topic 3 3.4.1 Mass transport in animals

Question 1

Describe the role of red blood cells & haemoglobin (Hb) in oxygen transport

Answer 1

● Red blood cells contain lots of Hb
○ No nucleus & biconcave → more space for Hb, high SA:V & short diffusion distance
● Hb associates with / binds / loads oxygenat gas exchange surfaces (lungs) where partial
pressure of oxygen (pO2) is high
● This forms oxyhaemoglobin which transports oxygen
○ Each can carry four oxygen molecule, one at each Haem group
● Hb dissociates from / unloads oxygen near cells / tissues where pO2
is low

Question 2

Describe the structure of haemoglobin

Answer 2

● Protein with a quaternary structure
● Made of 4 polypeptide chains
● Each chain contains a Haem group containing an iron ion (Fe 2+)

Question 3

Describe the loading, transport and unloading of oxygen in relation to the
oxyhaemoglobin dissociation curve

Answer 3

Areas with low pO2 - respiring tissues

● Hb has a low affinity for oxygen
● So oxygenreadily unloads / dissociates with Hb
● So % saturation is low

Areas with high pO2 - gas exchange surfaces :

● Hb has a high affinity for oxygen
● So oxygenreadily loads / associates with Hb
● So % saturation is high

Question 4

Explain how the cooperative nature of oxygen binding results in an
S-shaped (sigmoid) oxyhaemoglobin dissociation curve

Answer 4

1. Binding of first oxygen changes tertiary / quaternary structure of haemoglobin
2. This uncovers Haem group binding sites, making further binding of oxygens easier

Question 5

Describe evidence for the cooperative nature of oxygen binding

Answer 5

At low pO2, Hb saturation increases slowly as oxygen binds.

At higher pO2, Hb saturation increases rapidly, indicating easier binding.

Question 6

What is the Bohr effect?

Answer 6

Effect of CO2 concentration on dissociation of oxyhaemoglobin → curve shifts to right

Question 7

Explain effect of CO2 concentration on the dissociation of oxyhaemoglobin

Answer 7

1. Increasing blood CO2 eg. due to increased rate of respiration
2. Lowers blood pH (more acidic)
3. Reducing Hb’s affinity for oxygen as shape / tertiary / quaternary structure changes slightly
4. So more / faster unloading of oxygen to respiring cells at a given pO2

Question 8

Describe evidence for the Bohr effect

Answer 8

At a given pO2 %, the saturation of Hb with oxygen is lower

Question 9

Explain the advantage of the Bohr effect (eg. during exercise)

Answer 9

More dissociation of oxygen → faster aerobic respiration / less anaerobic respiration → more ATP produced

Question 10

Explain why different types of haemoglobin can have different oxygen
transport properties

Answer 10

● Different types of Hb are made of polypeptide chains with slightly different amino acid sequences
● Resulting in different tertiary / quaternary structures / shape
● So they have different affinities for oxygen

Question 11

Explain how organisms can be adapted to their environment by having
different types of haemoglobin with different oxygen transport properties

Answer 11

Curve shift left
Hb has higher affinity for O2 :
● More O2 associates with Hb more readily
● At gas exchange surfaces where pO2
is lower
● Eg. organisms in low O2 environments - high
altitudes, underground, or foetuses

Curve shift right
Hb has lower affinity for O2 :
● More O2 dissociates from Hb more readily
● At respiring tissues where more O2
is needed
● Eg. organisms with high rates of respiration /
metabolic rate (may be small or active)

Question 12

Describe the general pattern of blood circulation in a mammal

Answer 12

Closed double circulatory system - blood passes through heart twice for every circuit around body:

1. Deoxygenated blood in right side of heart pumped to lungs; oxygenated returns to left side
2. Oxygenated blood in left side of heart pumped to rest of body; deoxygenated returns to right

Question 13

Suggest the importance of a double circulatory system

Answer 13

● Prevents mixing of oxygenated / deoxygenated blood
○ So blood pumped to body is fully saturated with oxygen for aerobic respiration
● Blood can be pumped to body at a higher pressure (after being lower from lungs)
○ Substances taken to / removed from body cells quicker / more efficiently

Question 14

Draw a diagram to show the general pattern of blood circulation in a
mammal, including the names of key blood vessels +

Label a diagram to show the gross structure of the human heart (inside)

Answer 14

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Question 15

Name the blood vessels entering and leaving the heart and lungs

Answer 15

● Vena cava – transports deoxygenated
blood from respiring body tissues → heart
● Pulmonary artery – transports
deoxygenated blood from heart → lungs

● Pulmonary vein – transports oxygenated
blood from lungs → heart
● Aorta – transports oxygenated blood
from heart → respiring body tissues

Question 16

Name the blood vessels entering and leaving the kidneys

Answer 16

● Renal arteries – oxygenated blood → kidneys
● Renal veins – deoxygenated blood to vena cava from kidneys

Question 17

Name the the blood vessels that carry oxygenated blood to the heart muscle

Answer 17

Coronary arteries - located on surface of the heart, branching from aorta

Question 18

Suggest why the wall of the left ventricle is thicker than that of the right

Answer 18

● Thicker muscle to contract with greater force
● To generate higher pressure to pump blood around entire body

Question 19

Explain the pressure & volume changes and associated valve movements
during the cardiac cycle that maintain a unidirectional flow of blood

Answer 19

Atrial systole
● Atria contract
● So their volume decreases,
pressure increases
● Atrioventricular valves open
when pressure in atria
exceeds pressure in ventricles
● Semilunar valves remain shut
as pressure in arteries
exceeds pressure in ventricles
● So blood pushed into
ventricles

Ventricular systole:

● Ventricles contract
● So their volume decreases,
pressure increases
● Atrioventricular valves shut
when pressure in ventricles
exceeds pressure in atria
● Semilunar valves open when
pressure in ventricles exceeds
pressure in arteries
● So blood pushed out of heart
through arteries

Diastole :
● Atria & ventricles relax
● So their volume increases,
pressure decreases
● Semilunar valves shut when
pressure in arteries exceeds
pressure in ventricles
● Atrioventricular valves open
when pressure in atria
exceeds pressure in ventricles
● So blood fills atria via veins &
flows passively to ventricles

Question 20

Explain how graphs showing pressure or volume changes during the cardiac
cycle can be interpreted, eg. to identify when valves are open / closed

Answer 20

Semilunar
valves closed

● Pressure in [named] artery higher than in ventricle
● To prevent backflow of blood from artery to ventricles

Semilunar
valves open

● When pressure in ventricle is higher than in [named] artery
● So blood flows from ventricle to artery

Atrioventricular
valves closed

● Pressure in ventricle higher than atrium
● To prevent backflow of blood from ventricles to atrium

Atrioventricular
valves open

● When pressure in atrium is higher than in ventricle
● So blood flows from atrium to ventricle

Question 21

How can heart rate be calculated from cardiac cycle data?

Answer 21

Heart rate (beats per minute) = 60 (seconds) / length of one cardiac cycle (seconds)

Question 22

Describe the equation for cardiac output

Answer 22

Cardiac output (volume of blood pumped out of heart per min)
= stroke volume (volume of blood pumped in each heart beat) x heart rate (number of beats per min)

Question 23

Explain how the structure of arteries relates to their function

Answer 23

Function – carry blood away from heart at high pressure :

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Question 24

Explain how the structure of arterioles relates to their function

Answer 24

Function – (division of arteries to smaller vessels which can) direct blood to different capillaries / tissues

● Thicker smooth muscle layer than arteries
○ Contracts → narrows lumen (vasoconstriction) → reduces blood flow to capillaries
○ Relaxes → widens lumen (vasodilation) → increases blood flow to capillaries
● Thinner elastic layer → pressure surges are lower (as further from heart / ventricles)

Question 25

Explain how the structure of capillaries relates to their function : Function - allow efficient exchange of substances between blood and tissue fluid (exchange surface)

Answer 25

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Question 26

Explain how the structure of veins relates to their function

Answer 26

Function – carry blood back to heart at lower pressure

● Wider lumen than arteries → less resistance to blood flow
● Very little elastic and muscle tissue → blood pressure lower
● Valves → prevent backflow of blood

Question 27

Explain the formation of tissue fluid

Answer 27

At the arteriole end of capillaries:
1. Higher blood / hydrostatic pressure inside capillaries (due to
contraction of ventricles) than tissue fluid (so net outward force)
2. Forcing water (and dissolved substances) out of capillaries
3. Large plasma proteins remain in capillary

Question 28

Explain the return of tissue fluid to the circulatory system

Answer 28

At the venule end of capillaries:
1. Hydrostatic pressure reduces as fluid leaves capillary (also due to friction)
2. (Due to water loss) an increasing concentration of plasma proteins lowers water potential in
capillary below that of tissue fluid
3. Water enters capillaries from tissue fluid by osmosis down a water potential gradient
4. Excess water taken up by lymph capillaries and returned to circulatory system through veins

Question 29

Suggest and explain causes of excess tissue fluid accumulation

Answer 29

● Low concentration of protein in blood plasma
○ Water potential in capillary not as low → water potential gradient is reduced
○ So more tissue fluid formed at arteriole end / less water absorbed at venule end by osmosis
○ Lymph system may not be able to drain excess fast enough
● High blood pressure (eg. caused by high salt concentration) → high hydrostatic pressure
○ Increases outward pressure from arteriole end AND reduces inward pressure at venule end
○ So more tissue fluid formed at arteriole end / less water absorbed at venule end by osmosis
○ Lymph system may not be able to drain excess fast enough

Question 30

What is a risk factor? Give examples for cardiovascular disease

Answer 30

● An aspect of a person’s lifestyle or substances in a person’s body / environment
● That have been shown to be linked to an increased rate of disease
● Examples - age, diet high in salt or saturated fat, smoking, lack of exercise, genes