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AQA A Level Biology > 3-7 Mass Transport > Flashcards

3-7 Mass Transport Flashcards

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1
Q

What is the structure of haemoglobin?

A

Quaternary protein structure
Each polypeptide is associated with a haem group- contains a ferrous Fe2+ ion

Each ferrous ion can bond with one O2 molecule

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2
Q

What is the role of haemoglobin?

A

to transport oxygen, readily associate where gas exchange takes place, readily dissociate at required tissues

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3
Q

What are oxygen dissociation curves?

A

The oxygen dissociation curve is a graph with oxygen partial pressure along the horizontal axis and oxygen saturation on the vertical axis, which shows an S-shaped relationship. Oxygen and carbon dioxide are transported in the blood as a result of changes in blood partial pressures

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4
Q

What is an open circulatory system?

A

Open circulatory systems are systems where blood, rather than being sealed tight in arteries and veins, suffuses the body and may be directly open to the environment at places such as the digestive tract.

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5
Q

What is a single closed circulatory system?

A

single circulation systems consist of blood, blood vessels and a heart. The fluid contained within the network of vessels must be moved around the system in the correct direction by heartbeats

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6
Q

What is a double closed circulatory system?

A

The human circulatory system is a double circulatory system. It has two separate circuits and blood passes through the heart twice: the pulmonary circuit is between the heart and lungs. the systemic circuit is between the heart and the other organs.

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7
Q

What do the heart valves do?

A

prevent backflow

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8
Q

What is the aorta?

A

connected to the left ventricle, carries oxygenated blood to the body

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9
Q

What is the vena cava?

A

connected to the right atrium, brings back deoxygenated blood from the body

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10
Q

What is the pulmonary artery?

A

connected to the right ventricle, carries deoxygenated blood to the lungs

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11
Q

What is the pulmonary vein?

A

connected to the left ventricle, brings back oxygenated blood from the lungs

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12
Q

What is an artery?

A

carry blood from the heart to arterioles, thick muscle, thick elastic, no valves

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13
Q

What are arterioles?

A

smaller arteries that control blood flow to capillaries, thicker muscle than arteries, less elastic

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14
Q

What are capillaries?

A

tiny vessels linking arterioles to veins, very narrow, mostly lining layer

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15
Q

What are veins?

A

carry blood back to the heart, thin muscle, thin elastic

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16
Q

How is tissue fluid formed?

A

pumping blood creates hydrostatic pressure, causing tissue fluid to be released from blood plasma, only the smallest molecules can flow out

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17
Q

How is tissue fluid returned to the system?

A

the loss of tissue fluid reduces hydrostatic pressure, therefore the hydrostatic pressure outside the capillary is higher and so the fluid goes back in

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18
Q

How does water move across the cells of a leaf>

A

lose water due to evaporation from the sun, this is replaced as water comes up the leaf by cohesion, this is the transpiration pull and puts negative pressure on the xylem, which is the cohesion-tension theory

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19
Q

How is the xylem specialised?

A

dead hollow cells with no organelles

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20
Q

What is the apoplast pathway?

A

The apoplast is the space outside the plasma membrane within which material can disperse freely.

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21
Q

What is the symplast pathway?

A

The symplast is the inner side of the plasma membrane in which the water and low-molecular-weight solutes can freely diffuse.

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22
Q

What is translocation?

A

Translocation is the movement of sugar produced in photosynthesis to all other parts of the plant for respiration and the other processes described above. This occurs in phloem cells.

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23
Q

What is the mass flow hypothesis?

A

Mass flow hypothesis is the theory that translocation of sugars in the phloem is brought about by a continuous flow of water and dissolved sugars between sources and sinks.

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24
Q

What were the mass flow experiments?

A

ringing experiments - take bark, bulbs at at bottom

tracer experiments - radioactive substance traced through plant

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25
Q

Why are there different haemoglobins?

A

Different affinities of oxygen allow for different uses across the different needs of species which survive in different environmental conditions

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26
Q

What is the explanation of the oxygen dissociation curve?

A
  1. shape makes first oxygen molecule hard to bind, at low oxygen concentrations the gradient is shallow
  2. first binding oxygen changes the molecule shape, this makes it easier for three extra oxygen molecules
  3. positive cooperativity where it takes a smaller increase in partial pressure for the 2nd oxygen to bind, gradient of the curve steepens
  4. after 3rd binding, binding site is harder to find because of probability, gradient reduces, graph flattens off
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27
Q

How can different oxygen association curves be interpreted?

A

The further left it is, the greater the affinity for oxygen so it loads readily but unloading isn’t as easy
And vice versa

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28
Q

What is partial pressure?

A

The pressure that the amount of gas contributes to the total pressure of the gas mixture
Measured in kiloPascals

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29
Q

How is haemoglobin affected at the gas exchange surface?

A

Concentration of CO2 is low because it diffuses across
Oxygen affinity is increased

High concentration of oxygen in lungs
Oxygen is readily loaded by haemoglobin
Reduced CO2 concentration shifts the oxygen dissociation curve to the left

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30
Q

How is haemoglobin affected at rapidly respiring tissues?

A

CO2 concentration is high
Affinity for oxygen is reduced

Oxygen is readily unloaded from the haemoglobin into muscle cells
Oxygen dissociation curve is shifted to the right

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31
Q

Why does an increased CO2 concentration cause the release of oxygen?

A

Dissolved CO2 is acidic and low pH cause haemoglobin to change shape

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32
Q

What is the process for loading, transport and unloading of oxygen by haemoglobin?

A

At gas-exchange surface, CO2 is constantly being removed
pH is slightly raised due to low concentration of CO2

Higher pH changes haemoglobin shape, it loads oxygen readily
Shape also increases affinity so it isn’t released while being transported to tissues
In tissues CO2 is being produced by respiring cells
CO2 is acidic so the pH of the blood in the tissues is lowered
Lower pH changes the shape of haemoglobin into one with a lower affinity for oxygen
Haemoglobin releases its oxygen into respiring tissues

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33
Q

What is the relationship between the activeness of tissue and the loading, transport and unloading of oxygen by haemoglobin?

A

The more active a cell is, the more oxygen is unloaded

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34
Q

What is the mammalian system of transport?

A

A mass transport system due to the large distances

Specialist exchange surfaces to absorb nutrients and respiratory gases and remove excretory muscles

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35
Q

What are the common features of the mammalian transport system?

A

Suitable medium in which to carry materials
A form of mass transport in which the transport medium is moved around in bulk over large distances

A closed system of tubular vessels that distributes the transport medium
A mechanism for moving the transport medium within vessels

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36
Q

How do mammals move the transport medium within vessels?

A

Muscular contraction, either of body muscles or a specialised pumping organ

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37
Q

What is the atrium?

A

Thin-walled, elastic, stretches, collects blood

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38
Q

What does the right ventricle do?

A

It pumps blood to the lungs

Has a thinner muscular wall than the left

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39
Q

What lies between the atrium and the ventricle?

A

Valves that prevent backflow to blood into the atria when ventricles contract
Left is the left atrioventricular (bicuspid) valve

Right is the right atrioventricular (tricuspid) valve

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40
Q

What does the aorta do?

A

It carries oxygenated blood to all parts of the body except the lungs
It is connected to the left ventricle

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41
Q

What does the pulmonary artery do?

A

It carries deoxygenated blood to the lungs where oxygen is added and carbon dioxide is removed
It is connected to the right ventricle

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42
Q

What does the pulmonary vein do?

A

It brings oxygenated blood back from the lungs

It is connected to the left atrium

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43
Q

What are the two phases of the cardiac cycle?

A

Contraction (systole) and relaxation (diastole)

44
Q

What are the steps of relaxation of the heart?

A

Diastole
Atria and ventricles are relaxed

Atria fill with blood
Semi lunar valves closed
Left and right atrioventricular valves closed
Blood enters ventricles from atria

45
Q

What are the steps of the atrial systole?

A

Atria contract to push remaining blood into the ventricles
Semi lunar valves are closed

Left and right atrioventricular valves are open
Ventricles remain relaxed

46
Q

What are the steps of the ventricular systoles?

A

Blood pumped into arteries and aorta
Semi lunar valves open

Atrioventricular valves closed
Ventricles contract and walls thicken
Atria relax

47
Q

What is the function of atrioventricular valves?

A

They prevent back flow of blood when contraction of the ventricles means that ventricular pressure exceeds atrial pressure
Closure means that blood moves to the aorta and not back into the atria

48
Q

What is myocardial infarction?

A

Blockage of coronary arteries
Because an area of the heart muscle is deprived of blood and oxygen, the muscle cells are unable to respire aerobically and die

49
Q

How does the muscle layer of arteries relate to it’s function?

A

Muscle layer is thick compared to veins

Smaller arteries can be dilated and constricted to control the volume of blood

50
Q

How does the elastic layer of arteries relate to it’s function?

A

Elastic layer is relatively thick compared to veins
As it is important for blood pressure to be high to reach extremities

Elastic wall is stretched at systole and springs back at diastole
Stretching and recoiling helps to maintain high pressure and smooth pressure surges created by the heart

51
Q

How does the overall thickness of the walls of arteries relate to their function?

A

This resists the vessel bursting under pressure

52
Q

How does the lack of valves of arteries relate to their function?

A

Because blood is under constant high pressure due to the heart pumping, blood tends not to flow backwards
Valves are only found in arteries leaving the heart

53
Q

What is the structure of arterioles in relation to other blood vessels?

A

Muscle layer is relatively thicker than in arteries

Elastic layer is relatively thinner than in arteries

54
Q

How does the muscular layer in arterioles relate to their function?

A

Muscle layer is thicker than in arteries
The contraction of the muscle layer allows construction of the lumen which restricts blood flow and so control movement into the capillaries which supply tissues with blood

55
Q

How does the elastic layer in arterioles relate to their function?

A

Thinner than in arteries because the blood pressure is lower

56
Q

What is the structure of veins in relation to other blood vessels?

A

Muscle layer is thin compared to arteries
Elastic layer is thin compared to arteries

Overall thickness of the wall is small
Has valves at intervals throughout

57
Q

How does the muscular layer in veins relate to their function?

A

Thin compared to arteries

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

58
Q

How does the elastic layer in veins relate to their function?

A

Thin compared to arteries

Low pressure of blood will not cause them to burst and is too low to create a recoil action

59
Q

How does the overall wall thickness in veins relate to their function?

A

Small overall thickness
Pressure in the veins is too low to create a bursting risk

Allows them to be flattened easily so aids the flow of blood within them

60
Q

How do the valves in veins relate to their function?

A

Valves occur at intervals throughout
This ensures that blood does not flow backwards

Blood pressure is so low that without valves, blood might flow backwards

61
Q

How do valves work?

A

Blood can flow easily through one side of a valve
If blood flows form the opposite direction, the valves are pushed closed and blood is prevented from flowing any further in this direction

62
Q

What is the structure of capillaries in relation of other blood vessels?

A

Walls mostly consist of the lining layer
Numerous and highly branched

Narrow diameter
Lumen is narrow
Spaces between the lining (endothelial cells)

63
Q

How does the lining layer in capillaries relate to their function?

A

Mostly made of the lining layer
Makes them extremely thin to reduce diffusion distance

This allows for rapid diffusion between the blood and the cells

64
Q

How does the capillaries being numerous and highly branched relate to their function?

A

Provide a large surface area for exchange

65
Q

How does the capillaries having a narrow diameter relate to their function?

A

Can permeate tissues

No cell is far from a capillary so there is a short diffusion pathway

66
Q

How does the capillaries having a narrow lumen relate to their function?

A

Red blood cells are squeezed flat against the side of the capillary
Brings them even closer to the cells to which they supply oxygen

Reduces diffusion distance

67
Q

How does the capillaries having spaces between the lining cells relate to their function?

A

Allows white blood cells to escape in order to deal with infections within tissues

68
Q

Why is tissue fluid needed?

A

Capillaries cannot serve every single cell directly

The final journey of metabolic materials is made in tissue fluid which bathes the tissues`

69
Q

How is tissue fluid normally returned to the circulatory system?

A

Loss of tissue fluid from capillaries reduces the hydrostatic pressure inside them
At the venous end of the capillary network, the hydrostatic pressure is lower than the tissue fluid

Therefore tissue fluid is moved back into the capillaries
Plasma has lost water and contains proteins so has a lower water potential than the tissue fluid
Water leaves by osmosis down a water potential gradient
Tissue fluid has gained CO2 and waste but lost nutrients and oxygen to the cells

70
Q

How does water out through the stomata?

A

Humidity of the atmosphere is less than that of the air spaces next to the stomata
When stomata are open, water vapour molecules diffuse out of the air spaces into the surrounding air

Water lost by diffusion from the air spaces is replaced by water evaporating from the cell walls of surrounding mesophyll cells
By changing the size of the stomatal pores, plants can control their rate of transpiration

71
Q

How does water move across the cells of a leaf?

A

Mesophyll cells lose water to the air spaces by evaporation due to heat
Cells have a lower water potential so water enters via osmosis from neighbouring cells

Loss of water from neighbouring cells lowers water potential
They take water from neighbouring cells
This creates a water potential gradient where water moves to the mesophyll then into the atmosphere

72
Q

How does water move up the xylem stem?

A

Water evaporates from mesophyll cells due to heat
Water molecules form hydrogen bonds and stick together- cohesion

Water forms a continuous column across mesophyll cells and down the xylem
As water evaporates, more molecules are drawn up via cohesion (transpiration pull)
Transpiration puts the xylem under tension which creates negative pressure (cohesion tension theory)

73
Q

What is the structure of the xylem?

A

Long cells
Have thick cells containing lignin

Lignin waterproofs walls of cells and strengthens them
Cells die from lignin which forms a long tube
Lignification is not complete and pores (called pits or bordered pits) allow water to move between vessels or into living parts
Lignin forms rings or spirals around the vessel and strengthen the tube

74
Q

What is the apoplastic pathway?

A

Movement between walls of neighbouring cells

75
Q

What is the symplastic pathway?

A

Movement through plasma membranes and plasmodesmata to cytoplasms from cell to cell

76
Q

What is the vacuolar pathway?

A

Same as the symplastic pathway but also through vacuoles

77
Q

What are the effects of the cohesion tension theory?

A

In daytime there is greater transpiration which creates a higher tension thats pulls the xylem walls inward and shrinks the trunk Therefore the trunk is wider at night
Xylem vessel is broken which allows air to enter it. No water is drawn up because the continuous column of water is broken and cohesion is stopped

Or the xylem vessel is broken so water does not leak because air is drawn in instead which creates tension

78
Q

Is transpiration pull an active/passive process?

A

Passive process and xylem tissue is dead so cannot actively move water

79
Q

Is transpiration an active/passive process?

A

An active process as heat from the sun evaporates water from the leaves

80
Q

How does xylem tissue withstand the pressure of cohesion tension?

A

It is strengthened with lignin

81
Q

What is translocation?

A

The process by which organic molecules and some mineral ions are transported from one part of a plant to another

82
Q

What is the function of phloem tissue?

A

It transports biological sugars from sites of production, sources, to the places where they are stored or used, sinks

83
Q

What is the structure of the phloem?

A

Sieve tube elements
Long thin structures arranged end to end

Walls are perforated to form sieve plates
Associated with the sieve tube elements are cells called companion cells

84
Q

What molecules does the phloem transport?

A

Organic: sucrose and amino acids
Inorganic: phosphate, potassium, chloride, magnesium ions

Sucrose is the most common translocated process

85
Q

In which direction do phloem tissues transport material?

A

As sinks can be above or below the source, translocation occurs in either direction

86
Q

What is the function of companion cells?

A

They transport products of photosynthesis to sieve tube elements through plasmodesmata

87
Q

What is the tissue which transports biological molecules?

A

Phloem

88
Q

What is a source or sink in the phloem transport system?

A

A source is the site where sugars are produced, e.g. the leaf
A sink is where they are used directly or stored for future use. Sinks can be anywhere in the plant

89
Q

In which direction are substances moved in the phloem?

A

Both ways as the sink can be above or below the source

90
Q

Which kinds of substances does the phloem transport?

A

Organic molecules including sucrose and amino acids

Inorganic ions such as potassium, chloride, phosphate and magnesium ions

91
Q

Is mass flow an active or passive process in the phloem system?

A

Passive process but occurs as a result of the active transport of sugars do it classed as active
This means it is affected by temperature and metabolic poisons

92
Q

How does sucrose move into companion cells?

A

Sucrose is manufactured in chloroplasts (source)

Sucrose diffuses down a concentration gradient by facilitated diffusion into companion cells

93
Q

How do hydrogen ions move into companion cells?

A

They are actively transported

94
Q

How does hydrogen move into sieve tube elements?

A

Hydrogen ions use carrier proteins to move into sieve tube elements

95
Q

How is sucrose moved into sieve tube elements?

A

Sucrose is transported along with hydrogen ions via co-transport proteins

96
Q

How does water move into the sieve tubes?

A

Sucrose produced by chloroplasts is actively transported into sieve tubes in step 1
This decreases water potential in the phloem

Water moves into the phloem by osmosis from a high water potential to a low water potential

97
Q

How does water move into the sink?

A

At the sink, sucrose is used up or converted to starch for storage
This decreases sucrose content so sucrose is actively transported into the sink

This reduces the water potential at the sink
The low water potential causes water to move into the sink from sieve tubes by osmosis
This lowers hydrostatic pressure in the sieve tubes

98
Q

What is the mass flow theory?

A

High hydrostatic pressure at the source and low at the sink

Mass flow of sucrose solution down this hydrostatic gradient

99
Q

What are the stages of transport or organic substances in the phloem?

A

Sucrose moves into companion cells
Hydrogen ions move into companion cells

Hydrogen moves into sieve tube elements
Sucrose moves into sieve tube elements
Water moves into the sieve tubes
Water moves into the sink

100
Q

What is the evidence supporting the mass flow hypothesis?

A

Concentration of sucrose is higher at source than sink
Downward movement of phloem occurs in light but ceases in darkness

Increases in leaf sucrose levels is linked to an increase in phloem sucrose
Companion cells contain many mitochondria

101
Q

What evidence contradicts the mass flow hypothesis?

A

Function of sieve plates is unclear as they hinder mass flow
Not all solutes move at the same speed

Sucrose is delivered at roughly the same rate to all regions

102
Q

What are the steps of a ringing experiment?

A

Section of the outer layers of the plant are removed (protective layers and phloem)
After time, the region above will swell

The swelling is caused by the sugars of the phloem accumulating above the ring
Some tissues below the ring wither and die
This is due to the interruption of the flow of sugars below the ring
This proves that the phloem is responsible for transporting sugars

103
Q

What are the steps of a tracer experiment?

A

Radioactive isotope used for tracing: e.g 14C
14C is used by the plant to make carbon dioxide

14C isotope is used to make sugars
Radioactive sugars can be traced as they move through the plant by x-rays

104
Q

What is the evidence of translocation of organic molecules occurs in the phloem?

A

When the phloem is cut, a solution of organic molecules flow out
Plants provided with radioactive carbon dioxide can be shown 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

105
Q

What are the xerophyte adaptations in the leaves?

A

Hairs so ‘trap’ water vapour
and water potential gradient

decreased;
Stomata in pits/grooves so
‘trap’ water vapour and water
potential gradient decreased;
Thick (cuticle/waxy) layer so
increases diffusion distance;
Waxy layer/cuticle so reduces
evaporation/transpiration.
Rolled/folded/curled leaves so
‘trap’ water vapour and water
potential gradient decreased;
Spines/needles so reduces
surface area to volume ratio

AQA A Level Biology (19 decks)

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