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Biology > 7.Mass transport > Flashcards

7.Mass transport Flashcards

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1
Q

What are haemoglobins

A

A group of chemically similar molecules found in many different organisms

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2
Q

Define haemoglobin

A

Globular protein in blood that readily combines with oxygen to transport it around the body. It compromises of 4 polypeptide chains around an iron containing haem

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3
Q

Describe the haemoglobins structure

A

Has a quaternary structure of 4 polypeptides each associated with a haem group containing a iron group.

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4
Q

What is loading

A

The process by which haemoglobin binds with oxygen. In humans this takes place in the lungs.

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5
Q

What is unloading

A

The process by which haemoglobin releases its oxygen. In humans this takes place in the tissues.

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6
Q

Describe things haemoglobin must do to be efficient to transport oxygen

A
  • readily associate with oxygen at the surface where gas exchange takes place
  • readily dissociate from oxygen at those tissues requiring it
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7
Q

How does haemoglobin readily associate with oxygen but also be able to readily dissociate with oxygen

A

It’s affinity for oxygen changes under different conditions as its shape changes under different conditions (eg. the presence of CO2)

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8
Q

Why do different haemoglobins have different affinities for oxygen

A

Each species produces a haemoglobin with a slightly different amino acid sequence. Therefore each species therefore has a slightly different tertiary and quaternary structure hence different binding properties

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9
Q

What does the oxygen dissociation curve show

A

The relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen

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10
Q

Explain why the shape of the curve is initially shallow

A
  • shape of the haemoglobin molecule makes it difficult for the first oxygen molecule to bind to one of the sites on the four polypeptide subunits because they are closely united
  • this means at low O2 concentrations little oxygen binds to haemoglobin
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11
Q

Explain why the gradient of the curve gets steeper

A
  • after the first oxygen molecule binds it changes the quaternary structure of the haemoglobin molecule
  • this change of shape makes it easier for other molecules to bind
  • it therefore takes a smaller increase of oxygen to bind the 2nd molecule than the first one (positive cooperativity)
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12
Q

Explain why the gradient of the curve flattens off

A
  • as 3 sites are already filled there is a much lower probability that oxygen collides with the haemoglobin and binds
  • this causes the curve to flatten
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13
Q

The further to the left of the dissociation curve…

A

the greater the affinity of the haemoglobin for oxygen (so loads oxygen readily but unloads less)

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14
Q

The further to the right of the dissociation curve…

A

the lower the affinity of the haemoglobin for oxygen (so loads oxygen less readily but unloads more easily)

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15
Q

What is the Bohr effect

A

Haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide.

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16
Q

When CO2 concentration is reduced, the curve shifts to the…

A

Left, as it means the haemoglobin has a higher affinity so loads more easily but unloads less

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17
Q

When CO2 concentration is increased, the curve shifts to the…

A

Right, as this reduces the affinity so oxygen loads less easily but unloads more readily

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18
Q

Why does oxygen unload at respiring cells

A
  • high concentration of CO2
  • low concentration of O2
  • means haemoglobin has a low affinity and unloads easily
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19
Q

Why does oxygen load at the lungs

A
  • high concentration of O2
  • low concentration of CO2
  • means haemoglobin has a high affinity and loads easily
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20
Q

Explain the Bohr effect

A

Dissolved CO2 is acidic and lowers the pH, changing its quaternary shape which lowers its affinity.

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21
Q

Why does the Bohr effect help ensure there is always sufficient oxygen

A
  • at higher times of activity
  • more respiration
  • more CO2 produced
  • the greater the shape change of haemoglobin
  • lower affinity for oxygen
  • more oxygen available for respiration
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22
Q

Why do some organisms need a transport system

A
  • they are larger (small SA:V ratio)

- they are active organisms (need for oxygen for respiration is greater)

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23
Q

What are features of a transport system

A
  • suitable medium to carry materials
  • a form of mass transport in which the transport medium is moved over large distances (faster than diffusion)
  • a closed system of tubular vessels that contain the medium reaching all parts of the organism
  • a mechanism for transporting the medium within vessels (requires a pressure distance)
  • mechanism to maintain mass flow in one direction (eg. valves)
  • a means of controlling the flow of the transport medium
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24
Q

How do animals and plants achieve mass transport

A
  • animals use contraction of muscle eg. heart

- plants rely on passive processes such as evaporation

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25
Q

What circulatory system do mammals have

A

A closed double circulatory system as blood is confined to vessels and passes through the heart twice for one complete circuit

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26
Q

Advantage of a closed double circulatory system

A

It means that high blood pressure can be maintained around the body increasing the speed of circulation. This is important as mammals have high metabolic rate (as they are high temperatures) so need substances to be delivered around the body quickly

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27
Q

What is the atrium

A

A thin-walled and elastic chamber which stretches as it collects blood

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28
Q

What is the ventricle

A

A thicker muscular chamber that contracts to pump blood through the double circulatory system

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29
Q

Name the valves found between the atria and the ventricles

A
  • left atrioventricular valve

- right atrioventricular valve

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30
Q

What is the function of an atrioventricular valve

A

To prevent the backflow of blood into the atria when the ventricles contract

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31
Q

What are the vessels connecting the lungs to the heart called

A

Pulmonary vessels

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32
Q

The aorta is

A
  • connected to the left ventricle

- carries oxygenated blood to all parts of the body (expect the lungs)

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33
Q

The vena cava is

A
  • connected to the right atrium

- brings deoxygenated blood back from the tissues of the body (expect the lungs)

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34
Q

The pulmonary artery is

A
  • connected to the right ventricle

- carries deoxygenated blood to the lungs where O2 is replenished and CO2 is removed

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35
Q

Why is the pulmonary artery/vein unusual

A
  • artery carries deoxygenated blood

- vein carries oxygenated blood

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36
Q

What is the pulmonary vein

A
  • connected to the left atrium

- brings oxygenated blood back from the lungs

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37
Q

Describe the path of blood from the lungs

A
  • vena cava
  • right atrium
  • right ventricle
  • pulmonary artery
  • lungs
  • pulmonary vein
  • left atrium
  • left ventricle
  • aorta
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38
Q

How is the heart supplied with oxygen

A

By coronary arteries that branch of shortly after bloodleaves the heart

39
Q

What can blockage of coronary arteries cause

A

Myocardial infarction (heart attack)

40
Q

What is diastole

A

The part of the cardiac cycle where the heart muscle relaxes

41
Q

What is systole

A

The part of the cardiac cycle where the heart muscle contracts

42
Q

What occurs in diastole

A
  • atria relax and fill with blood from pulmonary vein or vena cava
  • increases pressure causing the atrioventricular valves to open and blood to flow into ventricle
  • as ventricle is relaxed it causes the pressure to be lower
  • this means semi-lunar values close
43
Q

What occurs in atrial systole

A
  • atria contract pushing remaining blood into the ventricles from the atria
  • throughout this process ventricles remain relaxed
44
Q

What occurs in ventricular systole

A
  • a short period after atrial systole (to allow ventricles to fill with blood)
  • ventricular walls contract simultaneously
  • this increases blood pressure in the ventricle which closes the atrioventricular valves (preventing backflow)
  • with valves closed pressure rises further
  • once it exceeds pressure of aorta and pulmonary artery, blood is forced from the ventricles into the vessels
45
Q

Why are the ventricle walls thicker than the atriums

A

Thicker muscle allows high pressure to be created to force blood all round the body

46
Q

Why is the left ventricle wall thicker than the right

A

The left has to pump blood to the extremities of the body while the right just has to pump to the lungs

47
Q

Where are the semi-lunar valves located

A

In the aorta and the pulmonary artery

48
Q

What are pocket valves

A
  • valves found in the venous system

- to endure when veins are squeezed (eg. by muscle contraction) there is no backflow of blood

49
Q

What is the cardiac output equation

A

cardiac output = heart rate x stroke volume

50
Q

Name all 4 types of blood vessels

A
  • arteries
  • arterioles
  • capillaries
  • veins
51
Q

What are arteries

A

Blood vessels that carry blood away from the heart into arterioles

52
Q

What are arterioles

A

Smaller arteries that control blood flow from arteries to capillaries

53
Q

What are capillaries

A

Tiny blood vessels that link arterioles to veins

54
Q

What are veins

A

Blood vessels that carry blood from capillaries back to the heart

55
Q

Describe the basic structure of arteries, arterioles and veins

A
  • tough fibrous outer layer (resists pressure changes from inside an outside)
  • muscle layer (contract to control the flow of blood)
  • elastic layer (helps maintain blood pressure by stretching and recoiling)
  • endothelium (thin inner lining that is smooth and thin to reduce friction and allow diffusion)
  • lumen (central cavity of the blood vessel)
56
Q

How does the structure of arteries relate to its function

A
  • thicker muscle compared to veins (to control blood flow by contraction and relaxation)
  • elastic layer is thicker than veins (to keep blood pressure high so blood can reach extremities. Elastic wall is stretched at systole and recoils at diastole) to maintain high pressure)
  • overall thicker wall (resists the vessel bursting under pressure)
  • there are no valves (blood is under constant high pressure due to the heart pumping blood into the arties so there is no backflow)
57
Q

How does the structure of arteriole relate to its function

A
  • thicker muscle compared to arteries (allows constriction of the lumen to control the movement of blood into the capillaries that supply the tissues with blood
  • the elastic layer is thinner than arteries (because the pressure is lower)
58
Q

How does the structure of veins relate to its function

A
  • thinner muscle compared to arteries (because veins carry blood away from the tissues they cannot control the blood flow to tissues via constriction)
  • thinner elastic compared to arteries (pressure is too low to cause them to burst or to create a recoil action)
  • overall thinner wall (there is no need for a thick wall as the pressure is too low for risk of bursting. Also allows them to be flattered easily aiding the flow of blood within them)
  • valves at intervals throughout (to ensure that blood does not flow backwards which is a possibility due to the low pressure)
59
Q

How does the structure of capillaries relate to its function

A
  • wall consists mainly of lining layer (one cell thick. Short diffusion pathway means rapid diffusion)
  • numerous and highly branches (provide large SA for exchange)
  • narrow diameter (permeate tissues which means no cell is far from a capillary meaning there is a short diffusion pathway)
  • narrow lumen (red blood cells are squeezed flat against the side of a capillary so there is a short diffusion pathway)
  • there are spaces between the endothelial (lining) cells (allows white blood cells into tissues in order to deal with infections)
60
Q

What is tissue fluid

A

Fluid that surrounds the cells of the body. Its composition is similar to that of blood plasma except that it lack protein. It supplies nutrients to the cells and removes waste products.

61
Q

What nutrients does tissue fluid supply

A
  • glucose
  • amino acids
  • fatty acids
  • ions
  • oxygen
62
Q

Describe the formation of tissue fluid

A
  • pumping by the heart causes hydrostatic pressure at the arterial end of capillaries
  • this hydrostatic pressure causes tissue fluid to move out the blood plasma
  • this is opposed by hydrostatic pressure outside the capillaries and the lower water potential of the blood due to the plasma proteins
  • overall pressure pushes tissue fluid out of the capillaries at the arterial end
  • this pressure is only enough to force small molecules out of the capillaries leaving cells and proteins in the blood as they are too large to cross membranes
  • this is called ultrafiltration
63
Q

Describe how tissue fluid returns to the circulatory system

A
  • the loss of tissue fluid from the capillaries reduces the hydrostatic pressure inside them
  • as a result when the blood reaches the venous end of the capillary network its hydrostatic pressure is usually lower than that of the tissue fluid outside it
  • this means tissue fluid is forced back into the capillaries by the higher hydrostatic pressure outside them
  • in addition the plasma has lost water (in tissue fluid) and still contains proteins meaning it has a lower water potential than the tissue fluid
  • water keeves the tissue via osmosis down the water potential gradient
64
Q

Where does the remaining tissue fluid go if it does not return to the capillaries

A
  • it is carried back to the lymph system
  • a system of vessels that begin in the tissues and form a network around the body
  • these vessels drain their contents back into the blood stream via two ducts that join veins close to the heart
65
Q

How are the contents of the lymphatic system moved around the body

A
  • hydrostatic pressure of the tissue fluid that has left the capillaries
  • contraction of body muscles that squeeze the lymph vessels. There are valves in the lymph vessels ensuring they move in the right direction
66
Q

In what is water transported in, in the plant

A

Xylem vessels

67
Q

What is the main force moving water through the xylem vessels

A

Transpiration

68
Q

Describe how water moves out the stomata

A
  • humidity of the atmosphere is usually less than that of the air spaces next to the stomata
  • as a result there is a water potential gradient between the air spaces and the air outside the stomata
  • provided the stomata are open water vapour molecules diffuse out of the air spaces
  • water lost by diffusion from the air spaces is replaced by water evaporating from the cell walls of surrounding mesophyll cells
69
Q

How can plants control the rate of transpiration

A

-changing the size of the stomatal pores

70
Q

Describe the movement of water across the cells of a leaf

A
  • mesophyll cells lose water to the air spaces by evaporation (due to heat supplied to the sun)
  • these cells have a lower water potential and so water enters via osmosis from neighbouring cells
  • loss of water from these neighbouring cells lowers their water potential
  • in turn they take water from their neighbours via osmosis
71
Q

Name a property of water that movement of water up the xylem relies on

A

Cohesion-tension

72
Q

Describe the movement of water up the stem of the xylem

A
  • water evaporates from the mesophyll cells due to heat from the sun leading to transpiration
  • water molecules form hydrogen bonds between one another causing water to have a property known as cohesion
  • water forms a continuous unbroken column across the mesophyll cells and down the xylem
  • as more water evaporates from the mesophyll cells into air spaces more water molecules are drawn up by cohesion
73
Q

What is the name for the column of water being pulled up the xylem

A

Transpiration pull

74
Q

Describe xylem vessels

A
  • dead cells

- no end walls which means that the xylem forms a continuous unbroken tube from root to leaves

75
Q

What energy drives the process of transpiration

A

Heat energy, from the sun, that evaporates water from leaves

76
Q

What is translocation

A

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

77
Q

What are sources

A

Sites of production of sugars (having being produced during photosynthesis)

78
Q

What are sinks

A

Sites where sugars are stored for future use

79
Q

What is the name of the mechanism of translocation

A

Mass flow theory

80
Q

Outline the 3 phases of mass flow theory

A
  • transfer of sucrose into sieve elements from photosynthesising tissue
  • mass flow of sucrose through sieve tube elements
  • transfer of sucrose from sieve tube elements
81
Q

Describe the transfer of sucrose into sieve elements from photosynthesising tissue

A
  • sucrose is manufactured by products of photosynthesis in cells with chloroplasts
  • sucrose diffuses down a concentration gradient by facilitated diffusion from the photosynthesising cells into companion cells
  • H+ are actively transported from companion cells into the spaces within cell walls using ATP
  • these H+ ions then diffuse down a concentration gradient through carrier proteins (co-transport proteins) into the sieve tube elements
  • sucrose molecules are transported along with the hydrogen ions (co-transport)
82
Q

By what processes do sucrose move out into the sieve elements

A

Co-transport (involving passive and facilitated diffusion and active transport)

83
Q

Describe the mass flow of sucrose through sieve tub elements

A
  • sucrose produced by photosynthesising cells are transported into the sieve tubes (co-transport)
  • this causes the sieve tubes to have a lower water potential
  • this causes water from xylem (with a higher water pot) to move into the sieve tubes via osmosis down a water potential gradient
  • this creates high hydrostatic pressure in the sieve tubes
  • at the sink sucrose is used up during respiration
  • therefore sucrose moves into these cells via active transport
  • due to a water potential gradient water moves into these respiring cells via osmosis
  • this decreases hydrostatic pressure
  • as a result water moves from a source to a sink down the hydrostatic pressure gradient
84
Q

What does mass flow in the phloem rely on

A

A difference in hydrostatic pressure in the phloem by the sink and the source

85
Q

What affects mass flow

A

-temperature
-metabolic poisons
as it relies on active transport

86
Q

Name evidence supporting mass flow theory

A
  • there is pressure within tubes as sap is released when cut
  • concentration is higher in source than sink
  • downward flow in the phloem occurs in daylight but ceases when leaves are shaded
  • increased levels of sucrose in leaves is followed by increase in sucrose levels in phloem later
  • lack of oxygen/metabolic poisons inhibit translocation of sucrose in the phloem
  • companion cells posses many mitochondria
87
Q

Name evidence against mass flow hypothesis

A
  • function of sieve plates is unclear as they would hinder mass flow
  • not all solutes move at the same speed (they should do if movement is by mass flow)
  • sucrose is delivered at more or less the same rate to all regions rather than going more quickly to the ones with the lowest sucrose concentration (which mass flow would suggest)
88
Q

Describe the transfer of sucrose from the sieve tube elements into storage into storage or other sink cells

A

-the sucrose is actively transported by companion cells out of the sieve tubes and into the sink cells

89
Q

Describe the ringing experiments and its results

A
  • woody stems have a protective layer of bark on the inside of which is a layer of phloem
  • at the start of this experiment these layers are removed
  • after a period of time the region of the stem immediately above the missing ring is seen to swell.
  • samples of this liquid are found to ne rich in sugars and dissolved organic substances
  • some non-photosynthetic tissues in this region below the ring wither and die while those above continue to grow
90
Q

Explain the results in the ringing experiment

A
  • swelling in region above the missing ring is due to sugars of the phloem accumulating above the ring leading to swelling in this region
  • death of tissues in region below the missing ring is due to the interrupting of flow of sugars in the phloem
91
Q

What is the conclusion drawn from the ringing experiment

A

The phloem, not the xylem is responsible for translocating sugars

92
Q

Describe the tracer experiment

A
  • plant is grown in atmosphere containing 14-CO2 (CO2 with radioactive carbon 14 isotope )
  • 14-CO2 will be incorporated into sugars of the plant
  • using autoradiography plant can be x-rayed
  • results showed blackened regions (signalling 14-CO2) corresponded with where the phloem is
93
Q

What is the conclusion drawn from the tracer experiment

A

The phloem is responsible for translocating sugars

Biology (23 decks)

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