Mass transport (7)

Question 1

What is the structure of haemoglobin?

Answer 1

• globular
• water soluble
• 4 polypeptide chains each carrying a haem group (quaternary structure)

Question 2

What is the role of haemoglobin?

Answer 2

O2 molecules bind to haem groups and are carried around body to where they are needed in respiring tissues

Question 3

Where is haemoglobin found?

Answer 3

in red blood cells

Question 4

What do oxyhaemoglobin dissociation curves show?

Answer 4

saturation percentage of haemoglobin with O2
plotted against partial pressure of O2 (kPa)
curve to left shows haemoglobin has high affinity for O2

Question 5

What are 3 reasons for the mammalian circulatory system?

Answer 5

1) suitable medium for transport as it is water-based to allow substances to dissolve
2) means of maintaining pressure throughout body
3) means of controlling flow so it remains unidirectional such as valves

Question 6

What is translocation?

Answer 6

where organic materials are transported around the plant

Question 7

Why does O2 bind to haemoglobin in the lungs?

Answer 7

1) partial pressure of O2 is high
2) low concentration of CO2 in lungs so affinity is high
3) positive cooperativity

Question 8

What is positive cooperativity?

Answer 8

after 1st O2 binds, binding of subsequent molecules is easier, but slightly harder for the 4th as there is low chance of finding a binding site

Question 9

What are 3 factors affecting O2 and haemoglobin binding?

Answer 9

1) partial pressure/concentration of O2
2) partial pressure/concentration of CO2
3) saturation of haemoglobin with O2

Question 10

How does high partial pressure of O2 affect O2 and haemoglobin binding?

Answer 10

if partial pressure of O2 is high, affinity of haemoglobin for O2 will also be high, so O2 binds tightly to haemoglobin

Question 11

How does low partial pressure of O2 affect O2 and haemoglobin binding?

Answer 11

if partial pressure of O2 is low, O2 is released

Question 12

How does high partial pressure of CO2 affect O2 and haemoglobin binding?

Answer 12

if partial pressure of CO2 is high, conditions become acidic causing haemoglobin to change shape, so affinity of haemoglobin for O2 decreases, releasing O2 (this is known as the Bohr effect)

Question 13

What is the Bohr effect?

Answer 13

when partial pressure of CO2 is high, conditions become acidic causing haemoglobin to change shape, so affinity of haemoglobin for O2 decreases, releasing O2

Question 14

How does the saturation of haemoglobin with O2 affect O2 and haemoglobin binding?

Answer 14

• hard for 1st O2 molecule to bind
• once it does it changes shape to make it easier for 2nd + 3rd molecules to bind (this is known as positive cooperativity)
• it becomes slightly harder for 4th as low chance of finding a binding site

Question 15

Label diagram of heart.

Answer 15

Use notes.

Question 16

What are the 2 chambers of the heart?

Answer 16

atria and ventricles

Question 17

What is the structure of the atria and how does this relate to its function?

Answer 17

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

Question 18

What is the structure of the ventricles and how does this relate to its function?

Answer 18

thick muscular walls pump blood under high pressure

Question 19

Which side of the heart is thicker and why?

Answer 19

left
has to pump blood all the way round the body

Question 20

What are the 2 vessels in the heart?

Answer 20

arteries and veins

Question 21

What is the structure of the arteries and how does this relate to its function?

Answer 21

• thick walls to handle high pressure without tearing
• muscular and elastic tissue to control blood flow

Question 22

What is the structure of the veins and how does this relate to its function?

Answer 22

thin walls due to low pressure, therefore need valves
less muscular and elastic tissue as they don’t control blood flow

Question 23

Why are both the pumps (left and right) needed?

Answer 23

• to maintain blood pressure around whole body
• when blood passes through narrow capillaries, pressure drops sharply, without 2 pumps it would not flow strongly enough to continue around the whole body
• returned to heart to increase pressure

Question 23

What are the 2 steps that happen during atrial systole?

Answer 23

1) atria contract
2) remaining blood pushed into ventricles

Question 24

What are the 7 steps that happen during cardiac diastole?

Answer 24

1) heart is relaxed
2) blood enters atria
3) pressure increases
4) atrioventricular valves pushed open
5) allows blood to flow into ventricles
6) heart pressure lower than in arteries
7) semilunar valves remain closed

Question 25

What are the 3 stages of blood movement through the heart?

Answer 25

cardiac diastole
atrial systole
ventricular systole

Question 26

What are the 5 steps that happen during ventricular systole?

Answer 26

1) ventricles contract
2) pressure increases
3) atrioventricular valves close
4) semilunar open
5) blood flows into arteries

Question 27

What is meant by myogenic?

Answer 27

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

Question 28

How does the structure of capillaries relate to its function?

Answer 28

• walls only 1 cell thick so short diffusion path
• very narrow so can permeate tissues and red blood cells can lie flat against wall, effectively delivering O2 to tissue
• numerous and highly branches so have large SA

Question 29

What is tissue fluid?

Answer 29

watery substance containing glucose, amino acids, O2 and other nutrients

Question 30

What is the function of tissue fluid?

Answer 30

supplies glucose, amino acids, O2 and other nutrients to cells and removes waste materials

Question 31

How is tissue fluid formed?

Answer 31

• blood pumped through increasingly small vessels creating hydrostatic pressure, which forces fluid out of capillaries
• bathes cells, then returns to capillaries when hydrostatic pressure is low enough

Question 32

How is water transported in plants?

Answer 32

through xylem vessels

Question 33

What are xylem vessels?

Answer 33

long, continuous columns that also provide structural support to the stem

Question 34

What are the 3 components of phloem vessels?

Answer 34

sieve tube elements
companion cells
plasmodesmata

Question 35

What is the role of sieve tube elements?

Answer 35

form a tube to transport sucrose in the dissolved form of sap

Question 36

What is the role of companion cells?

Answer 36

involved in ATP production for active loading of sucrose into sieve tubes

Question 37

What is the plasmodesmata and its role?

Answer 37

gaps between cell walls where cytoplasm links, allowing substances to flow

Question 38

What are 3 pieces of evidence for the mass flow hypothesis?

Answer 38

• sap released when stem cut so must be pressure in phloem
• higher sucrose concentration in leaves than roots
• high sucrose levels in leaves means high levels of sucrose in the phloem

Question 39

What are 3 pieces of evidence against the mass flow hypothesis?

Answer 39

• structure of sieve tube elements hinders mass flow
• not all solutes move at same speed, but would in mass flow
• sucrose delivered at same rate, not to areas of low concentration first

Question 40

What are the 2 experiments that provide evidence for the mass flow theory?

Answer 40

tracing experiment
ringing experiment

Question 41

What is the tracing experiment?

Answer 41

• plants grown in presence of radioactive CO2
• incorporated into plant’s sugars
• autoradiography shows areas exposed to radiation, which is where the phloem is

Question 42

What is the ringing experiment?

Answer 42

1) bark and phloem removed in a ring, leaving behind the xylem
2) tissues above swell due to accumulation of sucrose as tissue below begins to die
3) therefore sucrose must be transported in the phloem

Question 43

What is the cohesion-tension theory?

Answer 43

• water molecules form H bonds with each other, causing them to ‘stick’ together (cohesion)
• surface tension of water also creates this sticking effect
• therefore, as water is lost through transpiration, more can be drawn up the stem

Question 44

How does sucrose move into the phloem?

(2 points)

Answer 44

1) enters companion cells by active loading, which uses ATP + diffusion gradient of H+
2) sucrose diffuses into sieve tube elements through plasmodesmata

Question 45

How does the phloem transport sucrose in the plant?

Answer 45

1) as sucrose moves into the sieve tube elements, water potential in phloem reduces
2) water enters via osmosis from xylem and increases hydrostatic pressure
3) water moves along sieve tube elements towards area of lower hydrostatic pressure
4) sucrose diffuses into surrounding cells where is it needed