7-Mass Transport

Question 1

Haemoglobin Structure

Answer 1

PRIMARY- Sequence of amino acids in 4 polypeptide chains.
SECONDARY- Each polypeptide chain is coiled into a helix.
TERTIARY- Each chain is folded into a specific shape with the important ability to carry O2.
QUATERNARY- All 4 polypeptide chains are linked together to form an almost spherical shape. Each chain is attached to a haem group, containing a ferrous (Fe2+) ion. Each ferrous ion can bind to an O2 molecule so 4 O2 molecules can be carried by 1 haemoglobin molecule.

Question 2

Loading (Associating)

Answer 2

Process of O2 binding with haemoglobin.

Question 3

Unloading (Dissociation)

Answer 3

Process of haemoglobin releasing the attached O2.

Question 4

Affinity of O2 in Haemoglobin

Answer 4

The likelihood for haemoglobin to take up O2. Haemoglobin with high affinity takes up O2 easier but releases it less easily and vice versa.

Question 5

Haemoglobin’s Efficiency when Transporting O2

Answer 5

Readily associates with O2at surface where gas exchange takes place.
Readily dissociates with O2 at tissues requiring it.

Question 6

Oxygen Dissociation Curve

Answer 6

1) At low O2 conc, less O2 binds with haemoglobin due to shape of haemoglobin molecule. This gives curve an initial shallow gradient.
2) The binding of the first O2 molecule induces the other subunits to bind to O2 because it changes its quaternary shape.
3) Positive Cooperativity occurs because binding of first molecule makes binding of second easier. Gradient of curve steepens.
4) After binding to 3rd molecule the 4th isn’t easier as it should be since it’s less probable for it to come in contact with O2. Gradient of curve reduces and curve flattens off.

Question 7

Positive Cooperativity

Answer 7

A smaller increase in partial pressure of O2 is required for second molecule of O2 to bind to haemoglobin than first because it’s easier.

Question 8

The further the Oxygen Dissociation Curve is to the left…

Answer 8

…The greater the affinity of haemoglobin for O2.

Question 9

The further the Oxygen Dissociation Curve is to the right…

Answer 9

…The lower the affinity of haemoglobin for O2.

Question 10

Effects of CO2 conc on Oxygen Dissociation Curve

Answer 10

At gas exchange surface there’s low CO2 conc so O2 affinity of haemoglobin is increased so O2 is loaded and curve shifts left.
At rapidly respiring tissues there’s high CO2 conc so O2 affinity of haemoglobin is decreased so O2 is unloaded and curve shifts right.

Question 11

Loading, Transport & Unloading of Oxygen

Answer 11

1) CO2 constantly removed at gas exchange surface.
2) pH raised due to low CO2 conc which changes shape of haemoglobin into one that readily loads O2.
3) New shape also raises affinity of O2 for haemoglobin so O2 isn’t released when being transported in blood to tissues.
4) CO2 is produced by respiring cells in the tissues which lowers pH of blood.
5) Lower pH changes shape of haemoglobin to one with lower affinity of O2 so is released into respiring tissues.

Question 12

Oxygen Dissociation Curve of a Lugworm

Answer 12

Shifted very far left than that of a human curve because it needs as much O2 as possible since it doesn’t move very far away from its burrow.

Question 13

Closed Double Circulatory System of Mammals

Answer 13

Blood is confined to vessels and passes 2x through the heart for each complete circuit of the body.

Question 14

Atrium

Answer 14

Thin walled and elastic and stretches as it collects blood.

Question 15

Ventricle

Answer 15

Thick muscular wall since it has to contract strongly to pump blood, either to lungs or rest of the body.

Question 16

Valves

Answer 16

Formation that prevents back flow of blood.

Question 17

Aorta

Answer 17

Connected to left ventricle and carries deoxygenated blood from the heart to the rest of the body (except the lungs).

Question 18

Vena Cava

Answer 18

Connected to right atrium and brings back deoxygenated blood from rest of the body (tissues).

Question 19

Pulmonary Artery

Answer 19

Connected to right ventricle and carries deoxygenated blood to lungs where it’s O2 is replenished and CO2 is removed.

Question 20

Pulmonary Vein

Answer 20

Connected to left atrium and brings oxygenated blood back from lungs.

Question 21

Coronary Arteries

Answer 21

Arteries that branch off of the Aorta on to the surface of the heart and provide itself with oxygenated blood to continue working.

Question 22

Myocardial Infarction (heart attack)

Answer 22

Blockage of coronary arteries (possibly by a blood clot) causing an area of the heart muscle to to be deprived of blood and O2. Muscle cells in the area are unable to respire (aerobically) so die.

Question 23

Cardiac Cycle

Answer 23

Sequence of events that is repeated around 70 times each minute when at rest in humans.

Question 24

Diastole (relaxation of heart)

Answer 24

1) Blood returns to the atria through the pulmonary vein and vena cava.
2) As atria fill, pressure rises. When pressure in atria exceeds pressure in ventricles, the atrioventricular valves open to allow blood to flow into ventricles.
3) Muscular walls of both atria and ventricles are relaxed at this point.
4) Relaxation of ventricle walls causes them to recoil and reduces pressure in ventricles which cause the pressure to be lower than that of the aorta and pulmonary artery.
5) Semi-lunar valves in aorta and pulmonary artery close.

Question 25

Atrial Systole (contraction of atria)

Answer 25

Contraction of atrial walls and recoil of relaxed ventricle walls forced remaking blood into ventricles from atria.

Question 26

Ventricular Systole (contraction of ventricles)

Answer 26

After ventricles fill with blood, their walls contract simultaneously to increase blood pressure within them. This shuts atrioventricular valves to prevent back flow of blood into atria. Pressure in ventricles rises and when it’s greater than that of aorta and pulmonary artery blood is forced from ventricles into these vessels.

Question 27

Atrioventricular Valves

Answer 27

Between left atrium and ventricle as well as between right atrium and ventricle.
Prevents back flow of blood when contraction of ventricles makes ventricular pressure greater than atrial pressure.
Closure of these valves ensures blood moves from ventricles to pulmonary artery and aorta instead of back into atria.

Question 28

Semi-Lunar Valves

Answer 28

In aorta and pulmonary artery.

Prevent back flow of blood into ventricles.

Question 29

Pocket Valves

Answer 29

In veins and occur throughout the venous system.

Ensures when veins are squeezed, blood flows towards heart rather than away from it.

Question 30

Cardiac Output(dm3min-1) =

Answer 30

Heart Rate(min-1) x Stroke Volume(dm3)

Question 31

Arteries

Answer 31

Carry blood away from heart into arterioles.

Question 32

Arterioles

Answer 32

Smaller arteries that control blood flow from arteries to capillaries.

Question 33

Capillaries

Answer 33

Tiny vessels that link arterioles to veins.

Question 34

Veins

Answer 34

Carry blood from capillaries back to the heart.

Question 35

Structure of Arteries, Arterioles & Veins (outside to inside)

Answer 35

TOUGH FIBROUS OUTER LAYER- to resist pressure changes both inside and out.
MUSCLE LAYER- that can contract and control blood flow.
ELASTIC LAYER- that helps maintain blood pressure by stretching and springing back (recoiling).
ENDOTHELIUM (THIN INNER LINING)- is smooth to reduce friction and thin to allow diffusion.
LUMEN- the central cavity of the blood vessel which blood flows through.

Question 36

Artery Structure related to Function

Answer 36

Thick muscle layer
Thick elastic layer
Thick wall overall
No valves

Question 37

Arterioles Structure related to Function

Answer 37

Thick muscle layer

Thin elastic layer

Question 38

Vein Structure related to Function

Answer 38

Thin muscle layer
Thin elastic layer
Thin overall wall
Has valves at intervals

Question 39

Capillary Structure related to Function

Answer 39

Walls consist mostly of endothelium
Numerous and highly branched
Narrow diameter
Narrow lumen
Spaces between endothelium

Question 40

Tissue Fluid

Answer 40

A watery liquid containing glucose, amino acids, fatty acids, ions in solution and O2. Supplies all these substances to tissues and receives CO2 and other waste materials from tissues.

Question 41

Formation of Tissue Fluid

Answer 41

1) Pumping by heart creates hydrostatic pressure at the arterial end of capillaries.
2) The hydrostatic pressure causes tissue fluid to move out of blood plasma.

Question 42

Return of Tissue Fluid to Circulatory System

Answer 42

1) Loss of tissue fluid from capillaries reduces hydrostatic pressure inside them.
2) By the time blood reaches venous end of capillary network hydrostatic pressure is lower than that of outside tissue fluid.
3) Tissue fluid is forced back into capillaries by higher hydrostatic pressure outside.

Question 43

Movement of Water in Leaf Cell

Answer 43

1) Mesophyll cells lose water to air spaces by evaporation due to heat from sun.
2) Cells have a low water potential so water enters by osmosis from neighbouring cells.
3) Loss of water from neighbouring cells lowers their water potential.
4) They take water from neighbours by osmosis.

Question 44

Movement of Water up Stem in Xylem

Answer 44

1) Water evaporates from mesophyll cells due to heat from sun leading to transpiration.
2) Water molecules from H-bonds between each other and stick together (cohesion).
3) Water forms a continuous unbroken column across mesophyll cells and down the xylem.
4) As water evaporates from mesophyll cells, more water molecules are drawn up as a result of cohesion.
5) Column of water is pulled up xylem as a result of transpiration (TRANSPIRATION PULL).
6) Transpiration Pull puts xylem under tension, there’s a negative pressure in xylem, so the name given is COHESION-TENSION THEORY.

Question 45

Mechanism of Translocation

Answer 45

1) Transfer of sucrose into sieve elements from photosynthesising tissue
2) Mass flow of sucrose through sieve tube elements
3) Transfer of sucrose from sieve tube elements into storage or other sink cells

Question 46

Transfer of sucrose into sieve elements from photosynthesising tissue

Answer 46

1) Sucrose manufactured in cells with chloroplasts from products of photosynthesis.
2) Sucrose diffuses down conc gradient by facilitated diffusion from photosynthesising cells into companion cells.
3) H+ ions actively transported from companion cells into spaces within walls using ATP.
4) Sucrose molecules co-transported with H+ ions by co-transport proteins.

Question 47

Mass flow of sucrose through sieve tube elements

Answer 47

1) Sucrose produced by the source (photosynthesising cells) is actively transported to sieve tubes.
2) Causes sieve tubes to have a lower (more negative) water potential.
3) Xylem has a higher (les negative) water potential so water moves into sieve tubes from xylem by osmosis creating a high hydrostatic pressure within them.
4) At the sink (respiring cells) sucrose is either used up in respiration or converted to starch for storage.
5) Cells have low sucrose content so sucrose is actively transported into them from sieve tubes, lowering water potential.
6) Due to lowered water potential, water moves out of sieve tubes into cells by osmosis.
7) Hydrostatic pressure of sieve tubes is lowered in this region.
8) Water entering sieve tube at source and leaving at the sink so high hydrostatic pressure at source and low hydrostatic pressure at sink.
9) There’s a mass flow of sucrose solution down hydrostatic gradient in the sieve tubes.

Question 48

Transfer of sucrose from sieve tube elements into storage or other sink cells

Answer 48

Sucrose is actively transported by companion cells out of sieve tubes and into sink cells.

Question 49

Ringing Experiments

Answer 49

Ring of outer layer around stem is removed.
After some time the region of stem directly above removed ring swells.
Sample of this region indicates it’s rich in sugars and other dissolved organic substances.
Non-photosynthetic tissues in region below ring are found to wither and die.
Observations suggest sugars of phloem accumulate above the ring to result in swelling and interruption of flow of sugars to region below ring causes death of tissues in that area.

Question 50

Tracer Experiments

Answer 50

The 14C isotope can be used to make radioactively labelled 14CO2.
Plants grown in atmosphere containing 14CO2 have 14C incorporated into sugars produced in photosynthesis.
The radioactive sugars’ movement can be traced using autoradiography and blacken parts of X-ray film.