3.3.4 - 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 oxygen at 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

The haemoglobins are a group of (1) molecules found in many different organisms

Answer 3

(1) chemically similar

Question 4

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

Answer 4

> Areas with low pO2 - respiring tissues
● Hb has a low affinity for oxygen
● So oxygen readily 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 5

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

Answer 5

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

Question 6

Describe evidence for the cooperative nature of oxygen binding

Answer 6

● 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 7

What is the Bohr effect?

Answer 7

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

Question 8

Explain effect of CO2 concentration on the dissociation of oxyhaemoglobin

Answer 8

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 9

Describe evidence for the Bohr effect

Answer 9

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

Question 10

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

Answer 10

More dissociation of oxygen → faster aerobic respiration / less anaerobic respiration → more ATP produced and so more energy can be released for muscle contraction

Question 11

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

Answer 11

● 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 12

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

Answer 12

> 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 13

Describe the general pattern of blood circulation in a mammal

Answer 13

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 14

Suggest the importance of a double circulatory system

Answer 14

● Prevents mixing of oxygenated / deoxygenated blood
○ So blood pumped to body/respiring tissues 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 15

Name the blood vessels entering and leaving the heart and lungs

Answer 15

• Vena Cava
• Pulmonary artery
• Pulmonary vein
• Aorta

Question 16

Vena cava

Answer 16

Transports deoxygenated
blood from respiring body tissues → heart

Question 17

Pulmonary artery

Answer 17

Transports
deoxygenated blood from heart → lungs

Question 18

Pulmonary vein

Answer 18

Transports oxygenated
blood from lungs → heart

Question 19

Aorta

Answer 19

Transports oxygenated blood from heart → respiring body tissues

Question 20

Name the blood vessels entering and leaving the kidneys

Answer 20

● Renal arteries – oxygenated blood → kidneys

● Renal veins – deoxygenated blood to vena cava from kidneys

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

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

Answer 23

> 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 24

Atrial systole

Answer 24

● Atria contract

● So their volume decreases, and their
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

Question 25

Ventricular systole

Answer 25

● Ventricles contract ● So their volume decreases, and 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

Question 26

Diastole

Answer 26

● Atria & ventricles relax ● So their volume increases, and their pressure decreases ● Semi-lunar 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 27

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

Answer 27

> 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 28

Semilunar valves closed

Answer 28

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

Question 29

Semilunar valves open

Answer 29

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

Question 30

Atrioventricular valves closed

Answer 30

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

Question 31

Atrioventricular valves open

Answer 31

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

Question 32

How can heart rate be calculated from cardiac cycle data?

Answer 32

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

Question 33

Describe the equation for cardiac output

Answer 33

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 34

Function of the arteries

Answer 34

carry blood away from heart at high pressure

Question 35

Explain how the structure of arteries relates to their function Function – carry blood away from heart at high pressure

Answer 35

- Thick smooth muscle tissue > Can contract and control / maintain / withstand 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 > Withstands high pressure / prevents bursting - Smooth / folded endothelium > Reduces friction / can stretch - allow blood to flow at fast rate - Narrow lumen > Increases / maintains high pressure

Question 36

Function of arterioles

Answer 36

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

Question 37

Explain how the structure of arterioles relates to their function

Answer 37

● 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 38

Function of capillaries

Answer 38

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

Question 39

Explain how the structure of capillaries relates to their function

Answer 39

- Wall is a thin (one cell) layer of endothelial cells > Reduces diffusion distance - Form Capillary bed - 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 40

Function of veins

Answer 40

carry blood back to heart at lower pressure

Question 41

Explain how the structure of veins relates to their function

Answer 41

● Wider lumen than arteries → less resistance to blood flow ● Very little elastic and muscle tissue → blood pressure lower so doesn't stretch and recoil as , to reduce pressure surges / maintain high pressure ● Valves → prevent backflow of blood

Question 42

Explain the formation of tissue fluid

Answer 42

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 43

Explain the return of tissue fluid to the circulatory system

Answer 43

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 44

Suggest and explain causes of excess tissue fluid accumulation

Answer 44

● 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 45

What is a risk factor? Give examples for cardiovascular disease

Answer 45

● 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