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Biology > B7 - Mass Transport > Flashcards

B7 - Mass Transport Flashcards

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1
Q

Why do we need a circulatory system?

A

All cells need a constant supply of reactants for metabolism: oxygen and glucose
Microscopic organisms: can gain these directly through diffusion
Larger organisms: made of layers of cells → diffusion distance would be too far to supply all cells with these reactants
Have evolved mass transport systems - digestive, circulatory system

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2
Q

What is mass transport?

A

The bulk movement of gases or liquids in one direction, usually via a system of vessels & tubes to exchange site

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3
Q

Is a red blood cell a globular or fibrous protein?

A

Globular

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4
Q

What is the structure of haemoglobin?

A

Quaternary structure (4 polypeptide chains)
4 subunits (two α–globins and two β–globins) held together by disulphide bonds
Each subunit contains a haem prosthetic group: these contains Fe2+ which reversibly combine with oxygen molecules → forms oxyhaemoglobin

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5
Q

What is the equation for oxygen and haemoglobin?

A

Oxygen + Haemoglobin ⇌ Oxyhaemoglobin
4O2 + Hb ⇌ Hb4O2

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6
Q

What happens when oxygen binds with haemoglobin?

A

Bind of the first oxygen molecules causes conformational change in the structure of Hb → makes it easier for each successive O2 molecule to bind - this is called cooperative binding
This binding is reversed in tissues, as oxygen dissociates from Hb

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7
Q

What is partial pressure of oxygen (pO2)?

A

It is a measure of oxygen concentration

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8
Q

What is haemoglobin saturation?

A

When all four of its binding sites are taken up with oxygen

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9
Q

What is the affinity for oxygen?

A

The ease at which Hb associates and disassociates with oxygen

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10
Q

What is the oxygen dissociation curve?

A

When Hb, oxygen binds at different rates as the pO2 changes → results in a curve
Affinity changes at different pO2
1 - The first O2 molecule binds to Hb slowly
2 - Hb molecule undergoes conformational change → easier for the next two Hb subunits to bind O2 - what is this called?
3 - Hb molecule approaches saturation - takes longer for the last O2 to bind

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11
Q

What does a high concentration of oxygen mean for haemoglobin?

A

Hb loads all available subunits & has a high affinity for oxygen, Once saturated, oxygen does not dissociate easily here

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12
Q

What does a low concentration of oxygen mean for haemoglobin?

A

Hb has unloaded most of its oxygen & has a low affinity for oxygen

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13
Q

What does a medium concentration of oxygen mean for haemoglobin?

A

Small decrease in pO2 causes a large decrease in %saturation of Hb → leading to easy release of plenty of oxygen to the cells

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14
Q

What is the Bohr shift?

A

The changes in the oxygen dissociation as a result of carbon dioxide levels

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15
Q

What happens when the partial pressure of CO2 is high and why?

A

Hb’s affinity for oxygen is reduced because:
CO2 combines with water
Forms carbonic acid (which lowers the pH)
Carbonic acid dissociates into hydrogen carbonate ions & hydrogen ions
H+ ions bind to Hb →causes the release of oxygen (and therefore reduces the affinity of oxygen)

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16
Q

What does the Bohr shift look like on the oxygen dissociation curve?

A

The curve shifts to the right when CO2 levels increase
At any given pO2, the % saturation of Hb is lower at higher levels of CO2

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17
Q

What does the effect of altitude look like on the oxygen dissociation curve?

A

Higher altitude = curve shifted to the left
pO2 in the air is LOWER at higher altitudes
Llamas = have Hb that binds much more readily to oxygen
beneficial, as it allows them to obtain a sufficient level of oxygen saturation in their blood when the pO2 in the air is low

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18
Q

What does foetal Haemoglobin look like on the oxygen dissociation curve?

A

A foetus needs to obtain oxygen from its mother’s blood at the placenta
Foetal Hb therefore has a higher affinity for oxygen than adult Hb → can bind oxygen at low pO2 (In the placenta, where the mother’s Hb is dissociating w/ oxygen)
So the curve shifts to the left - at any partial pressure, foetal Hb has a higher %saturation than adult Hb

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19
Q

What is a closed circulatory system?

A

When blood is pumped around the body & is contained within a network of blood vessels

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20
Q

What is an open circulatory system?

A

When blood is not contained within blood vessels & is pumped directly into body cavities (Arthropods and molluscs)

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21
Q

What circulatory system do humans have?

A

Humans have a closed double circulatory system: in one circuit of the body, blood passes through the heart twice
Right side: deoxygenated blood is pumped to the lungs for gas exchange (Pulmonary system)
Left side: oxygenated blood returns to the heart, then is pumped at high pressure around the body (Systemic circulation)

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22
Q

What is the role of the pulmonary artery?

A

Carries deoxygenated blood away from the heart, towards the lungs

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23
Q

What is the role of the pulmonary vein?

A

Carries oxygenated blood away from the lungs, towards the heart

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24
Q

What is the role of the coronary arteries?

A

Deliver oxygen & nutrient-rich blood to the heart muscle, for aerobic respiration
Present on the surface of the heart
Important that they remain unblocked

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25
Q

What is the role of the aorta?

A

Carries oxygenated blood out of the heart and to the rest of the body

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26
Q

What is the role of the vena cava?

A

Carries deoxygenated blood into the heart

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27
Q

What is the role of the renal artery?

A

Supplies the kidneys with oxygenated blood

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28
Q

What is the role of the renal vein?

A

Carries deoxygenated (and filtered) blood away from the kidneys, towards the heart

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29
Q

What is the heart protected by?

A

Pericardium - tough & fibrous sac

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30
Q

What is the left and right side of the heart separated by?

A

Left & right side separated by the septum (muscular tissue)
Septum between the atria: interatrial septum
Septum between the ventricles: interventricular septum

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31
Q

What is the role of the valves?

A

Valves maintain pressure & prevent the backflow of blood

32
Q

What does it mean when a valve is open?

A

The pressure of blood behind them is greater than the pressure in front of them. So the chamber behind is contracting

33
Q

What does it mean when a valve is closed?

A

The pressure of blood in front of them is greater than the pressure behind them. So the chamber behind is relaxed

34
Q

What is the valve that separates the right atrium and the right ventricle?

A

The Atrioventricular / tricuspid valve

35
Q

What is the valve that separates the right ventricle and the pulmonary artery?

A

Pulmonary valve

36
Q

What is the valve that separates the left atrium and left ventricle?

A

Mitral / bicuspid valve

37
Q

What is the valve that separates the left ventricle and the aorta?

A

Aortic valve

38
Q

Where are the thickest and most muscular walls?

A

The left ventricle has the thickest walls, as blood has to be under high pressure to be pumped around the body

39
Q

What is the contraction of the heart called?

A

Systole

40
Q

What is the relaxation of the heart called?

A

Diastole

41
Q

What happens when the heart muscles contracts?

A

Heart muscle contracts → volume decreases in the chamber → pressure increases

42
Q

What happens when the heart muscles relax?

A

Heart muscle relaxes → volume increases in the chamber → pressure decreases

43
Q

What is atrial systole?

A

Walls of atria contract
Atrial volume decreases
Atrial pressure increases
Atrioventricular (AV) & Mitral valves OPEN
Blood is forced into the ventricles
Slight increase in ventricular pressure, as it is receiving the blood from the atria
Ventricular diastole is occurring here, as the ventricles are yet to contract

44
Q

What is ventricular systole?

A

Walls of ventricles contract
Ventricular volume decreases
Ventricular pressure increases
Atrioventricular (AV) & Mitral valves are forced CLOSED
Pulmonary and aortic valves OPEN
Blood is forced into the arteries and out of the heart
Atrial diastole is also occurring here, as blood begins to fill the atria again

45
Q

What is diastole?

A

Walls of atria and ventricles both relax
Pressure in the ventricles decrease
Pulmonary and aortic valves CLOSE
Atria continue to fill with blood (via the vena cava & pulmonary vein)
Pressure in the atria rises again
Atrioventricular (AV) & Mitral valves OPEN
Blood also flows passively into the ventricles
Atrial systole begins again

46
Q

What occurs in the cardiac cycle (in the left side)?

A

Starts with the end of diastole where the atrium fills with blood
Pressure is higher in the atrium, so the mitral valve opens
Atrial systole then occurs, the LA contracts → increase atrial pressure
Ventricular pressure increases slightly as it fills with blood
Ventricular systole starts
LV contracts → increases in ventricular pressure
LA pressure drops, as the muscle relaxes
Mitral valve close
Ventricles continue to contract
Pressure in the LV is higher than the aorta → Aortic valve opens → blood is forced into the aorta
Diastole begins
Left ventricle has been emptied of blood
Left muscular wall relaxes → pressure falls → aortic valve closes
Ventricles remain relaxes → ventricular pressure decreases
Blood begins to flow into the relaxed atrium (via the pulmonary vein) → increase in pressure
Relaxed atrium fills with blood → pressure in atrium increases → Mitral valve opens
left ventricle expanded due to relaxing muscles
LV volume increases, pressure decreases
Blood slowly flows through the newly-opened mitral valve, into the LV
This causes a brief decrease in ventricular pressure
Pressure in the LA & LV increases slowly as they continue to fill w/ blood

47
Q

What is cardiac output?

A

the vol. of blood pumped by the heart (both ventricles) per unit of time
Cardiac output = heart rate x stroke volume

48
Q

What is Coronary Heart Disease (CHD)?

A

Any condition that interferes with the coronary arteries which supply blood to the heart muscle

49
Q

What are the main risk factors of CHD?

A

Genetic factors
Age and sex
High blood pressure
Smoking
High concentrations of low-density lipoproteins (LDLs)

50
Q

What are arterioles?

A

Blood vessels which connect arteries to capillaries

51
Q

How does the structure of arteries relate to its functions?

A

The walls contain thick layers of collagen, smooth muscle and elastic fibres, surrounding a narrow lumen
Elastic fibres allow arteries to expand and recoil when the heart contracts and relaxes
Arteries must withstand high pressures generated by heart contractions, and maintain that pressure when the heart is relaxes

52
Q

How does the structure of veins relate to its functions?

A

Walls contain thinner layers of collagen, smooth muscle & elastic fibres, surrounding a larger lumen
Also contain valves - prevent backflow of blood
Veins receive blood that has passed through capillary networks (at a low pressure)

53
Q

How does the structure of arterioles relate to its functions?

A

Have a lower proportion of elastic fibres and a large number of muscle cells - allows them to contract and close their lumen to stop blood flow
They can contract and partially cut off blood flow to specific organs

54
Q

How does the structure of capillaries relate to its functions?

A

Capillaries have thin walls with pores which allows blood plasma to leak out, and form tissue fluid
They form networks called capillary beds
Have a very small lumen - forces blood to travel slowly → diffusion more likely to occur
Capillary walls are made from a single layer of endothelial cells - reduces diffusion distance for carbon dioxide and oxygen, between the blood and tissues of the body

55
Q

What is tissue fluid used for?

A

It bathes all cells in this fluid
Exchange of substances between cells and blood occurs via the tissue fluid

56
Q

How does tissue fluid form?

A

Arterial end of the capillary: the increased hydrostatic pressure forces molecules OUT of the capillary
Protein remain the blood, which creates a water potential gradient between the capillary and tissue fluid
Venous end of the capillary: hydrostatic pressure decreases → less fluid is pushed out, some water begins to flow back into the capillary
Overall, more fluid leaves the capillary than returns, leaving tissue fluid behind to bathe cells

57
Q

How does some of the tissue fluid get back to the heart?

A

The lymph capillaries - these are separate from the circulatory system
Larger molecules that can’t leave through capillary walls enter the lymphatic system as lymph, through small valves
Lymph moves around large lymphatic vessels by compression and backflow is prevented by valves
Lymph eventually re-enters the bloodstream through veins close to the heart
Plasma proteins that have escaped the blood are returned to the blood via the lymph capillaries - this prevents the water potential being lowered and impairing water reabsorption

58
Q

What is the structure of the xylem?

A

Made of dead cells → forms a long, hollow tube (no pores between cells)
Contain lignin - for structural support

59
Q

How does the movement of water occur?

A

Evaporation of water vapour from the leaves and the cohesive and adhesive properties exhibited by water molecules
The water potential gradient drives water movement - Plant roots take up water from the soil, up plant stems, then out into the atmosphere via the leaves and stomata

60
Q

What is transpiration?

A

Transpiration is the loss of water vapour via the stomata by diffusion

61
Q

What is transpiration important for?

A

Cooling the plant via evaporative cooling
Helps to uptake mineral ions
Provides turgor pressure to provide support to the leaves

62
Q

What is the transpiration stream?

A

Water evaporates out of the stomata
The water vapour lost by transpiration lowers the water potential in the air spaces surrounding the mesophyll cells
Water in the mesophyll cell walls evaporates into these air spaces → causes a transpiration pull as there is a water gradient
Water goes up the xylem vessels by cohesive + adhesive forces, to replace the water lost from the mesophyll cells

63
Q

Does stomata being open increase the rate of transpiration?

A

Yes

64
Q

What does high air movement do to transpiration rate?

A

Increases the rate of transpiration, maintains gradient

65
Q

What does high humidity do to transpiration rate?

A

Decreases the rate of transpiration, weaker concentration gradient

66
Q

What does high light intensity do to transpiration rate?

A

Increases the rate of transpiration, stomata open

67
Q

What does high temperature do to transpiration rate?

A

Increases the rate of transpiration, molecules move faster and evaporation is quicker

68
Q

What is the structure of the phloem?

A

Made of living cells + pores between cells

69
Q

What is translocation?

A

Translocation within phloem tissue is the transport of assimilates (e.g., sucrose) from source to sink, which requires ATP

70
Q

What are assimilates transported in?

A

Phloem saps

71
Q

What is the mass flow hypothesis?

A

This hypothesis was the model used to explain the movement of assimilates in the phloem tissue

72
Q

What is the mass flow hypothesis mechanism?

A

Sucrose is actively loaded into the sieve elements at the source which lowers the water potential of the sap
Water moves into the sieve elements by osmosis from xylem
Hydrostatic pressure increases at the source
Sucrose is unloaded from the sieve elements at the sink which decreases the hydrostatic pressure, water goes back to xylem
The difference in pressure creates a gradient, causing a mass flow of water containing dissolved substances (the phloem sap)

73
Q

What is the tracer and ringer experiment?

A

Involves the removal of a ring of the phloem from the stem of the plant, while leaving the xylem intact
After ringing, the plant is exposed to a radioactive tracer (normally 14CO2) to investigate the rate & direction of translocation

74
Q

What is the evidence supporting the mass flow hypothesis?

A

When the phloem sieve tube is punctured, phloem sap oozes out, suggests that it is under pressure
Phloem sap taken from near a source has a higher sucrose concentration than sap taken from near a sink, suggests that different water potentials would result in osmosis into & out of the tubes

75
Q

What is the evidence against the mass flow hypothesis?

A

Amino acids appeared to travel more slowly than sucrose
The mass flow hypothesis states should be flowing at the same rate
Some scientists have conducted experiments that detected different substances moving in opposite directions
The mass flow hypothesis states everything should be flowing in one direction

Biology (19 decks)

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