Mass Transport

Question 1

describe the structure of haemoglobin

Answer 1

globular
water soluble
4 polypeptide chains each with a haem group

Question 2

describe the role of haemoglobin

Answer 2

present in red blood cells
oxygen molecules bind to the haem groups and are carried around the body to where they are needed in respiring tissues

Question 3

name the three factors affecting oxygen-haemoglobin binding

Answer 3

1. partial pressure/concentration of oxygen
2. partial pressure/concentration of carbon dioxide
3. saturation of haemoglobin with oxygen

Question 4

how does partial pressure of oxygen affect oxygen-haemoglobin binding

Answer 4

as partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases, so oxygen binds tightly to haemoglobin, when partial pressure is low, oxygen is released from haemoglobin

Question 5

how does partial pressure of carbon dioxide affect oxygen-haemoglobin binding

Answer 5

as partial pressure of co2 increases, the conditions become acidic causing haemoglobin to change shape. the affinity of haemoglobin for oxygen therefore decreases, so oxygen is released from haemoglobin. this is known as the Bohr effect

Question 6

how does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding

Answer 6

• hard for first oxygen molecule to bind
• changes shape to make it easier for second and third to bind = POSITIVE COOPERATIVITY
• then slightly harder for fourth oxygen molecule as there is a lower chance of finding a binding site

Question 7

why oxygen binds to haemoglobin in the lungs

Answer 7

• partial pressure of oxygen is high
• low concentration of carbon dioxide in the lungs, so affinity is high
• positive cooperativity (after first oxygen molecule binds, binding of subsequent molecules is easier)

Question 8

explain why oxygen is released from haemoglobin in respiring tissues

Answer 8

• partial pressure of oxygen is low
• high concentration of carbon dioxide in respiring tissues, so affinity decreases

Question 9

what do oxyhaemoglobin dissociation curves show

Answer 9

saturation of haemoglobin in oxygen (in %), plotted against partial pressure of oxygen (in kPa)

Question 10

what do curves further to the left in oxyhaemoglobin dissociation curves show

Answer 10

higher affinity for oxygen

Question 11

how does CO2 affect the position of dissociation curve

Answer 11

curve shifts to the right because haemoglobin’s affinity for oxygen has decreased

Question 12

name some common features of mammalian circulatory system

Answer 12

1. suitable medium for transport, water-based to allow substances to dissolve
2. means of moving the medium and maintaining pressure throughout the body, such as the heart
3. means of controlling flow so it remains unidirectional, such as valves

Question 13

relate structure of atria to their function

Answer 13

thin-walled and elastic, so they can stretch when filled with blood

Question 14

relate structure of ventricles to their function

Answer 14

thick muscular walls pump blood under high pressure
left ventricle is thicker than the rigt because it has to pump blood all the way around the body

Question 15

relate structure of arteries to their function

Answer 15

thick walls to handle high pressure without tearing, and are muscular and elastic to control blood flow

Question 16

relate structure of veins to their function

Answer 16

thin walls due to lower pressure, therefore requiring valves to ensure blood doesn’t flow backwards
have less muscular and elastic tissue as they don’t have to control blood flow

Question 17

why are 2 pumps needed in heart

Answer 17

• maintain blood pressure
• when blood passes through narrow capillaries of lungs, pressure drops sharply and therefore will not be flowing strongly enough to continue to whole body
• returned to heart to increase pressure

Question 18

what happens in cardiac systole

Answer 18

• heart is relaxed
• blood enters atria, increasing the pressure and pushing open the atrioventricular valves
• allows blood to flow into ventricles
• pressure in heart lower than arteries, so semilunar valves are closed

Question 19

what happens in atrial systole

Answer 19

atria contract, pushing any remaining blood into ventricles

Question 20

what happens in ventricular systole

Answer 20

ventricles contract, pressure increases, closing the atrioventricular valves to prevent backflow, opening the semilunar valves
blood flows into the arteries

Question 21

name the nodes involved in heart contraction

Answer 21

• SAN (sinoatrial node)
• AVN (atrioventricular node)

Question 22

where is the SAN

Answer 22

wall of right atrium

Question 23

where is AVN

Answer 23

between the two atria

Question 24

what does myogenic mean

Answer 24

heart’s contraction is initiated from within the muscle itself, rather than by nerve impulses

Question 25

explain how the heart contracts

Answer 25

- SAN initiates and spreads impulse across the atria, so they contract - AVN receives, delays and then conveys the impulse down the bundle of His - impulse travels into the Purkinje fibres which branch across the ventricles, so they contract from the bottom up

Question 26

why is the impulse delayed

Answer 26

otherwise valves would not have enough time for all blood to pass through and for valves to close

Question 27

how is the structure of capillaries suited to their function

Answer 27

- walls are only one cell thick; short diffusion pathway - very narrow, so can permeate tissues and red blood cells can lie flat against the wall, effectively delivering oxygen to tissues - numerous and highly branched, providing large surface area

Question 28

what is tissue fluid

Answer 28

watery substance containing glucose, amino acids, oxygen and other nutrients. supplies these to the cells while also removing any waste materials

Question 29

how is tissue fluid formed

Answer 29

as blood is pumped through increasingly small vessels, this creates hydrostatic pressure which forces fluid out of the capillaries. it bathes the cells and then returns to the capillaries when hydrostatic pressure is low enough

Question 30

how is water transported in plants

Answer 30

through xylem vessels; long, continuous columns that provide structural support to the stem

Question 31

explain cohesion-tension theory

Answer 31

water molecules form hydrogen bonds with each other, causing them to 'stick' together (cohesion) this creates sticking effect, therefore water is lost through transpiration, more can be drawn up the stem

Question 32

what are the three components of phloem vessels

Answer 32

- sieve tube elements = form a tube to transport sucrose in the dissolved form of sap - companion cells = involved in ATP production for active loading of sucrose into sieve tubes - plasmodesmata = gaps between cell walls where cytoplasm links, allowing substances to flow

Question 33

name the process whereby organic materials are transported around the plant

Answer 33

translocation

Question 34

how does sucrose in leaf move into phloem

Answer 34

sucrose enters companion cells of the phloem vessels by active loading, which uses ATP and a diffusion gradient of H+ sucrose then diffuses from companion cells into sieve tube elements through the plasmodesmata

Question 35

how do phloem vessels transport sucrose around plant

Answer 35

as sucrose moves into the tube elements, water potential inside the phloem is reduced. this causes water to enter via osmosis from the xylem and increases hydrostatic pressure. water moves along the sieve tube towards areas of lower hydrostatic pressure. sucrose diffuses into surrounding cells where it is needed

Question 36

give evidence for the mass flow hypothesis of translocation

Answer 36

- sap is released when a steam is cut, therefore there must be pressure in the phloem - there is a higher sucrose concentration in the leaves than in the roots - increasing sucrose levels in the leaves results in increased sucrose in the phloem

Question 37

give evidence against mass flow hypothesis of translocation

Answer 37

- structure of sieve tubes seems to hinder mass flow - not all solutes move at the same speed, as they would in mass flow - sucrose is delivered at the same rate throughout the plant, rather than to areas with the lowest sucrose concentration first

Question 38

how can ringing experiments be used to investigate transport in plants

Answer 38

bark and phloem of tree are removed in a ring, leaving behind the xylem eventually the tissues above the missing ring swells doe to accumulation of sucrose as the tissue below begins to die therefore sucrose must be transported in the phloem

Question 39

how can tracing experiments be used to investigate transport in plants

Answer 39

plants are grown in the presence of radioactive co2, which will be incorporated into the plant's sugars. using autoradiography, we can see that the areas exposed to radiation correspond to where the phloem is