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Biology aqa AS > exchange and transport systems > Flashcards

exchange and transport systems Flashcards

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1
Q

why do cells need oxygen

A

for aerobic respiration and nutrients

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2
Q

what waste products to cells excrete

A

carbon dioxide and urea

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3
Q

what needs to be exchanged between organisms

A

heat (as cells need to be kept at roughly the same temperature)

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4
Q

surface area to volume ratio

A

smaller animals = bigger SA:V, which means more heat loss

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5
Q

what do multicellular organism need

A

exchange organs and mass transport systems (as diffusion is too slow)

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6
Q

what is the mass transport system

A

circulatory system, which uses blood to carry hormones, antibodies, waste, glucose and oxygen around the body

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7
Q

heat exchange factors

A

size and shape

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8
Q

size on heat exchange

A

bigger surface area to volume ratio=faster heat loss, therefore small animals need a high metabolic rate to generate to stay warm

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9
Q

shape

A

compact=small SA:V, minimises heat loss

high SA:V =faster heat loss, lose moer water

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10
Q

what do small mammals need to eat

A

high energy foods such as seeds and nuts to deal with high metabolic rate

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11
Q

gas exchange surfaces adaptations

A

large surface area, thin (short diffusion pathway), maintains concentration gradient

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12
Q

single-celled organisms absorbing and releasing gas

A

by diffusion through their outer surface, through large surface area, thin surface

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13
Q

oxygen once it enters the cell

A

can take part in biochemical reactions as soon as it diffuses into the cell

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14
Q

what system do fish use for gas exchange

A

counter-current system

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15
Q

what is the counter-current system

A

water and blood flow in opposite directions which maintains a concentration gradient and means diffusion occurs as long as possible

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16
Q

how do fish get oxygen

A

water containing oxygen goes through its mouth and out the gills

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17
Q

what are gills made up of

A

thin plates called gill filaments (which gives a big surface area for exchange of gases)

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18
Q

what are gill filaments covered in

A

covered in lots of tiny structures called lamellae (which increase surface area further)

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19
Q

lamellae structure

A

lots of blood capillaries, thin surface layer of cells (to speed up diffusion)

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20
Q

what do insects use to exchange gases

A

tracheae

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21
Q

what are tracheae

A

microscopic air-filled pipes used for gas exchange

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22
Q

how does air move through the tracheae

A

through pores on the surface called spiracles , down the concentration gradient

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23
Q

tracheae branches

A

tracheoles

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24
Q

tracheoles adaptations to effective oxygen diffusion

A

have thin, permeable walls and go to individual cells (diffuses directly into respiring cells)

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25
Q

how do insects move air in and out of spiracles

A

rhythmic abdominal movements

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26
Q

carbon dioxide removal from insects

A

down concentration gradients towards the spiracles and released

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27
Q

what are dicotyledonous plants

A

group of flowering plants

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28
Q

why do dicotyledonous plants need C02

A

for photosynthesis

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29
Q

why do dicotyledonous plants need 02

A

respiration (produces CO2 as waste product)

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30
Q

what is the main exchange surface of dicotyledonous plants

A

surface of mesophyll cells in the lead

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31
Q

how are mesophyll cells adapted for gas exchange

A

large surface area

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32
Q

how do gases move through the leaf

A

in through stomata

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33
Q

what are stomata

A

special pores in the epidermis

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34
Q

what can stomata do

A

open to allow gas exchange, and close if the plant is losing too much water

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35
Q

what controls the stomata

A

guard cells

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36
Q

how to insects prevent losing too much water

A

close spiracles using muscles, have waxy cuticle over body, tiny hairs around spiracles (reduce evaporation)

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37
Q

how do guard cells control stomata

A

water enters the cells, making them turgid and opens stomata when plant has lots of water, when plant is dehydrated the guard cells lose water and become flaccid which closes the stomata

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38
Q

what are xerophytes

A

plants that live in warm, dry or windy conditions

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39
Q

what are plants that live in warm, dry or windy conditions

A

xerophytes

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40
Q

xerophyte adaptations

A 
stomata sunk in pits
layer of hairs
curled leaves
reduced number of stomata
waxy, waterproof cuticles
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41
Q

stomata sunk in pits adaptation

A

trap moist air, reducing concentration gradient between leaf and air, and reducing diffusion out of the leaf and reducing evaporation

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42
Q

layer of hairs adaptation

A

traps moist air around stomata

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43
Q

curled leaves adaptation

A

(with stomata inside) protects from wind which reduces rate of evaporation and diffusion

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44
Q

reduced number of stomata adaptation

A

fewer places for water to escape

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45
Q

waxy, waterproof cuticle adaptation

A

reduces evaporation

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46
Q

lung structure

A

trachea, splits into 2 bronchi (one leading to each lung), branches into bronchioles, end in air sacs called alveoli

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47
Q

ventilation

A

breathing in and out - inspiration and expiration

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48
Q

inspirtation

A

air breathing in

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49
Q

inspiration sequence

A 
active process
external intercostal muscles contract
diaphram muscles contract
ribcage moves upwards and outwards
diaphram flattens
thoratic cavity volume increased
lung pressure decerases 
air flows from high-low pressure, so flows into lungs
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50
Q

expiration

A 
passive process, but can be forced
external intercostal muscles relax
diaphram muscles contract
diaphram becomes curved again
ribcage moves downwards
thoratic cavity volume decreases
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51
Q

forced expiration

A

internal intercostal muscles contract which pulls ribcage further down and in , movement of the two sets of intercostal muscles is antagonistic

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52
Q

what is antagonistic

A

opposite

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53
Q

where does gas exchange in humans occur

A

alveoli

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54
Q

alveoli adaptations for gas exchange

A

lots in lungs (big surface area)
surrounded by network of capillaries (short diffusion distance)
thin exchange surface - alveolar epithelium is only one cell thick (short diffusion pathway)
steep concentration gradient

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55
Q

O2 across alveoli

A

diffuses out across alveolar epithelium and capillary endothelium, and into the haemoglobin in the blood

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56
Q

CO2 across alveoli

A

diffuses into the alveoli from the blood and is breathed out

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57
Q

lung diseases

A

pulmonary tuberculosis
fibrosis
asthma
emphysema

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58
Q

pulmonary tuberculosis

A

immune system builds a wall around the bacteria in the lungs forming tubercles (small hard lumps), infected tissue within these die and tidal volume is decreased
symptoms = cough, blood & mucus, chest pains

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59
Q

fibrosis

A

formation of scar tissue in lungs through e.g infection, so lungs can’t expand as much and tidal volume is reduced

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60
Q

what is tidal volume

A

volume of air in each breath

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61
Q

what is ventilation

A

number of breaths per minute

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62
Q

what is forced expiratory volume

A

volume of air that can be breathed out in 1 second

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63
Q

forced vital capacity

A

maximum volume of air possible to breathe forcefully out after a deep breath

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64
Q

asthma

A

airways become inflames/irritated, during an attack the smooth muscle lining in bronchioles contracts and mucus is produced, which constricts airways

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65
Q

emphysema

A

caused by smoking or long term exposure to air pollution, inflammation which attracts phagocyes to the area which produce an enzyme that breaks down elastin, so lungs can’t recoil, or destruction of alveoli

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66
Q

what is elastin

A

protein found in walls of alveoli

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67
Q

during dissection of the lungs

A

sharp but not too sharp tools, cutting board, cut lengthways along cartlidge

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68
Q

what breaks food down into smaller molecules

A

digestion

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69
Q

why are foods broken down

A

large molecules can’t be absorbed as they are too big to cross cell membranes (e.g starch, proteins)

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70
Q

what happens during digestion

A

large molecules are broken down into smaller molecules

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71
Q

why does digestion occur

A

so the molecule can be transported across the cell membrane and transported around the body

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72
Q

what are fats broken down into

A

fatty acids and monoglycerides

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73
Q

how are fats broken down

A

hydrolysis reactions

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74
Q

what are proteins broken down into

A

amino acids

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75
Q

how are proteins broken down

A

hydrolysis reactions

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76
Q

what breaks down the biological molecules during digestion

A

digestive enzymes

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77
Q

what are digestive enzymes produced by

A

specialised cells in the digestive system

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78
Q

where are digestive enzymes released into

A

the gut

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79
Q

what is amylase

A

digestive enzyme

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80
Q

what does amylase do

A

catylses conversion of starch into maltose

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81
Q

how does amylase do this

A

hydrolysis, breaks the glycosidic bonds

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82
Q

what produces amylase

A

salivary glands and pancreas

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83
Q

where is amylase released into

A

from the salivary glands = the mouth, from pancreas = small intestine

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84
Q

what are carbohydrates broken down by

A

amylase and membrane-bound disaccharides

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85
Q

what are membrane-bound disaccharides

A

enzymes attached to the membranes of epithelial cells lining the ileum

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86
Q

what is the ileum

A

final part of small intestine

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87
Q

what do membrane-bound disaccharides do

A

help break down disaccharides (e.g maltose, lactose, sucrose) into monosaccharides (glucose, fructose, galactose)

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88
Q

how do membrane-bound disaccharides do this

A

hydrolysis reactions, breaking gylcosidic bonds

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89
Q

how do monosaccharides move across the cell membranes of the ileum

A

specific transporter proteins

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90
Q

how are lipids broken down

A

lipase and the help of bile salts

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91
Q

what is lipase

A

digestive enzyme

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92
Q

what do lipase enzymes do

A

catalyse the breakdown of lipids into monoglycerides and fatty acids

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93
Q

how do lipases do this

A

hydrolysis, breaking ester bonds

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94
Q

where are lipases made

A

pancreas

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95
Q

where does lipase work

A

small intestine

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96
Q

where are bile salts produced

A

liver

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97
Q

what do bile salts do

A

emulsify lipids

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98
Q

why are bile salts important in lipid digestion

A

they increase the surface area that lipases can work on, by creating lots of small droplets instead of one big droplet

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99
Q

what are micelles

A

monoglycerides and fatty acids stuck with the bile salts

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100
Q

what do monoglycerides and fatty acids with bile salts form

A

tiny structures called micelles

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101
Q

what are proteins broken down by

A

endopeptidases

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102
Q

what are endopeptidases

A

a form of proteases

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103
Q

how do endopeptidases work

A

hydrolyse the peptide bonds inside a protein to break it down into amino acids

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104
Q

endopeptidases examples

A

trypsin
chymotrypsin
pepsin

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105
Q

where is trypsin made

A

synthesised in the pancreas

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106
Q

where is trypsin released

A

small intestine

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107
Q

where is chymotrypsin made

A

synthesised in the pancreas

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108
Q

where is chymotrypsin released

A

small intestine

109
Q

where is pepsin released into

A

the stomach

110
Q

where is pepsin released from

A

stomach lining

111
Q

what conditions does pepsin work in

A

acidic

112
Q

how are the acidic conditions produced in the stomach

A

the hydrochloric acid

113
Q

what are proteins broken down into

A

exopeptidases

114
Q

what do exopeptidases do

A

hydrolyse peptide bonds at the ends of protein molecules, and remove single amino acids from proteins

115
Q

exopeptidases examples

A

dipeptidases

116
Q

what do dipeptidases do

A

seperate the 2 amino acids that make up dipeptides by hydrolysing the peptide bond between them

117
Q

where are dipeptidases found

A

cell-surface membrane of epithelial cells in the small intestine

118
Q

what are the products of digestion

A

monosaccharides, monoglycerides and fatty acids, amino acids

119
Q

what are the monosaccharides produced that are absorbed

A

glucose , galactose, fructose

120
Q

how is glucose absorbed

A

by active transport with sodium ions via a co-transporter protein

121
Q

how is galactose absorbed

A

by active transport with sodium ions via a co-transporter protein

122
Q

how is fructose absorbed

A

by facilitated diffusion through a different co-transporter protein

123
Q

where are the products of digestion transported across

A

across the ileum epithelial into the bloodstream

124
Q

how are monoglycerides and fatty acids absorbed

A

diffuse directly across the membrane as they are lipid-soluble

125
Q

what helps monoglycerides and fatty acids move towards the epithelium

A

micelles

126
Q

how do micelles help move the products

A

they constantly break up and re-form, so release monoglycerides and fatty acids to be absorbed

127
Q

how are amino acids absorbed

A

diffusion with sodium ions through a sodium-dependent transporter protein

128
Q

how do sodium ions move into the iluem from epithelial cells

A

by active transport

129
Q

how is oxygen carried around the body

A

haemoglobin

130
Q

where is haemoglobin found

A

red blood cells

131
Q

what do red blood cells contain

A

haemoglobin

132
Q

what is haemoglobin

A

large protein with a quaternary structure (made up of 4 polypeptide chains)

133
Q

what does each polypeptide chain contain in haemoglobin

A

haem group

134
Q

what does the haem group contain

A

iron ion

135
Q

what does the iron ion in the haem group do

A

gives haemoglobin its red colour

136
Q

what does haemoglobin have

A

high affinity for oxygen

137
Q

what does high affinity for oxygen mean

A

high tendancy to combine with oxygen

138
Q

how many oxygen molecules can each haemoglobin molecule carry

A

4

139
Q

what is oxyhaemoglobin

A

haemoglobin in the lungs joined with oxygen

140
Q

how does oxyhaemoglobin form

A

when oxygen joins to haemoglobin in the red blood cells via a reversible reaction

141
Q

what does oxygen dissociating mean

A

oxygen leaves oxyhaemoglobin

142
Q

what is the chemical symbol for haemoglobin

A

Hb

143
Q

what is the chemical symbol for oxyhaemoglobin

A

HbO8

144
Q

what is the partial pressure of oxygen (pO2)

A

measure of oxygen concentration, greater concentration of dissolved oxygen in cells = higher partial pressure

145
Q

what is the partial pressure of carbon dioxide (pCO2)

A

measure of concentration of C02 in a cell

146
Q

what factor affects haemoglobins affinity for oxygen

A

the partial pressure of oxygen

147
Q

what happens to haemoglobin when there is a high partial pressure of oxygen

A

oxygen loads onto haemoglobin to form oxyhaemoglobin

148
Q

what happens to haemoglobin when there is a low partial pressure of oxygen

A

oxyhaemoglobin offloads oxygen

149
Q

how does oxygen enter blood capillaries

A

at the alveoli in the lungs

150
Q

what is the pO2 of alveoli

A

high

151
Q

what happens to the haemoglobin at the alveoli

A

oxygen loads onto it to form oxyhaemoglobin due to high pO2

152
Q

what happens to pO2 when cells respire

A

it lowers, as oxygen is used up (red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads its oxygen to be used)

153
Q

what happens after oxyhaemoglobin offloads its oxygen to respiring cells

A

returns to the lungs to collect more oxygen and become oxyhaemoglobin again

154
Q

what does a dissociation curve show

A

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

155
Q

what does the dissociation curve look like

A

S shaped

156
Q

what does the first oxygen entering the Hb do to the molecule

A

it makes it easier

157
Q

how does carbon dioxide concentration affect oxygen offloading

A

higher partial pressure of carbon dioxide=haemoglobin gives up its oxygen more readily

158
Q

what effect is carbon dioxide affecting oxygen offloading called

A

Bohr effect

159
Q

why does carbon dioxide concentration affect oxygen offloading

A

it means cells recieve more oxygen during activity, as when cells respire they produce carbon dioxide which highers pCO2

160
Q

what happens to the dissociation curve when there is high PCO2

A

it shifts right

161
Q

what is different about haemoglobin in different organisms

A

different type, with different oxygen transporting capabilities

162
Q

what haemoglobin do organisms in a low oxygen concentration habitat have

A

haemoglobin with a higher affinity for oxygen than humans, so the dissociation curve is to the left of ours

163
Q

what does a shift left in the dissociation curve mean

A

haemoglobin with a higher affinity for oxygen

164
Q

what haemoglobin do active organisms with a high oxygen demand have

A

haemoglobin with a lower affinity for oxygen than humans, so dissociation curve shifts to right

165
Q

what does a shift to the right in the dissociation curve mean

A

haemoglobin with lots of surrounding oxygen

166
Q

what transport system is the circulatory system

A

mass transport system

167
Q

where does the circulatory system carry marterials to and from

A

carries them from specialised exchange organs to their body cells

168
Q

what is the circulatory system made up of

A

the heart and blood vessels

169
Q

what does the heart do

A

pumps blood through blood vessels to reach different parts of the body

170
Q

what are blood vessels

A

arteries, veins, capillaries

171
Q

what does blood transport

A

respiratory gases, products of digestion, metabolic wastes and hormones

172
Q

what are the 2 circuits in the circulartory system

A

1=takes blood from the heart to the lungs then back to the heart,
2=around the rest of the body from the heart

173
Q

how does the heart get its blood supply

A

left and right coronary arteries

174
Q

what are arteries function

A

carry oxygenated blood from the heart to the rest of the body (except pulmonary arteries, which take deoxygenated blood to the lungs)

175
Q

what are arteries adaptations

A

thick and muscular walls with elastic tissue (so can stratch and recoil as the heart beats), which helps maintain high pressure, folded inner lining which allows it to stretch and maintain high pressure

176
Q

what is the inner lining of arteries

A

endothelium

177
Q

what do arteries divide into

A

smaller vessels called arterioles

178
Q

what do arterioles do

A

form a network throughout the body which have muscles inside that carry blood around the body by contracting to restrict blood flow or relaxing to allow full blood flow

179
Q

what do veins do

A

take deoxygenated blood back to the heart under low pressure (except pulmonary veins which take oxygenated blood to the heart from the lungs)

180
Q

what are veins adaptations

A

wider lumen with very little elastic or muscle tissue, contain valves to stop blood flowing backwards, body muscles surrounding contract to help with blood flow

181
Q

what do arterioles branch into

A

capillaries

182
Q

what are the smallest blood vessel

A

capillaries

183
Q

where are capillaries found

A

near cells in exchange tissues

184
Q

why are capillaries found here

A

so there’s a short diffusion pathway

185
Q

how thick are capillary cell walls

A

one cells thick

186
Q

why are capillary cell walls this thick

A

so there’s a short diffusion pathway

187
Q

how many capillaries are there

A

a large number

188
Q

why are there this number of capillaries

A

to increase surface area for exchange

189
Q

what are networks of capillaries in tissue called

A

capillary beds

190
Q

what is tissue fluid

A

fluid that surrounds cells in tissues

191
Q

what is tissue fluid made from

A

small molecules that leave the blood pasma, doesn’t contain red blood cells or big proteins (too big to be pushed through capillary walls)

192
Q

what gets taken out of tissue fluid by cells

A

oxygen and nutrients

193
Q

what do cells put into tissue fluid

A

metabolic waste

194
Q

what is the hydrostatic pressure are the start of the capillary bed

A

greater than in the tissue fluid

195
Q

what does the difference in hydrostatic pressure mean

A

it forces fluid out of the capillaries and into the spaces around the cells, forming tissue fluid

196
Q

what happens as the fluid leaves

A

hydrostatic pressure reduces in the capillaries, meaning it is lower than at the venule end

197
Q

what does the fluid loss mean

A

the concentration plasma proteins also increases, and water potential at the venule end of the capillary bed is lower than the water potential in the tissue fluid

198
Q

what does the water potential difference mean

A

some water re-enters the capillaries from the tissue fluid at the venule end by osmosis

199
Q

what happens to excess tissue fluid

A

it is drained into the lymphatic system

200
Q

what does the right hand side of the heart do

A

pumps deoxygenated to the lungs

201
Q

what does the left hand side of the heart do

A

pumps oxygenated blood to the whole body

202
Q

what is the thickness of the left ventricle muscular wall

A

thicker

203
Q

why is the left ventricle this thickness

A

so that it can powerfully contract to pump blood all

204
Q

why are the ventricle walls thicker than the atria

A

because they have to push the blood out of the heart around the body

205
Q

what do the atrioventricular valves do

A

link the atria to the ventricles and stop blood flowing backwards

206
Q

what do the semilunar valves do

A

link the ventricles to the pulmonary artery and aorta and stops blood flowing back into the heart

207
Q

what do the cords between the atrioventricular valves do

A

connect the valves, and stops them from being forced up into the atria when the ventricles contract

208
Q

what opens and closes the valves

A

the pressure in the heart chamber, higher pressure behind the valves forces the opens but high pressure infront forces it shut

209
Q

what does the cardiac cycle do

A

pumps blood around the body

210
Q

first stage of the cardiac cycle

A

ventricles relax, atria contract which decreases the chamber volume and increases the pressure which pushes blood into the ventricles increasing pressure and volume which ejects the blood

211
Q

second stage of the cardiac cycle

A

atria relax, ventricles contract which decreases their pressure and increases their pressure, which forces the AV valves shut stopping back flow. pressure in ventricles is higher than in the aorta and pulmonary which forces the SL valves open

212
Q

third stage of the cardiac cycle

A

ventricles and atria relax, blood returns to the heart and pressure starts to increase again

213
Q

what do most cardiovascular diseases start with

A

atheroma formation

214
Q

what is atheroma

A

when the inner lining of an artery is damaged, which causes white blood cells and lipids from the blood to clump together under the lining and form fatty streaks. overtime they build up and harden to form a fibrous plaque called atheroma

215
Q

what does an atheroma do

A

blocks the lumen which restricts blood flow and increases blood pressure

216
Q

example of cardiovascular disease

A

coronary heart disease, which occurs when artieries have lots of atheromas

217
Q

what do atheromas do

A

increase the risk of aneurysms and thrombosis

218
Q

what is an aneurysm

A

baloon-like swelling of the artery

219
Q

how do atheromas increase the risk of aneurysms

A

they damage and weaken the arteries and narrow them (increasing blood pressure), and so when blood flows through the weakened artery at a high pressure it can push out the inner layers through the outer elastic layer and cause an aneurysm

220
Q

what is caused if an aneurysm busts

A

haemorrhage

221
Q

what is a haemorrhage

A

bleedin

222
Q

what is thrombosis

A

formation of a blood clot

223
Q

how can atheromas increase the risk of thrombosis

A

ruptures the endothelium, which damages the artery and leaves a rough surface where platelets and fibrin accumulate and form a blood clot, and debris from the rupture can cause another blood clot to form further down the artery

224
Q

what can happen to the blood clot in arteries

A

can cause a blockage or become dislodged and block a blood vessel in another place

225
Q

what causes a myocardial infarction

A

interrupted blood flow to the heart

226
Q

what is a myocardial infarctions other name

A

heart attack

227
Q

what are the symptoms of myocardial infarctions

A

pain in chest, shortness of breath, sweating

228
Q

factors that increase risk of cardiovascular disease

A

high cholesterol and poor diet, cigarette smoking, high blood pressure, age, sex

229
Q

how does high cholesterol and poor diet increase risk of cardiovascular disease

A

cholesterol is main consistuent of fatty deposits that form atheromas, diet high in fat increaes cholesterol, diet high in salts increases risk of high blood perssure

230
Q

how does cigarette smoking increase risk of cardiovascular disease

A

because it contains nicotine and carbon monoxide, and decreases the amount of antioxidants in the blood, important for protecting cells

231
Q

how does nicotine increase risk of cardiovascular disease

A

increases risk of high blood pressure

232
Q

how does carbon monoxide increase risk of cardiovascular disease

A

combines with haemoglobin and reduces the amount of oxygen transported by the blood to tissues, so the heart doesn’t recieve enough oxygen

233
Q

how does high blood pressure increase risk of cardiovascular disease

A

increases risk of damage to artery walls and so increases risk of atheroma formation

234
Q

interpreting data on risk factors

A

describe data, draw conclusions, check any conclusions are valid, sample size

235
Q

tissues involved in transport in plants

A

xylem and phloem

236
Q

what does the xylem transport

A

water and mineral ions in solution

237
Q

what does the phloem transport

A

organic substances (e.g sugars) both up and down the plant

238
Q

what are the xylem vessels

A

long, tube-like formed from dead cells, no end walls, the part if the xylem tissue that trasnports the water and ions

239
Q

how does water move up the xylem

A

cohesion and tension, the cohesion-tension theory

240
Q

what is the cohesion-tension theory

A

water evaporated from the leaves (transpiration) which creates tension and pulls more water into the leaf and due to water molecules being cohesive and sticking together it means the whole column moves upwards, water enters through the roots

241
Q

what is transpiration

A

the loss of water from a plants surface through evaporation

242
Q

how does transpiration occur

A

water evaporates from the moist cell walls and accumulates in the spaces between cells in the leaf which moves down the concentration out of the cell when the stomata open

243
Q

what factors affect transpiration rate

A

light, temperature, humidity, wind

244
Q

how does light affect transpiration rate

A

lighter = faster transpiation rate as the stomata open for photosynthesis

245
Q

how does temperature affect transpiration rate

A

higher temperature = faster rate as warmer molecules have more energy so evaporate faster, concentration gradient increases so water diffuses out faster

246
Q

how does humidity affect transpiration rate

A

lower humidity = faster transpiration rate as concentration gradient increased

247
Q

how does wind affect transpiration rate

A

windier = faster rate as concentration gradient decreased (water molecules moved away from the stomata)

248
Q

what can a potometer be used for

A

estimate transpiration rate

249
Q

how to use a potometer

A

cut it sideways, count bubbles

250
Q

how to dissect plants

A

use tweezers and dissect them in water, transfer to dish containing stain and leave for a minute, rinse off in water and mount each onto a slide

251
Q

how is phloem tissue adapted for transporting solutes

A

they have sieve tube elements and companion cells

252
Q

what are solutes

A

dissolved substances

253
Q

what are sieve tube elements

A

living cells that form the tube for transporting solutes, they have no nucleus and few organelles

254
Q

what are companion cells

A

cells surrounding the phloem that carry out living functions for sieve cells (e.g providing energy needed for active transport of the solutes)

255
Q

what is translocation

A

energy requiring movement of solutes to where theyre needed in plants through the phloem

256
Q

whats another name for solutes

A

assimilates

257
Q

where does translocation move to and from

A

from the source to the sink

258
Q

what is the source

A

where its made (high concentration)

259
Q

what is the sink

A

where its used up (low concentration)

260
Q

how does the source and sink maintain a concentration gradient

A

through enzymes

261
Q

how do enzymes maintain a concentration gradient between the source and sink

A

by breaking down the solutes at the sink into something else, which ensures a lower concentration

262
Q

what explains phloem transport

A

mass flow hypothesis

263
Q

first step of mass flow hypothesis

A

active transport is used to actively load the solutes from companion cells into the sieve tubes of the phloem at the source which lowers the water potential inside sieve tubes so water enters by osmosis from xylen to companion cells, which creates a high pressure inside the sieve tubes at the source end of the phloem

264
Q

second step of mass flow theory

A

at the sink end, solutes are removed from phloem to be used up which increases the water potential and means water leaves the tubes by osmosis, which lowers pressure inside sieve tubes

265
Q

third step of mass flow theory

A

result is a pressure gradient from the source to the sink which pushes solutes along the sieve tubes towards the sink to be used or stored

266
Q

evidence for mass flow (4)

A

radioactive tracer can be used to track movement of organic substances, pressure in the phloem can be investigated using aphids (where sap flows out quicker nearer leaves), metabolic inhibitor stops translocation (active transport is involved), ring of bark removed = bulge above the ring (shows it flows downwards)

267
Q

evidence against mass flow (2)

A

sugar travels to many different sinks not the one with highest water potential, sieve plates would create a barrier to mass flow (lots of pressure required to get through them at a reasonable rate)

268
Q

how can the translocation of solutes be demonstrated experimentally

A

using radioactive tracers

269
Q

method of translocation of solutes being demonstrated experimentally

A

supplying part of plant with an organic substance that has a radioactive label which will then be incorporated into organic substances produced and moved by translocation, and can be tracket using autoradiography to see which part of the plant its been spread to (by freezing the plant, then placed on photographic film where the plant that contains radioctive material will turn black)

Biology aqa AS (7 decks)

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