Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

biology alevel aqa > organisms respond to changes in their internal and external environments 3.6 > Flashcards

organisms respond to changes in their internal and external environments 3.6 Flashcards

aqa alevel biology

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

when does action potential get generated?

A

when neurones voltage increases beyond threshold from resting potential

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is the structure of a neurone?

A
  • cell body
  • dendrites (towards cell body)
  • axon (away from cell body)
  • myelin sheath
  • nodes of ranvier
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

how is resting potential set up in the neurone membrane?

A
  • 3Na+ are actively transported out of the axon 2K+ are transported into axon using the Na+/K+ pump and ATP
  • this creates an electrochemical gradient where K+ has a higher concentration inside axon and theres a higher concentration of Na+ outside axon
  • differential membrane permeability is formed as it is permeable to K+ (channels open) and not permeable to Na+ (channels closed)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what is depolarisation of membrane?

A
  • the specific stimulus arrives and Na+ channels open
  • membrane permeability to Na+ increases and Na+ diffuses into axon down the gradient leading to depolarisation (less negative)
  • if threshold potential reached an action potential is generated
  • more voltage gated Na+ channels open so more Na+ diffuse into axon
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is repolarisation of the membrane?

A
  • voltage gated Na+ channels close
  • voltage gated K+ channels open
  • K+ ions diffuse out of membrane
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is hyper polarisation? (refractory period)

A
  • K+ gated channels to slow to close so theres a slight overshoot (to many K+ ions diffuse out of axon)
  • this is restored by Na+/K+ pump
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is the all or nothing principle?

A
  • for an action potential to be produced depolarisation must exceed threshold potential
  • AP produced are always the same magnitude (size) potential
  • but if bigger stimuli registered an increase in frequency of AP
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what are the differences between unmyelinated axon and myelinated axon?

A
  • unmyelinated has no myelin sheath whereas myelinated axon does
  • unmyelinated sheath has no nodes of ranvier but myelinated does
  • unmyelinated has slower speed of transmission but myelinated has faster speed of transmission
  • depolarisation spreads across the whole axon membrane whereas depolarisation only occurs at the nodes of ranvier (saltatory conduction)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is saltatory conduction of a nerve impulse?

A

action potential jumps from nodes of ranvier to the next because nerve impulse cant travel along myelin sheath

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

how does myelin sheath affect speed of nerve impulses?

A
  • insulates axon
  • prevents action potential forming at parts of axon where myelin sheath is
  • depolarisation only occurs in nodes of ranvier
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

how does diameter of axon affect speed of nerve impulses?

A
  • greater the diameter of the axon
  • the faster the speed of conduction
  • less leakage of ions from larger axon
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

how does temperature effect speed of nerve impulses?

A
  • increases rate of diffusion of ions as more kinetic energy so leads to faster transmission
  • affects the Na+/K+ pump which requires enzymes and ATP
  • can denature proteins in plasma membrane (voltage gated channels etc) if temperature to high
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is the refractory period?

A
  • following an action potential when another action potential cant be generated
  • membrane has to repolarises before aother action potential can be generated
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is the importance of refractory period?

A
  • impulses are discrete so can travel in one direction and cant travel backwards
  • limits frequency of action potential (important in neuronal signalling)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is a stimulus?

A

detecable change in the environment detected by receptors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

how do organisms increase their chances of survival?

A

by responding to changes in their environment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what are tropisms?

A

growth of a plant in response to a directional stimulus (can be negative or positive)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is positive tropism?

A

grow towards stimulus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what is negative tropism?

A

grow away from stimulus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is gravitropism?

A

growth of plant in response to gravity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what is phototropism?

A

growth of plant in response to light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what are tropisms controlled by?

A

growth factors for example IAA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

where is IAA produced?

A

tips or shoots of plants

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what is the role of IAA?

A

controls cell elongation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

what is the effect of IAA in plant shoots? (positive phototropism)

A
  • cells in shoot tip produce IAA
  • diffuses down evenly initally
  • IAA moves to shades side so concentration increases
  • high concentration of IAA stimulates cell elongation
  • shoots bend towards the light
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what is the effect of IAA in plant roots? (negative phototropism)

A
  • cells in root tips produce IAA
  • diffuses down evenly initally
  • IAA moves to more shades side so concentration increases
  • high concentration of IAA inhibits cell elongation
  • roots bend away from light
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

what is the effect of IAA in plant shoots? (negative gravitropism)

A
  • IAA will diffuse from upper to lower side
  • if plant verticle causes cell elongation and plants grow vertically and up
  • if plants on its side shoots bend upwards
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

what is the effect of IAA in plant roots? (positive gravitropism)

A
  • IAA moves to lower side of root
  • so upper side elongates
  • roots bend down towards gravity and anchors plant in
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

what is taxis?

A

when an organism moves its entire body towards (favourable) or away from (unfavourable) a stimulus

30
Q

what is positive taxis?

A

organism moves towards stimulus

31
Q

what is negative taxis?

A

organism moves away from stimulus

32
Q

why do earthworms show negative phototaxis?

A

move away from light to dark to avoid dehydration and predators and find food

33
Q

why do bacteria show positive chemotaxis?

A

move towards certain chemicals to aid survival

34
Q

what is kinesis?

A

when an organism changes the speed of movement and the rate it changes direction

35
Q

when do organisms increase the rate it changes direction?

A

when it crosses the boundary between favourable and unfavourable stimuli so will move around more to quickly get back into favourable conditions

36
Q

when do organisms decrease the rate it changes direction?

A

when in an area surrounded by negative stimuli will walk in a relative straight line to increase chances of finding favourable conditions again

37
Q

what is the order of the reflex arc?

A

1) stimulus
2) receptor
3) sensory neurone
4) intermediate neurone (passes spinal cord)
5) motor neurone
6) effector (muscle)

38
Q

what is the structure of motor neurone?

A
  • motor nerve endings
  • dendrons with dendrites carry nerve impulse to cell body
  • schwann cells wrap around the axon and insulate forming myelin sheath
  • node of ranvier (gap between schwann cells)
  • axon takes impulse away from cell body to muscle
39
Q

describe factors of hormal system

A
  • communication by hormones
  • tranmission by blood system
  • slow transmission
  • travels around whole body but only target cells respond
  • response widespread
  • slow response
  • long lasting response
  • effect may be permanent and irreversible
40
Q

describe factors of nervous system

A
  • communication by nerve impulse
  • transmission by neurones
  • rapid transmission
  • impulses travel to specifc parts of the body
  • response localised
  • rapid response
  • short lived response
  • effect is temporary and reversible
41
Q

what is the function of a synapse?

A

where one neurone communicates with another or with the effector

42
Q

what is the structure of a neurone?

A
  • synaptic knob
  • synaptic vesicle (contains neurotransmitter acetylcholine)
  • lots of mitochondria
  • Ca2+ channels
  • pre synaptic membrane
  • synaptic cleft
  • post synaptic membrane
  • Na+ channel proteins
  • receptors on post synapse
43
Q

what happens in the pre synaptic neurone for a synaptic transmission?

A
  • depolarisation of pre synaptic membrane causes openings of voltage gated Ca2+ channels
  • Ca2+ diffuse into neurone
  • causes vesicles containing acetylecholine to move and fuse with pre synaptic membrane
  • this releases ACH into synaptic cleft via exocytosis
44
Q

what happens in post synaptic neurone during a synaptic transmission?

A
  • ACH diffuses across synaptic cleft to bind to specific receptors on post synaptic membrane
  • this causes Na+ channels to open and diffuse into post synaptic knob cause depolarisation
  • if threshold met an action potential generate
45
Q

what happens to acetylcholine after a synaptic transmission?

A
  • ACH is hydrolysed by acetylcholinerase
  • the products (choline and ethanoic acid) reabsorbed by pre synaptic neurone to stop over stimulation
46
Q

what would happen if choline and ethanoic acid wasnt removed from post synaptic knob?

A

aceytlcholine would keep binding to receptors causing depolarisation

47
Q

what is temporal summation?

A
  • when a single pre synaptic neurone releases neurotransmitters many times over in a short period of time
  • if conc of neurotransmitter exceed threshold value of post synaptic neurone then new action potential triggered
48
Q

what is spatial summation?

A
  • many presynaptic neurones share one post synaptic cleft
  • collectivelu release sufficient neurotransmitters to reach threshold level to trigger new action potential
49
Q

what are inhibitory synapses?

A
  • post synaptic receptor have Cl- channels
  • Cl- channels open so Cl- ions diffuse in causing hyperpolarisation
  • membrane potential more negative than resting potential
  • so not enough Na+ ions to reach threshold level to generate new action potential in post synaptic neurone
50
Q

what is an example of inhibitory synapses?

A

GABA

51
Q

what are receptors?

A

cells that detect and respond to specific stimuli

52
Q

what is the structure of a pacinian corpuscle?

A
  • lamellae
  • axon
  • sensory neurone
53
Q

how does a pacinian corpuscle respond to pressure?

A
  • mechanical stimulus deforms lamellae and stretch mediated channels change)
  • so Na+ channels in membrane open and Na+ diffuse into sensory neurone
  • causes depolarisation leading to a generator potential
  • if generator potential reaches threshold it triggers action potential across sensory neurone
54
Q

how many cone cells are connected to a bipolar neurone?

A

one

55
Q

how many rod cells are connected to a bipolar neurone?

A

three

56
Q

what does visual sensitivity to light?

A

how well you can see in different light intensity (mainly low)

57
Q

what is the visual sensitivity to light for rods and cones?

A

rods - high visual sensitivity
cones - low visual sensitivity

58
Q

what is the visual sensitivity to colour for rods and cones?

A

rods - low (black/white vision)
cones - high (coloured vision)

59
Q

what is the visual acuity for rods and cones?

A

rods - low
cones - high

60
Q

what is the name of the pigment in rods?

A

rhodopsin

61
Q

what is the pigment in cones?

A

iodopsin

62
Q

how does rhodopsin affect rods sensitvity to light?

A
  • breaks down easily in low light intensities
  • threshold level reached and generator potential in bipolar neurone
  • an action potential passes to optic nerve
63
Q

how does iodopsin affect cones sensitivity to light?

A

needs high light inetnsity to be broken down

64
Q

what are the three types of wavelengths cones are sensitive to?

A

blue light
red light
green light

65
Q

how do pupils constrict?

A

circular muscle contract and radial muscle relax

66
Q

how do pupils dilate?

A

circular muscle relax and radial muscle contracts

67
Q

what does myogenic stimulation mean?

A

the contracts is initated from within the muscle itself rather than a nerve impulse

68
Q

how is heart rate initiated?

A
  • SAN sends electrical impulse across atria causing atria to contract simulataenously (atriol systole)
  • non conductive tissue between atria/ventricles prevent impulse passing directly to ventricles (prevents immediate contraction of ventricles)
  • waves of electrical activity reach AVN which delays impulse (allows atria to fully contract + empty)
  • AVN sends wave of electrical activity down bundle of HIs conducting wave between ventricle to apex where it branches into puncyne tissue causing ventricles to contract
69
Q

what is the parasympathetic route to heart rate being controlled?

A
  • pressure revceptors in aorta and carotoid detect high BP
  • sends nerve impulse along sensory neurone to the medulla oblongata that decreases heart rate
  • sends more impulses along parasympathetic pathway
  • aceytlcholine relased
  • slows down heart rate and BP returns back to normal
70
Q

what is the sympathetic route to heart rate being controlled?

A
  • pressyre receptors in aorta and carotoid detect low BP
  • sends nervse impulse along sensory neurone to medulla oblongata to increase heart rate
  • sends more impulses along sympathetic pathway
  • noradrenaline released
  • speeds up heart rate and BP back to normal

biology alevel aqa (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions