Mass transport

what is partial pressure

the concentration of gasses in a mixture of gasses

what is an erythrocyte

a red blood cell

features of erythrocytes

• biconcave shape- flexible

• Large SA/V ratio for diffusion of gasses

• formed continuously in red bone marrow

• last 120 days

• contain haemoglobin

• no organelles- more space for haemoglobin- can carry more O2

What are the components of haemoglobin

• haem prosthetic group

• 4 poly peptide chains

• 1 oxygen molecule can bind to each haemoglobin molecule

how is oxyhaemoglobin formed

oxygen binds loosely to haemoglobin to form oxyhaemoglobin

this is a reversible reaction

haemoglobin + oxygen = oxyhaemoglobin

what makes haemoglobin efficient at transporting oxygen

• readily associates with oxygen at gas exchange surfaces

• readily dissociates from oxygen at oxygen requiring tissues

• high affinity for oxygen

Why is oxygen associated at gas exchange surfaces

at high partial pressure of O2 haemoglobin has a high affinity for O2

there is a low partial pressure of CO2

= Oxygen associated

How is O2 dissociated at respiring tissues

• at a low O2 partial pressure haemoglobin has a lower affinity for O2

• High CO2 partial pressure from aerobic respiration

  This causes haemoglobin to have a low affinity for oxygen because:

• CO2 lowers pH of blood

• CO2 combines with water to form carbonic acid

• carbonic acid dissociates into hydrogen carbonate ions and hydrogen ions

• hydrogen ions bind to haemoglobin causing the release (dissociation) of O2 (Bohr shift)

how does oxygen associate to haemoglobin molecules

1) there is a low partial pressure of O2, so oxygen doesn’t bind readily to haemoglobin. The binding of the first O2 molecule to the haemoglobin molecule causes a conformational change in the haemoglobin molecule, which makes it easier for other O2 molecules to bind to the haemoglobin molecule

2) there is a higher partial pressure of O2, which makes it easier for O2 molecules to bind (positive cooperatively

3) the haemoglobin molecule continues to become saturated as there is still a high partial pressure of O2

4) it’s harder for the 4th O2 molecule to bind because there is a lower concentration of O2 in the blood to bind at the right speed, energy and orientation to the haemoglobin molecule, due to collision theory

how does haemoglobin differ within different species

• different haemoglobin have different affinities for oxygen

• each species produces haemoglobin with a slightly different amino acid sequence, therefore the haemoglobin has a different tertiary and quaternary structure to other haemoglobin molecules in different species. Because the tertiary structure of the protein is different it will have different structural and functional properties, therefore different oxygen binding properties

describe fetal haemoglobin

• shift to the left of the oxygen dissociation graph- has a higher affinity for O2 than adult haemoglobin

• becomes saturated more easily at the same partial pressures than adult haemoglobin, but dissociates less readily than the normal oxygen dissociation curve

what is the importance of fetal haemoglobin

• the foetus is fully dependent on the mother for oxygen

• maternal oxygenated blood runs close to the foetal deoxygenated blood

• fetal haemoglobin has a higher affinity to oxygen at the same partial pressure than maternal haemoglobin

• this causes oxygen to move from the maternal haemoglobin to the fetal haemoglobin

what would happen to the baby if it didn’t have fetal haemoglobin

little to no oxygen would move from the maternal haemoglobin to the fetal haemoglobin because the haemoglobin in the mother and the foetus would have the same affinity for oxygen

describe the movement of Co2 in the blood and where it goes to

• plasma (5%)

• haemoglobin into carbaminohaemoglobin (10%)

• Co2 dissolves in water and forms carbonic acid which then dissociates into hydrogen carbonate ions an hydrogen ions (85%)

what is the Bohr effect

when the partial pressure of CO2 in the blood is high, which causes haemoglobin’s affinity for O2 to be reduced, which means that O2 is dissociated more readily

reduces haemoglobin affinity for O2 at the same partial pressure

why does the Bohr effect occur

• Occurs because CO2 lowers the pH of the blood;

• CO2 combines with water to form carbonic acid

• carbonic acid dissociates into hydrogen carbonate ions and hydrogen ions

• hydrogen ions the combine with haemoglobin causing the release of O2

why is the Bohr effect useful

it allows O2 to dissociate from haemoglobin at the same partial pressure more readily in respiring tissues that need it for aerobic respiration, such as muscle tissues

what is the Bohr shift

the shift to the right of the oxygen dissociation graph because the partial pressure of CO2 is higher

• this means that at any given partial pressure of O2 the percentage of saturation of haemoglobin is lower at higher CO2 concentrations (because haemoglobin has a lower affinity for O2 due to Bohr effect)

Label the heart

what is the epicardium

thin external membrane of the heart

what is the myocardium

thick cardiac muscle that makes up the bulk of the heart wall

what is the endocardium

flattened cells and connective tissue which lines the whole of the circulatory system

what are the properties of cardiac muscle

• myogenic- it can contract on its own without external stimulation via nerves or hormones. This allows the heart to beat at its own regular intervals

• it doesn’t tire or fatigue- so it allows the heart to beat continuously throughout an individuals life

• the cardiac muscle fibres form a network that spreads through the walls of the atria and ventricles which allows the chambers of the heart to contract

• cardiac muscle fibres are connected to each other via specialised connections called intercalated discs

why do animals meed specialised transport systems

• high metabolic demand

• molecules need to travel large distances

• small SA:V ratio

• waste products need to be removed

what is a double closed circulatory system

blood goes through the heart twice per cycle which allows oxygenated blood from the lungs to go back to the heart and get pumped around the body at high pressure

why do mammals have a double loop rather than a single loop

because mammals are bigger so oxygenate blood needs to travel further. In single loop systems blood is still deoxygenated as it leaves the heart and then gets oxygenated after before going to the body.

label the human circulatory system

how long does it take for one cycle of blood to pass through the heart

0.8 seconds

which is longer, diastole or systole

diastole

what is the difference between diastole and systole

systole is the contraction phase of the heart

diastole is the relaxation phase of the heart

describe the movement of blood on the right side of the heart

• deoxygenated blood from the vena cava enters the right atrium at a low pressure

• as the blood flows into the right atrium, pressure in the right atrium increases which causes the atrioventricular (tricuspid) valve to open and let blood pass into the right ventricle

• when both the right atrium and right ventricle are filled with blood the right atrium contracts, forcing all of the blood into the right ventricle which stretches the ventricle walls

• as the right ventricle contracts the atrioventricular (tricuspid) valve closes to prevent the back flow of blood into the atrium

• the right ventricle contracts which decreases the volume of the right ventricle, which increases the pressure of the blood in the right ventricle

• this forces the pulmonary semilunar valve to open and deoxygenated blood is pumped into the pulmonary artery

describe the movement of blood at the left side of the heart

• oxygenated blood enters the left atrium through the pulmonary vein from the lungs at a low pressure

• as blood flows into the left atrium pressure builds up in the left atrium which causes the atrioventricular (bicuspid) valve to open because pressure is higher in the LA than the LV. This allows blood pass into the left ventricle

• when both the left atrium and left ventricle are filled up with blood the left atrium contracts (atrial systole) all the blood is forced into the left ventricle which stretches the walls of the left ventricle

• as the left ventricle contracts the bicuspid valve closes to prevent the back flow of blood into the left atrium

• the left ventricle fully contracts which decreases the volume of the ventricle chamber which increases the pressure, forcing the aortic semilunar valve to open because the pressure of blood in the left ventricle is higher than the pressure of blood in the aorta.

• This causes oxygenated blood to be pumped through the aortic semilunar valve and into the aorta

when do valves open and close

open when pressure is higher behind the valve

close when pressure is higher in front of the valve

what is the function of a valve

to prevent the back flow of blood

How does CHD develop

• atheroma formation- partial blockage of lumen- reduced blood flow and increased blood pressure

atheroma increases the risk of

• aneurysm- swelling of the artery

• thrombosis- blood clot

These cause interrupted blood flow to the heart which can lead to myocardial infarction (heart attack)

how can an atheroma form

damage occurs to endothelial lining of artery

white blood cells (macrophages) and lipids (from low density lipoproteins)

the higher the blood LDL level is (from diet high in fats) the more lipids are used to repair the damage

the fatty tissue builds up to form a lump (atheroma)- partially block lumen- reduced blood blow and high blood pressure

how can an aneurysm form

aneurysm- a ballon like swelling of the artery

atheroma:

• weakens artery

• reduce blood flow

• higher blood pressure

now when blood passes through the weakned artery it may push the inner layers of the artery through the outer layer and form a ballon like swelling

this can burst and form a haemorrhage (bleeding)

how can thrombosis occur

thrombosis- formation of a blood clot

atheroma can rupture the endothelial (inner lining) of the artery

this has to be repaired by platelets and fibrin which forms a blood clot (a thrombus)

the blood clot can completly block the artery or can become disloged and block a blood vessel somewhere else

how can aneurysms and thrombosis lead to myocardial infarction

coronary arterys supply the heart with oxygenated blood- for respiration

oxygen supply to cardiac muscle can be cut off due to blood clots or bleeding

cardiac muscle recieves less O2- damage or death of cardiac muscle

what are the symptoms of myocardial infarction

• pain in chest

• shortness of breath

• sweating

how does heart failure occur

if O2 supply is cut off to large areas of the heart

what factors can increase the risk of CHD

• high concentration of LDL’s from poor diet

• smoking cigarettes

• high blood pressure

• age

• gender

• being overweight

how does LDL concentration increase the risk of CHD

when damage to the endothelial lining of the coronary arteries occurs white blood cells (macrophages) and lipids from LDL’s are used to repair the damage which clump together and form an atheroma

atheromas can increase blood pressure, reduce blood flow and lead to a blood clot (a thrombus)

this can block blood from flowing to the heart and recieving oxygen which could result in myocardial infarction

how does smoking lead to CHD

carbon monoxide binds to haemoglobin instead of O2

if the heart doesn’t recieve enough oxygen for respiration then it won’t be able to produce the energy required to contract the geart which can lead to myocadrial infarction

how does high blood pressure lead to CHD

blood pressure can cause damage to endothelial lining of the coronary arterys

leads to formation of atheroma

atheroma can rupture the endothelial lining which leads to the formation of a blood clot

cuts off blood and O2 supply to the heart

heart can respire which can lead to myocardial infarction

can also lead to an aneurysm as high blood pressure may push inner layer of artery through the outer layer- forms haemorrhage which is likely to burst- less blood and O2 to heart

define cardiac output

the volume of blood pumped out of one ventricle of the heart per minute

what is the equation for cardiac output

HR (bpm) x SV (ml/beat)

explain how cardiac output can increase

• initially with exercise both HR and SV will increase

• at 40-60% of maximal exercise SV plateaus

• any further increases in Co are due to an increase in Hr which doesn’t plateau as quickly as SV

How do you work out a persons maximum HR

220-age

how does a person gain a lower resting HR

through aerobic training, as a result of cardiac hypertrophy

why do athletes have a lower resting HR

their heart is stronger due to cardiac hypertrophy, cardiac muscle is stronger so can contract with more force which leads to a higher SV. So their heart doesn’t need to beat as many times per minute to get the same amount of blood to the body and maintain resting cardiac output

what is bradycardia

having a resting HR below 60 bpm

indicates being a trained athlete

describe the structural features of arteries

• thick muscle layer to contract and dilate (vasoconstriction and vasodilation) to control blood flow

• thick elastic layer to maintain high pressure and pressure changes. Stretches and recoils which smooths out blood flow

• thick walls to resist high blood pressure

• no valves

• small lumen

• smooth and flat endothelial lining to reduce friction which aids blood flow

• collagen provides structural support to maintain the shape and volume of the artery

describe the difference in structural features of arterioles compared to arteries

• thicker muscle layer because arterioles play more of a role in vasoconstriction and vasodilation than arteries do

• thinner elastic layer because arterioles don’t have to resit as high pressure as arteries do (aorta) because arteries branch off into arterioles

describe the structural features of veins

• thin muscle layer as blood is carried away from tissues (no need for vasoconstriction or vasodilation)

• thin elastic layer because blood is at a low pressure

• lack of thickness because there is a low risk of veins bursting because blood is at a low pressure. Also allows for veins to be compressed when body muscles contract to help get blood back to the heart against gravity

• pocket valves to prevent the back flow of blood

how do veins get blood back to the heart at low pressure and against gravity

• pocket valves close to prevent the back flow of blood

• bigger veins run through muscles, muscles can contract which sequeezes the vein, increasing pressure of blood in the vein and forcing blood back to the heart

• breathing pressure changes- helps move blood back to the heart

describe the structural features of capillaries

• walls are made up of a 1 cell thick layer of endothelial lining, shortens diffusion distance, increases the rate of diffusion

• lot of them and are branched which increases the SA for diffusion to occur

• narrow diameter which decreases diffusion distance

• narrow lumen so that red blood cells have to squeeze through the capillary and move slower which allows for more efficient oxidation of RBC’s and also shortens the diffusion distance, which increases the rate of diffusion

• Spaces between the endothelial cells allow WBC’s to move into tissues and fight infections

what are the components of blood plasma

• glucose

• amino acids

• mineral ions

• hormones

• large plasma proteins

what is tissue fluid

• the fluid that surrounds cells in tissues

• tissue fluid has the same composition as plasma but without the plasma proteins because they are too big to pass through the capillaries

why do we need tissue fluid

not every cell lies next to a capillary

how is tissue fluid formed and re uptaken back into the capillaries

Hydrostatic pressure at arterial end of capillary- forms

osmotic pressure at venous end of capillary- draws tissue fluid back in

how does hydrostatic pressure form tissue fluid

at the arterial end of the capillary

there is a higher hydrostatic pressure in the capillary than in the tissue fluid

this forces fluid out of the arterial end of the capillary into the spaces around the cells forming tissue fluid

how does osmotic pressure take back in water from tissue fluid

at the venous end

hydrostatic pressure ejected fluid from the capillary- decreased water potential

because of fluid loss and an increase in the concentration of plasma proteins in the venous end of the capillary

Water potential is lower in the capillary than in the tissue fluid- some water is drawn back into the capillary via osmosis

what happens to the tissue fluid than isn’t taken back into the capillary

excess tissue fluid is drained into the lymphatic system

what is the lymphatic system

a secondary circulatory system and a major part of the immune system

what is the lymphatic system made up of

• lymphatic capillaries

• lymph nodes

• lymphatic organs

what are lymphatic capillaries

vein like lymph vessels that contain valves

what are lymph nodes

sac like organs that trap pathogens and foreign substances and contain large amounts of white blood cells

what are lymphatic organs

the spleen, thymus and tonsils which all contain large amounts of WBC’s

What is lymph

a pale yellow fluid that is similar to tissue fluid but contains more lipids

how does lymph form

Not all tissue fluid returns to the capillaries. 90% does but the excess 10% is drained into the lymphatic system where it forms lymph

where does the lymphatic system drain into

into the circulatory system near the vena cava via the thoracic duct

why do we need the lymphatic system

you would die within 24h without the lymphatic system as the rate of water loss would be too large (need to get all water back into the circulatory system)

this would lead to a build up of tissue fluid in the tissues called oedema

how do the contents of the lymphatic system transported

• hydrostatic pressure of the tissue fluid that has left the capillaries

• contraction of muscles that squeeze lymph vessels to ensure the fluid inside them moves away from tissues in the direction of the heart

what are the characteristics and functions of the xylem

• transport water and mineral ions up the plant

• cells are joined without a cell wall end which forms a hollow tube

• contains lignin to provide extra support, forms in spirals to ensure the xylem vessels don’t collapse under the transpiration pull

why do plants need water

• water is a raw material for photosynthesis

• mineral ions and the products of photosynthesis are transported in aqueous solutions

• the loss of water via evaporation helps to keep the plant cool

• turgor pressure (hydrostatic pressure) as a result of osmosis helps to form a hydrostatic skeleton to support the stem and leaves

what are the adaptations of root hair cells

• large SA:V ratio

• short diffusion pathway into cell

• lower water potential inside the cell to maintain concentration gradient (so rate of osmosis is maintained)- water can move into the root hair cell from soil via osmosis

• small size so can penetrate through soil particles easily- access water and mineral ions

• lots of mitochondria to provide energy for active transport of mineral ions (higher conc of mineral ions inside root hair cell than in soil)

• no chloroplast because they are underground (no sunlight)

what is root pressure and how is it created

the solute concentration in the cytoplasm of the endodermal cells is lower than in the xylem cells because minerals are actively transported into root hair cells

the endodermal cells move mineral ions into the xylem via active transport. This increases the pressure in the xylem and further lowers the water potential of the xylem. This increases the rate of water movement into the xylem from the endodermal cells via osmosis. This is known as root pressure

how is the rate of transpiration controlled

by stomata

this is a turgor driven process

• when there is sunlight potassium ions are actively transported into the guard cells. This lowers the water potential of the guard cells which causes water to passively move into the guard cells which makes the guard cells more turgid, which opens the pore- increases the rate of transpiration and allows for gas exchange during photosynthesis

  • when it’s dark photosynthesis can’t occur so the stomata must close to prevent water loss. Potassium ions are actively transported out of the guard cells which increases the water potential. This causes water to passively move out of the guard cell which makes the guard cell become flaccid. This closes the pore and reduces the rate of transpiration

describe the process of transpiration

• water molecules evaporate from the mesophyll cells into the air spaces in the leaf- leads to an increase in water vapour potential

• water molecules then move out of the leaf through the stomata via diffusion down the water vapour potential gradient

• this lowers the water potential of the cell so water moves in through osmosis by the apoplast and symplast pathways

• this carries on up through the xylem then through the leaf

what is the transpirational pull and the cohesion tension theory

water forms hydrogen bonds with other water molecules- cohesion (forms a continuous column of water)

water molecules form hydrogen bonds with carbohydrates in the walls of the xylem- adhesion

cohesion + adhesion = capillary action

water is constantly drawn up the xylem to replace the water lost via transpiration/evaporation

the transpirational pull puts the xylem under tension- creates negative pressure in the xylem (cohesion tension theory)

what research is there to support capillary action

during sunlight when trees are photosynthesising their diameter decreases

water is being used for photosynthesis, being lost via stomata during evaporation/transpiration

the water concentration gradient and capillary action cause negative pressure in the xylem and the trees diameter to reduce

what different factors affect the rate of transpiration

• light intensity

• temperature

• humidity

• wind speed

how does light intensity affect the rate of transpiration

the rate of transpiration increases in the light because stomata open- more water is lost

how does temperature affect the rate of transpiration

when temperature is higher the rate at which water is evaporated is faster

how does humidity increase the rate of transpiration

Humidity: When the air around the plant is humid, this reduces the diffusion gradient between the air spaces in the leaf and the external air. The rate of transpiration therefore decreases in humid air and speeds up in dry air

how does wind speed affect the rate of transpiration

the moving air removes any water vapour that is in the air nearby the stomata. This increases the concentration gradient between the air spaces in the leaf and the external environment- increases the rate of diffusion of water vapour out of the stomata.

what is translocation

the transport of the products of photosynthesis (assimilates) from parts of the plant where assimilates are produced/stored (sources) to where they are needed (sinks)

what are the different sources

leaves and stem

food stores in seeds upon germination

storage organs

what are the different sinks in plants

meristem (plant stem cells)

roots that are absorbing ions or growing

what is a source

parts of the plant which produces or possesses more carbohydrates than it requires

what is a sink

part of a plant where carbohydrates are required for growth, active transport, or storage

what are assimilates

glucose is converted into sucrose which is then transported

When sucrose arrives at sink:

• converted into glucose for respiration

• converted into starch for storage

• connected into amino acids for growth

why is glucose converted into sucrose before it’s transported

sucrose is less soluble in water than glucose

so sucrose is less likely to be metabolised when being transported

what is the phloem tissue made up of

sieve tube elements:

• living cells that form the tube which transports assimilates

• have sieve plates between them

• they have no organelles or nucleus- need companion cells (less resistance for mass flow)

Companion cells:

• provide the energy needed for the active transport of assimilates

describe the mass flow theory

• Sucrose produced from glucose in leaves by photosynthesis (source)

• Sucrose moves by facilitated diffusion into companion cell

• Companion cell actively transports sucrose into the phloem (sieve tube element)

• This lowers the water potential in the phloem which draws water into the phloem from the xylem by osmosis

• This increases the volume of fluid in the phloem which increases the pressure.

• Higher pressure in the phloem near the source is greater than lower pressure near the sink (the root cells)

• This different in pressure forces the sap down the phloem by mass transport/ bulk transport

• Sucrose moves out of the phloem into the companion cells then into the root cells (sink) by facilitated diffusion

• This increases the water potential in the lower part of the phloem

• Water moves back into the xylem by osmosis lowering the volume and hence pressure in the lower part of the phloem.

provide evidence for translocation

sap is released when the phloem is cut suggesting that there is high pressure in the phloem

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

metabolic toxins (that stop the production of ATP), and lack of O2 inhibit the movement of sucrose through the phloem

companion cells have high concentrations of mitochondria for ATP production

give some evidence against the mass flow theory

sieve plate function is unclear (may have a structural role), but their design would seem to hinder mass flow in the phloem

not all solutes in the phloem move at the same rate (would mean it’s not mass flow)

describe ringing experiements

the phloem lies just underneath the bark

in a ringing experiment the phloem is removed

this causes the region above the removed section to swell up, and parts of the plant blow this will die

suggests that the phloem transports sugars (sucrose)

describe tracer experiements

uses radioactive CO2 from radioactive C14

C14 is then incorporated into sugars produced from photosynthesis

the sugars movement around the plant can be tracked by autoradiography (thin sections of tissue are placed on x-ray film and C14 appears black