6 - Stimuli, nerves & Homeostasis Flashcards
(98 cards)
1
Q
What is a Tropism
A
Growth of a plant in response to a directional stimulus
2
Q
How does Indoleacetic acid (IAA) affect cell elongation roots vs shoots
A
Shoots - high concentrations of IAA stimulates cell elongation
Roots - high concentrations of IAA inhibits cell elongation
3
Q
Describe gravitropism
A
- cells in tip of shoot produce IAA
- IAA diffuses down shoot/roots
- IAA moves to lower side of shoot/roots
- so shoots bend away from gravity but roots bend towards gravity
4
Q
Describe phototropism
A
- cells in tip of shoot/root produce IAA -> diffuses down shoot/root
- IAA moves to shaded side of shoot/root
- shoots bend towards light but roots bend away from light
5
Q
Describe what Taxes are
A
- directional response
- movement towards or away from a stimulus
6
Q
Describe what Kineses are
A
- non directional response
- speed of movement or rate of direction change
- depends on intensity of stimulus
7
Q
Describe a simple reflex arc
A
Stimulus -> receptor -> sensory neurone -> relay neurone -> motor neurone -> effector -> response
8
Q
Suggest why the same organism is not used more than once (RP)
A
- reduces stress on wood lice
- prevents chance of learned behaviours
9
Q
Why where the Woodlice left for 15 mins before their movement was recorded
A
- time to establish humidity
- woodlice no longer effected by handling
- so that behaviour is typical of humidity
10
Q
Explain how to ensure ethical and safe handling of animals
A
- handle carefully/return to habitat ASAP
- cover open wounds, wash hands with soap to minimise risk of infection
11
Q
Why use a mesh platform (woodlice RP)
A
To keep woodlice a safe distance from drying agent
12
Q
Why use a clean Petri dish/maze each time
A
- animals may leave chemicals/scents
- which influence behaviour of other animals
13
Q
Describe how potential is generated in a pacinian corpuscle 3m
A
- pressure deforms lamellae and stretch-mediated Na+ ion channels
- Na+ channels in membrane open and Na+ DIFFUSE into sensory neurone
- Greater pressure causes more Na+ channels to open and more Na+ to enter
14
Q
What is the all or nothing principle
A
- for an action potential to be produced, depolarisation most exceed threshold potential
- action potentials produced are always the same magnitude/size/peak at same potential
Bigger stimuli frequency of action potentials
15
Q
Describe nerve impulse along a myelinated axon
A
- myelination provides electrical insulation
- depolarisation of axon at nodes of ranvier only resulting in saltatory conduction (local currents circuits)
- so there is no need for depolarisation along the whole length of axon
16
Q
What’s the effect of multiple sclerosis or any other nerve disease
A
damage to the myelin sheath so slow responses & jerky movement:
- less/no saltatory conduction, depolarisation occurs along whole length of axon so nerve impulses take longer to reach neuromuscular junction, delay in muscle
- ions/depolarisation may pass/leak to other neurones which causes wrong muscle fibres to contract
17
Q
What is the refractory period
A
The time taken to restore axon to resting potential when no further action potential can be generated because Na+ channels are closed/inactive/will not open
18
Q
Why is the refractory period important
A
- ensures discrete impulses are produced (action potentials don’t overlap)
- limits frequency of impulse transmission at a certain intensity
. Higher intensity stimulus causes higher frequency of action potentials
. But only up to certain intensity - also ensures action potentials travel in one direction - can’t be propagated in a refractory region
19
Q
What are the 3 factors affecting speed of nerve impulses
A
- myelination
- axon diameter
- temperature
20
Q
How does axon diameter effect transmission speed
A
Bigger diameter means less resistance to flow of ions in cytoplasm
21
Q
How does temperature effect transmission speed
A
- increases rate of diffusion of Na+ and K+ as more kinetic energy
- but proteins/enzymes could denature at a certain temperature
22
Q
What are Rod and cone cells in the eye
A
Rod - black and white
Cones - colour
23
Q
Why are cones less sensitive to light
A
- each cone is connected to a single neurone
- no spatial summation
24
Q
Why do cones give higher visual acuity
A
- each cone connected to a single neurone
- cones send separate impulses to the brain
25
How do cones allow colour vision
3 types of cones: red green blue SENSITIVE
- each cone has different optical pigments which absorb different wavelengths
- stimulation of different combinations of cones gives a range of colours
26
Why are Rods more sensitive to light
- Several rods connected to a single neurone
- Spatial summation to reach / overcome
threshold (as enough neurotransmitter released) to generate an action potential
27
Why do rods give lower visual acuity
- Several rods connected to a single neurone
- So several rods send a single set of impulses to the brain (so can’t distinguish between separate sources of light)
28
Why do rods only let you see black and white
Only 1 type of rod containing one pigment
29
What does it mean that cardiac muscle is myogenic
The heart can contract / relax without receiving electrical impulses from nerves.
30
Where are chemoreceptors and baroreceptors located
In the aorta and carotid arteries
31
What part of the brain controls the heart rate and how
via the autonomic nervous system (2 divisions):
- Sympathetic nerves → increase heart rate
- Parasympathetic nerves → decrease heart rate
32
What do baroreceptors detect
They detect the rise/fall in blood pressure
33
What do the baroreceptors do when blood pressure is low
- more frequent impulses to medulla
- more frequent impulses sent to SAN along sympathetic neurones
- more frequent impulses sent from SAN to cardiac muscle which contracts more frequently so heart rate increases
34
What do the baroreceptors do when blood pressure is high
- more frequent impulses to medulla
- more frequent impulses sent to SAN along parasympathetic neurones
- less frequent impulses sent from SAN – cardiac muscle contracts less frequently so heart rate decreases
35
What do the chemoreceptors do when CO2 conc in blood is high/pH is low
- more frequent impulses to medulla
– more frequent impulses sent to SAN along sympathetic neurones
- more frequent impulses sent from SAN – cardiac muscle which contracts more frequently so heart rate increases
36
What do the chemoreceptors do when CO2 conc in blood is low/pH is high
- more frequent impulses to medulla
- more frequent impulses sent to SAN along parasympathetic neurones
- less frequent impulses sent from SAN – cardiac muscle which contracts less frequently so heart rate decreases
37
Explain why Increased intensity of exercise leads to an increased heart rate (3m)
- Oxygen/CO2 detected by chemoreceptors and pressure detected by baroreceptors
- Medulla / cardiac centre involved
- More impulses to SAN / along sympathetic nerve
38
What does the sinoatrial node (SAN) do
acts as pacemaker → sends regular waves of electrical activity across atria
● Causing atria to contract simultaneously
39
What’s the role of the atrioventricular node (AVN)
Sends wave of electrical activity down bundle of His, conducting wave between ventricles to apex where branches into Purkyne tissue
● Causing ventricles to contract simultaneously from base up
40
Describe the process of cholinergic synaptic transmission 6m
1. Depolarisation of presynaptic membrane causes opening of voltage gated Ca2+ channels
2. Ca2+ ions diffuse into presynaptic neurone
3.Causing vesicles containing acetylcholine to move and fuse with pre synaptic membrane and release acetylcholine into synaptic cleft (exocytosis)
4. Acetylcholine diffuses across synaptic cleft and binds to specific receptors on post synaptic membrane which causes Na+ channels to open
5. Na+ diffuses into post synaptic knob causing depolarisation
6. If threshold is met an action potential is triggered.
41
Give 4 advantages of simple reflexes
- rapid
- protect against damage to body tissues
- they do not need to be learnt
- they help escape from predators
42
What is the role of glycogen granules in skeletal muscle
- as a store of glucose
- for respiration
43
How does a fall in pH lead to a reduction in calcium ion ability to stimulate muscle contraction
- low pH changes shape of calcium ion receptors
- fewer calcium ions bind to tropomyosin and move away
- fewer binding sites on actin revealed
44
What is the role of ATP in myofibril (muscle) contraction
- reaction with ATP allows binding of myosin to actin
- provides energy to move myosin head
45
Explain how a resting potential is maintained across the axon membrane in a neurone
- sodium ions diffuse in
- membrane less permeable to sodium ions
- sodium ions actively transported out and potassium ions in
46
Describe how dopamine stimulates the production of nerve impulses in postsynaptic neurones
- dopamine diffuses across synapse
- attaches to receptors on postsynaptic membrane
- stimulates entry of sodium ions and action potential
47
Explain how morphine can provide pain relief
- it attaches to opioid receptors
- more dopamine is released to provide pain relief
48
Explain how neurotransmitter is released when a nerve impulse arrives at a synapse 3m
- nerve impulse causes Ca2+ channel to open
- Ca2+ enter by diffusion
- causes synaptic vesicles to fuse with presynaptic membrane
49
How does a myosin molecule move a mitochondria towards the presynaptic membrane
- myosin head attaches to actin and bends
- this pulls mitochondria along the actin
- the next myosin head attaches to actin and bends
50
What’s the advantage of the movement of mitochondria to the presynaptic membrane
- supplies ATP
- to move vesicles
51
What’s the effect of caffeine on heart rate
- more impulses along sympathetic pathway to SAN which increases the heart rate
52
When the heart beats both ventricles contract at the same time explain this
- electrical activity only through Bundle of His
- wave of electrical activity passes over both both ventricles at the same time
53
What is homeostasis in mammals
- maintenance of a stable internal environment with restricted limits
- by physiological control systems
54
What happens if blood pH is above or below optimum pH or if core temperature is too high
- hydrogen bonds in tertiary structure break
- enzymes denature and active sites change shape so fewer ESCs
55
What is hypoglycaemia and effects
When blood glucose conc is too low
- not enough glucose for respiration
- so less ATP produced
- so active transport can’t happen - cell death
56
What is hyperglycaemia and effects
When blood glucose conc is too high
- water potential of blood decreases
- water lose from tissue to blood via osmosis
- kidneys can’t absorb all glucose
- more water lost in urine causing dehydration
57
Describe process of negative feedback
- receptors detect change from optimum
- effectors respond to counteract change
- returning levels to optimum
(Involved in homeostasis)
58
Describe process of positive feedback
- receptors detect change from optimum
- effectors respond to amplify change
- producing a greater deviation than normal
(Not involved in homeostasis)
59
What is glycogenesis
Converting glucose —> glycogen
(Decreases blood glucose concentration)
60
What is glycogenolysis
Converting glycogen —> glucose
(Increases blood glucose concentration)
61
What is gluconeogenosis
Converting amino acids and glycerol —> glucose
(Increases blood glucose concentration)
62
What do the beta cells in the islets of langerhans in the pancreas do when the blood glucose conc is too high
They detect the blood glucose conc is too high so secrete insulin
63
Describe the action of insulin (to decrease blood glucose conc)
Insulin attaches to specific receptors on cell surface membranes of target cells
1. Causing more glucose channel proteins to join cell surface membrane which increases permeability to glucose so more enters the cell by facilitated diffusion
2. It also activates enzymes involved in glycogenesis which lowers the glucose conc in cells. so glucose enters cells by facilitated diffusion down a conc gradient
64
Describe the action of glucagon (to increase blood glucose conc)
Alpha cells in islets of langerhans in the pancreas detect it’s too low so they secrete glucagon
1. Glucagon attaches to specific receptors on cell surface membranes of target cells
2. It activates enzymes involved in glycogenolysis and gluconeogenesis
3. This establishes a conc gradient so glucose leave cells and enters blood by facilitated diffusion
65
Describe the role of adrenaline to increase blood glucose concentration
Fear/stress/exercise - adrenal glands secrete adrenaline
- it attaches to specific receptors on cell surface membranes of target cells
- it activates enzymes involved in glycogenolysis)
- this establishes a conc gradient so glucose leaves cells and enters blood by facilitated diffusion
66
Describe the second messenger model of adrenaline and glucagon action
Adrenaline/glucagon attach to specific receptors on the cell membrane which:
1. Activates enzyme adenylate cyclase (changes shape)
2. Which converts many ATP to many Cyclic AMP (cAMP)
3. cAMP acts as the second messenger and activates protein kinase enzymes
4. Protein kinase activates enzymes for glycogenolysis
67
What is the advantage of the second messenger model of adrenaline and glucagon action
Amplifies signal from hormone as each hormone can stimulate production of many molecules of second messenger (cAMP) which can activate many enzymes for rapid increase in glucose
68
Describe what causes Type 1 diabetes
B cells in islets of langerhans in pancreas produce insufficient insulin
- normally caused in childhood due to a autoimmune response destroying B cells
69
Describe how to control Type 1 diabetes with insulin
Insulin injections (not by mouth as protein is digested)
70
Describe what causes type 2 diabetes
- Receptor loses responsiveness to insulin
- so fewer glucose transport proteins
- so less uptake of glucose
- less conversion of glucose to glycogen
71
Describe spatial summation
- many pre synaptic neurones share one synaptic cleft and all release enough neurotransmitter at once to reach the threshold and trigger an action potential
72
Describe temporal summation
- one presynaptic neurone releases neurotransmitter many times over a short time to reach threshold needed to trigger an action potential
73
What is the importance of summation at a synapse
- addition of a number of impulses converging on a single post synaptic neurone
- causing rapid buildup of neurotransmitter
- so threshold more likely to be reached to generate an action potential
74
How could drugs stimulate the nervous system
- similar shape to neurotransmitter
- stimulate release of more neurotransmitter
- inhibit enzyme that breaks down neurotransmitter -> Na+ continues to enter
75
How could drugs inhibit the nervous system
- inhibit release of neurotransmitters eg prevent opening of calcium ion channels
- block receptors by mimicking shape of neurotransmitter
76
What are differences between transmission across cholinergic synapses and neuromuscular junctions
C - neurone to neurone
N- neurone to muscle
C - neurotransmitters can be excitatory or inhibitory
N- neurotransmitters are always excitatory
C - action potential may be initiated in postsynaptic neurone
N - action potential propagates along sarcolemma down T tubules
77
Describe inhibitory synapses
Inhibitory neurotransmitters hyper-polarise postsynaptic membrane because:
- Cl- channels open -> Cl- diffuse in
- K+ channels open -> K+ diffuse out
- more Na+ required for depolarisation so reduces likelihood of threshold being met for an action potential
78
Why do synapses result in unidirectional nerve impulses
- Neurotransmitter only made in presynaptic neuron
- receptors only on postsynaptic membrane
79
1. Describe formation of glomerular filtrate (ultrafiltration)
1. High blood pressure
2. Small substances, e.g. water glucose ions, urea, forced into glomerular, filtrate and are filtered by:
- pores between capillary endothelial cells
- Capillary basement membrane
- podocytes
3. large proteins/blood cells remain in blood
80
Why is there high hydrostatic pressure in the glomerulus
Because the diameter of the afferent arteriole (IN) is wider than the efferent arteriole (OUT)
81
Describe the root filtrate takes in a nephron
1. Bowman capsule
2. proximal convoluted tubule
3. loop of Henlé
4. distal convoluted tubule
5. collecting duct
82
Describe reabsorption of glucose by the proximal convoluted tubule
1. Na+ actively transported out of epithelial cells to capillary
2. Na+ moves by facilitated diffusion into epithelial cells down conc gradient, bringing glucose against its conc gradient.
3. Glucose moves into capillary by facilitated diffusion down its concentration gradient.
83
Describe reabsorption of water by the proximal convoluted tubule
- Glucose in capillaries lowers water potential
- so water moves by osmosis down water potential gradient
84
What substances get reabsorbed during selective reabsorption in the PCT
- All glucose
- all amino acids
- most water
- some ions
- no urea
85
Why is all glucose not reabsorbed in someone with diabetes?
- blood glucose concentration is too high
- So glucose carrier proteins are saturated
86
Describe how a gradient of sodium ions is maintained in the medulla by the loop of Henle
Ascending limb:
- Na+ actively transported out
- impermeable to water so water remains
- increases conc of Na+ in medulla, lowering water potential
Descending limb:
- water leaves by osmosis
- Na+ diffuses back in
87
Why do animals that need to conserve water have long loops of Henle and thick medulla?
- More Na+ moved out so Na+ gradient is maintained for longer in medulla
- water potential gradient is maintained for longer and more water can be reabsorbed from collecting duct by osmosis
88
Describe reabsorption of water by the distal convoluted tubule and collecting duct
- Water moves out of the DCT and collecting duct by osmosis down a water potential gradient
- controlled by ADH, which increases their permeability
89
What is Osmoregulation?
Control of water potential of the blood by negative feedback
90
How does the body respond to a decrease in water potential e.g. by reduced water intake?
1. In the hypothalamus, osmoreceptors detect low water potential so hypothalamus produces more ADH
2. posterior pituitary gland, secretes more ADH into blood.
3. ADH, attaches to receptors on collecting duct and DCT, increasing permeability of cells to water
4. so more water reabsorbed from collecting duct and DCT by osmosis.
5. Urine = smaller volume and more concentrated.
91
During muscle contraction describe what happens to the length of bands
- H zone and I band get shorter
- A band stays same
- Z lines closer
92
Describe the role of phosphocreatine in muscle contraction 4m
- stored inside cells
- rapidly makes ATP by phosphorylating ADP
- It runs out after a few seconds, so it’s used in short bursts of vigourous exercise.
- It is anaerobic and alactic
93
Explain why glucose can be found in the urine of someone with diabetes 3m
- high concentration of glucose in blood
- not all the glucose is reabsorbed at the proximal convoluted tubule
- carrier proteins are working at maximum rate
94
How can increasing a cells sensitivity to insulin lower blood glucose levels
- more insulin binds to receptors
- stimulates uptake of glucose by channel proteins
95
Explain how inhibiting adenylate Cyclase may help lower blood glucose levels
- less ATP converted to cyclic AMP
- less kinase activated
- less glycogenolysis
96
What are I band, H zone and the darkest region made up of
I band/light - only actin
H zone - only myosin
Darkest - both
97
Explain how a decrease in calcium ion conc in muscles would decrease the force of contraction
- less tropomyosin moved from binding site
- fewer actinomyosin bridges formed
- myosin head doesn’t move
98
Describe the sliding filament theory of muscle contraction 6m
1. Calcium ions diffuse into myofibrils from sarcoplasmic reticulum and cause tropomyosin to move away from actin binding sites
2. Myosin head attaches to a binding site on actin which forms a actinomyosin bridge
3. ADP+Pi are released from myosin head causing it to move along actin (power stroke)
4. ATP binds to myosin head which detatches from actin
5. Myosin head hydrolyses ATP and returns to starting position
6. The process repeats causing the sarcomere to contract
