Mass Transport

Front 1

What is the structure of haemoglobin?

Back 1

It is made up of four polypeptide chains (two pairs), linked together to form an almost spherical molecule. Each polypeptide is associated with a haem group containing a ferrous ion (Fe2+), each of which can combine with an oxygen molecule

Front 2

How many oxygen molecules can each haemoglobin combine with?

Back 2

Four, one for each polypeptide chain (and therefore Fe2+ ion)

Front 3

If haemoglobin has a low affinity for oxygen what does that mean?

Back 3

It takes up oxygen less readily but releases it more easily

Front 4

What is the role of haemoglobin?

Back 4

To transport oxygen

Front 5

Why does haemoglobin change its affinity for oxygen in certain conditions?

Back 5

Its shape changes in the presence of certain substances, such as carbon dioxide- in the presence of carbon dioxide, the new shape of the haemoglobin molecule binds more loosely to oxygen, so the haemoglobin releases its oxygen

Front 6

Why do different species' haemoglobins have different affinities for oxygen?

Back 6

Each species produces a haemoglobin with a slightly different amino acid sequence, meaning each species' haemoglobin therefore has a slightpy different tertiary and quaternary structure and so different oxygen binding properties

Front 7

Why is it hard for the first oxygen molecule to bind with haemoglobin?

Back 7

The four polypeptide subunits are closely united before the first oxygen is loaded so it is difficult for the first oxygen molecule to bind

Front 8

Why do the second and third oxygens bind more readily to the haemoglobin?

Back 8

The binding of the first oxygen molecule changes the quaternary structure of the haemoglobin, making it to change shape in such a way that makes it easier for the other subunits to bind to an oxygen molecule

Front 9

What is positive cooperativity in haemoglobin loading?

Back 9

It takes a smaller increase in the partial pressure of oxygen to bind the second oxygen molecule than it did to bind the first one- this is known as positive cooperativity because binding of the first molecule makes the second easier and so on

Front 10

Why is it harder for the fourth oxygen molecule to bind with haemoglobin?

Back 10

In theory it is easier, however in practise it is harder due to probability- with the majority of binding sites occupied it is less likepy that a single oxygen molecule will find an empty site to bind to

Front 11

If an oxygen dissociation curve is shifted to the left, how has the affinity for oxygen been changed?

Back 11

The further to the left the curve, the greater the affinity of haemoglobin for oxygen.

Front 12

It the affinity for oxygen of haemonglobin is lowered, which way will the oxygen dissociation curve be shifted?

Back 12

To the right

Front 13

Why is haemoglobin's affinity for oxygen reduced in respiring tissues?

Back 13

In tissues, carbon dioxide is produced by the respuring cells which lowers the pH (as CO2 is slightpy acidic in solution). The lower pH changes the shape of haemoglobin into one with a lower affinity for oxygen. In addition, there is a low oxygen conc in the muscles, which also contributes to oxygen being readily unloaded from haemoglobin

Front 14

How is the oxygen affinity of haemonglobin affected at the lungs?

Back 14

There is a low CO2 concentration as it diffuses across the exchange surface and is excreted, which means that the pH is slightly raised and haemonglobin changes it shape to have an increased oxygen affinity

Front 15

How many oxygen molecules will normaply be released at a tissue with a low respuratory rate?

Back 15

Normally only one - therefore the haemonglobin in the blood returning to the lungs will be 75% saturated with oxygen

Front 16

How many oxygen molecules eould typically be released at a tissue with a high respiratory rate such as an exersising muscle?

Back 16

3 oxygen molecuoes would normally be unloaded from each haemonglobin

Front 17

If a species lives at a high altitude, which way will its oxygen dissociation curve be shifted?

Back 17

To the left, as due to the scarcity of oxygen at high altitudes their haemonglobin will have an increased affinity for oxygen to ensure that the haemoglobin is fully loaded with oxygen

Front 18

Why do mammals have a double circulatory system?

Back 18

The blood has to pass through tiny capillaries in the lungs in order to present a large SA for gas exchange, which causes a large pressure drop. If there was only a single circulatory system this would mean that the blood was pumped very slowly around the rest of the body- not fast enough to sustain the high metabolic rate needed to maintain body temerature in mammals

Front 19

What is the difference between the left and right ventricles?

Back 19

The right ventricle only pumps blood to the lungs so has a thinner muscular wall than the left ventricle, which needs to contract to create enough pressure to pump blood around the rest of the body

Front 20

What is the name of the vavle inbetween the left ventricle and atrium?

Back 20

Bicuspid valve (left atrioventricular valve)

Front 21

How is backflow of blood into the atrium prevented when the right ventricle contracts?

Back 21

The right atrioventricular valve, also known as the tricuspid valve, prevents backflow of blood

Front 22

Which part of the heart is the aorta connected to and what sort of blood does it pump?

Back 22

It is connected to the left ventricle and pumps oxygenated blood to the body (except lungs)

Front 23

Which blood vessel is connected to the right atrium and what type of blood does it carry?

Back 23

The vena cava is connected to the right atrium, it carries deoxygenated blood back from the body tissues (except lungs)

Front 24

Which part of the heart is the pulmoary artery connected to and what sort of blood does it carry?

Back 24

It is connected to the right ventricle and carries deoxygenated blood to the lungs, where the oxygenated blood is replenished and CO2 is removed

Front 25

Which blood vessel is connected to the left atrium and what blood does it carry?

Back 25

The pulmonary vein is connected to the left atrium, it brings oxygenated blood back from the lungs

Front 26

Why are the pulmonary vein and artery unusual?

Back 26

The pulmonary artery carries deoxygenated blood despite it being an artery, and the pulmonary vein carries oxygenated blood which is unusual for a vein

Front 27

How does the heart muscle get a blood supply?

Back 27

It is supplied with a network of blood vessels called the coronary arteries which branch off the aorta shortly after it leaves the heart

Front 28

What happens when the coronary arteries become blocked?

Back 28

A blockage, e.g caused by a blood clot, causes a myocardial infarction (heart attack) as an area of heart muscle is deprived of blood and therefore oxygen. The muscle cells in this region are unable to resire (aerobically) and so die

Front 29

What are four common features of the transport systems of many organisms?

Back 29

•A suitable medium to carry materials- most often a water-based liquid as water readily dissolves substances and can be moved around easily

•A form of mass transport in which the transport medium is moved around in bulk over long distances

•A system of tubular vessels that contain the transport medium and form a branching network to distribute it to all parts of the organism

•A mechanism for moving the transport medium within vessels-requires a pressure difference between one part of the system and another

Front 30

What happens in diastole?

Back 30

•Blood returns to the atria from the lungs and body. When the pressure in the atria exceeds that in the ventricles the atrioventricular valves open and the blood passes into the ventricles

•The ventricle walls are relaxed and the walls of the blood vessles recoil, causing the pressure in the ventricles to be lower that in the aorta and pulmonary artery, so the semilunar valves close

Front 31

What happens in atrial systole?

Back 31

The atrial walls contract, and the relaxed ventricle walls recoil, forcing the remaining blood into the ventricles from the atria. Throughout this stage the ventricle walls stay relaxed.

Front 32

Why are valves necessary?

Back 32

Sometimes in the circulatory system the pressure would make blood go in the opposite direction to that which is desirable, so valves prevent any umwamted backflow of blood

Front 33

What do the semi-lunar valves do?

Back 33

They are in the aorta and pulmonary artery and prevent backflow of blood into the ventricles when the recoil of the artery walls causes the pressure in the vessels to rise and the ventricle relaxation causes the pressure in them to fall

Front 34

What are the pocket valves?

Back 34

They occur in veins throught the circulatory system. They ensure that when veins are squeezed such as during muscles contraction, blood flows in the right direction

Front 35

What shape are valves?

Back 35

They are a number of flaps of tough but flexible fibrous tissue which are cusp shaped (like deep bowls). When pressure is greater on the convex side they move apart and let the blood pass, when pressure is great on the concave side blood collects within the bowl of the cusps, pushing them together and preventing blood flow.

Front 36

How do you measure cardiac output?

Back 36

Heart rate x Stroke volume. It is measured in dm3/min

Front 37

What are the 5 layers of blood vessels?

Back 37

•Tough fibrous outer layer- resists pressure changes from inside and outside

•Muscle layer-can contract and help control the flow of blood

•Elastic layer- helps maintain blood pressure by stretching then springing back (recoiling)

•Thin imner lining (endothelium)- smooth to reduce friction and thin to allow diffusion

•Lumen-the cavity in the middle where the blood flows

Front 38

Why do arteries have a thick elastic layer?

Back 38

The blood pressure must he kept high in arteries so the blood reaches the extremeties of the body. The elastic wall is stretched at each hearbeat then recoils when the heart relaxes, helping to maintain high pressure

Front 39

Why do arteries have a thick wall overall?

Back 39

To resist the artery bursting under pressure

Front 40

Why do arterioles have a thicker muscle wall than arteries?

Back 40

The contraction of the muscle layer allows constriction of the lumen of the arteriole, resticting the flow of blood so helping the arteriole control the movement of blood into the capillaries

Front 41

Why do veins have a thin muscle layer?

Back 41

Veins carry blood away from tissues so so their constriction and dilation can't control the flow of blood to the tissues

Front 42

Why do veins not need a thick wall?

Back 42

The pressure in the veins is too low to create a risk of bursting, and it allows the veins to be flattened easily, aiding the flow of blood within them

Front 43

What is the function of arteries?

Back 43

To transport blood rapidly under high pressure from the heart to the tissues

Front 44

What is the function of capillaries?

Back 44

To exchange metabolic materials such as oxygen, CO2 and glucose between the blood and the cells.

Front 45

Structure+function for capillaries? (5)

Back 45

•Numerous and highly branched to give max SA for exchange

•Narrow diameter so permeate tissues, ensuring no cell is far from a capillary (short diffusion pathway)

•Walls mostly consist of endothelium lining, which makes them extremely thin so theres is a short diffusion pathway

•Narrow lumen means red blood cells are squeezed flat against the capillary, bringing them even closer to the cells

•Spaces between the endothelial cells mean that white blood cells can escape to deal with infections in the tissues

Front 46

What is tissue fluid?

Back 46

A watery liquid containing glucose, amino acids, fatty acids, ions in solution, and oxygen. It is formed from blood plasma

Front 47

Why is tissue fluid formed?

Back 47

There is a hydrostatic pressure created by the beating of the heart at the arterial end of the capillaries which causes tissue fluid to move out of the blood plasma

Front 48

What are the two forces which oppose the outward hydrostatoc pressue at the arterial aend of the capillaries?

Back 48

•Hydrostatic pressure of the tissue fluid outside the capillaries

•The lower water potential of the blood die to the plasma proteins, which causes water to move back into the blood within the capillaries

Front 49

Why does tissue fluid not contain blood cells or proteins?

Back 49

Cells and proteins are left in the blood because they are too large to cross the membranes. This type of filtration under pressure is called ultrafiltration

Front 50

In which two ways does the tissue fluid return to the blood?

Back 50

Through reabsorbtion into the capillaries, and through being carried back via the lymphatic system

Front 51

Why is tissue fluid reabsorbed into the blood?

Back 51

By the time the blood has reached the venous end of the capillaries, its hydrostatic pressure is usually lower than that of the tissue fluid outside it. This means that the pressure forces tissue fluid back into the capillaries. This is helped by the fact that it is down a water potential gradient- the blood plasma has lost water but still contains proteins so has a lower water potential than the tissue fluid.

Front 52

What is the lymphatic system?

Back 52

A system of vessels that begin in the tissues that initially resemble capillaries (except dead-ended) but gradually merge into larger vessels forming a network throughtout the body, that drain their contents back into the bloodstream via two ducts that join veins close to the heart

Front 53

How are the contents of the lymphatic system (lymph) moved?

Back 53

•By hydrostatic pressure of the tissue fluid which has left the capillaries

•By contraction of body muscles that squeeze the lymph vessels- they contain valves which ensure that the fluid moves in the direction of the heart

Front 54

Why does water move out through the stomata?

Back 54

The humidity of the atmosphere is usually less than that of the air spaces next to the stomata, which means that water vapour molecules diffuse out of the air spaces into the surrounding air down a water potential gradient

Front 55

How is water lost from mesophyll cells to evaporation into the leafs air spaces replaced?

Back 55

Water reaches them from the xylem, either via cell walls or via the cytoplasm (the cells losing water lowers their water potential so water diffuses into them from the surrounding cells, lowering their water potential in turn, establishing a water potential gradient that pulls water from the xylem, across the mesophyll and out into the atmosphere)

Front 56

Why does water move up the xylem?

Back 56

Due to the cohesion of water (water molecules tend to stick together), as water evaporates from the mesophyll cells more molecules are drawn up behind it. A column of water is therefore drawn up the xylem- this is called the transpiration pull

Front 57

Why is the way water is pulled up the xylem called the cohesion tension theory?

Back 57

Transpiration puts the xylem under tension- i.e there is a negative pressure in the xylem, and the water is pulled up due to cohesion

Front 58

Give three pieces of evidence for the cohesion-tension theory

Back 58

•During the day, transpiration is at its highest, which makes the diameter of tree trunks smaller as the tension in the xylem is greater

•If a xylem vessel is broken and air enters the tree can no longer draw up water, as the continuous water column is broken

•If a xylem were under pressure, when it is broken, water would leak out. Instead, air is drawn in, showing that they are under tension

Front 59

How is sucrose transferred from sources into the sieve tubes?

Back 59

The sucrose moves out of photosynthesising cells into companion cells by faciliated diffusion. Hydrogen ions are actively transported from companion cells into the spaces within cell walls, where they diffuse into the sieve tubes through carrier proteins, carrying the sucrose with them (co-transport)

Front 60

Why do the sieve tubes have a high hydrostatic pressure at the source end?

Back 60

The sucrose produced by the sources is actively transported into the sieve tubes, causing them to have a lower water potential. This means water moves into them from the xylem by osmosis, creating a high hydrostatic pressure

Front 61

Why do the sink ends of the sieve tubes have a low hydrostatic pressure?

Back 61

Sucrose is used up in respiration/converted to starch at the sinks, causing the sink cells to have a low sucrose content so sucrose is actively transported in fron the sieve tubes. This lowers the sink cells' water potential so water also moves into them, lowering the hydrostatic pressure in the sieve tubes

Front 62

How does sucrose move from source to sinks?

Back 62

There is a high hydrostatic pressure at the sources and a low one at the sinks, causing a mass flow of sucrose solution down this hydrostatic gradient

Front 63

How do ringing experiments show that transport of sugars occurs in the phloem?

Back 63

If a ring of bark and phloem is removed around a plant, sugars accumulate above the ring, causing the tissue to swell, and non-photosynthetic tissue below the ring dies as the flow of sugars to it has been interrupted. This suggests that it is phloem rather than xylem that is responsible for sugar transport

Front 64

How would you use a radioactive tracer to show that the phloem is responsible for transport of sugars?

Back 64

Grow the plant in an atmosphere containing 14CO2 (with radioactivelly labelled carbon), it will incorporate the radioactive carbon into its sigars. If you take a thin cross section of the stem and place them on X-ray film, the film becomes blackened where the phloem are, indicating that these are where the sugar is carried