleacetic acid (IAA) is an important auxin

41

Where is IAA produced?

shoot tips

42

How does IAA move:
-over short distances?
-over long distance?

-by diffusion and active transport
-via phloem

43

How does IAA work?

IAA is moved around plant to control tropisms, different parts of plant have different concentrations of IAA, uneven distribution of IAA means uneven growth of plant

44

Phototropic response of IAA in shoot?

IAA concentration increases shaded side - cells elongate and the shoot bends towards the light

45

Phototropic response of IAA in root?

IAA concentration increases on shaded side - growth is inhibited so root bend away from the light

46

Gravitropic response of IAA in shoot?

IAA concentration increases on lower side - cells elongate so shoot grows upwards

47

Gravitropic response of IAA in root?

IAA concentration increases on lower side - growth is inhibited so root grows downwards

48

How do simple mobile organisms respond to stimuli?

simple mobile organisms, e.g. woodlice and earthworms, have simple responses to keep them in a favourable environment, response is tactic or kinetic

49

What is a tactic response (taxes)?

organism moves towards or away from a directional stimulus

50

Explain how phototactic response of woodlice keeps them in a favourable environment.

woodlice show a tactic response to light, they move away from a light source. Helps them survive as it keeps them concealed under stones during the day (safe from predators) and keeps them in damp conditions (reduces water loss)

51

What is a kinetic response (kineses)?

organisms' movement is affected by a non-directional stimulus

52

Explain how kinetic response of woodlice to humidity keeps them in a favourable environment.

in high humidity , they move slowly and turn less often, so they stay where they are. As air gets drier, they move faster and turn more often, so that they move into a new area. Increases chance that woodlouse will move to an area with high humidity. Increases survival chances - reduces water loss and helps keep them concealed

53

Why are receptors specific?

they only detect one particular stimulus

54

What are receptors?

some are cells e.g. photoreceptor cells connect to NS
some are proteins on cell surface membranes e.g. glucose receptor proteins in cell membranes of some pancreatic cells

55

Explain how receptor cells that communicate info via the NS work.

-when a NS receptor is in its resting state, there's a difference in charge between the inside and outside of the cell - generated by ion pumps and ion channels. so there's a potential difference (voltage) across the membrane.
-potential difference when cell is at rest is called its resting potential. when a stimulus is detected, cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell - altering the potential difference. (change in potential difference due to a stimulus is the generator potential)
-if the generator potential reaches the threshold level, an action potential is triggered. (if stimulus is too weak, generator potential won't reach the threshold, so no AP)

56

How does a bigger stimulus affect the generator potential?

a bigger stimulus excites the membrane more, causing a bigger movement of ions and a bigger change in potential difference - so a bigger generator potential is produced.

57

What is an action potential?

an electrical impulse along neurone

58

How is the strength of a stimulus measured?

action potentials are all one size, so strength of stimulus is measured by the frequency of APs (number of APs triggered during a certain time period)

59

What are pacinian corpuscles?

pressure receptors in skin (mechanoreceptors - only respond to mechanical stimuli)

60

What are mechanoreceptors?

they detect mechanical stimuli e.g. pressure and vibrations (found in skin)

61

Describe the structure of a pacinian corpuscle.

-pacinian corpuscle contain the end of a sensory neurone (sensory nerve ending), wrapped in loads of layers of connective tissue called lamellae

62

What happens when a pacinian corpuscle is stimulated?

-when a pacinian corpuscle is stimulated, e.g. by a tap on the arm, the lamellae are deformed and press on the sensory nerve ending
-this causes the sensory neurones's cell membrane to stretch, deforming the stretch-mediated sodium ion channels. channels open and sodium ions diffuse into cell, creating a generator potential.
-is generator potential reaches threshold, it triggers an AP

63

Describe the structure of the eye.

-light enters eye through pupil
-amount of light that enters is controlled by muscles of the iris
-light rays are focused by the lens onto the retina, which lines the inside of the eye. retina contains photoreceptor cells - these detect light
-fovea is an area of the retina where there are lots of photoreceptors
-nerve impulses from photoreceptor cells are carried from the retina to the brain by the optic nerve - bundle of neurones. where the optic nerve leaves the eye is called the blind spot - no photoreceptor cells so not sensitive to light

64

How do photoreceptors convert light into an electrical impulse?

-light enter the eye, hits photoreceptors and is absorbed by light-sensitive optical pigments
-light bleaches the pigments, causing a chemical change and altering the membrane permeability to sodium ions
-a generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neurone
-bipolar neurones connect photoreceptors to the optic nerve, which takes impulses to the brain

(light passes straight through the optic nerve and bipolar neurone to get to the photoreceptor)

65

What are the two types of photoreceptor?

rods and cones

66

Where are rods found?

peripheral parts of retina

67

Where are cones found?

packed together in the fovea

68

What type of info do rods give?

black and white (monochromatic vision)

69

What type of info do cones give?

colour (trichromatic vision)

70

3 types of cone cell?

each type contains a different optical pigment:
-red-sensitive
-green-sensitive
-blue-sensitive
when they're stimulated in different proportions, you see different colours

71

Describe sensitivity to light of rod cells.

rod cells are very sensitive to light (work well in dim light) because many rods join one neurone, so many weak generator potentials combine to reach the threshold and trigger an AP

72

Describe sensitivity to light of cone cells.

cones are less sensitive than rods (work best in bright light) because one cone joins to one neurone, so it takes more light to reach the threshold and trigger an AP

73

What is visual acuity?

the ability to tell apart points that are close together

74

Describe the visual acuity of rods.

rods give low visual acuity because many rods join the same neurone, which means light from two points close together can't be told apart

75

Describe the visual acuity of cones.

cones give high visual acuity because cones are close together and one cone joins one neurone. when light from two points hits two cones, two APs (one from each cone) go to the brain - so you can distinguish two points that are close together as two separate points

76

What controls the regular beating of the heart?

cardiac muscle

77

Why is the cardiac muscle 'myogenic'?

it can contract and relax without receiving signals from nerves

78

Where is the SAN (sinoatrial node)?

wall of right atrium

79

What is the role of the SAN?

SAN is like a pacemaker - it sets the rhythm of the heartbeat by sending out regular waves of electrical activity to the atrial walls, causing right and left atria to contract at the same time

80

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

a band of non-conducting collagen tissue prevents the waves of electrical activity from being passed directly from the atria to the ventricles

81

What is the role of the AVN?

waves of electrical activity are transferred from SAN to AVN (atrioventricular node) . AVN passes waves of electrical activity on to the bundle of His

82

Why is there a slight delay before the ventricles contract?

slight delay before the AVN reacts, to make sure the atria have emptied before the ventricles contract

83

What is the role of the bundle of His?

group of muscle fibres that conducts waves of electrical activity between the ventricles to the apex of the heart

84

What is the role of the Purkyne tissue?

bundle of His splits into finer muscle fibres in the right and left ventricle walls, Purkyne tissue carries the waves of electrical activity into the muscular walls of the left and right ventricles, causing them to contract simultaneously, from the bottom up

85

What controls the rate at which the SAN fires (i.e. heart rate)?

unconsciously controlled by a part of the brain called the medulla oblongata

86

Why do animals need to alter their heart rate?

to respons to internal stimuli e.g. prevent fainting due to low blood pressure or to make sure heart rate is high enough to supply body with enough oxygen

87

What are baroreceptors?
-where are they?
-how are they stimulated?

pressure receptors
-aorta and carotid arteries (major arteries in neck)
-stimulated by high and low blood pressure

88

What are chemoreceptors?
-where are they?
-what do they monitor?

chemical receptors
-aorta, carotid arteries and medulla
-monitor oxygen level in blood, carbon dioxide and pH (which are indicators of O2 level)

89

Describe response to high blood pressure.

stimulus - high blood pressure
receptor - baroreceptors detect high blood pressure
impulses sent to medulla along sensory neurones, which sends impulses along parasympathetic neurones.
these secrete acetylcholine (neurotransmitter), which binds to receptors on SAN
effector - cardiac muscle
response - heart rate slows down to reduce blood pressure back to normal

90

Describe response to low blood pressure.

stimulus - low blood pressure
receptor - baroreceptors detect low blood pressure
impulses sent to medulla along sensory neurones, which send impulses along sympathetic neurones.
these secrete noradrenaline (neurotransmitter), which binds to receptors on SAN
effector - cardiac muscle
response - heart rate speeds up to increase blood pressure back to normal

91

Describe response to high O2, low CO2 or high pH levels.

stimulus - high O2, low CO2 or high pH levels
receptor - chemoreceptors detect chemical changes in blood
impulses sent to medulla along sensory neurones, which send impulses along parasympathetic neurones.
these secrete acetylcholine (neurotransmitter), which binds to receptors on SAN
effector - cardiac muscle
response - heart rate decreases to return O2, CO2 and pH levels back to normal

92

Describe response to low O2, high CO2 or low pH levels.

stimulus - low O2, high CO2 or low pH levels
receptor - chemoreceptors detect chemical changes in blood
impulses sent to medulla along sensory neurones, which sends impulses along sympathetic neurones.
these secrete noradrenaline (neurotransmitter), which binds to receptors on SAN
effector - cardiac muscle
response - heart rate increases to return O2, CO2 and pH levels back to normal