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Biology A Level 2023 2 > Mass Transport > Flashcards

Mass Transport Flashcards

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1
Q

describe the structure of haemoglobin

A

globular
water soluble
4 polypeptide chains each with a haem group

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2
Q

describe the role of haemoglobin

A

present in red blood cells
oxygen molecules bind to the haem groups and are carried around the body to where they are needed in respiring tissues

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3
Q

name the three factors affecting oxygen-haemoglobin binding

A
  1. partial pressure/concentration of oxygen
  2. partial pressure/concentration of carbon dioxide
  3. saturation of haemoglobin with oxygen
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4
Q

how does partial pressure of oxygen affect oxygen-haemoglobin binding

A

as partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases, so oxygen binds tightly to haemoglobin, when partial pressure is low, oxygen is released from haemoglobin

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5
Q

how does partial pressure of carbon dioxide affect oxygen-haemoglobin binding

A

as partial pressure of co2 increases, the conditions become acidic causing haemoglobin to change shape. the affinity of haemoglobin for oxygen therefore decreases, so oxygen is released from haemoglobin. this is known as the Bohr effect

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6
Q

how does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding

A
  • hard for first oxygen molecule to bind
  • changes shape to make it easier for second and third to bind = POSITIVE COOPERATIVITY
  • then slightly harder for fourth oxygen molecule as there is a lower chance of finding a binding site
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7
Q

why oxygen binds to haemoglobin in the lungs

A
  • partial pressure of oxygen is high
  • low concentration of carbon dioxide in the lungs, so affinity is high
  • positive cooperativity (after first oxygen molecule binds, binding of subsequent molecules is easier)
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8
Q

explain why oxygen is released from haemoglobin in respiring tissues

A
  • partial pressure of oxygen is low
  • high concentration of carbon dioxide in respiring tissues, so affinity decreases
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9
Q

what do oxyhaemoglobin dissociation curves show

A

saturation of haemoglobin in oxygen (in %), plotted against partial pressure of oxygen (in kPa)

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10
Q

what do curves further to the left in oxyhaemoglobin dissociation curves show

A

higher affinity for oxygen

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11
Q

how does CO2 affect the position of dissociation curve

A

curve shifts to the right because haemoglobin’s affinity for oxygen has decreased

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12
Q

name some common features of mammalian circulatory system

A
  1. suitable medium for transport, water-based to allow substances to dissolve
  2. means of moving the medium and maintaining pressure throughout the body, such as the heart
  3. means of controlling flow so it remains unidirectional, such as valves
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13
Q

relate structure of atria to their function

A

thin-walled and elastic, so they can stretch when filled with blood

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14
Q

relate structure of ventricles to their function

A

thick muscular walls pump blood under high pressure
left ventricle is thicker than the rigt because it has to pump blood all the way around the body

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15
Q

relate structure of arteries to their function

A

thick walls to handle high pressure without tearing, and are muscular and elastic to control blood flow

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16
Q

relate structure of veins to their function

A

thin walls due to lower pressure, therefore requiring valves to ensure blood doesn’t flow backwards
have less muscular and elastic tissue as they don’t have to control blood flow

17
Q

why are 2 pumps needed in heart

A
  • maintain blood pressure
  • when blood passes through narrow capillaries of lungs, pressure drops sharply and therefore will not be flowing strongly enough to continue to whole body
  • returned to heart to increase pressure
18
Q

what happens in cardiac systole

A
  • heart is relaxed
  • blood enters atria, increasing the pressure and pushing open the atrioventricular valves
  • allows blood to flow into ventricles
  • pressure in heart lower than arteries, so semilunar valves are closed
19
Q

what happens in atrial systole

A

atria contract, pushing any remaining blood into ventricles

20
Q

what happens in ventricular systole

A

ventricles contract, pressure increases, closing the atrioventricular valves to prevent backflow, opening the semilunar valves
blood flows into the arteries

21
Q

name the nodes involved in heart contraction

A
  • SAN (sinoatrial node)
  • AVN (atrioventricular node)
22
Q

where is the SAN

A

wall of right atrium

23
Q

where is AVN

A

between the two atria

24
Q

what does myogenic mean

A

heart’s contraction is initiated from within the muscle itself, rather than by nerve impulses

25
Q

explain how the heart contracts

A
  • SAN initiates and spreads impulse across the atria, so they contract
  • AVN receives, delays and then conveys the impulse down the bundle of His
  • impulse travels into the Purkinje fibres which branch across the ventricles, so they contract from the bottom up
26
Q

why is the impulse delayed

A

otherwise valves would not have enough time for all blood to pass through and for valves to close

27
Q

how is the structure of capillaries suited to their function

A
  • walls are only one cell thick; short diffusion pathway
  • very narrow, so can permeate tissues and red blood cells can lie flat against the wall, effectively delivering oxygen to tissues
  • numerous and highly branched, providing large surface area
28
Q

what is tissue fluid

A

watery substance containing glucose, amino acids, oxygen and other nutrients.
supplies these to the cells while also removing any waste materials

29
Q

how is tissue fluid formed

A

as blood is pumped through increasingly small vessels, this creates hydrostatic pressure which forces fluid out of the capillaries. it bathes the cells and then returns to the capillaries when hydrostatic pressure is low enough

30
Q

how is water transported in plants

A

through xylem vessels; long, continuous columns that provide structural support to the stem

31
Q

explain cohesion-tension theory

A

water molecules form hydrogen bonds with each other, causing them to ‘stick’ together (cohesion)
this creates sticking effect, therefore water is lost through transpiration, more can be drawn up the stem

32
Q

what are the three components of phloem vessels

A
  • sieve tube elements = form a tube to transport sucrose in the dissolved form of sap
  • companion cells = involved in ATP production for active loading of sucrose into sieve tubes
  • plasmodesmata = gaps between cell walls where cytoplasm links, allowing substances to flow
33
Q

name the process whereby organic materials are transported around the plant

A

translocation

34
Q

how does sucrose in leaf move into phloem

A

sucrose enters companion cells of the phloem vessels by active loading, which uses ATP and a diffusion gradient of H+
sucrose then diffuses from companion cells into sieve tube elements through the plasmodesmata

35
Q

how do phloem vessels transport sucrose around plant

A

as sucrose moves into the tube elements, water potential inside the phloem is reduced. this causes water to enter via osmosis from the xylem and increases hydrostatic pressure. water moves along the sieve tube towards areas of lower hydrostatic pressure. sucrose diffuses into surrounding cells where it is needed

36
Q

give evidence for the mass flow hypothesis of translocation

A
  • sap is released when a steam is cut, therefore there must be pressure in the phloem
  • there is a higher sucrose concentration in the leaves than in the roots
  • increasing sucrose levels in the leaves results in increased sucrose in the phloem
37
Q

give evidence against mass flow hypothesis of translocation

A
  • structure of sieve tubes seems to hinder mass flow
  • not all solutes move at the same speed, as they would in mass flow
  • sucrose is delivered at the same rate throughout the plant, rather than to areas with the lowest sucrose concentration first
38
Q

how can ringing experiments be used to investigate transport in plants

A

bark and phloem of tree are removed in a ring, leaving behind the xylem
eventually the tissues above the missing ring swells doe to accumulation of sucrose as the tissue below begins to die
therefore sucrose must be transported in the phloem

39
Q

how can tracing experiments be used to investigate transport in plants

A

plants are grown in the presence of radioactive co2, which will be incorporated into the plant’s sugars. using autoradiography, we can see that the areas exposed to radiation correspond to where the phloem is

Biology A Level 2023 2 (17 decks)

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