Model Answers SNAB Exercise and Coordination (Topic 7)

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UNIT 5 TOPIC 7: Run For Your Life
The Heart
The location of the SAN is in the right atrium.
Describe the changes in the heart that bring about an increase in cardiac output during exercise
(4) *The heart rate, *stroke volume and *SAN activity increases whilst the *AVN time
delay decreases. Thus there is *more blood returning to the heart causing the heart muscle to stretch
and *the ventricles to contract with greater force.
Explain what is meant by the term myogenic: This means the *stimulation is generated from within
the muscle and not by external stimulation, leading to *depolarisation and contraction of the heart.
State one factor, other than heart rate, that could have affected the rate at which blood passed
through the heart.
*Stroke volume; *strength of (cardiac) muscle contraction; *blood viscosity; *size of the
atria/ventricles/chambers; *adrenaline.
Describe the role of the SAN in controlling heartbeats. (2)
*The SAN initiates the heartbeat by *starting a wave of excitation/depolarisation. *The SAN also
determines the heart rate.
Describe how the sequence of muscular contraction in the heart is coordinated and how the
movement of blood through the heart is controlled. (6)
*The Sinoatrial node/SAN *initiates depolarisation, the wave of depolarisation *passes through the
wall of the atria * causing atrial systole. After a short (0.13secs) delay (to give time for ventricles to
fill and atria to finish contracting, *the AVN then conducts the impulse to the ventricles along the
*Purkyne fibres that collectively are the bundle of His. *Ventricular systole follows from the apex up
whilst the *atrioventricular valves are closed (to prevent blood flowing back to atria). The *semilunar
valves are opened by the pressure causing the *blood to be forced into the arteries. The changed
pressure in diastole will then *close the semilunar valves.
Describe how the cardiovascular centre, in the medulla oblongata, affects the SAN during
exercise. (2)
*It will increase impulses to the SAN *via the sympathetic nervous system, *stimulating more
frequent depolarisation in SAN and *increasing the heart rate/cardiac output.

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Using the information in the table, describe the effect of an increase in heart rate on both the
ventilation rate and oxygen uptake by the blood, after the first ten seconds of exercise. (3)
*There is little difference in ventilation rate compared to the *oxygen uptake which increases.…read more

Page 3

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Joints and Muscles
The structures that connect muscles to bones are TENDONS
Protein in the thin filament is made up of ACTIN. Protein in the thick filament is made of MYOSIN
Describe the interaction between troponin and tropomyosin when a skeletal muscle fibre
contracts. (2)
*Ca2+ bind to troponin, causing it to *change shape and move away so it *displaces tropomyosin
away from myosin.
Muscles are attached to bones by tendons. In a joint, bones are joined to each other by ligaments.…read more

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Using the information in the graphs, compare the effect of pH on slow twitch and fast twitch
fibres. (2)
*The lower the pH, the less sensitive both become to calcium ions, so more calcium ions are needed
for (50%) contraction. But *the effect on slow twitch is greater though the *lower pH decreases
contraction in both. But *lower pH has no effect at high calcium ion concentration in both fibres.…read more

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P; this means the *repaired tissue will need to be stretched
Describe the function of a ligament (2)
It is strong to *hold/attach bones together, but it is flexible to *allow movement at the joint.
*As there is more muscle contraction/respiration more *heat energy is released, so that *more heat
energy is produced than lost.
Suggest an explanation for the constant core temperatures of both runners between 60 and 100
minutes of this race.…read more

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Describe the role of the human nervous system in returning a slightly raised body temperature
to its normal level. (4)
*Thermoreceptors in the hypothalamus *detect the increase in (core) blood temperature and
*activate the heat loss centre. This stimulates aspects of the *autonomic nervous system to send
*impulses down motor neurones *to effectors (e.g. skeletal muscles in shivering). *Other detailed
methods of heat loss.
Explain how shivering generates heat to return a slightly reduced body temperature to its
normal level.…read more

Page 7

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Carbon dioxide/CO2, because *the C has been removed from C6 or C5 compound.
Using information in the diagram, suggest what would happen in the Krebs cycle if acetyl CoA
became unavailable. (3)
*The cycle would stop and the *4 carbon compound would accumulate but the *6 & *5 carbon
compound would run short/not be synthesised. *The products T&H would be reduced.
The hydrogen (H) from the Krebs cycle enters the electron transport chain and oxidative
phosphorylation occurs.…read more

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Describe how a spirometer trace recorded immediately after a short period of exercise would
differ from this trace. (2)
There would be *a higher frequency of peaks in the same time/distance between consecutive peaks
would decrease, whilst the *distance from peak to trough would increase.
Name two substances, other than oxygen, that need to enter the mitochondrion to enable
energy to be released from fuel.…read more

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Lactate (lactic acid) can build up in the muscles of a sprinter. Suggest why the build-up of
lactate may prevent any further increase in speed. (2)
Because *lactate build up causes a drop in pH so it becomes more acidic and there's an increase in H+.
*The low pH may affect enzyme activity/shape so they denature, this will *slow down glycolysis/
ATP production/anaerobic respiration and may also *affect muscle contractions.
Explain the fate of lactate following a sprint.…read more

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Describe the role of the hydrogen ion concentration gradient in making available an accessible
supply of energy for biological processes (chemiosis). (2)
*On the stalked particles,*H+ ions follow the diffusion gradient *which causes an energy change/
makes energy available *forming ATP. *ATP is an energy source for (biological processes)
The energy required for contraction of muscle fibres is provided by ATP. Describe how enough
ATP is made available for contraction of fast twitch muscle fibres, despite there being only a
few mitochondria.…read more


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