6 Answers to end-of-chapter questions - Cambridge University Press

6 Answers to end-of-chapter questions
Multiple choice questions
1 A [1]
2 C [1]
3 A [1]
4 D [1]
5 B [1]
6 C [1]
7 D [1]
8 A [1]
9 A [1]
10 B [1]
Structured questions
11 a A – Ventricular systole [1]
B – Ventricular diastole [1]
b i • Ventricular pressure exceeds atrial pressure [1]
• Atrio-ventricular valve/mitral/bicuspid valve closes [1]
ii • Ventricular pressure exceeds pressure in aorta [1]
• Aortic valve opens [1]
iii • Ventricular pressure is less than pressure in aorta [1]
• Aortic valve closes [1]
iv • Atrial pressure exceeds ventricular pressure [1]
• Atrio-ventricular valve/mitral/bicuspid valve opens [1]
c • Both valves – atrio-ventricular and aortic – are closed [1]
• So no blood is entering or leaving – volume remains
constant [1]
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d • P wave – represents the wave of depolarisation that spreads from
the SA node throughout the atria
• The atria contracts/atrial systole
• Zero voltage period after P wave – time taken for impulse
to travel to AV node and Bundle of His
• Hence delay in contraction between contraction in atria
and ventricles
• So atria empty completely
• The QRS complex represents ventricular depolarization
that spreads through the right and left side of the
ventricles in the Purkyne fibres
• Ventricles contract from apex/upwards
• T wave – repolarisation
e • Closure of atrio-ventricular valves – 1st heart sound [1]
• Closure of semilunar valves – 2nd heart sound [1]
f • Contraction of the ventricle
• While the valves are closed
• AVP: some heart cells/monocytes contract by shortening
or by lengthening or by no change in length
• Heart becomes spheroid in shape
12 a I – left atrium
II – aortic valve
III – heart tendons/chordae tendineae
IV – papillary muscle
V – pulmonary artery
VI – tricuspid valve
b
Each point [1]
Max [4]
Each point [1]
Max [2]
5–6 points [3]
3–4 points [2]
1–2 points [1]
Correct flow [1]
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c i Atria walls are thin because they pump blood a very short
distance to the ventricles [1]
ii Left ventricle is the thickest (three times as thick as the right
ventricle) because:
• has to generate pressures up to 16 kPa to pump blood
to rest of body/systemic circulation/longer distance
• has to overcome resistance of systemic circulation that
has arch, branches and resistant walls opposing
pulsation and gravity
• blood in systemic circulation reaches the capillaries at
pressures which would allow efficient exchange to
materials Any point [1]
iii Right ventricle – not as thick as left ventricle but thicker than
atria because:
• Has to generate pressure up to 4 kpa to pump blood to
the lungs/shorter distance
• Lungs are delicate air filled alveoli which could
rupture at pressures higher than 4 kpa
• Lungs only have one capillary bed compared to systemic
circulation with portal and many capillary beds Any point [1]
d • Internal volume of both left and right ventricles is the same
• All the deoxygenated blood leaving the heart on the right
side returns to the heart in the left side
• Double circulation
• Any correct answer Any point [1]
e • IV contracts at same time as the ventricles and pulls III [1]
• III pulls down the atrio-ventricular valves and prevent them from
bursting up and opening into the atria under pressure during
contraction of ventricles [1]
f i, ii, iii [3]
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[3]

g • Produces impulses
• Which spreads across atrial wall causing the atria to
contract
• Sends impulses to AVN then to Bundle of His
• Through Purkyne fibres in the left and right side of
ventricles
• Causing contraction of ventricles from apex upwards
13 a • First oxygen molecule combines slowly to first haem group
• Thus first part of curve is not very steep
• Attachment changes shape of haemoglobin (Hb)
molecule
• 2nd and 3rd oxygen molecules attach easily because of
altered shaped of Hb
• Hence curve becomes steeper
• 4th oxygen does not attach easily to haem group
• Hence curve flattens
• Any correct answer – cooperative binding/rapid unloading
3–4 points [2]
1–2 points [1]
Any 2 parts of the curve
well explained [2]
Any 1 well explained [1]
b i 12 kPa [1]
ii 2 kPa [1]
c Red blood cells:
• No nucleus/few organelles/no mitochondria so more Hb
molecules (250 million molecules)
• Numerous (5 million per mm 3 of blood)
• Small size – to just fit through narrow capillaries (slowed
down for maximum exchange)
• Large surface area for increased oxygen uptake
• Biconcave to reduce size by folding while maintaining
large surface area
• Thin wall – short diffusion path
• Close to tissues for diffusion/exchange
• Elastic membrane allows for squeezing through
capillaries
• Has carbonic anhydrase (transport of carbon dioxide) Any 2 points [2]
Haemoglobin:
• 250 million molecules of Hb per red blood cell
• Contains iron to which oxygen binds
• Has 4 polypeptides to hold 4 haem groups
• Can carry 4 molecules of oxygen per Hb
• Outwardly pointing hydrophilic R groups to maintain
solubility
• Cooperative binding of oxygen: 1st oxygen added with difficulty,
2nd and 3rd easily and 4th with difficulty/helps with loading and
unloading at various tissues Any 2 points [2]
Biology Unit 2 for CAPE ® Examinations Original material © Cambridge University Press 2011 4

d i
Note that the partial pressure of oxygen in an actively respiring muscle
never reaches beyond about 4 kPa. [1]
ii Bohr effect [1]
iii • More oxygen released to respiring tissues/less affinity for
oxygen
• Enables more respiration at same partial pressures of oxygen Any point [1]
e • Carbon dioxide diffuses into red blood cells
• Carbon dioxide reacts with water to give carbonic acid
• Enzyme: carbonic anhydrase
• Carbonic acid dissociates to produce H + + HCO3 - ions
• Reduces pH of cell
• Hb has higher affinity for H + ions
• Unloads oxygen and picks up H +
• To form HHb/haemoglobinic acid
• Increases pH of cell
7–8 points [4]
5–6 points [3]
3–4 points [2]
1–2 points [1]
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Essay questions
14 a • Blood flowing under low pressure
• Made up of three layers – tunica intima, tunica media,
tunica externa
• Tunica externa – made of collagen and some
elastin/largest layer in large veins
• Tunica media – relatively thin, containing smooth muscle
and some elastic fibres
• Tunica intima/endothelium – smooth and squamous
• Large lumen
• Semilunar valves
• Thin wall – allows for contraction of lumen by skeletal
muscles/low pressure in blood
• Smooth endothelium – reduce friction/easier flow of
blood
• Wide distended lumen – accommodates large quantities
of blood/acts as blood reservoir
• Valves – prevent back flow of blood
• Any correct answer
b • Blood flowing under high pressure
• Tunica adventitia – made up of mainly of collagen fibres
and some elastic fibres
• Tunica media – thickest of three layers/made up of elastin
and smooth muscle and some fine collagen fibres
• Tunica intima – has smooth folded endothelium
• Collagen fibres – provide main strength
• Stop arteries from bursting when pressure is high
• Elastin/elastic fibres – most located close to heart
• Elastin – allows expansion of lumen without causing
damage
• Keeps pressure high by elastic recoil/stores potential
energy in elastic tissue for subsequent recoil
• Smooth out flow of blood/even out surges of
pressure/maintain flow of blood/smooth out large
fluctuations in pressure
• Smooth muscle
• Maintain pressure
• Can contract to reduce or increase blood
flow/vasoconstriction/vasodilation
• Narrow/well defined lumen – to maintain pressure
• Smooth endothelium
• Reduces friction
• Folded – to allow for expansion as blood passes
3 structures well described
[2]
3 adaptations [3]
2 structures well described
[1]
3 structures well
described [2]
3 adaptations [3]
2 structures well
described [1]
1 adaptation [1]
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c • Endothelium is one cell thick – reduces diffusion distance
• Cell is made of flattened squamous epithelium – short
diffusion distance
• Smooth endothelium – reduces friction
• Pores in the wall between the squamous cells – allows for
faster movement of substances and large molecules
• Narrow diameter of lumen (8.0 μm) – slows flow of
blood to allow for maximum exchange/short diffusion
distance
• Narrow diameter – allows for red blood cells to travel
sideways and singly – slows flow of blood to allow for
maximum exchange
• Close to body cells – allows for faster diffusion
• Large cross-sectional areas – large surface area for
diffusion
15 a i • Pacemaker
• Myogenic
• Produces action potentials that initiate the heart beat
• Sends out impulses across atria and to AVN
• Causes of contraction of atria together and before the
ventricles
ii • Delays impulses to ventricles
• Allows ventricles to fill/atria to fill
• Produces impulses that spreads to Purkyne fibres which cause
contraction of ventricles Any 2 points [2]
iii • Carries impulses from AVN to left and right side of the
ventricles [1]
• Causes ventricles to contact from base/apex upwards [1]
iv • Papillary muscle contracts at same time as the ventricles and
pulls heart tendons [1]
• Heart tendons pulls down the atrio-ventricular valves and
prevent them from bursting up and opening into the atria
under pressure during contraction of ventricles [1]
b i • Blood flows into atria from veins
• From higher pressure in veins to lower pressure in
atria
• Since pressure is higher in atria than ventricles, blood
flows into ventricles
• Back flow into veins stopped by valves at base of veins
Each point [1]
Max [5]
3–4 points [2]
1–2 points [1]
3–4 points [2]
1–2 points [1]
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ii • Muscles in ventricles contract in different ways/fibres contract
iostonically or isometrically, pressure increases in ventricles
• Atrio-ventricular valves close to prevent back flow of
blood
• Ventricular pressure exceeds aortic pressure or
pressure in pulmonary artery, semilunar valves open
• Blood flows into the arteries
• Pressure decreases in ventricles
• When pressure in ventricles decreases/becomes less
than in arteries, semilunar valves close
• pressure in ventricles becomes less than atria, atrioventricular
valves open Any 2 points well explained [2]
c • Nervous system: stimulation by sympathetic nervous
system/accelerator nerve would speed up heart beat and
force with which cardiac muscle contracts/inhibition by
parasympathetic/vagus nerve slows down heart beat
• Hormones: adrenaline and noradrenaline act directly on
SAN thereby increasing rate and force of muscle
contractions and heart rate
• Changes in the volume of blood entering the heart
through the veins – if larger volume of blood enters the
heart walls and stretches the walls of the atria more than
usual, heart rate and force of contraction increase
• Any correct answer
16 a i • Pulse rate: number of times the heart beats per
minute [1]
• Blood pressure: how hard the heart is working to
pump blood around the body/force developed by
blood pushing against the walls of blood vessels [1]
ii • When the blood is pumped out of the heart into the
arteries, the surge of blood distends the arteries
because of the elastic tissue
• Stretch and subsequent recoil of elastic tissue in aorta
and arteries travels as a wave or pulse
• Hence pulse rate is identical to heart rate
b • Heart rate
• Stroke volume
• Age – arteries lose elasticity hence more resistance to
flow
• Exercise – can cause an increase in heart rate and stroke
volume
• Strength of the heart beat
• Resistance to flow of blood due to narrowing of blood
vessels/plaque
• Smoking – effect of nicotine on arterioles and adrenal
glands/narrowing of arterioles and release of adrenaline
• Excitement – increase in adrenaline production which
stimulates SAN
• Any correct answer
Each point [1]
Max [3]
Each point [1]
Max [3]
Any point well
explained [1]
Max [5]
Biology Unit 2 for CAPE ® Examinations Original material © Cambridge University Press 2011 8

c • Increased muscle contraction during exercise
• Increased respiration
• Increased carbon dioxide production
• Causes pH to decrease
• Detected by chemoreceptors in the carotid and aortic
bodies
• Impulses sent to the cardiac accelerator centre (CAC) in
the medulla
• Impulses sent along the accelerator nerve of the
sympathetic nervous system
• Noradrenaline released
• Stimulates SAN
• Causes heart rate to increase
9–10 points [5]
7–8 points [4]
5–6 points [3]
3–4 points [2]
1–2 points [1]
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