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AQA A Level Biology > Exchange and Transport Systems > Flashcards

Exchange and Transport Systems Flashcards

1
Q

smaller organisms SA:V

A

higher surface area : volume ratiom

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2
Q

larger organisms SA:V

A

lower SA : V than smaller organsim’s

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3
Q

volume

A

width x height x length

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4
Q

surface area

A

area x no. of faces
if the area for different faces is different make sure you take this into account, check pg 139

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5
Q

surface area measurements

A

squared

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6
Q

volume measurements

A

cubed

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7
Q

surface area of a sphere formula

A

4πr2

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8
Q

volume of cylinder formula

A

πr2h

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9
Q

volume of a sphere formula

A

4/3 (πr3)

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10
Q

how do single celled organisms exchange substances?

A

substances can diffuse directly into/out of the cell across cell surface membrane.
Diffusion rate is quick because of the small distances the substances have to travel –> short diffusion pathway

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11
Q

How do multicellular organisms exchange substances?

A

they need specialised exchange organs and an efficient system to carry substances to and from their individual cells - THIS IS CALLED MASS TRANSPORT

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12
Q

in multicellular organisms diffusion across outer membrane is too slow because?

A
  • some cells are deep within the body and therefore there is a big distance between them and the outside environment
  • larger animals have a low SA:V ratio so it is difficult to exchange enough substances to supply a large volume of animal through a relatively small outer surface
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13
Q

mass transport in humans?

A

circulatory system - transport of blood which carries glucose hormones antibodies and waste e.g. CO2

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14
Q

mass transport in plants?

A

transport of water in the xylem and solutes in the phloem

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15
Q

what creates heat?

A

metabolic activity

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16
Q

why do smaller organisms need a high metabolic rate?

A

in order to generate enough heat to stay warm, as they have larger SA:V ratios so heat is lost more easily

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17
Q

compact shape –>

A

less heat loss as they have a small SA:V

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18
Q

not compact shape (sticky out bits) –>

A

increased heat loss due to a larger SA:V

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19
Q

what impacts heat exchange?

A

body shape and body size

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20
Q

adaptation of foxes and why?

A

arctic fox –> small ears and round head to make it more compact in order to reduce its SA:V and thus reduce its heat loss
African bat-eared fox –> large ears more pointed nose to increase SA:V as it is less compact and increase heat loss
European fox –> intermediate to match enviornmental temp

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21
Q

Adaptation to help prevent desert animals with a high SA:V ratio from losing water

A

some of these animals have kidney structure adaptations so that they produce less urine to compensate

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22
Q

cold region small mammals adaptation in order to support their high metabolic rates?

A

eat lots of high energy food e.g. seeds and nuts

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23
Q

what do smaller mammals have in order to protect them when it gets cold?

A

thick layers of fur or they hibernate

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24
Q

larger organisms in hot regions adaptations, e.g. elephant and hippo

A

beahvioural adaptation for hippos - spend majority of day in water to help them lose heat
Elephants have developed large flat ears which increase their SA allowing them to lose more heat

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25
Q

properties of gas exchange surfaces:

A

thin - short diffusion pathway
large surface area

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26
Q

what do organisms do in order to increase the rate of diffusion?

A

they maintain a steep conc grad

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27
Q

single celled organisms - gas exchnage?

A

simple diffusion already have a relatively large SA and thin so diffusion quick and can take part in metabolic reactions as soon as it is in cell - no need for specialised gas exchange systems

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28
Q

water - o2

A

lower pO2 in water compared to air so fish need specialised gas exchange system

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29
Q

benefit of lamellae?

A

good blood supply - lots of blood capillaries and a thin surface layer of cells to speed up diffusion between water and blood
they increase SA further on top of gill filaments

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30
Q

countercurrent system

A

steep conc grad maintained along the whole length of the lamellae/gill filament/gill/capillary
Oxygen conc is always higher in water than blood

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31
Q

water and blood flow

A

in OPPOSITE directions

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32
Q

apart from the countercurrent system, what else maintains the steep conc grad?

A

the normal circulation of the fish as the blood that becomes oxygenated by the gills is replaced with more deoxygenated blood
also, normal ventilation of the fish ensure that more water with a relatively high conc of oxygen is taken in

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33
Q

main gas exchange surface in dicotyledonous plants is?

A

the surface of the mesophyll cells in the leaf –> they have a large surface area

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34
Q

why would stomata close?

A

if the leaf is losing too much water

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35
Q

spiracles and stomata are?

A

pores within the exchange surface of insects and plants

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36
Q

insect gas exchange system

A

tracheae branch into tracheoles
gases move through spiracles
air moves into tracheae through spiracles and then the air moves into the tracheoles

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37
Q

tracheoles? what do they allow?

A

thin permeable walls and go to individual cells thus allowing oxygen to diffuse directly into respiring cells

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38
Q

what does the circulatory system of a terrestrial insect not do?

A

transport oxygen

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39
Q

how do insects move air in and out of the spiracles?

A

rhythmic abdominal movements

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40
Q

what are tracheoles lined with and why?

A

lined with thin single layer of cells to minimise diffusion distance

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41
Q

Give ways in which a terrestrial insects gas tracheal system isn adapted for efficient gas exchange?

A

tracheoles have thin walls SO short diffusion distance
large no. of tracheoles/ highly branched tracheal system SO short diffusion distance to cells
Large no. of tracheoles/hb SO large surface area
Tracheae provide tubes full of air SO fast diffusion
Fluid in the end of the tracheoles that moves out during exercise SO faster diffusion (miss estruch vid) through the air to the gas exchange system
Body can be moved by abdominal muscles to move air SO maintain diffusion gradient for O2/CO2

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42
Q

turgid - limp

A

guard cells swollen
guard cells limp

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43
Q

reducing water loss in insects:

A

close spiracles
waxy cuticle layer that is waterproof all over body - red eva
tiny hairs around spiracles - reducing evap

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44
Q

plant gets dehydrated what happens?

A

guard cells become limp as they lose water which closes the pore
as water enters guard cells it makes them turgid which opens the stomatal pores

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45
Q

xerophytes

A

specially adapted to reduce water loss as they are found in environments where water loss is a problem

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46
Q

xerophytic adaptations:

A

sunken stomata –> trap water vapour increases WP outside so reduced evaporation
layer of hairs on the epidermis –> trap water vapour etc.
rolled/curled leaves w/ stomata inside –> protecting from wind as windy conditions increase rate of evap
reduced no. of stomata –> fewer places for water to escape from
thicker waxy waterproof cuticles on leaves and stems –> reduce evaporation

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47
Q

how do windy conditions increase evaporation?

A

wind blows away water vapour, decreases the WP outside the plant so more water moves out down the WP gradient

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48
Q

inhalation in humans:

A

diaphragm contracts, external intercostal muscles contract
rib cage up and out
increased volume
decreased pressure in thoracic cavity to below atmospheric pressure
pressure grad
air moves down pressure grad from high to low into the lungs

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49
Q

exhalation in humans:

A

diaphragm relaxes and external intercostal muscles relax
internal intercostal muscles contract (during forced expiration)
rib cage moves down and in
decreased volume
increased pressure in thoracic cavity above atmospheric pressure
pressure grad created
air moves down pressure grad out of the lungs

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50
Q

human gas exchange system structure?

A

mouth/nose trachea bronchi bronchioles alveoli

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51
Q

ventilation:

A

inspiration and expiration

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52
Q

when do internal and external intercostal muscles act as an antagonistic pair?

A

during forced expiration

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53
Q

alveoli surrounded by?

A

network of capillaries

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54
Q

where is epithelial tissue usually found?

A

on exchange surfaces

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55
Q

what is the wall of each alveolus made from?

A

single layer of thin flat cells called the alveolar epithelium

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56
Q

walls of capillaries are made from?

A

capillary endothelium

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57
Q

pathway of oxygen from alveoli to capllary?

A

across alveolar epithelium acorss capillary endothelium

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58
Q

how does ventilation and circulation support a steep conc grad?

A

air high in oxygen is continually supplied
blood high in oxygen is continually replaced with blood low in oxygen

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59
Q

4 measure of lung function?

A

tidal volume(vol of air/breath)
ventilation rate (no. of breaths /min)
forced expiratory volume (max vol. air breathed out in 1 sec)
forced vital capacity(max. vol air out after max vol air in)

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60
Q

tuberculosis:

A

bacteira - immune cells build wall around bacteria in lungs forming tubercles - tissues infected with these die, gas exchange surface damaged –> tidal volume decrease –> results in fibrosis as well –> further reducing tidal volume –> reduced tidal volume so increased ventilation rate (make up for reduced volume in eahc breath so breathe quicker)

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61
Q

fibrosis:

A

formation of scar tissue in lungs
result of infection or exposure to dust/asbestos
scar tissue thicker and less elastic
SO lungs are less able to expand + can’t hold as much air, reducing tidal volume so FVC reduced (smaller vol of air forcefully breathed out)
reduction in gas exchange rate –> diffusion slower across a thicker scarred membrane
so faster ventilation rate
to get enough air into lungs to oxygenate blood

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62
Q

asthma:

A

inflamed + irritated airways
smooth muscle lining the bronchioles contracts and large amount of mucus produced
constriction of airways
can’t breathe properly
air flow in and out severely reduced
forced expiratory volume reduced

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63
Q

emphysema:

A

smoking or long-term exposure to air pollution caused
foreign particles in smoke become trapped in the alveoli
causing inflammation attracting phagocytes which produces an ezyme that breaks down the elastin
less elastic so alveoli stuggle to return to normal shape after inhaling and exhaling
alveolis can’t recoil to expel air - so it remains trapped in alveoli
destruction of alveoli walls
reduces SA of alveoli
rate of gas exchange decreases
increased ventilation rate

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64
Q

lung disease

A

reduce rate of gas exchange in alveoli
less oxygen able to diffuse down conc grad into blood
body cells receive less oxygen so rate of aerobic resp reduced
less energy released - feel weak and tired

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65
Q

restrictive disease?

A

FVC severely reduced but FEV1 likely to be high in comparison as restrictive diseases still allow you to breathe out normally ish

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66
Q

when describing a graph, what should you do?

A

use specific values/numbers from that graph

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67
Q

what can dissecting pins be used for?

A

used with a wax filled dissection tray to pin a specimen in place during the dissection

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68
Q

ensure all dissecting tools are all…?

A

sharp, clean and rust-free
sharp to ensure they cut well and you don’t injure yourself

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69
Q

why would you put lungs into a plastic bag when wanting to see them inflate?

A

to ensure that you stop bacteria inside the lungs from being released into the room

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70
Q

what is the trachea supported by?

A

C - shaped ring of cartilage

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71
Q

why does lung tissue feel spongy?

A

due to the air trapped inside the alveoli

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72
Q

what to do after dissections?

A

dispose of organs separately
wash hands
disinfect work surfaces

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73
Q

operculum?

A

bony flap that covers the gills

74
Q

why do tracheae appear silver?

A

because they’re filled with air

75
Q

what is the point of the rings of chitin in the walls of the tracheae?

A

act as supports like the rings of cartilage in the human trachea

76
Q

amylas results in the production of what?

A

maltose

77
Q

amylase produced?

A

salivary glands and pancreas

78
Q

membrane-bound disaccharidases where?

A

attached to the cell membranes of the epithelial cells lining the ileum

79
Q

monoglyceride?

A

a glycerol molecule attached to one fatty acid

80
Q

lipase function?

A

catalyses break down of lipids into monoglycerides and fatty acids
involved HYDROLYSIS of an ESTER BOND

81
Q

Lipases produced? act?

A

pancreas and then they act in the small intestine

82
Q

bile salts?

A

produced in liver
emulsify lipids - they cause the lipids to form really small droplets

83
Q

why bile salts?

A

several small droplets of lipid instead of one big one, larger surface area for the same volume of lipid

84
Q

what happens once the lipids have been broken down by lipase?

A

the monoglycerides and fatty acids stick with the bile salts to form tiny structures called micelles

85
Q

peptidases AKA

A

proteases

86
Q

exopeptidases?

A

remove single amino acids from tbe ends of protein molecules

87
Q

dipeptidase?

A

an exopeptidase that works specifically on dipeptides

88
Q

dipeptidases where?

A

often found in the cell surface membrane of epithelial cells in the small intestine ileum and duodenum
the dipeptidases found on the cell surface membranes are known as membrane-bound dipeptidases

89
Q

products of digestion, what happens to them?

A

absorbed across the ileum epithelium into the bloodstream

90
Q

absorption of glucose? galactose?

A

absorbed by active transport w/ Na+ via a co-transporter protein, galactose is exactly the same

91
Q

absorption of fructose?

A

via facilitated diffusion through a different transporter protein

92
Q

absorption of monoglycerides and fatty acids?

A

micelles help move them towards the epithelium
micelles can release monoglycerides and fatty acids allowing them to be absorbed
monoglycerides and fatty acids are lipid-soluble so they can diffuse directly across the epithelial cell membrane

93
Q

absorption of amino acids?

A

similar to glucose/galactose
Na+ actively transported out of the epithelial cells into the ileum itself, then diffuse back into the cells through sodium-dependent transporter proteins in the epithelial cell membranes carrying AA with them

94
Q

visking tubing?

A

partially permeable, allows smaller molecules not larger ones like proteins

95
Q

advantages of micelle formation and lipid droplet formation?

A

makes MG and FA water soluble
many small droplets of lipids and same volume increases the surface areaSO FASTER HYDROLYSIS ACTION of lipase and thus faster hydrolysis of triglyceride
micelles carry and release MG and FA at the epithelial lining of the ileum
Micelles increase the conc of MG and FA at the epithelial cell lining of the ileum

96
Q

what are micelles?

A

tiny structure that consist of bile salts and FA/MG bound togetheer

97
Q

absorption of fatty acids?

A

by diffusion

98
Q

process of digestion/absorption and transport of lipids?

A

micelles contain bile salts and FA/MG
micelles carry FA/MG to cell lining of the ileum
FA/MG absorbed by diffusion
Triglycerides reformed in cells
vesicles move to cell membrane

99
Q

haemoglobin is found…

A

in all veterbrates
some plants bacteria insects
earthworm and starfish

100
Q

haemoglobin structure?

A

quarternary
each pp chain has a haem group

101
Q

how many oxygens can each molecule of haemoglobin carry?

A

4

102
Q

equation for the binding of oxygen to haemoglobin (IT IS A REVERSIBLE REACTION)

A

Hb + 4O2 <–> HbO8
( it can carry 4 molecules of oxygen but each molecule of oxygen has two atoms)

103
Q

what does an oxygen dissociation curve show?

A

shows how saturated the haemoglobin is with oxygen at any given partial pressure

104
Q

when oxygen dissociation graph is steep…?

A

a slight change in partial pressure of oxygen causes a large change in the amount of oxygen carried by the haemoglobin

105
Q

curve of oxygen dissociation graph?

A

sigmoid

106
Q

oxyhaemoglobin curve, describe the shifts of the curves when there is a low partial pressure of oxygen or a high respiration/activity rate?

A

curve shifts to the Left when organsims live in environments with a LOW partial pressure (so there haemoglobin has a high affinity for oxygen) of oxygen e.g. underwater, underground, high altitudes
Curve shifts to the Right when organism’s have a high respiration rate

107
Q

describe the affinity for oxygen in very active organsims?

A

their haemoglobin has a low affinity for oxygen because they need to be able to readily unload oxygen so that it is available for them to use
their curve lies to the right

108
Q

what is metabolic rate?

A

the rate at which energy is used

109
Q

higher metabolic rate…

A

higher respiratory rate –> higher o2 demand

110
Q

How does the size of an organsim have an effect on their haemoglobin?

A

smaller mammals –> larger SA:V–>
lose heat quickly –> higher metabolic rate in order to replace heat loss –> higher resp rate –> higher oxygen demand –> lower affinity for oxygen (than humans if smaller) –> need to unload oxygen readily –> meet high oxygen demand

111
Q

what does the circulatory system do and what is it?

A

it is a specialised mass transport system that carries raw materials from specialised exchange organs to their body cells

112
Q

describe the pressure in the vena cava:

A

blood travels from high to low pressure
the vena cava is always the final blood vessel that takes blood back to the heart from the body, so it has the LOWEST PRESSURE

113
Q

pulmonary artery

A

heart to lungs

114
Q

pulmonary vein

A

lungs to heart

115
Q

aorta

A

heart to rest of body

116
Q

vena cava

A

body to heart

117
Q

renal artery

A

body to kidneys

118
Q

renal vein

A

kidney to vena cava

119
Q

what happens to the pressure along a blood vessel?

A

pressure decreases along a blood vessel due to friction

120
Q

what happens to an artery so that it can cope with high pressure?

A

an artery STRETCHES to cope with high pressure and then RECOILS under low pressure

121
Q

describe arteries walls:

A

thick muscular and have elastic tissue in order to stretch and recoil
when the heart beats

122
Q

describe the inner lining of the artery:

A

the inner lining is called the endothelium and it is folded which allows the artery to stretch and also helps it to maintain a high pressure

123
Q

what are arterioles?

A

arteries divide into smaller blood vessels called arterioles
they form a network throughout the body
blood is directed to different areas of demands in the body by the muscles inside the arterioles
these muscles contract to restrict blood flow and relax to allow full blood flow

124
Q

veins?

A

take blood back to heart under a low pressure
wider lumen than equivalent arteries e.g. pulmonary vein has a wider lumen than pulmonary artery
very little elastic or muscle tissue
valves prevent backflow blood
blood flow through veins is helped by the contraction of body muscles surrounding them

125
Q

what do capillaries connect?

A

they connect arterioles to venules at capillary beds

126
Q

what is tissue fluid made from?

A

from small molecules that leave the blood plasma e.g. oxygen water and nutrients
does not contain any RBC
contains some small proteins

127
Q

In a capillary bed, how do substances move out of the capillaries?

A

they move out of the capillaries into the tissue fluid by pressure filtration

128
Q

tissue fluid

A

forced out at the arteriole end and liquid reabsorbed at the venule end back into the capillary

129
Q

venule end of capillary?

A

low pressure as all the liquid was forced out and lower water potential compared to tissue fluid

130
Q

what is within the liquid that is being reabsorbed from the tissue fluid back into the capillary?

A

waste products that the cells are releasing - as the tissue fluid surrounds the cells the waste products can diffuse right into the tissue fluid from the cells e.g. CO2 and urea they dissolve in the water in tissue fluid and reabspbred back into blood to be removed from body

131
Q

why is not all of the tissue fluid reabsorbed into the blood?

A

because an equilibrium is reached so no water potential gradient

132
Q

how is the rest of the tissue fluid reabosrbed once an equilibrium is reached between the tissue fluid and the blood?

A

it is reabsorbed by the lymphatic system

133
Q

lympatic system and lymph vessels?

A

the system is made up of lympg vessels which are very similar to veins as they have valves
the lymph vessels surround the blood vessels so any liquid not reabsorbed back into capillaries gets absorbed into lymphatic system and is called lymph
Eventually lymphatic system brings the liquid back into blood

134
Q

at what end of the capillary is pressure the highest and why?

A

at the arteriole end of the capillary and this is caused by the left ventricle contracting and sending blood out of the heart through the arteries arterioles at high pressure

135
Q

right side and left side of heart?

A

right pumps deox blood to lungs and left pumps oxy blood to whole of body

136
Q

what is the use of the cords in the heart?

A

they attach the AV valves to the to the ventricles to stop them being forced up into the atria when the ventricles contract

137
Q

flow of blood?

A

unidirectional

138
Q

cardivascular disease?

A

disease associated with heart and blood vessels

139
Q

atheromas?

A

restrict blood flow to heart - can lead to myocardial infarction
fibrous plaque
if damage occurs to endothelium of artery e.g. from high bp, WBC and lipids from blood clump together under the lining to form fatty streaks. Over time, more WBC and lipids and connective tissue build up and harden –> form fibrous plaques (atheromas)
it partially blocks the lumen of artery and restricts blood flow causing blood pressure to increase

140
Q

coronary heart disease?

A

coronary arteries have lots of atheromas

141
Q

aneurysm?

A

swelling of artery
when blood travels through a weakened artery, due to atheromas, it may push the inner layers of the artery through the outer elastic layer forming an aneurysm - it may burst and thus cause a haemorrhage

142
Q

thrombosis?

A

formation of blood clot
starts with atheromas
atheroma ruptures endothelium
damages wall + leaves rough surface
platelets and fibrin (protein) accumulate at site of damage and form a blood clot (thrombus)
can cause a complete blockage of the artery
or the thrombus can become dislodged and block another blood vessel, debris from the rupture can cause another blood clot to form further down the artery

143
Q

myocardial infarction?

A

a coronary artery becomes blocked e.g. by thrombus/blood clot then an area of the heart muscle becomes cut off from its blood supply, receives no oxygen, causing a myocardial infarction
This can cause damage and death to the heart muscle, if large parts of the heart muscle are affected, it can cause complete heart failure

144
Q

how can smoking lead to an atheroma formation?

A

smoking decreases antioxidants in blood and antioxidants are important for protecting cells from damage, therefore damage to coronary artery wall is more likely to occur leading to an atheroma formation –> blocks artery restrits blood flow could lead to blood clots and myocardial infarction

145
Q

xylem structure?

A

long tube like structures formed from dead cells (vessel elements) joined end to end
there are no end walls on these cells making an uninterrupted tube that allows water to pass through

146
Q

cohesion?

A

supports whole columns of water up against the force of gravity

147
Q

as transpiration increases…

A

water movement up a plant incrwases because as water evaporates from the top of the leaves (transpiration) tension is created which pulls more water into the leaf

148
Q

transpiration?

A

water evaporates from the moist cell walls and accumulates in the spaces between cells in the leaf - when stomata open it moves out of the leaf down WP grad (as more water inside leaf than outside)
Water evaps from plant’s surface e.g. leaves

149
Q

if you want to compare water loss between different types of plants what do you need to do to ensure its fair?

A

you need to measure surface area of the leaves as it varies with the type of plant

150
Q

factors affecting rate of transpiration?

A

humidity, air movement (wind), temperature, light intensity

151
Q

light intensity - affect on transpiration rate?

A

higher - faster rate
positive correlation
more stomata open when its light in order to let in CO2 for photosynthesis,
more stomata open so larger surface area fpr water to evap out of
when dark –> stomata close (reduce water loss) so little transpiration

152
Q

temperature - affect on transpiration rate?

A

higher temp faster rate
warmer water molecules have more energy (kinetic) so evap from cells inside leaf much faster
water molecules move faster
(increases WP gradient between inside and outside leaf making water diffuse out faster)

153
Q

humidity - affect on transpiration rate?

A

negative correlation
more humid air surrounding
leaf –> more water vapour in air outside so WP more positive outside compared to inside thus reducing WP gradient so less water moves out as it can’t go from lower to higher WP so water can’t evaporate out

154
Q

air movement - affect on transpiration rate?

A

the wind removes the water vapour away from the outside of the leaf as wind removes humid air
positive correlation - faster wind movement = faster rate
Therefore maintaining the water potential gradient

155
Q

why cut shoot underwater when carrying out the potometer experiment?

A

prevents air from entering the xylem

156
Q

why cut the plant shoot at a slant - potometer experiment?

A

increases surface area available for water uptake

157
Q

what else do you do to ensure no air bubbles enter?

A

assemble the potometer apparatus underwater and insert the shoot with the apparatus still under water

158
Q

purposeful air bubble that is put into the capillary tube is called?

A

air-water meniscus

159
Q

how to work out rate of water uptake in mm3 per minute?

A

distance moved by air bubble and diameter of the capillary tube

160
Q

what graph can be plotted for the data where the distance moved by the bubble is measured per minute, what does this allow us to calculate?

A

a distance time graph - can calculate the rate of water uptake using the gradient of the line

161
Q

lignin?

A

a woody substance that helps to support the walls of xylem cells

162
Q

what stain can be used to see the xylem under an optical microscope?

A

toluidine blue O (TBO)
xylem cells stained blue-green

163
Q

what stain do you use for staining the lignin in the xylem and then for the nucleus/cell walls?

A

lignin –> phloroglucinol turns it red
nu/wall –> aniline blue turns nucleus blue and cell wall yellow-brown

164
Q

translocation?

A

movement of solutes (sucrose) up and down stem of plant/throughout plant
companion cell and sieve tube elements
source cell produces sucrose
sucrose actively transported into the phloem
by companion cells
lowers water potential in sieve tube elements and water enters via osmosis
increase in hydrostatic pressure causes mass movement of sucros towards sink cell
sink cell uses sucrose for respiration or storage

165
Q

sieve tube elements?

A

living cells that form the tube for transporting solutes (dissolved substances) - NO NUCLEUS
FEW ORGANELLES
there is a companion cell for each sieve tube element because of this

166
Q

companion cell?

A

they carry out the living functions for sieve cells e.g. providing energy for the active transport of solutes

167
Q

what are assimilates?

A

substances that become incorporated into the plant tissue
AKA solutes

168
Q

what type of process is phloem?

A

an energy requiring process
e.g. active transport of sucrose into sieve tube elements by companion cells from source cell

169
Q

sinks of sucrose?

A

food storage organs, the meristems (areas of growth) in the roots stems and leaves

170
Q

source of sucrose?

A

leaves

171
Q

how is a concentration gradient maintained for translocation?

A

enzymes break down the solutes e.g. sucrose at sink cells, used in respiration or stored as energy, this makes sure that there is always a lower concentration at the sink than the source. Also causes water to move out of the sieve tube elements into the xylem or the sink cells by osmosis creating a lower hydrostatic pressure.

172
Q

higher rate of translocation due to?

A

the higher the concentration of sucrose/solutes at the source

173
Q

companion cells contain?

A

many mitochondria so they can provide lots of ATP for the active transport of solutes from the companion cell to the sieve tube elements

174
Q

how can we support the mass flow theory?

A

Ringing experiment
Tracers (radioactive)

175
Q

describe the ringing experiment to support the mass flow theory?

A

Cut a ring of bark containing the phloem - not the xylem
and remove it from a woody stem
a BULGE forms above the ring
the bulge above the ring has a higher concentration of sugars than below the ring - as the sugars cannot move past the area where the bark (phloem) has been removed
This evidences the fact that there can be a downward flow of sugars
the build up of sugars above the ring lowers the water potential so water moves into the cells adding to the bulge

176
Q

How is the pressure gradient proved for the mass flow hypothesis?

A

aphids - they pierce the phloem, then their bodies are removed leaving the mouthparts behind so that sap can flow out. The sap flows out quicker nearer the leaves than further down the woody stem, showing that there is a higher pressure nearer the leaves and a lower pressure further down (SINK cells) proving the presence of a pressure gradient

177
Q

Describe how a tracer can be used to prove the mass flow hypothesis?

A

isolate the plant that they are investigating and only supply carbon dioxide that has been radioactively labelled
over time the plant will absorb that carbon dioxide through its stomata by diffusion. That carbon dioxide will be used by photosynthesis and thus create the sugars e.g.sucors/glucose
The carbons will be radioactively labelled, if placed on x-ray film it will turn it black. Take thin slices from the stem and place on x-ray film, turns it black which highlights where the phloem is and shows that the sugars are transported by the phloem.
we often use carbon-14 isotope

178
Q

why is a metabolic inhibitor used to prove the mass flow hypothesis?

A

it stops ATP production which will prevent the active transport of the sucrose into the sieve tube elements from the source cell by the companion cells therefore translocation will stop

179
Q

why is there a downward flow of sugars?

A

because sugars are made in the leaves - downward flow from source to sink

180
Q

how do we get sucros?

A

photosynthesis produces glucose, glucose is then converted to sucrose to be transported around the plant

181
Q

what are the two objections to the mass flow hypothesis?

A
  • that the sieve plats should act as a barrier to the mass flow/transport of sugars, and that a lot of pressure would be needed for the solutes to get through at a reasonable rate
  • sugars travel to many different sinks, not just the ones with the highest water potential
182
Q

describe the slightly altered tracers technique for mass flow hypothesis?

A

movement of the substances (sugars via translocation) is tracked using a technique called autoradiography. To reveal the radioactive carbon, the plant is killed e.g. using liquid nitrogen to freeze it and the plant is put onto photographic film. Where it turns black - sugars are

AQA A Level Biology (23 decks)

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