mass transport (topic 3)

Question 1

general blood vessel structures and functions
outer, muscle, elastic layers, endothelium, lumen, valves

Answer 1

tough outer layer - resists pressure changes
muscle layer - contracts/relaxes to control blood flow
elastic layer - stretch/recoil to maintain blood pressure
endothelium - smooth layer to prevent friction
lumen - cavity allows blood to flow
valves - maintain direction of blood flow

Question 2

artery structure

Answer 2

transports blood rapidly under high pressure
- muscle layer thicker than veins, can contract/relax to constrict/dilate to control vol blood passing through
- elastic layer thicker than veins to allow stretch/recoil of walls to maintain high pressure
- wall thickness is great to resist damage and bursting under high pressure
- no valves due to high pressure

Question 3

arterioles structure

Answer 3

lower pressure than arteries (wider lumen)
=> capillaries
- thicker muscle layer than arteries to constrict/dilate lumen to regulate blood flow
- thinner elastic layer than arteries as BP is lower

Question 4

vein structure

Answer 4

transport blood slowly at low pressure from tissues
- thin muscle layer compared to arteries, can’t control constriction/dilation of the lumen
- thin elastic layers, minimal risk of damage
- small overall thickness, can be flattened easily as surrounding muscles contract
- valves prevent back flow of blood, maintains flow towards heart. as muscles contract, veins are compressed which creates pressure and so movement of blood

Question 5

capillary structure

Answer 5

site of metabolic exchange between tissues and blood (O2, CO2, glucose etc)
- slow blood flow to allow sufficient exchange of materials
- no outer, muscle, elastic layer and no valves
- walls are mostly lining layer so very thin to decrease diffusion distance, lumen narrow for this too
- numerous capillaries and highly branched, large SA
- small spaces between cell lining for WBC to leave blood and carry out immune response
- bathed in tissue fluid

Question 6

the 4 features of a circulatory system

Answer 6

• medium (blood)
• means of moving the medium (pump eg heart)
• mechanism to control flow (valves in veins)
• closed system of vessels

Question 7

why do ventricles have thicker walls than atria

Answer 7

they pump blood around the body or to the lungs

Question 8

formation of tissue fluid: arterial end

Answer 8

due to heart contractions, high hydrostatic pressure (pushing water out capillaries)
- minorly opposed by hydrostatic pressure of tissue fluid outside capillaries
and water potential gradient (lower in blood than fluid)

Question 9

formation of tissue fluid: venous end

Answer 9

loss of water from the capillaries reduces hydrostatic pressure inside them. greater HS pressure in tissue fluid so it is forced back in.
- as water is lost at arterial end but plasma proteins are kept, so water potential is lowered.
WP is lower in blood plasma than tissue fluid so 90% of the water osmosises back into blood

Question 10

formation of tissue fluid: lymph

Answer 10

remaining 10% of tissue fluid (now lymph) enters lymphatic capillary
- closed ends and pores to allow large molecules to pass through
- moves by compression caused by body movement
- valves to prevent back flow
- eventually reenters blood by veins near heart

Question 11

haemoglobin structure

Answer 11

protein making up 95% of an rbc’s dry mass
quaternary structure: 4 polypeptide chains (2 identical α chains, 2 identical β chains)
all coiled in a helix
each subunit bound to a prosthetic group haem Fe2+ , these can each associate with with one oxygen molecule (4 in total)

Question 12

dissociation curves , what goes on the axis

Answer 12

X = partial pressure of oxygen (pO2)
Y = % of haemoglobin saturation

Question 13

explaining oxygen dissociation curves

Answer 13

1st O2 - HARDER TO LOAD as the shape of the Hb molecules make it difficult for first o2 to load as the subunits (chains) are CLOSELY UNITED, at low o2 conc, little o2 loads + curve is shallow

2 + 3 - as first loads it changes the shape, UNCOVERING another binding site so the 2nd o2 loads more easily, takes a smaller increase in pO2 to load 2nd o2. enables 3rd o2 to load more easily (positive cooperativity)

4th O2 - HARDER to load due to PROBABILITY as most of the binding sites are occupied. less likely a single o2 will find an empty site to associate with

Question 14

how does affinity for oxygen affect ability to load

Answer 14

haemoglobin with high affinity loads o2 easily, unloads less easily
low affinity loads o2 less easily, unloads easily

Question 15

effect of carbon dioxide

Answer 15

hb has a reduced affinity for oxygen in presence of co2 (the greater conc of co2, more readily hb releases o2) the Bohr effect

co2 dissolves in blood plasma forming a weak acid. releases H+ ions so pH falls. low pH changes shape of haemoglobin which reduces affinity for o2 and attraction is weaker

clue: if curve moves to the right, hb releases oxygen easier

Question 16

different types of haemoglobin in different species

Answer 16

different sequences of amino acids and therefore slightly different shapes, so different affinities for oxygen

• if they have a high affinity for o2 they load easily but not unload CURVE is to the LEFT (used by animals that live in low oxygen environment)
• if they have a low affinity they don’t load easily and unload easily CURVE is to the RIGHT (used by small animals, they have a larger SA:V ratio so lose more heat, higher metabolic + respiration rate)

Question 17

cardiac cycle overview

Answer 17

diastole -> atrial systole -> ventricular systole

diastole = relaxing
systole = contracting

Question 18

diastole

Answer 18

atria and ventricles relax
blood returns and fills the atria, increasing the pressure until AV valves open and blood flows into the ventricles

AV valves open, SL valves closed

Question 19

atrial systole

Answer 19

atria contract, forcing any remaining blood into the ventricles

Question 20

ventricular systole

Answer 20

ventricles contract, increasing pressure so AV close and SL valves open
blood leaves either by the aorta or the pulmonary artery

Question 21

factors affecting rate of transpiration - humidity

Answer 21

measures conc of water vapour in air
high water vapour conc in air spaces of the leaf so high humidity => lower WP gradient so SLOWER rate

Question 22

factors affecting rate of transpiration - temperature

Answer 22

increased temp means particles have more kinetic energy so move faster
therefore evaporate quicker from the cell surface to the air spaces, to diffuse out of the leaf
FASTER rate

Question 23

factors affecting rate of transpiration - light intensity

Answer 23

increased LI, more photosynthesis in the palisade cells so stomata are open for gas exchange
water molecules diffuse out of air spaces quicker
FASTER rate

Question 24

factors affecting rate of transpiration - wind speed

Answer 24

faster the wind, faster the water vapour that has diffused out the leaf is moved away
maintains steep WP gradient
FASTER rate

Question 25

transpiration (cycle) in plants - water from soil into root

Answer 25

water enters root hair cells and moves into the xylem tissue as the water potential is higher in the soil than in the root hair cells, due to dissolved substances in the cell sap
root hair cells provide a large SA for the movement of water to occur
minerals are also absorbed through the root hair cells by active transport, as they need to be pumped against the concentration gradient

Question 26

transpiration in plants - 2 pathways

Answer 26

apoplast => water moves through cell walls, water filled spaces between cellulose molecules. as it doesn’t pass through plasma membranes it can carry dissolved mineral ions and salts
it reaches a part of the root called endodermis, contains a layer of suberin called CASPARIAN STRIP, cannot move through it so joins the symplast pathway

symplast => water enters cytoplasm, through plasma membrane, passes through cells by plasmodesmata (channels connecting cell cytoplasms)

Question 27

transpiration in plants - cohesion tension theory in xylem

Answer 27

water moves down a concentration gradient across the mesophyll cells.
evaporates and turns to water vapour when enters air spaces, now the cell has lower WP so water from neighbour cell moves into it. this carries on

Question 28

structure of xylem

Answer 28

no end walls between cells
dead cells due to being impregnated with lignin
one way only

Question 29

structure of phloem

Answer 29

cells are living but need support from companion cells with organelles (plasmodesmata (holes) between CC and sieve tube element)
end walls (sieve plates) ((with no nucleus/less organelles))
sieve tube is like the actual tube
two way movement, of organic molecules

less cytoplasm so sugars can flow easily

Question 30

what is translocation

Answer 30

requires energy, transports assimilates like sucrose between sources and sinks

Question 31

how does translocation work

Answer 31

• hydrogen ions pumped out of companion cells via active transport. CC contain many mitochondria for ATP
• a high conc of H+ ions build up outside CC. they move back in down a conc gradient via co-transport protein, with sucrose. sucrose builds up in the companion cells
• sucrose diffuses into sieve tube elements via plasmodesmata, increasing the sucrose conc, which decreases water potential
• water moves via osmosis from the xylem. the increase in water inside the sieve tube elements increases hydrostatic pressure.
• at sink, sucrose moves into cells surrounding sieve tube elements (to be converted into starch for storage or glucose for respiration)
• reduced sucrose in sieve tube means increased water potential. water moves out of sieve tube via osmosis, lowering hydrostatic pressure

therefore sucrose moves down a hydrostatic pressure gradient

Question 32

potometers - how to prevent air bubbles

Answer 32

cut stem of plant underwater
assemble apparatus underwater
add petroleum jelly to the joinings