Chapter 7 - Mass transport

Question 1

what is the quarternary structure of haemoglobin?

Answer 1

four polypeptides, each associated with a haem group which contains Fe 2+ which can combine with one molecule of oxygen each

Question 2

what is the term for taking up oxygen in haemoglobin?

Answer 2

loading and unloading

Question 3

what is the role of haemoglobin? (2)

Answer 3

• readily associate with oxygen at gas exchange (high partial pressure)
• readily dissociate at low partial pressures such as respiring tissues

Question 4

why are their different haemoglobin in different animals?

Answer 4

different partial pressure e.g. high altitude

different dissociating required e.g. lugworms

Question 5

explain the shape of oxygen dissociation curves (4)

Answer 5

• difficult for first molecule to bind = shallow curve gradient
• first molecule binding changes the shape making it easier for subsequent molecules to bind
• positive cooperativity, the gradient steepens
• lower probability of oxygen binding when oxygen is highly loaded means gradient levels off

Question 6

what are the effects of CO2 on haemoglobin? (3)

Answer 6

• reduced affinity for oxygen
• release oxygen more readily at high CO2 conc. ,e.g. respiring tissues
• slightly acidic, CO2 changes shape of haemoglobin

Question 7

state the sequence of vessels in the heart from the vena cava to the aorta (12)

Answer 7

• vena cava
• right atrium
• atrioventricular valve
• right ventricle
• semi-lunar valve
• pulmonary artery
• (lungs)
• pulmonary vein
• left atrium
• atrioventricular valve
• left ventricle
• semi-lunar valve
• aorta

Question 8

name the 3 stages of the cardiac cycle

Answer 8

diastole
atrial systole
ventricular systole

Question 9

what are the valves in veins and what do they do?

Answer 9

pocket valves prevent backflow

Question 10

what is the action of diastole? (3)

Answer 10

• blood returns to atria through vena cava and pulmonary vein
• when pressure exceeds that in the ventricles the semi-lunar valves open allowing blood to drain into ventricles by gravity
• semi-lunar valves remain open until the pressure in the atria has decreased below that of the ventricles

Question 11

what is the action of atrial systole?

Answer 11

both atria contract at the same time along with further recoil of the ventricles, forcing the remaining blood in the atria into the ventricles

Question 12

what is the action of ventricular systole? (2)

Answer 12

• ventricles contract together, AV valves shut
• pressure within ventricles rises further forcing the semilunar valves of aorta open due to higher pressure in ventricles
• (creates high pressure for blood to go round whole body and back)

Question 13

state the cardiac output calculation

Answer 13

heart rate x stroke volume = cardiac output

Question 14

name the types of blood vessels (4)

Answer 14

• arteries
• arterioles
• capillaries
• veins

Question 15

what are capillaries made from?

Answer 15

lining layer/epethelial cells

Question 16

name the structures of arteries arterioles and veins (5)

Answer 16

• tough fibrous outer layer
• muscle layer - contraction for blood pressure
• elastic layer - recoil
• endothelium - reduce friction
• lumen - cavity

Question 17

compare the main function of arteries to that of capillaries (2)

Answer 17

• arteries carry blood around whole body by maintaining constant high blood pressure
• capillaries, allow diffusion due to short diffusion pathway

Question 18

outline tissue fluid formation (2)

Answer 18

• hydrostatic pressure created by pumping of the heart and narrow capillaries
• at arteriole end of capillaries hydrostatic pressure forces tissue fluid into surrounding cells

Question 19

what forces resist the formation of tissue fluids? (2)

Answer 19

• hydrostatic pressure of surrounding cells and fluid outside
• lower water potential of blood due to plasma proteins

Question 20

outline the return of tissue fluid to the circulatory system (5)

Answer 20

• reduced hydrostatic pressure at venous end due to loos of fluid
• tissue fluid forced back into capillaries
• capillaries have lower water potential
• water moves down water potential gradient
• remainder absorbed into lympatic capillaries which drain into the blood

Question 21

name the process of water loss through evaporation in plants

Answer 21

transpiration

Question 22

how does water move up the stem into the leaves?

Answer 22

in a continuous column of water up the xylem (caused by cohesion) known as transpiration pull, cohesion tension theory

Question 23

what is the function of the xylem?

Answer 23

to carry water up the stem from the roots (transport of water)

Question 24

what is the evidence in support of cohesion tension theory? (2)

Answer 24

• change in diameter of tree trunks e.g. after rain
• if xylem is broken, column of water is broken and water no longer passes upwards, in addition the the fact air is drawn in showing tension

Question 25

what is the function of the phloem?

Answer 25

transport of organic molecules

Question 26

what theory governs the mechanism of translocation?

Answer 26

mass-flow hypothesis

Question 27

outline the process by which sucrose enter sieve elements (3)

Answer 27

- sucrose is manufactured and diffuses down conc. gradient into companion cells - hydrogen ions are actively transported from companion cells into spaces in the cell wall - hydrogen ions diffuse back down concentration gradient into the phloem through specific co-transport proteins with sucrose

Question 28

outline the process of mass flow through sieve elements (4)

Answer 28

- lower water potential in the sieve element, water moves in from xylem - causes greater hydrostatic pressure - inverse is true at sink with respiring cells - mass flow of sucrose solution down hydrostatic pressure gradient to sink

Question 29

by what process does the sucrose leave the sieve elements once at the sink?

Answer 29

active transport

Question 30

what is the evidence to support mass flow? (5)

Answer 30

- sap released from sieve tubes when cut shows pressure - conc. of sucrose higher in leaves - downward flow only occurs in day when leaves are photosythesising - sucrose increase in leaves results in sucrose increase in phloem - companion cells contain many mitochondria for active transport

Question 31

evidence questioning mass flow? (3)

Answer 31

- unclear function of sieve plates - not all solutes move at same speed - sucrose delivered at same rate to all regions

Question 32

types of xylem/phloem experiments (2)

Answer 32

- ringing experiments | - tracer experiments

Question 33

what is the evidence that translocation occurs in the phloem? (3)

Answer 33

- phloem cut, organic molecules come out - plants given tracer CO2 show tracer in phloem after a short time - removal of a ring of phloem on a plant leaves sugars building up above the ring

Question 34

outline a ringing experiment on a tree and the expected results (2)

Answer 34

- remove ring of protective layer and phloem | - area immediately above ring swells with sugars

Question 35

outline a tracer experiment and the expected results (4)

Answer 35

- radioactive carbon absorbed by plant and incorporated into sugars - after some time thin slices of plant take and placed over X-ray photography film - were film is blackened shows where radioactive isotope in sugars is - these correspond with where the phloem is