mass transport in animals

Question 1

Describe the role of red blood cells and haemoglobin in oxygen transport

Answer 1

● Red blood cells contain lots of haemoglobin (Hb) - no nucleus, biconcave, high SA:V, short diffusion path
● Hb associates with / binds / loads O2at gas exchange surfaces where partial pressure of O2 (pO2) is high
● This forms oxyhaemoglobin which transports O2 (each can carry 4O2 - one at each Haem group)
● Hb dissociates from / unloads O2 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 O2
● So O2 readily unloads / dissociates with Hb
● So % saturation is low

Areas with high pO2 (gas exchange surfaces):
● Hb has a high affinity for O2
● So O2 readily 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

● A low pO2 as oxygen increases there is little / slow increase in % saturation of Hb with oxygen
○ When first oxygen is binding
● At higher pO2
, as oxygen increases there is a big / rapid increase in % saturation of Hb with oxygen
○ Showing it has got easier for oxygens to bind

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

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

Answer 8

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

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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 11

Describe the general pattern of blood circulation in a mammal

Answer 11

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 12

Suggest the importance of a double circulatory system

Answer 12

● 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 13

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

Answer 13

see flash card

Question 14

Name the blood vessels entering and leaving the heart and lungs

Answer 14

● 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 15

Name the blood vessels entering and leaving the kidneys

Answer 15

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

Question 16

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

Answer 16

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

Question 17

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

Answer 17

see flash card

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 → 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 → 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 →
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

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

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

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

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

Question 21

Describe the equation for cardiac output

Answer 21

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 22

How can heart rate be calculated from cardiac cycle data?

Answer 22

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

Question 23

Explain how the structure of arteries relates to their function

Answer 23

Function – carry blood away from heart at high pressure

● Thick smooth muscle tissue → can contract and control / maintain blood flow / pressure
● Thick elastic tissue → can stretch as ventricles contract and recoil as ventricles relax, to
reduce pressure surges / even out blood pressure / maintain high pressure
● Thick wall → withstand high pressure / stop bursting
● Smooth / folded endothelium → reduces friction / can stretch
● Narrow lumen → increases / maintains high pressure

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 veins relates to their function

Answer 25

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 26

Explain how the structure of capillaries relates to their function

Answer 26

Function - allow efficient exchange of substances between blood and tissue fluid (exchange surface)

● Wall is a thin (one cell) layer of endothelial cells → reduces diffusion distance
● Capillary bed is a large network of branched capillaries → increases surface area for diffusion
● Small diameter / narrow lumen → reduces blood flow rate so more time for diffusion
● Pores in walls between cells → allow larger substances through

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 OR high salt concentration
○ 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
● High blood pressure → high hydrostatic pressure
○ Increases outward pressure from arterial 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