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A-Level Biology > Module 6: Response to Stimuli > Flashcards

Module 6: Response to Stimuli Flashcards

1
Q

stimuli definition

A

a change in the internal or external environment

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2
Q

why do organisms need to respond to stimuli

A

for survival

  • predators
  • prey awareness
  • homeostasis
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3
Q

how do simple organisms respond to stimuli

A

taxis and kinesis

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4
Q

what is taxis?

A

directional response to a stimuli

-towards or away from

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5
Q

what is kinesis?

A

non-directional movement from an unfavourable area to a favourable area
organism moves rapidly and randomly in unfavourable area until they reach the favourable area where they move slowly and less randomly
spends more time in favourable area, less time in unfavourable area

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6
Q

example of response to stimuli in plants

A

tropism

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7
Q

what is tropism?

A 
directional growth in plants in response to a stimuli
towards= positive and away=negative
light=photo, water=hydro, gravity=geo
shoots show positive photo
roots show positive hydro and geo
controlled by IAA
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8
Q

what controls tropisms?

A 
Indoleacetic Acid (IAA)
example of an auxin
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9
Q

what does IAA stand for?

A

Indoleacetic Acid

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10
Q

what is a plant growth factor?

A

equivalent to animal hormones

difference: made by cells throughout the plant, only affects cells locally, affects growth

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11
Q

effects of IAA?

A

promotes growth in the shoot

inhibits growth in the root

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12
Q

how does positive phototropism in the shoot take place?

A

normally the shoot tip produces IAA, sending it down both sides of the plant, causes shoot to grow forwards
if light is present on one side the IAA will redistribute to the shaded side
causes the shaded side to grow faster
shoot bends towards the light

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13
Q

how does negative geotropism in the shoot take place?

A

if gravity is present on one side, IAA will redistribute to the same side
causes the same side to grow faster
shoot will bend away from gravity and towards the light

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14
Q

how does positive geotropism/hydrotropism in the root take place?

A

if gravity/water is present on one side, IAA will redistribute to the same side
causes the same side to grow slowly, opposite side grows faster
so the root bends towards the gravity/water

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15
Q

evidence for tropism (positive phototropism in the shoot)

A

removing/covering the shoot tip prevents tropism (tip causes tropism)
placing micin which prevents movement of chemicals inhibits tropism (tropism caused by movement of chemicals)
placing gelatine which prevents movement of electrical signals doesn’t effect tropism (not affected by electrical signals)
if shoot tip is moved to one side that side grows faster and shoot bends the other way (IAA promotes growth in the shoot)
when in light/darkness the overall levels of IAA remain the same (light doesn’t break down or inhibit IAA but redistributes it)

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16
Q

response to stimuli in mammals?

A

uses nervous system and hormonal system to coordinate response to stimuli

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17
Q

job of the nervous system?

A

coordinate response to certain stimuli

response is fast, short-acting and localised

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18
Q

pathway of the nervous system

A 
stimuli
receptor
sensory
spinal cord
brain
spinal cord
motor neurone
effector
response
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19
Q

role of a receptor

A

detects stimuli
coverts stimuli energy into nerve impulse
acts as a transducer by converting one type of energy into another
each stimuli has specific receptor
uses stimuli energy to send Na+ ions into the start of the sensory neurone

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20
Q

examples of receptors

A

Pacinian corpuscle

Retina of the eye

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21
Q

Pacinian corpuscle role

A

touch receptor that responds to pressure
found in skin, fingers and toes
apply pressure, corpuscle is compressed, stretch-mediated Na+ channels are opened, Na+ ions move into the start of the sensory neurone q

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22
Q

structure of the pacinian corpuscle

A 
layers of connective tissue (lamellae)
blood capillary to increase O2 supply
neurone ending 
viscous gel for protection and to determine pressure intensities 
sensory neurone
capsule for protection
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23
Q

how does the retina of the eye work

A

retina detects light so the brain can generate an image, made of rod and cone cells

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24
Q

cone cells

A

iodopsin pigment which is only broken down at high light intensities (3 different pigments: green,red,blue)
produces a coloured image
one cone cell connects to one bipolar neurone which connects to one sensory neurone (no retinal convergence)
as one cone cell connects to one bipolar neurone which connects to one sensory neurone, each stimuli is detected therefore high visual acuity

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25
Q

where are rod cells most numerous

A

everywhere except fovea

located in periphery of the retina

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26
Q

where are cone cells most numerous

A

fovea
20:1 ratio
where light intensity is the highest

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27
Q

rod cells

A

rhodopsin pigment which is broken down at low light intensities
a few rod cells connect to one bipolar neurone which connects to one sensor neurone
retinal convergence can occur so can detect low light intensity
a few rod cells per bipolar neurone per sensory neurone the stimuli are merged together therefore low visual acuity

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28
Q

what is retinal convergence

A

additive effect of low light intensities

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29
Q

what is the central nervous system CNS

A

made of brain and spinal cord
brain= analyses and coordinates response to stimuli
spinal cord= connects brain to sensory and motor neurones

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30
Q

what is the peripheral nervous system PNS

A

made of the sensory and motor neurone
neurone transmits nerve impulse
sensory takes nerve impulse from receptor to CNS
motor neurone takes nerve impulse from CNS to effector
sensory has cell body in middle and dendron and axon
motor has cell body at the start and only has a long axon

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31
Q

2 types of motor neurone

A

voluntary- somatic

involuntary-autonomic

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32
Q

somatic motor neurone

A

supplies to skeletal muscle

under conscious control

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33
Q

autonomic motor neurone

A

supplies to cardiac muscle, smooth muscle,glands

under subconscious control

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34
Q

what can autonomic motor neurones be divided into?

A

sympathetic and parasympathetic

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35
Q

how does the pacinian corpuscle respond to pressure

A 
pressure is applied 
PC changes shape
causes the membrane to stretch 
the stretch-mediated sodium channels widen 
Na+ ions diffuse in 
generator potential is established
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36
Q

intensity of pressure on pacinian corpuscle

A

if you increase the frequency of stimulus, increases frerquency of nerve impulse
maintained stimulus doesn’t generate multiple impulses
intermittent stimuli will generate multiple responses

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37
Q

what controls your heart beat

A 
sinoatrial node (SAN)
atrioventricular node (AV)
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38
Q

heart beat regulation process

A
  1. Electrical impulse from SAN spreads across atria, it contracts
  2. Atrioventricular septum is non-conductive tissue so stops this impulse travelling to ventricles
  3. Electrical activity travels to AV node
  4. Pause and wait for ventricles to fill
  5. AV sends impulse down bundle of His
  6. Bundle of His conducts impulse through AV septum to bottom of ventricle
  7. Smaller Purkinje fibres continue throughout ventricle walls, ventricles contract from base up
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39
Q

importance of purkinje fibres

A

smaller branching network which sends nerve impulse to cells in ventricles of heart

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40
Q

examples of things controlled by sympathetic nervous system

A

primary role is to stimulate fight/flight

heightens awareness, stimulates effectors, helps to cope with stress

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41
Q

examples of things controlled by parasympathetic nervous system

A

primary role is to rest and digest

state of relaxation, conserving energy, inhibits effectors to slow activity

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42
Q

What is a nerve impulse

A

Movement of an action potential along a neurone
Action potential= change in membrane potential (charge’ in one section of the neurone)
Changes from negative (polarised) to positive (depolarised) back to negative (repolarised/hyperpolarised)

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43
Q

What is resting potential

A

Membrane potential of neurone at rest
Is -65mV
Polarised
Caused by having more positive ions outside neurone compared to inside
Involves Na+/K+ pump, pumping 3 Na+ ions out and 2K+ ions in
K+ channel allowing K+ ions to diffuse out (K+ will eventually stop diffusing out due to a positive potential outside)

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44
Q

What happens during an action potential

A

Stimuli causes Na+ ions to enter the start of the neurone
Makes membrane potential less negative
If it reaches threshold (-50mV), Na+ channels open
Therefore more Na+ ions diffuse into the neurone, therefore membrane potential becomes positive (depolarised)
Membrane potential reaches +40mV
Then the Na+ channels close, K+ channels open
Therefore K+ ions diffuse out, therefore membrane potential becomes negative (repolarised)
Too many K+ ions move out so the membrane potential becomes more negative than Normal (hyperpolarised)
One action potential= depolarisation, repolarisation, hyperpolarisation

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45
Q

How does an action potential move along a neurone

A

By local currents
If the stimuli energy is large enough and enough Na+ ions enter the start of the neurone, threshold will be reached and an AP will occur (1st AP is called a generator potential)
Na+ ions that move in during depolarisation of the generator potential diffuse along the neurone causing the next section to reach the threshold and an AP to occur
Process continues along the neurone

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46
Q

Why does an action potential not move back ?

A

Because previous section has jus finished an action potential
It is in the refractory period (Na+ channels can’t be opened) and is hyperpolarised (therefore threshold can’t be reached)

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47
Q

How does the size of the stimuli affect a nerve impulse

A

Doesn’t affect the size of the action potential (AP is all or nothing, react threshold then get AP, doesn’t reach then no AP)
Larger stimuli increases the frequency of APs

48
Q

What affects the speed of a nerve impulse

A

Temperature
Axon diameter
Myelination

49
Q

How does temperature affect the speed of a nerve impulse

A

Higher temp
Higher kinetic energy
Faster rate of diffusion of ions
Faster nerve impulse

50
Q

How does axon diameter affect the speed of a nerve impulse

A

Wider diameter
Nerueone less leaky
Faster nerve impulse

51
Q

How does myelination affect the speed of a nerve impulse

A 
Schwann cells wrap around the axon
Insulates axon preventing AP 
AP only occurs in gaps 
Called node of ran viler 
So AP jumps from node to node= saltatory conduction (faster nerve impulse)
52
Q

What is a synapse

A

Connection between 2 different neurons
Sends nerve impulses across the synaptic cleft using neurotransmitters (acetylcholine)
AP arrives in the end of the presynaptic neurone
Ca2+ channels open
Ca2+ ions enter presynaptic neurone
Cause vesicles containing neurotransmitter to move to presynaptic membrane
Vesicles binds to membrane releasing neurotransmitter into cleft
Neurotransmitter diffuses across the cleft
Binds to the complementary receptors on postsynaptic membrane
Na+ channels open, Na+ ions enter
If threshold is reached then action potential occurs

53
Q

Synapse, how does AP return to rest

A

Enzyme used to breakdown neurotransmitter e.g. acetylcholinesterase breaks down acetylcholine into ethanoic acid and choline, diffuses back into presynaptic neurone, ATP used to reform neurotransmitter into vesicles and actively transport Ca2+ ions out

54
Q

What are the properties of synapses

A

Unidirectionality
Filters out low level stimuli
Summation
Inhibitory

55
Q

Unidirectionality of synapses

A

AP/nerve impulses travels in one direction, from pre to post, pre has the neurotransmitter, post has the receptors

56
Q

Filters out low level stimuli (synapses)

A

Low level stimuli don’t release enough neurotransmitter, not enough Na+ ion channels open, not enough Na+ ions enter postsynaptic neurone for threshold to be reached, no AP produced

57
Q

Summation (synapses)

A

Low level stimuli add together to release enough neurotransmitter to produce an AP in postsynaptic neurone, temporal or spatial

58
Q

Temporal

A

Low level stimuli present for an extended period of time

59
Q

Spatial

A

Low level stimuli from a presynaptic neurone add together

60
Q

Inhibitory

A

Normal synapses are excitatory (cause AP), some can be inhibitory- prevent action potential from occurring by making postsynaptic neurone hyperpolarised

61
Q

What is a reflex

A

Rapid involuntary response to a stimuli
Doesn’t use the brain
Sensory connected to the motor neurone to intermediate to effector for response
Less damage is done and doesn’t require learning

62
Q

How is heart rate controlled

A

Heart is myotonic, heart beat is initiated by the SAN
Medulla oblongata in the brain can increase or decrease heart rate
Receives nerve impulse from chemoreceptors (respond to blood pH) in the carotid arteries and pressure receptors (respond to blood pressure) in the carotid arteries and aorta
Sends impulse in the sympathetic nerves to SAN to increase HR and send impulse in parasympathetic nerves to SAN to decrease HR

63
Q

How does exercise affect heart rate

A

Exercise= muscle contractions, require respiration
Waste product CO2 released into blood
Lower pH of blood (acidic)
Detected by chemoreceptors in carotid arteries
Sends impulses to medulla oblongata to SAN via the sympathetic nerves causing the heart rate to increase
Benefit= increase blood flow to lungs to remove CO2 and take in O2

64
Q

How does low blood pressure affect heart rate

A

If a person moves from lying/sitting to standing the blood pressure falls (reducing blood flow to the brain)
This is detected by pressure receptors in the carotid arteries and aorta
Sends impulses to medulla oblongata
Then medulla oblongata sends impulses to SAN via the sympathetic nerves causing the heart rate to increase
Benefit= increasing heart rate leads to an increase in blood pressure (so enough blood can reach the brain)

65
Q

Different types of muscles

A

Skeletal
Smooth
Cardiac

66
Q

Role of skeletal muscle

A

Moves the body skeleton
When muscle contracts (shortens)
Tendons pulls on joints causing movement

67
Q

Structure of skeletal muscle

A 
Basic structure- sarcomeres
Many sarcomeres-myofibril 
Many myofibrils-muscle fiber
Many muscle fibres- bundle 
Many bundles-whole muscle
68
Q

Sarcomeres

A

Made up of actin and myosin

When sarcomere contracts the whole muscle contracts/shortens by sliding filament mechanism

69
Q

Actin

A

Thin

Tropomyosin wrapped around it

70
Q

Myosin

A

Thick

Has heads

71
Q

Muscle fibre

A

Surrounded by a membrane called sarcolemma

Contains myofibrils, fluid called sarcoplasm and tubes called sarcoplasmic reticulum

72
Q

Locations in a sarcomere

A

A band= location of myosin [no change in contraction]
I band= location between the myosin [shortens in contraction]
H zone= location between the actin [shortens in contraction]
Z line= end line of sarcomere [moves closer together in contraction]

73
Q

What occurs in sliding filament mechanism

A

How the sarcomere shortens
Myosin head pulls actin inwards
Somatic motor neurone connects to the skeletal muscle via a neuro-muscular junction
One motor neurone connects to a few muscle fibres=motor unit (benefit=simultaneous muscle contraction and can control strength of contraction/0
Releases acetylcholine that binds to complementary receptors on the muscle I really membrane (sarcomere)
Na+ channels open, Na+ ions enter the muscle fibre causing depolarisation
Wave of depolarisation travels through sarcoplasmic reticulum
Causes release of Ca2+ ions into the sarcoplasm
Moves tropomyosin on the actin
Exposes binding sites on the actin
Myosin heads now bind to the actin (forms actin-myosin cross bridge)
Power stroke occurs, myosin pulling the actin inwards
ATP attaches to myosin head so it detaches
ATP broke down by ATPase to release energy
Causes myosin head to go back to its original position
So it reattaches, pulling actin further inwards

74
Q

Role of Ca2+ ions and ATP in muscle contraction

A

Ca2+ ions causes the tropomyosin to move exposing binding sites on actin
Ca2+ ions stimulate ATPase
ATP causes myosin head to detach
ATP releases energy so myosin head returns to original position
ATP actively transports Ca2+ ions back into sarcoplasmic reticulum when the muscle is relaxed

75
Q

2 types of muscle fibres

A

Fast twitch and slow twitch

76
Q

How do fast twitch muscle fibres work

A

Provide powerful but short lasting contractions
Found in biceps and sprinters
Adapted for anaerobic respiration
Has thicker myosin for powerful contractions
Contains more enzymes for anaerobic respiration
Contains phosphocreatine, provides phosphate to ADP to reform ATP

77
Q

How do slow twitch muscle fibres work

A

Provide less powerful by long lasting contractions
Found in thigh muscles ad marathon runners
Adapted for aerobic respiration
Has a rich blood supply
Contains many mitochondria
Contains glycogen
Contains myoglobin (stores oxygen)

78
Q

role of the hormonal system

A

coordinates response to certain stimuli
involves chemical messengers released by endocrine glands into the blood (exocrine glands release substances into open spaces)
protein hormones bind to complementary receptors on target cells, activates enzymes that convert ATP into cyclic AMP in the cell, cyclic AMP makes changes in the cell (2nd messenger system) e.g. insulin
lipid hormones enter cells by simple diffusion and cause direct changes e.g. oestrogen

79
Q

control of blood glucose levels

A

if high= should be in cells for respiration, lowers blood water potential
if low=not enough to supply cells of the brain, also increases blood water potential
controlled by pancreas
contains islets of langerhans made of alpha and beta cells
alpha=glucagon production
beta= insulin production

80
Q

high blood glucose levels

A

occurs after a meal
insulin is released
most cells in the body have complementary receptors
cause increase in glucose channels and carriers
glucose taken up and used in respiration
in muscle and liver cells, glucose converted into glycogen for storage (glycogenesis)
in liver cells glucose converted into fat

81
Q

glycogenesis

A

glucose converted to glycogen for storage

82
Q

low blood glucose levels

A

occurs after starvation or exercise
glucagon is released
only liver cells have complementary receptors
converts glycogen into glucose (glycogenolysis)
converts fats and amino acids into glucose (gluconeogenesis)
glucose released into the blood

83
Q

glycogenolysis

A

converts glycogen into glucose

84
Q

gluconeogenesis

A

converts fats and amino acids into glucose

85
Q

diabetes

A

loss of control of blood glucose levels
normally high hyperglycaemia
2 types
symptoms= tiredness, increased urination, thirst

86
Q

diagnosis of diabetes

A

high blood glucose levels on random testing and blood glucose levels remain high following a fasting blood glucose test

87
Q

2 types of diabetes

A

type 1

type 2

88
Q

type 1 diabetes

A

typically at a young age
person doesn’t make insulin
beta cells damaged by an autoimmune disorder
treatment=insulin injections

89
Q

type 2 diabetes

A

typically at middle age
person makes insulin but the cells are less sensitive
caused by obesity and diet high in simple sugars
treatment= diet and exercise, drugs, insulin injection

90
Q

homeostasis

A

maintenance of a constant internal environment (blood and tissue fluid) in animals
control: body temp, blood pH, blood glucose levels, blood water levels, blood salt levels, blood pressure

91
Q

homeostasis and negative feedbac k

A

the response to change is to oppose the change to bring levels back to normal
body temp increases- response to bring back to normal

92
Q

positive feedback

A

the response to change is to continue the change

e.g. Na+ ions entering a neurone stimulating more to enter in depolarisation

93
Q

why do organisms need to maintain a constant body temperature

A

maintain optimum temp for enzyme activity

94
Q

endotherms

A

animals that maintain a strict constant internal body temperature irrespective of external environmental temperature (mammals)

95
Q

ectotherms

A

animals internal body temperature maintained more generally and varies with changes in external environment

96
Q

benefits of being endotherm

A

can maintain activity over a range of settings

97
Q

benefit of ectotherm

A

require less food/energy

98
Q

how is internal body temperature controlled

A

anatomical,behavioural, physiological changes
endotherms mainly rely on physiological changes
ectotherms mainly rely on behavioural changes

99
Q

anatomical adaptations in organisms in warm areas

A

small body size= large surface area to volume ratio (lose heat)
less fur
less fat
large extremities e.g. hands/ears/feet (lose heat)

100
Q

anatomical adaptations in organisms in cold areas

A

large body size= small surface area to volume ratio
more fur
more fat
small extremities

101
Q

control of body temperature in endotherms

A

controlled by hypothalamus in brain
receives nerve impulse from peripheral thermoreceptors in the skin and central thermoreceptors in the hypothalamus
peripheral thermoreceptors monitor changes in the external environment temperature
central thermoreceptors monitor changes in core body temperature (blood supplying major organs)

102
Q

how does an endotherm warm itself up

A

reduce blood flow to skin surface= vasoconstriction, smooth muscle in arterioles to skin contract, lumen narrows, less blood to skin surface, less heat lost form blood by radiation
hair on skin stand up= hair erector muscles contract, hair stands up, traps air particles, forms an insulating layer, reduces heat loss
shivering= involuntary contraction of muscle, friction in sliding filament mechanism generates heat and respiration generates heat
increased respiration in liver= generates heat

103
Q

how does an endotherm cool down

A

increases blood supply to skin surface= vasodilation, smooth muscle in arterioles to skin relax, lumen widens, more blood to skin surface, more heat lost from blood by radiation
sweating= evaporation of water particles from skin surface using the heat in the blood

104
Q

structure of kidneys

A

outer region= cortex

middle region= medulla

105
Q

role of kidneys

A

filter blood

removes: urea, excess salts and water (combined=urine)

106
Q

why remove urea

A

toxic waste product made from excess amino acids

107
Q

why remove excess salts and water

A

maintain correct water potential and pressure in the blood

108
Q

how do kidneys filter

A

made up of millions of nephrons

each nephron filters the blood producing urine

109
Q

structure of nephron

A 
1st= bowmans capsules 
2nd= proximal convoluted tubule
3rd= loop of henles 
4th= distal convoluted tubule 
5th= collecting duct
110
Q

bowmans capsule

A

start of nephron
site of ultrafiltration
occurs between specialised capillaries- Glomerulus and Bowmans capsule
glomerulus located in the middle of an arteriole
afferent arteriole before glomerulus is wide, efferent arteriole after glomerulus is narrow
build up of hydrostatic pressure in the glomerulus pushes fluid and small substances from the glomerulus into the bowmans capsule
small substances= glucose, amino acids, salt, urea
only small substances can pass through the 3 layers (endothelium of glomerulus, basement membrane, podocytes of bowmans capsule)
results in glomerular filtrate in bowmans capsule (water + salts/aminoacids/glucose/urea)
job of the rest of nephron is to send all the glucose/amino acids and some of the salts/water back into the blood (reabsorption)

111
Q

proximal convoluted tubule

A

second part of nephron
site of selective reabsorption
all glucose/amino acids and some salts/water are sent back to blood (from lumen of PCT, through cells lining PCT, into the blood)

how:
salts (Na+) are actively transported from cells lining PCT into blood
lowers Na+ conc in the cells so Na+ diffuse from lumen of PCT into cells
as Na+ move they pull glucose and amino acids with them via co-transport
glucose and amino acids build up in the cell, then diffuse into the blood
movement of salt/glucose/amino acids lowers water potential in blood so water follows by osmosis

112
Q

loop of henle

A

3rd part of nephron
site of further water reabsorption
occurs by hairpin countercurrent multiplier

how:
sodium and chloride ions are actively transported out of the ascending limb of the loop of henle into the surrounding medulla of the kidney
lowers water potential of the medulla
water moves out of the descending limb of loop of henle (and collecting duct) by osmosis in the medulla
water moves into the blood
sodium and chloride ions then diffuse into the descending limb of the loop of henles
so the above process can be repeated

113
Q

distal convoluted tubule

A

4th part of nephron
site of further salt reabsorption
corrects required salt balance between blood ad urine

114
Q

collecting duct

A

final part of nephron
site of further water reabsorption and osmoregulation
end up being left with urine that is sent into the ureter to the bladder
water reabsorption occurs by hairpin countercurrent multiplier
amount of water being reabsorbed is controlled at this stage (osmoregulation)
(learn what happens if water levels are low and high)

115
Q

osmoregulation

A

process by which the hypothalamus controls water potential of the blood

116
Q

if water levels become low (dehydration)

A

osmoreceptors in hypothalamus shrink
stimulates release of ADH form posterior part of the pituitary gland
ADH stimulates the cells lining the collecting duct to increase the number of aquaporins (water channels)
so more water moves from the collecting duct back into the blood
less water lost in urine

117
Q

if water levels become high (overhydration)

A

less ADH released
less aquaporins in collecting duct
less water moves from collecting duct into the blood
more water lost in urine (reduces overhydration)

A-Level Biology (14 decks)

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