7: Mass Transport

• readily associate with oxygen at the lungs and transport oxygen to tissues to be used in aerobic metabolic pathways

• quaternary structure

• made up of 4 polypeptide chains

• 4 haem groups containing Fe 2+ which oxygen binds to

• different base sequences in DNA- different AA sequences-different quaternary structure and shape

the ability of Hb to attract or bind oxygen

when Hb is holding the maximum amount of oxygen it can bind

the binding of oxygen to Hb

when oxygen detaches from Hb

• at high partial pressures of oxygen, little oxygen binds as shape makes it difficult

• binding of first O2 changes quaternary structure causing Hb to change shape making it easier for other O2 molecules to bind

• harder for 4th O2 molecule to bind because less to likely to find empty site

• at low partial pressures of oxygen the affinity of Hb to oxygen is reduced causing oxygen to dissociate

• the further to the left the curve, the greater the affinity of Hb for oxygen so O2 loads easily but unloads less easily

• higher pH at the lungs due to a low CO2 concentration changes the shape of Hb so has a higher affinity for O2 so O2 readily associates

• lower pH at the tissues due to a high CO2 concentration changes shape of Hb so has a lower affinity for O2 so O2 readily dissociates

pulmonary artery

pulmonary vein

renal vein to vena cava
vena cava to right atrium
pulmonary artery from right ventricle to lungs

pulmonary vein from lungs to left atrium
aorta from left ventricle
renal artery to kidney

so that the left ventricle can contract to create a high enough pressure to pump blood to the rest of the body
right ventricle generates less pressure from the contraction of its thinner walls as blood only has to reach the lungs

connected to the LV and carries oxygenated blood to all parts of the body except the lungs

connected to the RA and carries deoxygenated blood back from the tissues

connected to the RV and carries deoxygenated blood back to the lungs

connected to the LA and brings oxygenated blood back from the lungs

Heart attack could occur because an area of the heart muscle is deprived of blood and oxygen as these arteries supply the heart with oxygen
Muscle cells are unable to respire aerobically and so die

1. carbon monoxide combines easily but irreversibly with Hb to form carboxy-haemoglobin

2. this reduces the oxygen carrying capacity of the blood

3. to supply the equivalent quantity of oxygen to the tissues, the heart works harder which leads to increased blood pressure, increasing the risk of coronary heart disease

1. heart must work harder to pump blood into arteries

2. more likely to develop and aneurysm and burst

3. to resist the higher pressure within them, the walls of the arteries tend to become harder and thicken which restricts blood flow

• thick muscular layer so smaller arteries can be constricted and dilated to control the volume of blood passing through them

• thick elastic layer that stretches and recoils to maintain high pressure and smooth pressure surges

• no valves as blood is always under high pressure so doesn’t flow backwards

• thicker muscle layer than arteries- muscle contracts to contract lumen to control blood flow

• thinner elastic layer- lower BP

• thin muscle layer- carry blood away from tissues so contriction and dilation doesn't need to control blood flow to tissues

• thin elastic layer as blood is carried under low pressure

• thin walls- low blood pressure so won't burst

• valves to ensure that blood doesn't flow backwards because of low BP

• thin walls-short diffusion distance so rapid diffusion between blood and cells

• highly branched- large SA fro exchange

• narrow lumen- red blood cells squeezed against the walls which decreases diffusion distance

1. Atria fill and the pressure rises

2. When pressure rises above that in the ventricles, the atrioventricular valves open and blood passes into the ventricles

3. relaxation of ventricle walls causes them to recoil and reduce pressure in the ventricles below pressure in aorta and pulmonary artery

4. this causes the semilunar valves to close

the contraction of the atrial walls, along with the recoil of the relaxed ventricle walls pushes remaining blood into ventricles from the atria

1. after a short delay to allow the ventricles to fill with blood their walls contract simultaneously

2. this increases the blood pressure within them, forcing shut the atrioventricular valves and preventing back flow of blood into the atria

3. pressure rises above that in pulmonary artery and aorta

4. semilunar valves open and blood flows into pulmonary artery and aorta

• low at first but gradually increases as the ventricles fill with blood as the atria contract

• atrioventricular valves close and pressure rises as ventricles contract

• as pressure rises above that of the aorta and pulmonary artery semilunar valves and blood is pushed in

• pressure falls as ventricles empty

• is always relatively low because the thin walls of the atrium cannot create much force

• pressure is highest when they are contracting but drops when the atrioventricular valve closes and its walls relax

• the atria then fill with blood which leads to a gradual build up of pressure until a slight drop when the atrioventricular valves open

• rises when ventricles contract as blood is forced into the aorta

• it then falls but never very low because of the elasticity of its wall which creates a recoil action which is essential if blood has to be constantly delivered to the tissues

• this creates a rise in pressure at the start of the relaxation phase

• rises as the atria contract and the ventricles fill with blood

• drops suddenly as blood is forced out into the aorta

1. Hydrostatic pressure of blood high at arterial end

2. Fluid/ water/ soluble molecules pass out

3. Proteins/ large molecules remain

4. Lowers water potential- becomes more negative

5. Water moves back into venous end of the capillary via osmosis/ diffusion

6. Lymph system collects any excess tissue fluid which returns to blood

• water potential gradient between air spaces in the leaf and air so water vapour molecules diffuse out of stomata

• water lost from air spaces is replaced by water evaporating from the cell walls of mesophyll cells

• mesophyll cells lose water to the air spaces by evaporating due to heat from the sun

• cells have a lower water potential so water enters from neighbouring cells

• this repeats in neighbouring cells

• in this way a water potential gradient is established that moves water from the xylem, across the mesophyll into the atmosphere

• water evaporates from mesophyll cells

• water molecules form hydrogen bonds and stick together (cohesion)

• water forms a continuous unbroken column

• water is pulled up the xylem as a result of transpiration

• during the day when transpiration is greatest, there is more tension in the xylem. This pulls the walls of the xylem in and causes the trunk or stem to shrink in diameter. At night there is less transpiration so less tension so diameter increases

• if a xylem vessel is broken and air enters it the tree can no longer draw up water because the continuous column of water is broken

1. sucrose diffuses down a concentration gradient from photosynthesising cells into companion cells

2. hydrogen ions are actively transported from companion cells to into the spaces within cell walls

3. hydrogen ions diffuse down a concentration gradient through carrier proteins into sieve tube elements

4. sucrose molecules are co-transported

1. water potential in sieve elements is lowered due to the active transport of sucrose into sieve elements

2. water moves from the xylem into the sieve tubes by osmosis down a water potential gradient, creating a high hydrostatic pressure within them

3. at the respiring cells sucrose is used up during respiration or converted to starch for storage

4. sucrose is actively transported from sieve tubes to respiring cells which lowers the WP in these cells

5. water moves into repairing cells by osmosis down a WP gradient

6. hydrostatic pressure in sieve tubes is lowered

7. hydrostatic pressure gradient created from source to sink which sucrose solution travels down

• there is pressure within sieve elements as shown by sap being released when they are cut

• the concentration of sucrose is higher in leaves (source) than the roots (sink)

• companion cells possess many mitochondria

• solutes don't all move at the same speed but they should do

• sucrose is delivered at the same rate to all regions rather than faster in regions with a lower sucrose concentration

• when the phloem is cut, a solution of organic molecules flow out

• plants provided with radio-actively labelled CO2 can be seen to have radioactively labelled carbon in phloem after a short time

• the removal of a ring of phloem from around the whole circumference of a stem leads to the accumulation of sugars above the ring and their disappearance below it