Mass transport

Question 1

Haemoglobin primary, secondary, tertiary and quaternary structure

Answer 1

P: Sequence of amino acids
S: Coiled helix
T: Folded to precise shape to carry oxygen
Q: 4 polypeptide molecules linked. Each polypeptide associated with haem group with Fe2+ which can each bond with O2.

Question 2

High/low affinity for O2 meaning

Answer 2

Associates easily, dissociates less easily/vice versa

Question 3

Roles of haemoglobin

Answer 3

Associate with O2 where gas exchange takes place.

Dissociate from oxygen at tissues.

Question 4

Explanation for oxygen dissociation curve shape (S shape)

Answer 4

Low O2 concentrations, hard to bind to first haem group, low gradient.
Binding of first O2 changes quaternary structure of haemoglobin to uncover 2nd binding site, gradient steepens. Positive cooperability.
After binding of 3rd molecule, probability means O2 is not as likely to bind to an empty site, decreasing gradient.

Question 5

How to read affinity from an O2 dissociation graph

Answer 5

Further left graph = higher affinity

Further right graph = lower affinity.

Question 6

Bohr effect (effect of CO2 conc.)

Answer 6

Greater conc of CO2, O2 offloads more easily (lower affinity).

Question 7

Bohr effect use in gas exchange

Answer 7

Conc of CO2 is low at gas exchange surface because it diffuses out of organism.
Affinity for O2 increases + high conc of O2 means it is loaded into haemoglobin.
Curve shifted left.

Question 8

Bohr effect in respiring tissues

Answer 8

CO2 conc. = high due to respiration.
Affinity for O2 reduced + low conc. of O2 (used in respiration) means O2 is readily unloaded.
Curve shifted right.

Question 9

Bohr effect in transport of oxygen

Answer 9

Lower conc. of CO2 means pH in blood raised at gas exchange surface.
Higher pH changes shape of haemoglobin so it can load oxygen readily and does not offload on the way to tissues.
Tissues produce CO2 which lowers pH of blood.
Haemoglobin then changes shape into one with lower affinity for O2 and O2 released into respiring tissues.

Question 10

Lugworm adaptations

Answer 10

Spends part of day buried so must use remaining oxygen in burrow to survive.
O2 dissociation curve shifted to left extremely, high affinity. Haemoglobin remains loaded even when there is little available oxygen.

Question 11

Llama adaptations

Answer 11

Lives in high altitude. Low atmospheric pressure and low partial pressure of O2.
Must have high affinity in order to stay loaded with O2.

Question 12

Why large organisms have transport systems

Answer 12

Low SA:V, needs of organisms cannot be met by body surface.
Materials must be transported between parts of organisms.
Materials from exchange surfaces to cells and vice-versa.

Question 13

Why must mammals have a closed, double circulatory system

Answer 13

When blood is passed through lungs, pressure is reduced, therefore blood is returned to heart to increase its pressure so substances are passed through body quickly.

Question 14

Structure of mammal circulatory system.

Answer 14

• Blood leaves right ventricle via pulmonary artery to lungs and returns to left atrium via pulmonary vein.
• Blood leaves left ventricle via aorta to body and returns to right atrium via vena cava.

Question 15

Name of vessels entering and leaving kidney and liver.

Answer 15

Renal artery, renal vein. Hepatic artery, hepatic vein.

Question 16

Why does left ventricle have a very thick wall

Answer 16

To contract to create enough pressure to pump blood to rest of the body.

Question 17

Names of valves and locations

Answer 17

Left atrioventricular valve - between left atrium and ventricle.
Right atrioventricular valve - between right atrium and ventricle.
Semilunar valves - to pulmonary artery and to aorta.

Question 18

Aorta connections and function

Answer 18

Connected to left ventricle and carries oxygenated blood around body

Question 19

Vena cava connections and function

Answer 19

Connected to right atrium and brings deoxygenated blood from body

Question 20

Pulmonary artery connections and function

Answer 20

Connected to right ventricle and carries deoxygenated blood to lungs to replenish O2 and remove CO2.

Question 21

Pulmonary vein connections and function

Answer 21

Connected to left atrium and carries oxygenated blood from lungs to be pumped around body.

Question 22

How is heart muscle supplied with O2

Answer 22

Coronary arteries that branch off aorta supply blood.

Blockage leads to myocardial infarction which means no O2 for heart muscles and they die.

Question 23

Cardiac cycle 3 stages

Answer 23

Diastole, atrial systole, ventricular systole

Question 24

Diastole

Answer 24

All heart relaxed. Blood returns to atria through pulmonary artery and vena cava, increasing pressure in atria.
When pressure in atria increases above pressure in ventricles, atrioventricular valves open and blood falls into ventricles by gravity.
As blood falls in ventricle, ventricle walls recoil and pressure and chamber volume increase. SL valves closed.

Question 25

Atrial systole

Answer 25

Atria contract, forcing remaining blood into ventricles from atria. Ventricles stay relaxed.

Question 26

Ventricular systole

Answer 26

Ventricles fill with blood then contract.
Blood pressure increases, forcing atrioventricular valves shut (preventing backflow).
Once blood pressure exceeds that of aorta and pul artery, blood is forced into the vessels as semilunar valves open.

Question 27

Atrioventricular valve function

Answer 27

Prevents backflow of blood when ventricle contracts and means blood flows to arteries.

Question 28

Semilunar valve function

Answer 28

Prevent backflow of blood into ventricles when pressure in vessels > ventricles after the ventricles relax again and vessel walls recoil.

Question 29

Formula for cardiac output (dm^3 min^-1)

Answer 29

Heart rate * stroke volume

Question 30

Look at pressure diagram

Answer 30

Online

Question 31

Blood vessels general structure

Answer 31

Tough outer layer to resist pressure change
Muscle layer to contract to control flow of blood
Elastic later to maintain blood pressure by stretching and recoiling.
Thin endothelium - smooth and thin to reduce friction and help diffusion
Lumen

Question 32

Artery structure and function

Answer 32

Thick muscle so smaller arteries can constrict and dilate to control blood flow volume.
Thick elastic layer so blood pressure is kept high (stretching and recoil keeps blood pressure high).
Thick walls to resist high bp.
No valves as high pressure means backflow does not happen.

Question 33

Arteriole structure and function

Answer 33

Thicker muscle layer to allow constriction of lumen, controls blood movement into capillaries.
Thin elastic layer as lower blood pressure.

Question 34

Vein structure and function

Answer 34

Thin muscle layer as veins carry blood away from tissues therefore constriction and dilation does not control.
Thin elastic layer - low bp means no stretch and recoil action.
Thin wall - low pressure in veins means no risk of bursting.
Valves to ensure blood does not flow back due to low pressure. Muscle contraction causes blood in veins to be pressurised so valves ensure they move in correct direction.

Question 35

Capillary structure and function

Answer 35

Extremely thin walls for shorter diffusion distance.
Many and highly branched for high SA.
Narrow lumen so RBC get squeezed against wall for shorter diffusion distance.
Spaces between lining that allow white blood cells to escape to deal with infections in tissue.

Question 36

How does tissue fluid form

Answer 36

Pumping from heart creates outward hydrostatic pressure.
Opposed by inward hydrostatic pressure of tissue and lower water potential of blood.
Overall pressure still pushes fluid out of capillaries.
Only small molecules can be pushed out of capillaries. Ultrafiltration.

Question 37

How does tissue fluid return to capillaries

Answer 37

Loss of tissue fluid in capillaries reduces hydrostatic pressure, also proteins and large molecules remain, lowering water potential.
This means when venous end is reached, the hydrostatic pressure is lower than that of tissue and water potential is lower.
Therefore tissue fluid forced back into capillaries and enters also via osmosis.
Remaining water returns via lymphatic system

Question 38

How is contents of lymphatic system moved

Answer 38

Hydrostatic pressure of tissue fluid that left capillaries.

Contraction of body muscles that squeeze vessels (valves make sure this goes towards heart).

Question 39

Movement of water out of stomata

Answer 39

Water vapour molecules diffuse out of the leaf stomata. Replaced by water evaporating from cell walls of mesophyll cells.

Question 40

Movement of water across leaf

Answer 40

Cytoplasmic route: mesophyll cells lose water by evaporation from heat from sun.
Lower water potential means that water moves into the cell via osmosis from neighbouring cell.
Water potential gradient established that pulls water from xylem.
Water also moves through cell walls.

Question 41

Movement of water up stem

Answer 41

Water evaporates from mesophyll cells and diffuse out of leaf due to sun leading to transpiration.
Water molecules cohesive due to hydrogen bonds so unbroken, continuous column formed across mesophyll cells and down xylem.
Evaporated water causes water to be drawn up behind it due to cohesion.
Column of water pulled up xylem (transpiration pull).
Transpiration pull puts xylem under pressure, cohesion-tension theory.

Question 42

Evidence for cohesion-tension

Answer 42

Tree trunks decrease in diameter when transpiration at greatest as there is more tension in the xylem and increase during night where less transpiration.
If xylem vessel is broken and air enters, tree no longer draws up water because continuous water column broken.
Water does not leak from xylem vessel, air is pulled in.

Question 43

How does sucrose enter sieve tube element

Answer 43

H+ ions actively transported out of companion cells and diffuse back via facilitated diffusion with co-transporter proteins, bringing with them sucrose.
Sucrose then diffuses out of companion cells down conc. gradient into sieve tube element through plasmodesmata.

Question 44

How is sucrose transported from the source cell to the sink cell

Answer 44

As sucrose enters sieve tube elements, water potential reduced so water enters via osmosis from xylem, increasing hydrostatic pressure. So water moves from an area of high to low hydrostatic pressure.
Sucrose is removed from sieve tube element by diffusion or active transport into sink cells, increasing water potential of sieve tube. This means water leaves sieve tube by osmosis into xylem, reducing hydrostatic pressure.

Question 45

Evidence for mass transport

Answer 45

If ring of bark removed, bulge above ring forms with fluid with higher concentration of sugar, evidence for downward flow.
Radioactive tracer like 14C can track movement of organic substances.
Sap flows out quicker nearer leaves when pierced therefore pressure gradient
Metabolic inhibitor stops translocation, evidence of active transport

Question 46

Evidence against mass transport

Answer 46

Sugar travels to many different sinks (not just one with highest water potential)
Sieve plates create barrier to mass flow.