organisms respond to changes in their internal and external environments 3.6 Flashcards
aqa alevel biology
1
Q
when does action potential get generated?
A
when neurones voltage increases beyond threshold from resting potential
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
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)
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
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
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
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
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)
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
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
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
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
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
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)
15
Q
what is a stimulus?
A
detecable change in the environment detected by receptors
16
Q
how do organisms increase their chances of survival?
A
by responding to changes in their environment
17
Q
what are tropisms?
A
growth of a plant in response to a directional stimulus (can be negative or positive)
18
Q
what is positive tropism?
A
grow towards stimulus
19
Q
what is negative tropism?
A
grow away from stimulus
20
Q
what is gravitropism?
A
growth of plant in response to gravity
21
Q
what is phototropism?
A
growth of plant in response to light
22
Q
what are tropisms controlled by?
A
growth factors for example IAA
23
Q
where is IAA produced?
A
tips or shoots of plants
24
Q
what is the role of IAA?
A
controls cell elongation
25
what is the effect of IAA in plant shoots? (positive phototropism)
- 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
26
what is the effect of IAA in plant roots? (negative phototropism)
- 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
27
what is the effect of IAA in plant shoots? (negative gravitropism)
- 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
28
what is the effect of IAA in plant roots? (positive gravitropism)
- IAA moves to lower side of root
- so upper side elongates
- roots bend down towards gravity and anchors plant in
29
what is taxis?
when an organism moves its entire body towards (favourable) or away from (unfavourable) a stimulus
30
what is positive taxis?
organism moves towards stimulus
31
what is negative taxis?
organism moves away from stimulus
32
why do earthworms show negative phototaxis?
move away from light to dark to avoid dehydration and predators and find food
33
why do bacteria show positive chemotaxis?
move towards certain chemicals to aid survival
34
what is kinesis?
when an organism changes the speed of movement and the rate it changes direction
35
when do organisms increase the rate it changes direction?
when it crosses the boundary between favourable and unfavourable stimuli so will move around more to quickly get back into favourable conditions
36
when do organisms decrease the rate it changes direction?
when in an area surrounded by negative stimuli will walk in a relative straight line to increase chances of finding favourable conditions again
37
what is the order of the reflex arc?
1) stimulus
2) receptor
3) sensory neurone
4) intermediate neurone (passes spinal cord)
5) motor neurone
6) effector (muscle)
38
what is the structure of motor neurone?
- 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
describe factors of hormal system
- 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
describe factors of nervous system
- 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
what is the function of a synapse?
where one neurone communicates with another or with the effector
42
what is the structure of a neurone?
- 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
what happens in the pre synaptic neurone for a synaptic transmission?
- 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
what happens in post synaptic neurone during a synaptic transmission?
- 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
what happens to acetylcholine after a synaptic transmission?
- ACH is hydrolysed by acetylcholinerase
- the products (choline and ethanoic acid) reabsorbed by pre synaptic neurone to stop over stimulation
46
what would happen if choline and ethanoic acid wasnt removed from post synaptic knob?
aceytlcholine would keep binding to receptors causing depolarisation
47
what is temporal summation?
- 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
what is spatial summation?
- many presynaptic neurones share one post synaptic cleft
- collectivelu release sufficient neurotransmitters to reach threshold level to trigger new action potential
49
what are inhibitory synapses?
- 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
what is an example of inhibitory synapses?
GABA
51
what are receptors?
cells that detect and respond to specific stimuli
52
what is the structure of a pacinian corpuscle?
- lamellae
- axon
- sensory neurone
53
how does a pacinian corpuscle respond to pressure?
- 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
how many cone cells are connected to a bipolar neurone?
one
55
how many rod cells are connected to a bipolar neurone?
three
56
what does visual sensitivity to light?
how well you can see in different light intensity (mainly low)
57
what is the visual sensitivity to light for rods and cones?
rods - high visual sensitivity
cones - low visual sensitivity
58
what is the visual sensitivity to colour for rods and cones?
rods - low (black/white vision)
cones - high (coloured vision)
59
what is the visual acuity for rods and cones?
rods - low
cones - high
60
what is the name of the pigment in rods?
rhodopsin
61
what is the pigment in cones?
iodopsin
62
how does rhodopsin affect rods sensitvity to light?
- breaks down easily in low light intensities
- threshold level reached and generator potential in bipolar neurone
- an action potential passes to optic nerve
63
how does iodopsin affect cones sensitivity to light?
needs high light inetnsity to be broken down
64
what are the three types of wavelengths cones are sensitive to?
blue light
red light
green light
65
how do pupils constrict?
circular muscle contract and radial muscle relax
66
how do pupils dilate?
circular muscle relax and radial muscle contracts
67
what does myogenic stimulation mean?
the contracts is initated from within the muscle itself rather than a nerve impulse
68
how is heart rate initiated?
- 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
what is the parasympathetic route to heart rate being controlled?
- 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
what is the sympathetic route to heart rate being controlled?
- 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
71
what type of muscle is a skeletal muscle?
antagonistic
72
what proteins are myofibrils made off?
actin and myosin (form sarcomeres)
73
what is the structure of myofibrils?
sarcomere
sarcoplasm
sarcolemma
sarcoplasmic reticulum
74
what is the sliding filament theory?
- when action potential reaches a muscle fibre it triggers Ca2+ release from sarcoplasmic reticulum to sarcoplasm
- Ca2+ binds to tropomyosin causing it to move and expose actin binding site
- with ADP and Pi still attached myosin head binds to actin binding site forming actinomyosin cross bridge
- once cross bridge forms myosin head bends pulling actin filament along (power stroke) releasing ADP + Pi and causing actin to slide over myosin
- a new ATP molecule binds to myosin head causing it to detach from actin filament
- within sarcoplasm ATPase hydrolyses ATP into ADP and Pi the energy released is used to reposition myosin head into original state
- if Ca2+ levels remain high cycle continues and when simulation stops Ca2+ actively transported back into sarcoplasmic reticulum and tropomyosin blocks binding sites again
75
what key roles do ATP have in sliding filament theory?
- break actinomyosin bridges
- to move/bend myosin heads
- for active transport of Ca2+ ions back into sarcoplasmic reticulum
76
what is the role of phosphoceratine in sliding filament theory?
if not enough ATP, phosphoceratine acts as rapid ATP source donating phosphate group to ADP ensures ATP produced in intense activity
77
what is the role of glycogen granules in skeletal muscles?
- store of glucose
- glucose used as respiratory substrate to provide ATP
78
what is the role of Ca2+ ions in muscle contraction?
bind to tropomyosin to expose binding sites on actin
79
what is the A band in sarcomere?
distance of myosin
80
what are Z lines in sarcomere?
start and end points
81
what is I band in sarcomere?
section of actin NOT overlapping with myosin
82
what is the H zone in sarcomere?
section of myosin with NO overlaps with actin
83
what happens when a muscle contracts?
H zone and I band decreases and Z lines come closer together
84
what are slow twitch fibres?
they contract slower to sustain aerobic respiration
produce ATP slowly but more ATP per glucose
large supply of myoglobin, lots of blood supply and mitochondria
for marathon running
85
what are fast twitch fibres?
contract faster for short bursts of energy powerful contractions
produce ATP faster but less ATP per glucose
uses anaerobic respiration
thicker more myosin filaments, large glycogen store and store of phosphoceratine
86
what is the neuromuscular junction?
where motor neurone meets skeletal muscle
87
what happens when an nerve impulse reaches skeletal muscle?
- nerve impilses arrives at presynaptic neurone
- depolarisation of membrane occurs
- Ca2+ channels open causes synaptic vesicles to diffuse and fuse with the membrane
- ACH is released and binds to receptors on sarcolemma
- Na+ channels open and Na+ diffuse in sarcolemma depolarise creates AP
- AP leads to voltage gated Ca2+ in membrane of sarcoplasmic reticulum
- Ca2+ diffuse out of sarcoplasmic reticulum
- enables muslce contraction
88
differences between neuromuscular and choligernic synapse?
neuromuscular is only excitatory and is the end point unlike choligernic
89
what is homeostasis?
maintenance of stable internal conditions within restricted limits
90
why is homeostasis important?
- to maintain stable core temperature
- stable blood pH in relation to enzyme activity
91
what is negative feedback?
any deviations from normal values are restored to original levels
92
when does blood glucose increase?
digestion of food and drinks containing carbohydrates
93
when does blood glucose decrease?
post excerise or when no food intake
94
how is pancreas involved in blood glucose concentration?
- detects change in blood glucose
- islets of langerhands cells release insulin and glucagon to bring glucose levels back to normal
95
what is insulin and glucagon?
insulin - released when blood glucose to high
glucagon - released when blood glucose to low
96
what is adrenaline?
released when in danger causes more glucose to be relased from hydrolysis of glycogen in liver
97
what is glycogenolysis?
breakdown of glycogen to glucose and occurs when glucose levels low stimulated by glucagon and adrenaline in th liver due to second messenger model
98
what is glycogenesis?
formation of glycogen (stored in liver) from glucose and occurs when glucose levels high stimulated by insulin in the liver
99
what is gluconeogenesis?
formation of glucose from non carbohydrate sources like amino acids etc occurs when glucose levels to low and need glucose stimulated by glucagon in the liver
100
what happens when blood glucose levels high?
- detected by b cells in islets of langerhan
- secrete insulin
- liver cells become more permeable to glucose and activates glycogenesis
- glucose is removed from the blood and stored as glycogen in cells
- inhibits gluconeogensis
101
what happens when blood glucose levels low?
- detected by a cells in islets of langerhan
- secrete glucagon
- adrenal gland secretes adrenaline
- second messenger model occurs to stimulate glycogenolysis
- glycogen hydrolysed and glucose released back into blood
- stimulates gluconeogensis
102
what is the action of insulin?
- attaches to receptors on surface of target cells changes tertiary structure leading to more glucose being absorbed by FD
- more protein channels incorporated into cell membrane so more glucose absorbed from blood into cells
- activating enzymes involved in conversion of glucose to glycogen (glycogenesis)
103
what is the action of glucagon?
- attaching to receptors on surface of target cells (liver cells)
- when it binds it causes a protein to be activated into adenylate cyclase and to convert ATP into cyclic AMP (cAMP)
- cAMP activates an enzyme protein kinase that can hydrolyse glycogen into glucose
- activating enzymes in coversion of glycerol/amino acids into glucose
104
what is the role of adrenaline in second messenger model?
- adrenaline binds to specific receptors on target cell surface
- causes a protein to be activated into adenylate cyclase and this converts ATP to cAMP
- cAMP activates an enzyme that can hydrolyse glycogen into glucose
105
what is type 1 diabetes?
unable to produce insulin starts in childhood potentially from autoimmune disease
106
what is type 2 diabetes?
receptors of target cells lose responsiveness to insulin starts in adulthood due to poor diet and obesity
107
what is osmoregulation?
controlling of water potential in blood
108
what is hypertonic?
blood with low water potential causes cells to shrivel
109
what is hypotonic?
blood with high water potential causes cells to burst
110
what happens in ultrafiltration?
- afferent arteriole wider than efferent arteriole causing high hydrostatic pressure
- fprces urea water glucose etc through endothelium
- filtrate passes through basement membrane
- basement membrane acts as filter abd prevents blood cells and larger proteins to pass through
111
where does selective reabsorption occur?
proximal convoluted tubule
112
what happens in selective reabsorption?
- Na+ actively transported out of epithelial cells along PCT by Na+/K+ pump and ATP
- Na+ diffuse into cells from lumen down concentration gradient by faciliated diffusion
- glucose/amino acids are contranported into into cells with Na+
- glucose/amino acids diffuse into blood by FD
- water enters by osmosis as lower water potential in cells compared to lumen
113
what happens when there is low water potential in blood?
- osmoreceptors detect change
- pituitary gland releases more ADH
- walls of distil convoluted tubule and collecting duct become more permeable to water as number of aquaporins increase
- more water reabsorbed into blood so more concentrated urine produced
114
what happens when there is high water potential detected in blood?
- osmoreceptors detect change
- pituitary gland release less ADH
- walls of distal convoluted tubule and collecting duct become less permeable to water as number of aquaporines decrease
- less water reabsorbed so less concentrated urine produced
