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topic 6 Flashcards

1
Q

what is a stimulus

A

a detectable change in the internal or external environment of an organism that produces a response in the organism

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2
Q

how does the ability to respond to stimuli increase chance of survival

A

organisms can detect and move away from predators/extreme temperatures; grow towards light

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3
Q

what is a tropism

A

the movement of part of a plant in response to an external stimulus. the movement is by growth and therefore slow.

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4
Q

what is the tropism for light and gravity

A

phototropism and geotropism

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5
Q

how do plants respond to the environment

A

plant growth factors- they may be used where they are made or transported within the plant by diffusion/active transport (short distances) or through the phloem (long distances)

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6
Q

where are auxins made

A

in the shoot apex and in young leaves

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7
Q

what is the primary auxin and what is it used for

A

IAA- involved in cell elongation and phototropism.
-makes cell walls loose and stretchy so they can elongate
-diffuses down the conc. gradient towards the shaded side of the shoot resulting in a higher concentration of IAA there
-this elongates cells on the shaded side, causing the shoot to bend towards the light. (+ve phototropism -ve geotropism)
-in roots, a high conc of IAA inhibits cell elongation on the shaded side, so causes roots to bend away from the light.(-ve phototropism +ve geotropism)

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8
Q

components of a motor neuron

A

cell body- contains organelles such as nucleus
dendrites- carry action potentials to surrounding cells
axon- conductive long fibre that carries the nervous impulse along the motor neurone
schwann cells- wrap around the axon to form the myelin sheath. the gaps between the myelin sheath are called the nodes of ranvier

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9
Q

what is a resting potential

A

when a neurone is not conducting an impulse, there is a difference between the electrical charge inside and outside of the neurone.
there are more positive Na+ and K+ outside so the inside is more negative at -70mV

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10
Q

how is a resting potential established

A

maintained by a sodium potassium pump involving active transport and therefore ATP
the pump moves 2K+ in and 3Na+ out
this creates an electrochemical gradient and results in K+ diffusing out and Na+ diffusing in.
the membrane is more permeable to K+ so more moves out resulting in -70mV inside the cell

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11
Q

what is the all-or-nothing principle

A

any stimulus that does trigger depolarisation to -55mV will always peak at the same maximum voltage. bigger stimuli just increase the frequency of action potentials

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12
Q

why is the all-or-nothing principle so important

A

to ensure that organisms only respond to large enough stimuli rather than every slight change in the environment

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13
Q

how do stimuli affect neurones

A

causes sodium channels to open
the membrane becomes more permeable to sodium so Na+ diffuses into the neuron down the electrochemical gradient
this makes the inside of the neuron less negative

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14
Q

describe depolarisation

A

if the potential difference reaches the threshold of -55mV, more sodium channels open causing more Na+ to diffuse rapidly into the neurone

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15
Q

describe repolarisation

A

at an action potential of around +30mV, the sodium ion channels close and the potassium ion channels open
the membrane is more permeable to potassium so K+ diffuses out of the neurone down the concentration gradient

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16
Q

describe hyperpolarisation

A

potassium ion channels are slow to close so there is a slight overshoot where too many K+ ions diffuse out of the neurone
the potential difference becomes more negative than the resting potential

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17
Q

resting potential

A

the ion channels are reset
the sodium potassium pump returns the membrane to its resting potential and maintains it until another stimulus is detected

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18
Q

what is the refractory period

A

after an action potential has been generated the membrane enters a refractory period when it cant be stimulated as Na sodium channels are recovering and cant be opened

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19
Q

why is the refractory period important

A

ensures that discrete impulses are produced so action potentials are separate from each other
ensures that action potentials travel in one direction
limits the numbers of impulses transmitted which is important to prevent overreaction to a stimulus

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20
Q

what factors affect the speed of an action potential

A

-myelination and saltatory conduction
-axon diameter
-temperature

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21
Q

explain how myelination and saltatory conduction affects speed of an action potential

A

the action potential jumps from node to node (saltatory conduction) which means the action potential travels along the axon faster as an action potential doesn’t have to be generated along the entire length, just at the nodes of ranvier

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22
Q

explain how axon diameter affects speed of an action potential

A

with a wider diameter, the speed of conductance increases
a wider diameter means there is less leakage of ions and therefore action potentials travel faster

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23
Q

explain how temperature affects speed of an action potential

A

high temperature increases speed of conductance as:
ions diffuse faster
the enzymes involved in respiration work faster so there is more ATP for active transport by the Na+/K+ pump

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24
Q

what is a synapse

A

synapses are the gaps between the end of the axon of one neuron and the dendrite of another one
here, the action potential is transmitted as neurotransmitters that diffuse across the synapse

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25
how does a synapse work
-an action potential arrives at the synaptic knob causes it to become depolarised -this leads to the opening of Ca2+ channels so Ca2+ diffuses into synaptic knob -vesicles containing neurotransmitter move towards and fuse with the presynaptic membrane. NT is released into the synaptic cleft -NT diffuses down concentration gradient across synaptic cleft to post synaptic membrane -it bind complementarily to receptors on the surface of the post SM -Na+ ion channels on the post SM open and Na+ diffuses in. if enough neurotransmitter, then enough Na+ diffuse in above threshold and post SM becomes depolarised -neurotransmitter is released from the receptor; the Na+ channels close and the post synaptic neuron can re-establish resting potential; the neurotransmitter is transported back into the pre synaptic neuron where it is recycled
26
what is spatial summation
many different neurons collectively trigger a new action potential by combining the neurotransmitter they release to exceed the threshold value
27
what is temporal summation
one neuron releases neurotransmitter repeatedly over a short period of time to add up to enough to exceed the threshold value
28
why is summation important
some action potentials do not result in sufficient concentrations of neurotransmitter being released to generate a new action potential
29
what is an inhibitory synapse
they cause chloride ions to move into the postsynaptic neuron and potassium ions to move out this makes the membrane potential -80mV, hyperpolarisation therefore an action potential is high unlikely
30
what is a neuromuscular junction
a synapse that occurs between a motor neurone and a muscle
31
similarity between neuromuscular junction and cholinergic synapse
unidirectional due to the neurotransmission receptors only being on the post SM
32
differences between neuromuscular junction and cholinergic synapse
neuromuscular junction: -only excitatory -connects motor neurone to muscles -this is the end point for the action potential -acetylcholine binds to receptors on muscle fibre membranes cholinergic synapse: -could be excitatory or inhibitory -connects two neurones which could be sensory, relay or motor -a new action potential is generated in the next neurone -acetylcholine binds to receptors on post synaptic membranes of neurones
33
what are antagonistic muscle pairs
pairs of muscles that pull in opposite directions. as one muscle contracts, the other relaxes
34
what are myofibrils
muscle fibres are made of lots of myofibrils which collectively bring about the force to cause movement myofibrils are made up of fused cells that share nuclei and sarcoplasm. there is a high number of mitochondria
35
what is a sarcomere
myofibrils are made up of 2 types of protein, myosin and actin, which form a sarcomere
36
what is the sliding filament theory
Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum; 2. (Calcium ions) cause movement of tropomyosin (on actin); 3. (This movement causes) exposure of the binding sites on the actin; 4. Myosin heads attach to binding sites on actin; 5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend; 6. (Bending) pulling actin molecules; 7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites).
37
what happens during anaerobic respiration
-when there is not enough ATP, anaerobic respiration takes place -the chemical phosphocreatine, which is stored in muscles, assists this by providing phosphate to regenerate ATP from ADP
38
what are A and I bands
when looking act a microfibril under an electron microscope, there are dark and light bands dark bands contain thick myosin filaments and some overlapping thin actin filaments- these are A bands light bands contain thin actin filaments only- these are I bands
39
what are components of sarcomeres
myofibrils are made up of short units called sarcomeres Z-lines mark the ends of sarcomeres M-lines are in the middle of sarcomeres H-zones are around the M-lines and they only contain myosin filaments
40
how are A-bands, I bands, H zones and the overall sarcomere affected when sarcomeres contract
A-bands stay the same length I-bands get shorter H-zones get shorter overall, the sarcomeres get shorter
41
compare the structure of slow-twitch fibres and fast-twitch fibres
slow-twitch fibres- contain a large store of myoglobin, a rich blood supply and lots of mitochondria fast-twitch fibres- thicker and more myosin filaments, a large store of glycogen, a store of phosphocreatine to help make ATP from ADP and a high conc. of enzymes involved in anaerobic respiration
42
where are slow-twitch fibres and fast-twitch fibres located
slow-twitch fibres- calf muscles fast-twitch fibres- biceps
43
what are general properties of slow-twitch fibres and fast-twitch fibres
slow-twitch fibres- contract slower and can respire aerobically for longer periods of time due to the rich blood supply and myoglobin oxygen store. these muscles are adapted for endurance work like marathons fast-twitch fibres- contract faster to provide a short burst of powerful contraction. these are adapted for intense exercise such as sprinting or weight-lifting.
44
describe what happens when the heart contracts and relaxes
-the SAN will release a wave of depolarisation across the atria causing it to contract -the AVN will release another wave of depolarisation when the first reaches it. there is a non-conductive layer between the atria and ventricles that will prevent the wave of depolarisation from travelling down to the ventricles. -the bundle of His, running through the septum can conduct and pass the wave of depolarisation down the septum and the Purkinje fibres in the walls of the ventricles -the apex and walls of the ventricles then contract. there is a short delay before this happens, whilst the AVN transmits the second wave of depolarisation -this allows enough time for the atria to pump all the blood into the ventricles -the cells repolarise and the cardiac muscle relaxes
45
what does the medulla oblongata do
the medulla oblongata in the brain controls the heart rate, via the autonomic nervous system. there are 2 parts- a centre linked to the sinoatrial node that increases heart rate via the sympathetic nervous system and another that decreases heart rate via the parasympathetic nervous system
46
what does heart rate change in response to and where
-pH and blood pressure and these stimuli are detected by chemoreceptors and pressure receptors in the aorta and carotid artery.
47
why does heart rate need to change in response to pressure
-if blood pressure is too high this can cause damage to the walls of the arteries -if blood pressure is too low, there may be an insufficient supply of oxygenated blood to respiring cells and removal of waste
48
why does heart rate need to change in response to pH
-pH of blood will decrease during times of high respiratory rate due to the production of carbon dioxide and lactic acid -excess acid must be removed from the blood rapidly to prevent enzymes from denaturing -this is achieved by increasing the heart rate so carbon dioxide can diffuse out into the alveoli more quickly
49
how does the heart respond to high blood pressure
receptors- baroreceptors detect high blood pressure neurone and transmitter- impulses are sent to the medulla oblongata, which sends impulses along parasympathetic neurones to the SAN effector-cardiac muscle, SAN tissues response-heart rate is reduced
50
how does the heart respond to low blood pressure
receptors- baroreceptors detect low blood pressure neurone and transmitter- impulses are sent to the medulla oblongata, which sends impulses along sympathetic neurones to the SAN effector-cardiac muscle, SAN tissues response-heart rate is increased
51
how does the heart respond to high blood pH
-chemoreceptors detect high blood pH neurone and transmitter- impulses are sent to the medulla oblongata, which sends impulses along parasympathetic neurones to the SAN effector-cardiac muscle, SAN tissues response-heart rate is reduced
52
how does the heart respond to low blood pH
-chemoreceptors detect low blood pH neurone and transmitter- impulses are sent to the medulla oblongata, which sends impulses along sympathetic neurones to the SAN effector-cardiac muscle, SAN tissues response-heart rate is increased
53
what is a stimulus
a detectable change in the environment
54
how is a response triggered
stimulus-->receptor-->coordinator-->effector-->response
55
what is the pacinian corpuscle
A receptor that responds to pressure changes occur deep in skin, mainly in fingers and feet consists of a single sensory neurone wrapped with layers of tissue separated by gel the sensory neurone in the
56
what are the channel proteins in the membrane of the pacinian corpuscle
stretch-mediated sodium channels- open and allow Na+ to enter the sensory neurone only when stretched and deformed
57
what happens when pressure is applied to the pacinian corpuscle
-in the resting state, Na+ channels are too narrow for Na+ to diffuse into the sensory neuron so resting potential is maintained -when pressure is applied, it deforms the neurone plasma membrane, stretches and widens the Na+ channels so Na+ diffuses in which leads to the establishment of a generator potential
58
what are the 2 photoreceptors in the retina
rods and cones
59
describe cones
-there are 3 types of cones, each with different iodopsin pigments which all absorb different wavelengths of light which when stimulated in different proportions, allow us to see different colours -they have low sensitivity because one cone joins to one neurone so more light is needed to reach the threshold and trigger an action potential -high visual acuity as cones are close together and one cone joins to one neurone
60
describe rods
-they cannot distinguish different wavelengths of light and process images in black and white -they have high sensitivity can detect low intensity light as many rod cells connect to one sensory neurone so many weak generator potentials combine to reach the threshold and trigger an action potential (summation) -they give low visual acuity because many rods join to the same neuron so light from 2 points close together can't be told apart
61
how is a generator potential created from rod and cone cells
light is absorbed by rhodopsin (the pigment of rod cells) or iodopsin (the pigment of cone cells) a generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neuron which connect photoreceptors to the optic nerve, which take impulses to the brain
62
how is blood glucose controlled
the pancreas detects changes in blood glucose levels contains endocrine cells in the islets of langerhans which release hormones (insulin and glucagon) to bring blood glucose levels back to normal adrenaline is released by adrenal glands when the body anticipates danger and this results in more glucose being released from stores of glycogen in the liver
63
what happens when blood glucose levels increase
-it is detected by beta cells in the islets of langerhans in the pancreas -the beta cells release insulin and the alpha cells stop secreting glucagon -the insulin binds to receptors on liver and muscle cells making them more permeable to glucose -glycogenesis occurs, cells take up more glucose and store it as glycogen -less glucose in blood
64
what happens when blood glucose levels decrease
-detected by alpha cells in the islets of langerhans in the pancreas -alpha cells release glucagon adrenal glands release adrenaline beta cells stop secreting insulin -glucagon binds to receptors on liver cells -glycogenolysis and gluconeogenesis is activated -cells release glucose into the blood
65
glycogenesis
when excess glucose is converted to glycogen when blood glucose is higher than normal- mainly occurs in the liver
66
glycogenolysis
hydrolysis of glycogen back to glucose in the liver. occurs when blood glucose is lower than normal
67
gluconeogenesis
creating glucose from non-carbohydrate store in the liver e.g. lipids occurs when all glycogen has been hydrolysed into glucose and the body still needs more glucose
68
how does insulin decrease blood glucose
-attaches to specific receptors on the surfaces of target cells and changes the tertiary structure of the channel proteins resulting in more glucose being absorbed by facilitated diffusion -more protein carriers are incorporated into cell membranes so more glucose is absorbed from blood to cells -activate enzymes that convert glucose to glycogen resulting in glycogenesis in the liver
69
how does glucagon increase blood glucose levels
-attaches to receptors on liver cells -activates enzymes in liver cells that break down glycogen into glucose (glycogenolysis) -also activates enzymes that form glucose from amino acids (gluconeogenesis)
70
how does adrenaline increase blood glucose levels
-attaches to receptors on liver cells -activates glycogenolysis and glucagon secretion -inhibits glycogenesis and insulin secretion
71
what is the second messenger model
-explains how glucagon and adrenaline can activate glycogenolysis inside a cell -adrenaline and glucagon bind to their specific receptors and activate an enzyme called adenylate cyclase -this converts ATP into a chemical signal called the second messenger which is cyclic amp -cAMP activates an enzyme called protein kinase A which activates a chain of reactions for glycogenolysis
72
where does osmoregulation occur
within the nephrons which are found in the kidneys nephrons are long tubules surrounded by capillaries
73
the nephron structure
-renal capsule with glomerulus -proximal convoluted tubule -loop of henle -distal convoluted tubule -collecting duct
74
describe ultrafiltration
-blood moves through the afferent arteriole and this splits into lots of smaller capillaries which make up the glomerulus -this causes high hydrostatic pressure -water and small molecules like glucose and mineral ions are forced out of the capillaries into the renal capsule, forming the glomerulus filtrate -large proteins and blood cells are too large to leave so remain in the blood which leaves via the efferent arteriole
75
describe selective reabsorption
occurs in the proximal convoluted tubule 85% of the glomerulus filtrate is reabsorbed back into the blood, leaving urea and excess mineral ions microvilli increase SA for reabsorption lots of mitochondria to provide energy for active transport of glucose
76
how is all of the glucose reabsorbed in selective reabsorption
-the conc of Na+ ions in the PCT cell decreases as they are actively transported into the blood in the capillaries -due to the conc grad Na+ ions diffuse from the lumen of the PCT into the cells lining the PCT -cotransport also takes place as the proteins which transport Na+ also carry glucose -the glucose can then diffuse from the PCT epithelial cells into blood stream
77
how is a sodium ion gradient maintained
-mitochondria in the walls of the cells provide energy to actively transport Na+ out of the ascending loop of henle -the ascending limb is impermeable to water so water stays inside the tubule -the accumulation of Na+ outside of the nephron in medulla lowers the water potential -w.p in the descending limb is higher than the medulla so water moves out by osmosis and is reabsorbed by the blood as it is permeable to water -this makes the filtrate more concentrated (the ions can't diffuse out as the descending limb isn't permeable to them) -near the base of the ascending limb, Na+ ions diffuse out into the medulla, further lowering its water potential
78
how is water reabsorbed
-due to the active transport of Na+ out of the loop of henle, when the filtrate reaches the top of the DCT it is very dilute -water moves out of the DCT by osmosis and is reabsorbed by the blood -ion conc in the medulla is high so water moves out of the collecting duct by osmosis -water in the medulla is reabsorbed into the blood by the capillary network
79
why would blood be hypertonic
-too much sweating -not drinking enough water -lots of ions/salt in diet
80
why would blood be hypotonic
-drinking too much water -not enough salt in diet
81
role of hypothalamus and posterior pituitary gland
-changes in wp of blood detected by osmoreceptors in hypothalamus -if wp too low, water leaves osmoreceptors by osmosis and shrivel -stimulates production of more ADH -ADH moves to the posterior pituitary and then released into the blood to the kidneys
82
what does ADH do
increases permeability of collecting duct and DCT to water more water leaves the nephron and is reabsorbed into the blood urine is more concentrated
83
what are aquaporins
protein channels for water to pass through helps more water leave collecting duct and DCT
84
what happens when wp of blood increases
detected by osmoreceptors in hypothalamus hypothalamus release less ADH DCT and collecting duct become less permeable to water less water is reabsorbed into the blood and more is lost in the urine

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