1
Q
explain how valve maintains a unidirectional flow of blood x2
A
-pressure in the left atrium is higher than in the ventricles causing the valves to open
-pressure in the left ventricle is higher than in the atrium causing valve to close
2
Q
exercise causes an increase in heart rate
A
- describe role of receptors and of the nervous system in this process x4
- chemoreceptor detects a rise in CO2/ carbonic acid / lowered pH in the blood
- sends impulses to the cardiac centre/medulla
-more impulses to SAN - by sympathetic
3
Q
When the heat beats both ventricle contract at the same time
A
- explain how this coordinated in the heart after imitation of the heartbeat by the SAN
- electrical activity only through the Bundle of His
- wave of electrical actvith passes over / through Purkyne fibres
4
Q
explain how the resting potential of -70mv is maintained in the sensory neurons when no pressure is applied
A
- more potassium ions the membrane is more permeable to sodium ions
- sodium ions actively transported / sodium potassium pump
-less permeable for sodium ions
5
Q
how does change in membrane potential caused by pressure
A
- pressure cases membrane to be stretched
-sodium ions channels in membrane open and sodium ions move in - greater pressure more channels open
6
Q
has reached it’s threshold
A
- reached maximum action potential
- all or nothing principle
7
Q
explain results in slow responses to stimulo when myelin sheath is destroyed
A
-less mylein sheith / less action potential
- impulse unable to jump node to node
-more depolarization
,- causes sodium ion channels to open
- more sodium moves into the neuron
8
Q
A myelinated axon conducts impulses faster than a non-myelinated axon - explain the difference
A
in myelinated action potential/depolarisation only at the node
- in mylinated nerve impulse jumps from node to node
- in mylinated action potential - does not travel along the whole length
9
Q
Cannabinoids are found in the pre synaptic membrane of neuromusclar junctions. When they bind to its receptors ir closes calcium ions channels
A
- suggest how cannabinoids could prevent muscle contraction
- prevents influx of calcium ions
-synaptic vesicle don’t fuse with membrane / don’t release neurotransmitter - neurotransmitter does not diffuse across synapse / do not bind to reports on post postsynaptic membrane
-no action potential/ depolarisatiom of post postsynaptic membrane /sodium ion channels do not open
10
Q
Explain how this distribution of IAA causes the root to bend
A
1 - a high conc of IAA at the bottom of the root/where IAA inhibits elongation
2- IAA at the top of the roots/ where IAA low conc leads to elongation
11
Q
give two reasons why it’s important for the light to be dim and even when worms are exposed to surface light
A
even - worms may move towards/away from bright light
dim- light may effect worms as they live in soil, which is dark
12
Q
Describe how the Pacinian corpuscle produces a generator potential when stimulated
A
1- increased pressure deforms/changes the stretch-mediated sodium ion channel
2- sodium channels open in membrane- sodium ions/diffuse in
4- greater pressure more channels open
3- depolarisation - leads to generator potential
13
Q
Explain how nervous control in a human can cause increased cardiac output during exercise
A
1- coordination via medulla/ cardiac centre
2- increased impulses along sympathetic nerve
3- to SAN/pacemakers
4- more impulses sent from SAN
14
Q
Explain why increased cardiac output is an advantage during exercise
A
1- produces more energy which is released for respiration
2-higher cardiac output which increases oxygen to muscles
3-increase glucose supply muscle
15
Q
mylein sheath surrounding neurons is destroyed. Explain how this results innslower response to stimuli
A
1- less impulses/ jumps of action potential at the node of Ranvier - less saltatory conduction
2- more depolarisation over length
16
Q
Describe how calcium ions are involved in synaptic transmission
A
1- calcium ions enter into presynaptic membrane - stimulate channels to open
2- causes it to fuse with vesicle of presynaptic membrane
17
Q
It is important that a neurotransmitter such as serotonin is transported back out of synapses. Explain why
A
- if they remain in the membrane it keeps bindings to receptor
- which keeps causing an action potential
18
Q
A myelinated axon conducts impulses faster than a non-mylineated axon
A
1- in mylineated action potential/depolarisation happens only at the nodes of Ranvier
2- myelinated nerve impulses jump from node to node
3- impulses do not travel along whole length
19
Q
Give one similarity and one difference between a taxis and a tropism
A
- similarity : directional response ones to a stimulus/ movement towards/away from stimulus
- difference : taxis is whole organism moves and tropism a growth response
20
Q
Damage to the myelin sheaths of neurones can lead to problems controlling the contraction of muscles. Suggest one reason why
A
-fewer action potentials
-less salatory conduction / less movement of potential
-muscles don’t contract /contract slower
21
Q
During an action potential, the membrane potential rises to +40 mV and then falls explain why
A
-potassium channels close
-potassium moves out
-sodijm channels close
22
Q
After exercise, some ATP is used to re-establish the resting potential in axons. Explain how the resting potential is re-established
A
-ATP is used in s/p pump against conc gradient
- where k+ is actively pumped in and na+ out
23
Q
Give three ways that reflex actions are important for organisms
A
-immediate/automatic response
-protection / escape predators
-homeostasis
24
Q
Explain how an increase in temp speeds up conductance of a nerve impulse
A
-higher temp / increases diffusion of ion in and out of the axon
- increases kinetic energy means faster movement
25
The potential across the membrane is reversed when an action potential; is produced
-sodium gates / channels open
-na diffuse in
26
A mylienated axon uses less atp to transmit a nerve impulse than an unmylienated axon of same diameter why
- atp required for active transport
- na actively moved out only at nodes in myelinated
27
why is sympathetic and parasympathetic nervous systems anatagonistic
- sympathetic speeds up heart rate
- parasympathetic slows down heart rate
28
Give two reasons why transmission across a synapse is unidirectional
- only post synaptic neurone has receptors for the neurotransmitter /acetylcholine
- only pre synaptic neurones have vesicles to release neurotransmitter
29
Describe the sequence of events following the relay of acetylcholine that leads to stimulation of a contraction
- calcium ions released by endoplasmic reticulum
- acetylcholine diffuses across synaptic cleft
- attaches to specific protein receptor sites on post synaptic membrane
-stimulates depolarisation / na channels open / na diffuse in
30
inhibitory synapses cause hyper polarisation in post synaptic neurone / this inhibits synaptic transmission explain why
-inside membrane / post synaptic membrane neurone is more negative
- more sodium ion enter for action potential / causes depolarisation
31
Describe sequence of event leading to release of acetylcholine
- action potential arrived at synaptic knob / enters axon
- calcium ions in pre synaptic membrane difffuse into synaptic knob
- calcium ions cuasss synaptic vesicle to fuse with pre synaptic membrane
- acetylcholine is released and diffuses across synaptic cleft
- binds to receptors on post synaptic membrane
- sodium ions enter post synaptic neurone
- causes depolarisation
32
fovea
- highest no. of cones which possses high visual acuity
- many cones which each synapse to a single neurone
33
no image perceived
- is a blind spot
- no rods or cones
34
Rod cells allow us to see objects in dim light / explain how the connection of rod cells to neurones in the retina make this possible
- rods have a high visual sensitivity
- due to serveral rod synapse with bipolar neurone / in dim light stimulation of several rods produce spatial summation
- bipolar neurone / more likely to reach threshold
35
Cones cells give higher visual acuity than rods / why
- cone synapse with one separate individual bipolar neurone to the brain
- no summation of impulse / no retinal convergence
36
banding pattern in a relaxed myofibril
- the darker band / myosin and actin overlap / is relax and shorten
The lighter band - actin only
- the dark band - myosin only
37
Explain how the difference in glycogen concentration is related to the different properties of these muscle fibres
- fast fibres produce atp quickly / slow fibres produce atp slowly
- fast fibres contract quickly compared to slow fibres
- fast uses anaerobic respiration and slow uses aerobic
38
when sacromere contracts what happens to length
I band- decreases
A band - stays the same
39
Tropomyosin
-covers the binding site on actin when calcium ions bind
- allowing myosin to bind to actin
40
Myosin
- head of myosin binds to actin and pulls actin past using atp
- myosin detaches from actin / move further along
41
explain advantage of capillaries supplying slow muscle fibres
- many capillary give a high conc / lots of oxygen
- high rate of aerobic respiration
42
Explain importance of atpase during muscle contraction
-to release/ hydrolysis atp for energy
- breaks down atp for energy
- used to form actin myosin bridges
43
Explain role of calcium ions and atp bringing about contraction of a muscle fibre
calcium ions - bind to troposmyoin / expose myosin binding sites
atp- produces energy to activate myosin heads / allows myosin to detach from actin/break cross bridges
44
Explain how an action potential is generated and propagated along a myelinated neurone
• A stimulus causes sodium ion channels to open, so Na⁺ diffuses in by facilitated diffusion.
• Membrane becomes depolarised (+40 mV) as more Na⁺ channels open (positive feedback).
• At peak potential, Na⁺ channels close and K⁺ channels open.
• K⁺ diffuses out, repolarising the membrane.
• Hyperpolarisation occurs briefly because K⁺ channels are slow to close.
• Resting potential restored by the sodium-potassium pump (3 Na⁺ out, 2 K⁺ in).
• In myelinated neurones, depolarisation only occurs at nodes of Ranvier, so impulses "jump" (saltatory conduction), making transmission faster.
45
Describe the sliding filament mechanism of muscle contraction
• An action potential causes Ca²⁺ to be released from the sarcoplasmic reticulum.
• Ca²⁺ binds to troponin, causing tropomyosin to move, exposing myosin-binding sites on actin.
• Myosin heads bind to actin forming cross-bridges.
• ADP + Pi are released from the myosin head, causing it to pivot, pulling the actin filament (power stroke).
• ATP binds to the myosin head, causing it to detach.
• ATP → ADP + Pi by ATPase (activated by Ca²⁺), re-cocking the head.
• If Ca²⁺ remains present, the cycle continues, shortening the sarcomere.
46
Explain how a Pacinian corpuscle function
• Pressure deforms the stretch-mediated sodium ion channels , which stretch Na⁺ channels in the sensory neurone.
• Na⁺ diffuses in, generating a generator potential.
• If threshold is reached, an action potential is produced.
47
Describe and explain the transmission across a cholinergic synapse
• Action potential arrives → Ca²⁺ channels open, Ca²⁺ diffuses into presynaptic knob.
• Causes vesicles containing acetylcholine (ACh) to fuse with membrane.
• ACh diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane.
• Na⁺ channels open, Na⁺ diffuses in → depolarisation → action potential.
• ACh is broken down by acetylcholinesterase and reabsorbed to prevent overstimulation.
48
Explain how IAA causes bending of shoots during phototropism
• IAA produced in shoot tip and moves to the shaded side.
• Higher IAA concentration causes greater cell elongation on the shaded side.
• Cells on shaded side stretch more (IAA ↑ plasticity of cell wall).
• Shoot bends towards light.
49
Explain how the difference in glycogen concentration is related to the different properties of these muscle fibres
- fast muscle fibres contract quickly
- slow muscles fibres contract slowly
-fast fibres respire anaerobically
- slow fibres respire aerobically
-fast fibres produce atp quickly
- slow fibres produce atp slowly
- glycogen is hydrolysed into glucose
50
Describe change in length in sacromere when myofibril contract
- h zone decreases
I band decreases
A band - no change
51
Describe the role of atp in muscle contraction
- break actin myosin bridges
- form actinmyosin
-to move or bend myosin head/arm
-actin filaments are moved
- for active transport of calcium ions
52
Both slow and fast muscle fibres contain ATPase. Explain why
1- hydrolysis of ATP
2- muscle contraction requires energy
53
Fast skeletal muscle / high proportion of atpase
- ATPase allows rapid hydrolysis of atp
54
Slow skeletal muscles / high proportion of atpase
- atpase allows rapid synthesis of atp
55
Function of actin
- attached to z line at the end of the sacromere
56
Function of ATPase
Breakdown of ATP to ADP and phosphate.
57
function of tropomyosin
covers myosin binding sites on actin in relaxed myofibril
58
If myosin molecules unable to bind to other myosin molecules, this prevents muscle contraction / suggest why
1- cannot form myosin / thick filaments
2- can't pull / can't move actin
3- myosin moves / if attached it doesn't move
4- can't move actin towards each other / middle of sacromere / between myosin
59
Why is do marathon runners have the highest percentage of mitochondria
- have the highest percentage of slow fibres / best for endurance / long periods of excerise/ avoids fatigue
- needed for aerobic respiration
60
Leg muscle of long distance cyclist are usually larger than the leg muscle of non athletes / suggest why
1- due to training / exercise
2- long distance cyclists have more higher % of slow fibres
3- slow fibres have a wider diameter than fast fibres
4- have more mirchdonria
5- have more capillaries
61
Describe the roles of calcium ions and ATP in the contraction of a myofibril
1. 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).
62
Give two ways in which atp is a suitable energy source for cells to use
- Releases relatively small amounts of energy (1)
- Releases energy instantaneously (1)
- can be rapidly synthesised
63
What is the role of phosphocreatine in providing energy during muscle contraction
Provides phosphate to make ATP
64
Explain how a decrease in conc of calcium ions within muscles tissues could cause a decreases in force of muscle contraction
- less/no tropmyosin moved from
65
in molecules;
7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites).
66
Give two ways in which atp is a suitable energy source for cells to use,
- Releases relatively small amounts of energy (1)
- Releases energy instantaneously (1)
- can be rapidly synthesised
67
What is the role of phosphocreatine in providing energy during muscle contraction,
Provides phosphate to make ATP
68
Explain how a decrease in conc of calcium ions within muscles tissues could cause a decreases in force of muscle contraction,
- less/no tropmyosin moved from binding site
-fewer/no actin myosin bridges formed
-myosin head does not move / does not pull actin towards each/ less atp hydrolase
69
Explain why converting pyruvate to lactate allows the continued production of atp by anaerobic respiration,
Regenerates NAD
-so glycolysis continues
70
During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a reduction in the ability of calcium ions to stimulate muscle contraction. Suggest how.,
1. Low pH changes shape of calcium ion receptors
Do not accept tropomyosin does not move
2. Fewer calcium ions bind to tropomyosin;
Accept troponin
3. Fewer tropomyosin molecules move away;
4. Fewer binding sites on actin revealed;
5. Fewer cross-bridges can form
OR
Fewer myosin heads can bind
71
Explain glycogen granules role in skeletal muscles,
As a store of glucose
- for respiration to provide atp
72
What is the role of ATP in muscle contraction?,
ATP breaks the myosin-actin cross-bridge, freeing the myosin for the next contraction.
73
Describe how stimulation of a Pacinian corpuscle produces a generator potential,
1. (There are) stretch-mediated sodium ion channels (in the membrane);
2. (Increased pressure) deforms/changes (sensory neurone/axon)
membrane/lamella(e) OR (Increased pressure) deforms/changes sodium ion
channels;
3. Sodium ion channels open;
4. Sodium ions diffuse in; 5. Depolarisation (leading to generator potential);
74
Inhibitory synapses cause hyper polarisation in post synaptic neurones Explain how this inhibits synaptic transmission,
- inside post synaptic neurone is more negative
- more sodium ions enter for depolarisation
75
Describe how a heartbeat is initiated and coordinated. (5),
1. SAN sends wave of electrical activity / impulses (across atria) causing atrial contraction;
2. Non-conducting tissue prevents immediate contraction of ventricles/prevents impulses reaching the ventricles;
3. AVN delays (impulse) whilst blood leaves atria/ventricles fill;
4. (AVN) sends wave of electrical activity / impulses down Bundle of His;
5. Causing ventricles to contract from base up;
76
Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta. (5),
1. Atrium has higher pressure than ventricle (due to filling/contraction);
2. Atrioventricular valve opens;
3. Ventricle has higher pressure than atrium (due to filling/contraction);
4. Atrioventricular valve closes;
5. Ventricle has higher pressure than aorta;
6. Semilunar valve opens;
7. Higher pressure in aorta than ventricle (as heart relaxes);
8. Semilunar valve closes;
9. (Muscle/atrial/ventricular) contraction causes increase in pressure;
77
When a wave of electrical activity reaches the AVN, there is a short delay before a new wave leaves the AVN. Explain the importance of this short delay. (2),
Allow ventricles to fill;
Before ventricles contract
78
A woman takes moderate exercise. Explain what causes her heart rate to increase while she exercises.,
1. rate of respiration increases (in muscle cells);
2. carbon dioxide concentration increases / pH falls / H+ increases / acidity increases;
3. chemoreceptors in aortic / carotid bodies / medulla (accept reference to aorta / carotid arteries not sinus);
4. (impulses to) medulla / cardioaccelerator centre;
5. increased frequency of impulses (award only once);
6. along sympathetic pathway to sinoatrial node / SAN (not pacemaker);
79
Structure and function of artery's, veins and capillaries,
Artery
-thickest wall / enables it to carry blood at high pressure / withstand
-most elastic tissue / smoothes out flow / maintains pressure
- most muscle which maintain pressure
Vein
- thin walls does have to withstand high pressure
Capillary
-thin wall / allowing diffusion/exchange
- only endothelium present / short diffusion pathway
80
During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a reduction in the ability of calcium ions to stimulate muscle contraction. Suggest how.,
1. Low pH changes shape of calcium ion receptors
2. Fewer calcium ions bind to tropomyosin;
3. Fewer tropomyosin molecules move away;
4. Fewer binding sites on actin revealed;
5. Fewer cross-bridges can form
OR
Fewer myosin heads can bind
81
This change prevents insulin binding to its receptor. Explain why this change prevents insulin binding to its receptor.,
-changes tertiary structure
- no longer complementary to receptor
82
Using your knowledge of the kidney, explain why glucose is found in the urine of a person with untreated diabetes.,
1. High concentration of glucose in blood/filtrate;
2. Not all the glucose is (re)absorbed at the proximal convoluted tubule;
3. Carrier/co-transport proteins are working at maximum rate
OR
Carrier/co-transport proteins/ are saturated;
83
Explain how increasing a cells sensitivity to insulin will lower the blood concentration,
- more insulin binds to receptors
- stimulates uptake of glucose by channel proteins
84
Explain how inhibiting adenylate cyclase may help to lower the blood glucose concentration.,
-less / no atp is converted to cyclic AMP
- less / no kinase is activated
- less/ no glycogen is converted to glucose
85
Describe the role of glucagon in gluconeogenesis,
1. (Attaches to receptors on target cells and) activates/stimulates enzymes;
2. Glycerol/amino acids/fatty acids into glucose;
86
Diabetes can damage the nervous system. The response of the rats with diabetes is different from the response of the healthy rats. Use your knowledge of the control of heart rate by the nervous system to suggest an explanation for these results.,
1. Damage to autonomic (nervous) system in diabetic rats;
2. (Could be) pressure receptors/baroreceptors (in arteries/aorta/carotid body) don't work as well;
3. Damage to medulla
OR
Change in (number of) impulses to/from medulla;
4. (When pressure drops damage to) sympathetic system, so doesn't speed up (enough);
5. (When pressure rises damage to) parasympathetic system, so doesn't slow down (enough);
87
Explain how the normal mice prevented their blood glucose concentration falling when they had not eaten for 48 hours.,
1. Release of glucagon;
2. Leads to formation of glucose in liver
(cells);
3. From non-carbohydrates/amino
acids/fatty acids
88
Explain how the formation of glycogen in liver cells leads to a lowering of blood glucose concentration.,
1. Glucose concentration in cell / liver falls below that in blood (plasma) which creates / maintains glucose concentration / diffusion gradient;
2. Glucose enters cell / leaves blood by facilitated diffusion / via carrier(protein) / channel (protein);
89
Describe how ultrafiltration occurs in a glomerulus.,
1. High blood/hydrostatic pressure;
2. Two named small substances pass out eg water, glucose, ions, urea;
3. (Through small) gaps/pores/fenestrations in (capillary) endothelium;
4. (And) through (capillary) basement membrane;
90
Give the location of osmoreceptors in the body of a mammal.,
1. Hypothalamus
91
When a person is dehydrated, the cell volume of an osmoreceptor decreases / explain why,
1. Water potential of blood will decrease;
2. Water moves from osmoreceptor into blood by osmosis.
92
Stimulation of osmoreceptors can lead to secretion of the hormone ADH. Describe and explain how the secretion of ADH affects urine produced by the kidneys.,
1. Permeability of membrane / cells (to water) is increased;
2. More water absorbed from / leaves distal tubule / collecting duct;
3. Smaller volume of urine;
4. Urine becomes more concentrated.
93
Describe how ultrafiltration produces glomerular filtrate,
1. Blood pressure / hydrostatic pressure;
2. Small molecules / named example;
3. Pass through basement membrane / basement membrane acts as filter;
4. Protein too large to go through / large so stays behind;
5. Presence of pores in capillaries / presence of podocytes;
94
Some people who have diabetes do not secrete insulin. Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin.,
1) High concentration of glucose in blood
2) High concentration in tubule/in filtrate
3) Reabsorbed by (facilitated diffusion/active transport)
4) Requires proteins/carriers
5) These are working at maximum rate (are saturated)
6) Not all glucose is reabsorbed, some is lost in urine
95
Some desert mammals have long loops of Henle and secrete large amounts of antidiuretic hormone (ADH). Explain how these two features are adaptations to living in desert conditions.,
1. More water (from filtrate) reabsorbed / returned to blood / less lost in
urine;
2. By osmosis;
3. From collecting duct / from end of second convoluted tubule;
4. Due to longer loop of Henle;
For loop of Henle, maximum 2 marks:
5. Sodium / chloride ions absorbed from filtrate in ascending limb;
6. Gradient established in medulla / concentration of ions increases down
medulla;
For ADH, maximum 2 marks:
7. Acts on collecting duct / distal convoluted tubule / second convoluted tubule;
8. Makes cells more permeable / inserts aquaporins in plasma
membranes;
96
A diabetic person and a non-diabetic person each ate the same amount of glucose. One hour later, the glucose concentration in the blood of the diabetic person was higher than that of the non-diabetic person. Explain why.,
1. Lack of insulin / reduced sensitivity of cells to insulin;
2. Reduced uptake of glucose by cells / liver / muscles;
3. Reduced conversion of glucose to glycogen;
97
If the glomerular filtrate of a diabetic person contains a high concentration of glucose, he produces a larger volume of urine. Explain why.,
Glucose in filtrate lowers water potential;
Lower Ψ gradient / less difference in Ψ filtrate − Ψ plasma;
Less water reabsorbed by osmosis;
98
Describe the effect of ADH on the collecting ducts in the kidney,
1- stimulates addition of channel proteins into the membrane
2- increases permeability of water
3 -"by osmosis
99
Suggest two signs or symptoms which may result from a decrease in ADH.,
- dehydrations
- less concentration of urine
100
Name the part of the body which releases antidiuretic hormone (ADH) into the blood.,
posterior pituitary
101
Give the location of the receptors that detect a decrease in blood pressure / explain how the release of adh will affect blood pressure,
- aorta / carotid artery
- adh increases reabsorption of water
- increases volume of blood and pressure increases
102
improvement / positive feedback,
- say positive correlation if there is a graph
- always say 'more'
103
improvement / p<0.01,
Means difference is significant
- probability of difference being is due to chance less than 0.01
104
Improvement / refractory period,
- refractory period can lead to separate nerve impulses
- when max frequency reached / there is no further increase in info / this means that we cannot identify difference between concentrations of sucrose sent to the brain
105
negative feedback in eating / improvement,
negative feedback stop the desire to eat / this limits amount eaten
- prevents risk of obesity
106
Synapses are unidirectional. Explain how acetylcholine contributes to a synapse being unidirectional. (2),
1. (Acetylcholine) released from / in presynaptic side;
2. Receptors in postsynaptic (side) / binds on postsynaptic (side);
107
Describe what is meant by negative feedback,
where a change triggers a response which reduces the effect of a change
108
Give two other ways in which water is removed from the body,
Sweating
Breathing
109
From which gland is ADH released?,
posterior pituitary
110
Name the part of the brain which acts as the coordinator in the control of water balance.,
hypothalamus
111
What is meant by homeostasis,
Maintaining a constant internal environment
112
Give one example, explain why homeostasis is important in mammals,
Temperature
Ph
Water potential
113
Describe how urea is removed from the blood,
1) Hydrostatic pressure
2) Cause ultrafiltration at (bowman's capsule/glomeruli/renal capsule)
3) Through basement membrane
4) Enabled by small size urea molecule
114
Explain how urea is concentrated in the filtrate,
1) Reabsorption of water by osmosis at the (proximal convoluted tubule/ descending loop of henle)
2) Ions actively transported at the distal convoluted tubule/collecting duct (glucose creates gradient)
115
Explain how inhibiting adenylate cyclase may help to lower the blood glucose concentration.,
1. Less/no ATP is converted to cyclic AMP/cAMP;
2. Less/no kinase is activated;
3. Less/no glycogen is converted to glucose
OR
Less/no glycogenolysis;
116
Explain how a rise blood pressure results in a decrease in the rate of a heartbeat
- pressure receptors / barorecptors in aorta and carotid walls
- send impulses to medulla
- impulses sent by parasympathetic nerves
- releases ach / decreases impulses from san
- decreases impulses from avn
117
Some drugs inhibit the transmission of nerve impulses to the heart / explain how these drugs reduce high blood pressure
- inhibits impulses in sympathetic nerves
- san not stimulated
118
ADH
-acts as a collecting duct
- makes cells more permeable
119
loop of Henle
- sodium / chloride ions absorbed from filtrate in ascending limb
- gradient established in medulla
120
Increase in muscle activity causes an increase in heart rate 4,mark
- increase in co2 detected by chemoreceptors
- sends more impulses to cardiac centre
-more impulses form centre along sympathetic pathway/ neurone
- to SAN
121
Explain how a resting potential is maintained across the axon membrane in a neurone
Higher concentration of potassium ions inside and higher
concentration of sodium ions outside (the neurone)
OR
potassium ions diffuse out
OR
sodium ions diffuse in;
2. 3. Accept ‘more’ for ‘higher concentration’.
Accept ‘sodium ions can’t diffuse in (due to
alternative explanation).
(Membrane) more permeable to potassium ions (leaving
than sodium ions entering)
OR
(Membrane) less permeable to sodium ions (entering
than potassium ions leaving);
Sodium ions (actively) transported out and potassium ions in;
122
Explain why the sped of transmission of impulses is faster along a mylienated axon than along a non-myelinated axon
1. Myelination provides (electrical) insulation;
Reject thermal insulation.
Accept description of (electrical) insulation.
2. (In myelinated) saltatory (conduction)
OR
(In myelinated) depolarisation at nodes (of Ranvier);
3. In non-myelinated depolarisation occurs along whole/length (of axon)
123
Describe the sequence of events involved in transmission across a chloinergic synapse
- depolarisation of presynaptic membrane
- ca channels open and ca ions enter synaptic knob
- ca ions cause synaptic vesicle move/fuse with pre synaptic membrane and release acetylcholine
-acetylcholine diffuses across synaptic cleft
- acetylcholine attaches to receptors on post synaptic membrane
- sodium ions enter post synaptic neurone leading to depolarisation
124
When a nerve impulse arrived at a synapse it causes the release of neurotransmitters from vesicles in the presynaptic knob
- nerve impulse/depolarisation of membrane causes ca channels to open
- ca enter by facilitiated diffusion
- causes vesicle to fuse with pre synaptic membrane
125
Suggest and explain one advantage of the movement of mitochondria towards the pre synaptic membrane when nerve impulses arrive at the synapse
- mitochondria supply atp
- to move vesicle / for active transport of ions
126
An action potential is produced in neurone A.
Describe how this action potential passes along the
neurone. 14.1
(Depolarisation of axon membrane causes) local currents to be set up;
Change permeability (of adjoining region) to Na+/open Na+ gates (in adjoining
region);
sodium ions enter
127
Nocturnal mammals are active at night. Describe how the number and distribution of rods and cones across the retina
would differ in a nocturnal mammal from the number and distribution in a human. 23.2
More rods
- fewer cones present
- rods at fovea
-rods have high sensitivity / show retinal convergence
- rhodopsin is bleached at low light intensities
128
Describe the role of ATP and phosphocreatine in producing contraction of a muscle fibre 27.1
ATP allows myosin to detach from actin /‘re-cocks’ myosin head/cross bridge;
phosphocreatine allows regeneration of ATP;
under anaerobic conditions;
phosphocreatine releases Pi to join ADP;
129
32.2 An action potential is generated at the cell body of a motor neurone.
Explain how this action potential passes along the motor neurone to the neuromuscular junction.
- depolarisation of axon membrane / influx of na
- changes permeability to na / opens na channels
- becomes depolarised
- process is repeated along axon
130
How does maintaining a constant body temperature allow metabolic reactions in cells to proceed with
maximum efficiency? 35.2
- body temp / optimum temp for enzymes / 37
- excess heat denatures enzymes / alters tertiary structure / shape of active site
- reactions slows down
- little / reduced kinetic energy molecules / move more slwoly
- fewer collisions / fewer e-s complexes form
131
41.1 Describe and explain how three features of the cells in the proximal convoluted tubule allow the rapid
reabsorption of glucose into the blood.
- microvilli / large surface area
- many channel / carrier proteins for facilitated diffusion
- many channel/ carrier proteins for active transport
-many channel/carrier proteins for co transport
- many mitochondria produce atp
132
44.3 In some forms of kidney disease, proteins from the blood plasma are found in the urine. Which part of the
nephron would have been damaged by the disease to cause proteins from blood plasma to be present in the urine?
Explain your answer.
- glomerlus / bowman’s capsule
- basement membrane
- proteins are large / cannot pass through filter / can on,t pass through if filter is damaged
133
46.2 Glomerulosclerosis is a disease in which the glomeruli of the kidney are damaged. Explain why protein is not
normally present in the urine of a healthy person but may be present in the urine of a person with glomerulosclerosis.-
proteins molecules to; large / cannot cross filter in healthy person
-proteins can cross if filter is damaged
unit 6
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