3.4 Mass transport

Question 1

what is the order blood travels around the body starting from the vena cava

Answer 1

vena cave > semi lunar valve > right atrium > right atrium tricuspid > right ventricle > semi lunar valves > pulmonary arteries > lungs > pulmonary veins > semi lunar valves > left atrium > left atrium bicuspid > left ventricle > semi lunar valves > aorta > Body

Question 2

what are the three stages of the cardiac cycle

Answer 2

diastole, atrial systole and ventricular systole

Question 3

describe diastole

Answer 3

1. blood enters the atria from the vena cava and the pulmonary vein
2. atria fill building pressure
3. pressure overcomes that of the ventricles and some of the food passively leaks into the ventricles

Question 4

describe atrial systole

Answer 4

1. atria contract - increasing pressure further and forcing blood into ventricles through bi and tricuspid valves
2. once pressure in ventricles overcomes the atria the valves snap shut preventing any back flow into the atria

Question 5

describe ventricular systole

Answer 5

1. ventricles contract increasing the pressure in ventricles above that of aorta and pulmonary artery
2. semi lunar valves open and blood is forced out until pressure is below that of arteries

Question 6

describe the arteries in terms of pressure, muscle layer, elastic layer, thickness and valves

Answer 6

1. high pressure away from the heart
2. muscle layer is thick compared to the veins
3. elastic layer is thick compared to the veins as it is important that the blood remains in high pressure so it can reach all around the body.
4. overall thickness is high
5. no valves are the pressure is so high there will be no backflow

Question 7

describe the arterioles in terms of pressure, muscle layer and elastic layer

Answer 7

1. lower pressure than the arteries
2. muscle layer is thicker than the arteries constricting the flow of blood controlling the movement of blood into the capillaries
3. elastic layer is thinner sa the blood pressure is lower

Question 8

describe the veins in terms of pressure, muscle layer, elastic layer, thickness and valves

Answer 8

1. low pressure towards the heart
2. the muscle layer is thin compared to the arteries
3. the elastic layer is thin compared to the arteries as the low pressure will not cause then to burst
4. the overall thickness of the wall is small as there is no need for the high thickness as the low pressure has no chance of it bursting
5. there are valves at intervals to ensure the blood does not flow backwards as the pressure is low

Question 9

describe the capillaries in terms of their use, flow of blood, walls, number, diameter, lumen and spaces between the cells

Answer 9

1. they exchange metabolic materials like oxygen and glucose between the blood and cells
2. the flow of blood is much slower allowing more time to exchange materials
3. their walls consist mostly of just the lining layer making home extremely thin so have a short diffusion distance
4. they are numerous and highly branched thus providing a large surface area for exchange
5. they have a narrow diameter so permeate tissue making it so no cell is far from a capillary
6. the lumen is so narrow that red blood cells are squeezed against the side of the capillary bringing them even closer to the cells
7. there are spaces between the lining of cells that allow white blood cells to escape in order to deal with infected tissue

Question 10

what is tissue fluid

Answer 10

the liquid that surrounds cells allowing for transport between blood and cells

Question 11

describe how tissue fluid is formed

Answer 11

1. as the capillaries narrow hydrostatic pressure forces tissue fluid out of the blood plasma
2. hydrostatic pressure forces plasma out into the tissue fluid as the capillaries are narrower
3. some of the water will leave through osmosis
4. as more water potential in the tissue fluid some water will move back into the capillary

Question 12

describe lymph and what is does

Answer 12

moved by hydrostatic pressure and contraction of body muscles
as not all fluid passes back into capillaries the lymphatic system takes it away
the lymph contains lots of waste products that were not taken in by the cells and contain lymphocytes

Question 13

describe the secondary structure of a haemoglobin

Answer 13

2 amino acids are coiled into an α-helix and 2 into a β-pleated sheet

Question 14

describe the quaternary structure of a haemoglobin

Answer 14

all four polypeptide chains are linked to form an almost spherical molecule, each polypeptide is associated with a haem group which contains a ferrous ion. each Fe2+ ion can combine with a single O2 molecule, so 4 oxygen molecules are carried by a single haemoglobin.

Question 15

describe association

Answer 15

when the first oxygen molecule binds to the first harm group and distorts the shape of the whole molecule so that a second, third and fourth oxygen molecule is taken up at an increasing rate. so each oxygen you gain makes it easier to bind however now there is less chance of a successful collision so some haemoglobin may only have three.

Question 16

describe dissociation

Answer 16

first the oxygen molecule is released and then the rest are released at a decreasing rate

Question 17

describe the Bohr shifts

Answer 17

the graph shifts to the left when there is low CO2 as there is a greater affinity for oxygen
the graph shifts to the right when there is high CO2 as there is a lower affinity for oxygen

Question 18

describe the graph of a foetal haemoglobin

Answer 18

foetal haemoglobin as a higher affinity for oxygen that adult haemaglobin. this is to maximise oxygen uptake from the mothers bloodstream, which has already lost some of its oxygen my the time it has reached the placenta

Question 19

describe the graph of myoglobin

Answer 19

myoglobin is similar to haemoglobin but only has one harm group. this means myoglobin will only dissociate the oxygen levels are low. it is found in muscles cells where it acts as a reserve for oxygen

Question 20

what direction would the lugworms graph shift and why

Answer 20

left
as has gills so when the tide goes out it doesn’t have access to oxygen so needs to hold onto more os it so it has higher affinity

Question 21

what direction would the llamas graph shift and why

Answer 21

left
as there is less oxygen available at higher altitudes so has a higher affinity to hold onto it more

Question 22

what direction would the graph shift for an animal with a fast metabolism and why

Answer 22

right
as it would respire more so less oxygen and more CO2 so lower affinity of oxygen so it can be released faster

Question 23

describe the cohesion tension theory (7 steps)

Answer 23

1. water evaporates from the spongey mesophyll cells and diffuses into the atmosphere due to absorbing energy from the sun
2. lower ψ in the leaf so water moves from down the ψ gradient via osmosis from cell to cell and diffusion
3. lower hydrostatic pressure/tension at the top of the xylem draws water up
4. water is pulled up xylem vessels in a column
5. when the water is moving faster the pressure is lower so the walls get pulled it
6. cohesive forces between water molecules prevent water column breaking
7. water moving across root from soil down the ψ gradient

Question 24

how does temperature increase transpiration and why

Answer 24

increases as provides latent heat of vaporisation increasing the kinetic energy so faster diffusion so warms the air

Question 25

how does increasing the humidity affect transpiration and why

Answer 25

decreases as there is a concentration gradient but is more water vapour in the atmosphere there is less gradient

Question 26

how does increasing the wind speed affect transpiration and why

Answer 26

increases as the increased air movement increases the rate of transpiration as it moves the saturated air so steeper gradient

Question 27

how does decreasing the atmospheric pressure affect transpiration and why

Answer 27

increases as less particles so higher gradient

Question 28

how does decreasing the water supply affect transpiration and why

Answer 28

decreases as if little water then the stomata will not be open as less CO2 needed for photosynthesis so less water lost through transpiration

Question 29

how does increasing the light intensity affect transpiration and why

Answer 29

increases as light used for photosynthesis so more stomata open as more CO2 needed

Question 30

describe the structure of the phloem tissue in terms of companion cells

Answer 30

the sieve tubes in the phloem tissue have less organelles and reduced cytoplasm so they can hold more solutes, this means they have companion cells to carry out living functions for the sieve tubes such as active transport

Question 31

describe the steps of translocation (8 steps)

Answer 31

1. sucrose manufactures from photosynthesis in palisade cells of the leaf. moves down concentration gradient into companion cells
2. active transport of H+ out of companion cell between cells wall then diffuse into phloem sieve tube element
3. sucrose co-transport with H+ into the phloem
4. increase in sucrose in sieve tube elements leads to lower water potential
5. water leaves xylem into phloem down water potential gradient (increasing hydrostatic pressure, so the substance moves from high to low pressure)
6. sucrose being used/stored in the sink
7. sucrose in actively transported from sieve tubes into cells lowering the water potential
8. therefore water moves into cells via osmosis lowing hydrostatic pressure if lower sieve tubes (creating the pressure gradient for substance to move down the phloem)

Question 32

describe the ringing experiments

Answer 32

remove the dead outer layer and the phloem from the stump, this makes it so substances like the sucrose and other minerals cannot move through so it accumulates and swells as it cannot move, this lowers the water potential drawing water into the bulge through osmosis. this proves that phloem is on the outside of the vascular bundle and that sugars move in the phloem

Question 33

describe the tracer experiments

Answer 33

radioactive carbon isotope 14C is used to make 14CO2.
The 14C is incorporated into the sugars produced during photosynthesis and autoradiography allows tracking of these sugars.
this proves that the phloem is used for translocating as radioactive areas are on the phloem

Question 34

3 pieces of evidence for the mass flow hypothesis

Answer 34

1. there is pressure within the sieve tubes as shown by sap being released when they are cut
2. the concentration os sucrose is higher inlaces (source) rather than in the roots (sink)
3. downward flow in the phloem occurs in daylight but ceases when leaves are shaded or at night

Question 35

3 pieces of evidence against the lass flow hypothesis

Answer 35

1. the functions of the sieve plates are unclear as they seen to hinder the mass flow, it is suggested that its because they help prevent the tubes to burst under the hydrostatic pressure
2. not all solutes move at the same speed but they should if movement if in mass flow
3. sucrose us delivered at pore is less the same rate to all regions, other than going more quickly to the ones with the lowest sucrose concentration which the mass theory would suggest.