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Biology A-Level > Topic 3 - Exchanging substances > Flashcards

Topic 3 - Exchanging substances Flashcards

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1
Q

describe the relationship btwn size and structure of an organism and its SA:V

A

as size increases, SA:V tends to decrease
more thin/flat/folded/elongated structures increase SA:V

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2
Q

how is SA:V calculated

A

divide surface area by volume

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3
Q

suggest an advantage of calculating SA:mass for organisms instead of SA:V

A

easier/quicker to find/more accurate because irrgular shapes

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4
Q

what is metabolic rate

A

the amount og energy used up by an organism within a given period of time

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5
Q

how could we measure metabolic rate

A

oxygen uptake as used in aerobic respiration to make ATP for energy release

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6
Q

explain the relationship btwn SA:V and metabolic rate

A

as SA:V increases, metabolic rate increase because:
- rate of heat loss per unit body mass increases
- organisms need a higher rate of respiration
- to release enough heat to maintain a constant body temperature i.e. replace lost heat

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7
Q

explain the adaptations that facilitate exchange as SA:V reduces in larger organisms

A
  • changes body shape to increase SA:V and overcome long diffusion distance/pathway
  • development of systems such as specialised surface/organ for gaseous exchange = increases SA:V and overcomes long diffusion distance/pathway, maintain a concentration gradient for diffusion e.g. ventilation/good blood supply
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8
Q

explain how the body surface of a single celled organism is adapted for gas exchange

A
  • thin flat shape, large SA:V
  • short diffusion distance to all parts of cell = rapid diffusion e.g. of O2 CO2
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9
Q

state 3 parts of the tracheal system of an insect

A

spiracles, tracheae, tracheoles

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10
Q

what are spiracles

A

pores on surface that can open/close to allow diffusion

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11
Q

what are tracheae

A

large tubes full of air that allow diffusion

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12
Q

what are tracheoles

A

smaller branches from tracheae, permeable to allow gas exchange with cells

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13
Q

explain how an insect’s tracheal system is adapted for gas exchange

A
  • tracheloles have thin walls = short diffusion distance to cells
  • high numbers of fhighly branched tracheoles = short diffusion distance to cells so large SA
  • tracheae provides tubes full of air = fast diffusion
  • contraction of abdominal muscles changes pressure in body = air moves in and out so maintains conc. gradient
  • fluid in end of tracheoles drawn into tissues by osmosis durinng excercise (lactate produced in anaerobic respiration lowers water potential of cells) = diffusion is fater through air rather than in fluid
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14
Q

explain the structural and functional compromises in terrestrial inisects that allow efficient gas exchange while limitinng water loss

A
  • thick waxy cuticle/exoskeleton = increases diffusion distance so less water is loss
  • spiracles can open to allow gas exchannge and close to reduce water loss
  • hairs around spiracles trap moist air, reducing water potential gradient so less water loss
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15
Q

expxlain how the gills of fish are adapted for gas exchange

A
  • gills are made of many filaments covered with many lamella = increased surface area for diffusion
  • thin lamellae wall/epithelium = short diffusion distance btwn water/blood
  • lamellae have a large number of capillaries = removes O2, brings CO2 quickly maintains conc. gradient
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16
Q

what is the counter current flow

A
  • blood and water flow in opposite directions through/over lamellae
  • oxygen conc. always higher in water so maintains conc. gradient of O2 btwn water and blood for diffusion along whole length of lamellae
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17
Q

explain how the leaves of dicotyledonous plants are adapted for gas exchange

A

many stomata (high density) - large SA for gas exchange
spongy mesophyll contains air spaces - large surface area for gases to diffuse through
thin - short diffusion distance

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18
Q

state 7 structures you’d find in a leaf cross section

A

waxy cuticle, upper and lower epidermis, palisade mesophyll, spongy mesophyll, stomata, guard cell

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19
Q

explain structural and functional compromises in xerophytic plants that allow efiicient gas exchange while limiting water loss

A
  • thicker waxy cuticle increases diffusion distance so less evaporation
  • sunken stomato in pets, rolled leaves, hairs = trap water vapour/protect stomata from wind, reduced water potential gradient btwn leaf/air so less evaporation
  • spines/needles reduce SA:V
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20
Q

describe the gross structure of the human gas exchange

A

trachea, bronchi, bronchioles, alveoli, capillary network

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21
Q

explain the essential features of the alveolar epithelium that makes it adapted as a surface for gas exchange

A

flattened cells - 1 cell thick = short diffusion distance
folded = large SA
permeable - allows diffusion of O2, CO2
moist - gases can dissolve for diffusion
good blood supply from large network of capillaries = maintains conc. gradient

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22
Q

describe how gas exchange occurs in the lungs

A

oxygen diffuses from alveolar air space into blood down its conc. gradient across alveolar epithelium then across capillary endothelium

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23
Q

explain the importance of ventilation

A

brings in air containing higher conc. of oxygen and removes air w lower conc. of oxygen maintaining conc. gradient

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24
Q

explain how humans breathe in (inspiration)

A

diaphragm muscles contract - flattens
external intercostal muscles contract, internal intercostal muscles relax - ribcage pulled up and out
increasing volume and decreasing pressure in thoracic cavity
air moves into lungs down pressure gradient

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25
Q

explain how humans breathe out (expiration)

A

diaphragm relaxes - moves upwards
external intercostal muscles relax, intercostal muscles contract
decreasing volume and increasing pressure in thoracic cavity
air moves lungs down pressure gradient

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26
Q

suggest why expiration is normally passive at rest

A

internal intercostal muscles do not normally need to contract
expiration is aided by elastic recoil in alveoli

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27
Q

suggest how different lung diseases reduce the rate of gas exchange

A

thickened alveolar tissue increases diffusion distance
alveolar wall breakdown reduces surface area
reduce lung elasticity = lungs expand/recoil less so it reduces conc. gradient of O2/CO2

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28
Q

suggest how different lung diseases affect ventilation

A

reduce lung elasticity (e.g. fibrosis, build up scar tissue) - reduces volume of air in each breath (tidal volume) and reduces the maximum volume of air breathed out in one breath (forced vital capacity)

narrow airway/reduce airflow in and out of lungs(e.g. asthma - inflamed bronchi) - reducing maximum volume of air breathed out in 1 second

reduced gas exchange - increased ventilation rate to compensate for reduced oxygen in blood

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29
Q

suggest why people with lung disease experience fatigue

A

cells receive less oxygen - rate of aerobic respiration reduced = less ATP made

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30
Q

suggest how you can analyse and interpret data to the effects of pollution, smoking and other risk factors on the incidence of lung disease

A

describe overall trend e.g. positive/negative correlation btwn risk factor and disease
manipulate data e.g. calculate % change
interpret standard deviations - overlap suggests difference in means are likely due to change
use statistical tests to identify whether difference/correlation is significant or due to chance

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31
Q

suggest how you can evaluate the way in which experimental data led to statutory restrictions on the sources of risk factors

A

analyse and interpret data and identify what does or doesn’t support statement
evaluate the method - was it representative enough, valid, showed effects and could show comparison:
- sample size,
- participant diversity
- control groups and variales
- duration
evaluate context - has a broad generalisation been made from a specific set of data
are there other risk factors that could have affected results

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32
Q

state 3 statistical tests

A

chi-squared
correlation coefficient
student’s t test

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33
Q

state when you would use a correlation coefficient test

A

when examining an association btwn 2 sets of data

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34
Q

state when you would use a student’s t test

A

when comparing the means of 2 sets of data

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35
Q

state when you would use a chi-squared test

A

for categorical data

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36
Q

what is correlation

A

when change in one variable is reflected by a change in another - identified on a scatter diagram

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37
Q

what is causation

A

when a change in one variable causes a change in another variable

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38
Q

what is the difference btwn correlation and casual relationships

A

correlation and causation

correlation doesn’t mean causation - other factors may be involved

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39
Q

explain what happens in digestion

A

large insoluble biological molecules are hydrolysed to smaller soluble molecuies that are small enough to be absorbed across cell membranes into blood

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40
Q

describe the digestion of starch in mammals

A

amylase produced by salivary glands hydrolyse starch to maltose
membrane bound maltase hydrolyses maltose into glucose
hydrolysis of glycosidic bond

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41
Q

describe the digestion of disaccharides in mammals

A

maltase -> maltose = glucose + glucose
lactase -> lactose = galactose + glucose
sucrase -> sucrose = fructose + glucose

hydrolysis of glycosidic bond

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42
Q

describe the digestion of lipids in mammals including action of bile salts

A

bile salts emulsify lipids causing them to form smaller lipid droplets
this increases SA of lipids for increased/faster lipase activity
lipase (pancreas) hydrolyses lipids -> monoglycerides + fatty acids
hydrolysis of ester bond

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43
Q

Describe the digestion of proteins by a mammal

A

Endopeptidases - hydrolyse internal peptide bonds w/n a polypeptide = smaller peptides so more ends, increased SA for exopeptidasees
Exopeptidases hydrolyse terminal peptide bonds at the ends of polypeptides - single amino acid
Membrane bound dipeptidases hydrolyse bond btwn a dipeptide - 2 amino acids

hydrolysis of peptide bonds

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44
Q

suggest why membrane-bound enzymes are important in digestion

A

membrane bound enzymes are located on cell membranes of epithelial cells lining ileum

through hydrolysisi at the site of absorption, conc. gradient is maintained for absorption

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45
Q

describe the pathway for absorption of products of digestion in mammals

A

lumen of ileum -> cells lining ileum -> blood

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46
Q

Describe the absorption of amino acids and monosaccharides in mammals

A

Co-Transport:
- Na+ actively transported from epithelial cells lining ileum to blood by Na+/K pump
- establishing a conc. gradient of Na+ (higher in lumen than epithelial cell)
- Na+ enters epithelial cell down its conc. gradient against its conc. gradient via a co-transporter protein
- Glucose moves down a conc. gradient into blood via facilitated diffusion

47
Q

Describe the role of micelles

A

they contain bile salts, monoglycerides and fatty acids:
- make monoglycerides and fatty acids = more soluble in water
- carry/release fatty aciids and monoglycerides to cell/lining of ileum
- maintain high conc. of fatty acids to cell/lining

48
Q

Describe the absorption of lipids by a mammal

A
  • monoglycerdies/fatty acids absorbed by diffusion
  • triglycerides reformed in epithelial cells and aggregate into globules
  • globules coated with proteins forming chylomicrons which are then packaged into vesicles
  • vesicles move to cell membrane and leave via exocytosis, enter lymphatic vessels and eventually return to blood circulation
49
Q

describe the role of red blood cells and haemoglobin in oxygen transport

A
  • red blood cells contain lots of haemoglobin - no nucleus, biconcave, high SA:V, short diffusion path
  • haemoglobin associates with/binds/loads O2 at gas exchange surfaces where partial pressure of O2 (pO2) is high
  • this forms oxyhaemoglobin which transports O2 (each can carry 4 O2)
  • haemoglobin dissociates from/unloads O2 near cells/tissues where pO2 is low
50
Q

describe the structure of haemoglobin

A

protein with a quaternary structure, made of 4 polypeptide chains. each chain contains a haem group containing on iron ion (FE2+)

they are a group of chemically similar molecules found in many different organisms

51
Q

Describe the loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociationi curve

A

areas with low pO2 (respiring tissues):
- haemoglobin has low affinity for O2
- so O2 readily unloads/dissociates with haemoglobin
- % saturation is low

areas with high pO2 (gas exchange surfaces):
- haemoglobin has a high affinity for O2
- O2 readily loads/associates with haemoglobin
- % saturation is high

52
Q

explain how the cooperative nature of oxygen binding results in an S-shaped oxyhaemoglobin dissociation curve

A
  • binding first oxygen changes tertiary/quaternary structure of haemoglobin
  • this uncovers haemoglobin group binding sites, making further binding of oxygens easier
53
Q

Describe evidence for the cooperative nature of oxygen binding

A
  • a low pO2 as oxygen increases there is little/slow increase in % saturation of haemoglobin with oxygen. first oxygen is binding
  • at higher pO2, oxygen increases there is a big/rapid increase in % saturation of haemoglobin with oxygen, showing it has gotten easier for oxygens to bind
54
Q

what is the bohr effect

A

effect of Co2 conc. on dissociation of oxyhaemoglobin -> curve shifts to the right

55
Q

explain the effect of CO2 conc. on the dissociation of oxyhaemoglobin

A
  • increasing blood CO2 e.g. due to increased rate of respiration
  • lowers blood pH (more acidic)
  • reducing haemoglobin’s affinity for ooxygen as shape/tertiary/quaternary structure changes slightly
  • more/faster unloading of oxygen to respiring cells at a given pO2
56
Q

hohw does the curve of the pO2 and % saturation of haem w O2 provide evidence of the effect of CO2 conc. on dissociationg of haem

A

at a given pO2 % saturation of haem is lower

57
Q

explain the advantage of Bohr effeect

A

more dissociation of oxygen -> faster aerobic respiration/less aerobic respiration -> more ATP produced

58
Q

explain why different types of haemoglobin can have different oxygen transport properties

A

different types of haem are made of polypeptide chains with slightly different amino acid sequences, resulting in different tertiary/quaternary structures/shape -> different affinities of oxygen

59
Q

explain how organisms can be adapted to their environment by having different types of haemoglobin with different oxygen transport properties if the curve on the graph shifts left

A

curve shifts left = haem has a higher affinity for O2

  • more O2 associates with haem more readily at gas exchange surfaces where pO2 is lower
    e.g. organisms in low environments - high altitudes, underground or foetuses
60
Q

explain how organisms can be adapted to their environment by having different types of haemoglobin with different oxygen transport properties if the curve on the graph shifts right

A

curve shifts right = haem has a lower affinity for O2
- more O2 dissociates from haem more readily at respiring tissues where more O2 is needed
e.g. organisms with high rates of respiration/metabolic rate (may be small or active)

61
Q

Describe the general pattern of blood circulation in a mammal

A

closed double circulatory system - blood passes through the heart twice for every circuit around body:

deoxygenated blood in the right side of the heart is pumped to lungs; oxygenated returns to the left side

oxygenated blood in the left side of the heart is pumped to the rest of the body; deoxygenated returns to the right

62
Q

suggest the importance of a double circulatory system

A

prevents mixing of oxygenated/deoxygenated blood so blood pumped to the body is fully saturated with oxygen for aerobic respiration
blood can be pumped to body at higher pressure after being lower from lungs, substances can be taken to/removed from body cells quicker/more efficiently

63
Q

name the blood vessels entering the heart and lungs and their role

A

vena cava - transports deoxygenated blood from respiring tissues -> heart
pulmonary artery - transports deoxygenated blood from heart -> lungs

64
Q

name the blood vessels leaving the heart and lungs and their role

A

pulmonary vein - transports oxygenated blood from lungs -> heart
aorta - transports oxygenated blood from heart -> respiring body tissues

65
Q

name the blood vessels entering and leaving the kidneys

A

renal arteries - oxygenated blood to the kidneys
renal veins - deoxygenated blood to vena cava from kidneys

66
Q

name the blood vessels that carry oxygennated blood to the heart muscle

A

coronary arteries are located on the surface of the heart, branching from the aorta

67
Q

what are the names of the valves

A

atrioventricular and semilunar valve

68
Q

suggeset why the wall of the left ventricle is thicker than that of the right

A

thicker muscle to contract with greater force to generate higher pressure to pump blood around entire body

69
Q

explain the presssures and volume changes and associated valve movements during the diastole part of the cardiac system which maintains a unidirectional flow of blood

A
  • atria and ventricles relax so volume increases, pressure decreases
  • semilunar valves shut when pressure in arteries exceeds pressure in ventricles
  • atrioventricular valves open when pressure in atria exceeds pressure in ventricles
  • blood fills atria via veins and flows passively to ventricles
70
Q

explain the presssures and volume changes and associated valve movements during the atrial systole part of the cardiac system which maintains a unidirectional flow of blood

A
  • atria contract = volume deacreases, pressure increases
  • atrioventricular valves open when pressure in atria exceeds pressure in ventricles
  • semilunar valves remain shut as pressure in arteries exceeds pressure in ventricles
  • blood pushed into ventricles
71
Q

explain the presssures and volume changes and associated valve movements during the ventricular systole part of the cardiac system which maintains a unidirectional flow of blood

A
  • ventricles contract = volume decreases, pressure increases
  • atrioventricular valves shut when pressure in ventricles exceeds pressure in atria
  • semilunar valves open when pressure in ventricles exceeds pressure in arteries
  • blood pushed out of the heart through the arteries
72
Q

explain how graphs showing pressure or volulme changes during the cardiac cycle can be interpreted

e.g. how to identify when valves are open/closed

A
  • semilunar valves closed:
    pressure in [named] artery is higher than in the ventricle to prevent backflow of blood from artery to ventricles
  • semilunar valves open:
    pressure in ventrile is higher than in [named] artery so blood flows from ventricle to artery
  • atrioventricular valves closed:
    pressure in ventricle higher than atrium to prevent backflow of blood from ventricles to atrium
  • atrioventricular valves open:
    pressure in atrium is higher than in ventricle so blood flows from atrium to ventricle
73
Q

what is the equation for caridac output

A

cardiac output = stroke volume x heart rate

74
Q

what is stroke volume

A

volume of blood pumped in each heart beat

75
Q

what is cardiac output

A

volume of blood pumped out of heart per min

76
Q

how can heart rate be calculated from cardiac cycle data

A

heart rate = 60 seconds / length of on cardiac cycle (seconds)

77
Q

what is the function of arteries

A

carry blood away from heart at high pressure

78
Q

how does the structure of arteries relate to its function

A
  • thick smooth muscle tissue can contract and control/maintain blood flow/pressure
  • thick elastic tissue can stretch as ventricles contract and recoil as ventricles relax to reduce pressure surges/even out blood pressure/maintain high pressure
  • thick wall to withstand pressure and stop from bursting
  • smooth/foolded endothelium reduces friction/can stretch
  • narrow lumen to increase/maintain high pressure
79
Q

what is the funcntion of arterioles

A

to direct blood to different capillaries/tissues

80
Q

what are arterioles

A

the divion of arteries to smaller vessels

81
Q

explain how the structure of arterioles relates to its function

A
  • thicker smooth muscle layer than arteries:
    contracts -> narrow lumen (vasoconstriction) reduces blood flow to capillaries
    relaxes -> widens lumen (vasodilation) increases blood flow to capillaries
  • thinner elastic layer = pressuree surges are lower due to being further away from the heart
82
Q

what is the fucntion of veins

A

carry blood back to heart at lower pressure

83
Q

explain how the structure of veins relates to their function

A
  • wider lumen than arteries = less resistance to blood flow
  • very little elastic + mucles tissue due to lower blood pressure
  • valves prevent the backflow of blood
84
Q

what is the function of the capillaries

A

to allow efficient exchange of substances btwn blood and tissue fluid

85
Q

explain how the structure of capillaries relates to their function

A
  • wall is thin, one cell thick layer of endothelial cells so reduces diffusion distance
  • capillary bed is a large network of branched capillaries -> increases SA for diffusion
  • smaller diamter/narrow lumen -> reduces blood flow rate so more time for diffusion
  • pores in walls btwn cells = larger substances can move through
86
Q

explain the formation of tissue fluid

A

arteriole end of capillaries:

higher blood/hydrostatic pressure inside capillaries due to contractioni of ventricles than tissue fluid so net outward force

forcing water and dissolved substances out of capillaries

large plasma proteins remain in the capillary

87
Q

explain the return of tissue fluid to the circulatory system

A

at the venulee end of capillaries:

hydrostatic pressure reduces as fluid leaves capillary due to friction

due to water loss an increasing conc. of plasma proteins lowers water potential in capillary below that of tissue fluid

water enters capillaries from tissue fluid by osmosis down a water potential gradient

excess water is taken up by lymph capillaries and returned to circulatory system through veins

88
Q

suggest and explain the causes of excess tissue fluid formation

A
  • low conc. of protein in bloow plasma or high salt conc.
    water potential in capillary not as low - water potential gradient is reduced
    more tissue fluid formed at arteriole end/less water absorbed at venule end by osmosis
  • high blood pressure = high hydrostatic pressure
    increases outward pressure from arterial end and reduces inward pressure at venule end
    more tissue fluid formed at arteriole end/less water absorbed at venule end by osmosis
    lymph system may not be able to drain excess fast enough
89
Q

what is a risk factor

A

an aspect of a person’s lifestyle or substance in a person’s body/environment that has been shown to be linked to an increased rate of disease

90
Q

state a few examples of risk factors for cardiovascular disease

A

age, high salt or saturated fat in diet, smoking, lack of excercise, genes

91
Q

describe the function of xylem tissue

A

transports water and mineral ions through the stem, up the plant to the leaves of plants

92
Q

suggest how xylem tissue is adapted for its function

A
  • cells joined with no end walls forming a long continuous tube = water flows at a continuous column
  • cells contain no cytoplasm/nucleus = easier water flow/no obstructions
  • thick cell wall with lignin = provides support.withstands tension/prevents water loss
  • pits in side walls which allows laterall water movements
93
Q

explain the cohesion-tension theory of water transport in the xylem

A

leaf:
- water lost from leaf by transpiration it evaporates from mesophyll cells into air spaces and water vapour diffuese through open stomata
- reducing water potential of mesophyll cells
- water drawn out of xylem down a water potential gradient

xylem:
- creating tension in the xylem
- hydrogen bonds result in cohesion btwn water molecules so water is pulled up as a continuous column
- water also adheres to the walls of xylem

root:
- water enters roots via osmosis

94
Q

Describe how ot set up a potometer

A
  • cut a shoot underwater at a slant - prevents air enetering the xylem
  • assemble the potometer with capillary tube end and submerge it under a beaker of water
  • insert shoot underwater
  • ensure apparatus is watertight/airtight
  • dry leaves and allow time for shoot to accclimatise
  • shut tap to reservoir
  • form an air bubble wuickly remove end of capillary tube from water
95
Q

what does a potometer do

A

it estimates transpiration rate by measuring water uptake

96
Q

describe how a potometer can be used to measure the rate of transpiration

A
  • record position of air bubble
  • record distance moved in a certain amount of time e.g. 1 minute
  • calculate volume of water uptake in a given time: use the radius of capillary tube to calculate cross sectional area of water (pi r squared), multiply this by distance moved by bubble
  • calculate rate of water uptake by dividing volume by time taken
97
Q

describe how a potometer can be used to investigate the effect of a named environmental variable on the rate of transpiration

A

measure rate of transpiration and change on variable at a time - wind, humidity, light or temperature
e.g. set up a fan, spary water in a plastic bag and wrap around the plant, change distance of a light source, change temperature of room
- keep all other variables constant

98
Q

suggest limitaitons in using a potometer to measure rate of transpiration

A
  • rate of water uptake might not be same as rate of transpiration: water is used for support,turgidity, used in photosynthesis and produced respiration
  • rate of movement through shoot in potometer may not be same as rate of movement through shoot of whole plant: shoot in potometer has no roots whereas a plant does. xylem cells are very narrow
99
Q

suggest how humidity affects rate of transpiration

A

increasing humidiity decreases the rate of transpiration

100
Q

explain why increasing humidity decreases rate of transpiration

A

more water in air so it has a higher water potential, decreasing water potential gradient from leaf to air. water evaporates slower

101
Q

suggest the effect of light intensity on the rate of transpiration

A

increasing light intensity increases the rate of transpiration

102
Q

explain why increasing light intensity increases rate of transpiration

A

stomato open in light to let CO2 in for photosynthesis, allowing more water to evaporate faster. stomata close when its dark so there is a low transpiration rate

103
Q

suggest the effect of temperature on rate of transpiration

A

increasing temperature increases rate of transpiration

104
Q

explain why increasing temperature increases rate of transpiration

A

water molecules gain kinetic energy as temperature increases so water evaporates faster

105
Q

suggest the effect of wind intensity on rate of transpirationi

A

increasing wind intensity increases rate of transpiration

106
Q

explain why increasing wind intensity increases rate of transpiration

A

wind blows away water moelcules from around stomata decreasing water potential of air around stomata, increasing water potential gradient so water evaporates faster

107
Q

describe the funciton of phloem tissue

A

transports organic substances e.g sucrose in plants

108
Q

suggest how phloem tissue is adapted for its function

A

sieve tube elements
- no nucleus/few organelles = maximum space for/easier flow of organic substances
- end walls btwn cells perforated sieves plates

companion cells
- many mitochondria = high rate of respiration to make ATP for active transport of solutes

109
Q

what is translocation

A

movement of assimilates/solutes such as sucrose from soruce cells to sink cells by mass flow

110
Q

explain the mass flow hypothesis for translocation in plants

A
  • at source, sucrose is actively transported into phloem sieve tubes/cells by companion cells
  • this lowers water potential in sieve tubes os water enters from xylem by osmosis
  • this increases hydrostatic pressure in sives tubes at source, creating hydrostatic pressure gradient
  • mass flow occurs, movement from source to sink
  • at sink, sucrose is removed by active transport to be used by respiring cells or stored in storage organs
111
Q

describe the use of tracer expirments to investigate transport in plants

A
  • leaf supplied with a radioactive tracer e.g. CO2 containing radioactive isotope 14C
  • radioactive carbon incorporated into organic substances during photosynthesis
  • these move around plant by translocation
  • movement tracked using autoradiography or a Geiger counter
112
Q

describe the use of ringing experiements to investigate transport in plants

A
  • remove/kill phloem e.g. remove a ring or bark
  • bulge forms on source side of ring
  • fluid from bulge has a higher conc. of sugars thann below which shows sugar is transported in phloem
  • tissue below the ring die as it cannot get organic substances
113
Q

suggest some points to consider when interpreting evidence from tracer and ringing experiments and evaluating evidence for/against the mass flow hypothesis

A
  • is there evidence to suggest phloem/respiration/active transport is invovled
  • is there evidence to show movements is from source to sink what are these in the experiment?
  • is there evidence to suggest movement is from high to low hydrostatic pressure
  • could movement be due to another factor e.g. gravity
114
Q

what is the difference btwn transpiration and transpiration stream

A

transpirtaion is the eloss of water vapour from leaves.

transpiration stream is the constant movement of water through the plant

Biology A-Level (11 decks)

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