transport in plants Flashcards
(154 cards)
1
Q
Pressure - phloem
A
2000 kPa
2
Q
why do cells need transport systems
A
- metabolic demands
- size
- surface area to volume ratio
3
Q
metabolic demands
A
- many parts of the plant can’t photosynthesize
- they need O2 and glucose transported
- hormones made in one part of a plant need to transporting to areas where they have an effect
- waste products of cell metabolism removed
- mineral ions absorbed by roots need to be transported to all roots
4
Q
Surface are : volume ratio
A
- leaves have a large SA:V for exchange of gases in the air
- size and complexity of multicellular plants means other part of the plant has a small SA:V r
- plant can’t rely on diffusion alone to supply cells with everything they need
5
Q
mineral ions
A
- enzymes
- cell structure
6
Q
Size
A
- large plants need an effective transport systems
- to move substances both up and down
- from root tips to topmost leaves/stems
7
Q
Dicotyledonous plants
A
- make seeds they contain 2 cotyledons
- herbaceous dicots
- woody dicots
8
Q
cotyledons
A
- organs they act as food stores
- for developing embryo plant and form the first leaves when the seed germinates
9
Q
herbaceous dicots
A
- soft tissues
- short life cycle
- die down at end of growing season
10
Q
woody dicots
A
- have hard lignified tissues
- long life cycle
11
Q
what are the transport vessels in dicotyledonous plants known as
A
vascular system
arranged in vascular bundles
12
Q
vascular bundles - stem
A
- around edge
- for strength and support
13
Q
vascular bundle arrangement - roots
A
- in the middle
- help plant withstand tugging strains
- that result from wind
14
Q
vascular bundle - arrangement in palisade mesophyll
A
- midrib of a dicot leaf = main vein
- carried vascular tissue through organ
- support
- small branching veins spread through leaf
15
Q
xylem
A
- non living tissue
- transports water and mineral ions
- supports plant
16
Q
flow in xylem
A
- roots to short and leaves
17
Q
xylem structure
A
- mainly composed of dead cells
- long hollow structures
- made by several columns of cells fused together end to end
- lignified secondary walls
18
Q
tissues associated with xylem tissue
A
- xylem parenchyma
- tannin
19
Q
xylem parenchyma
A
- packs around xylem vessels
- stores food
- contains tannin deposits
- thick walled
20
Q
tannin
A
- bitter chemical
- protects plant tissues from attack
21
Q
A
21
Q
lignin
A
- provides mechanical strength
- don’t transport water
22
Q
how can lignin be laid in xylem walls
A
- form rings
- spirals
- solid tubes
23
Q
unlignified areas in xylem
A
- bordered pits
24
bordered pits
- water leaves xylem
- moves into other areas of plant
25
phloem
- living tissue
- transports food in the form of organic solutes
- supplies cells with sugars and amino acids needed for respiration and synthesis of other molecules
26
phloem - flow
- up and down plants
- collects solutes from leaves
27
structure - phloem
- sieve tube elements
- sieve plates
- companion cells
28
sieve tube elements- structure
- made up of many cells joined end to end
- forms a long hollow structure
- not lignified
29
sieve plates
- areas between the cells where walls are perforated
- allow phloem contents through
30
phloem sieve tube elements and sieve plates- structure
- tonoplast breaks down
- nucleus and some other organelles break down
- phloem becomes a tube filled with phloem sap
31
companion cells
- closely linked to sieve tube elements
- linked to STE by plasmodesmata
- maintain nucleus and organelles of phloem
- active
- life support system for sieve tube cells
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plasmodesmata
- microscopic channels through cellulose cell walls
33
supporting tissues - phloem
- fibres
- sclereids
- cells with very thick walls
34
why is water important for plants
- turgor pressure
- turgor
- loss of water by evaporation
- mineral ions
35
turgor pressure
- provides a hydrostatic skeleton
- supports the stems and leaves
36
turgor pressure in leaf cells
- 1.5 MPa
37
Turgor
- drives cell expansion
- enables plant roots to force their way through tarmac and concrete
38
loss of water by evaporation
- helps keep plants cool
39
mineral ions
- products of photosynthesis
- transporter in aqueous solutions
40
root hair cells
- exchange surface in plants
- water is taken into the body of the plant from the soil
- long thin extension from a root hair cell
41
root hair cells - adaptations
- microscopic size = penetrate easily between soil particles
- large SA:V ratio
- thin surface layer = fast diffusion and osmosis
- concentration of solutes in cytoplasm of root hair cells maintains a water potential gradient between soil water and cell
42
how does water move from soil to roots of plant
- soil water has low concentration of dissolved minerals = high WP
- cytoplasm and vacuolar sap of root hair cell contain many different solvents so water potential of cell is lower
43
2 types of of transport pathways
- symplast
- apoplast
44
symplast pathway
- water moves through the continuous cytoplasm of living plant cells that’s connected via plasmodesmata
45
how does symplast pathway work
- root hair cell has a higher water potential than the next cell along
- due to water diffusing in from soil
- water moves from root hair cell into next cell along by osmosis
46
how is a steep concentration gradient maintained allowing as much water as possible continues to move from cell to soil
- water leaves root hair cell by osmosis
- water potential of cytoplasm falls again
47
apoplast pathway
- water moves through the cell walls and intercellular spaces
- water fills spaces between the loose open network of fibres in the cellulose cell wall
48
how is water pulled through the xylem in the apoplast pathway
- water molecules are pulled through the apoplast behind them
- due to cohesion
- creating tension
- continuous flow of water through open structure of cell wall
- little to no resistance
49
What does water move into after it has travelled in the symplast and apoplast pathways
- endodermis
50
endodermis
- layer of cells surrounding the vascular tissue
51
Casparian strip
- band of waxy suberin
- runs around each of the endodermal cells
- forms a waterproof layer
52
what happens to the apoplast pathway at the casparian strip
- water can’t travel any further
- forced into symplast pathway
53
why is it good that water is forced into cytoplasm at the casparian
- water must pass through selectively permeable membranes
- excluding any potentially toxic solutes in soil water from reaching living tissues
- as membranes would have no carrier proteins to admit them
54
how does water move into the xylem quickly by osmosis down the water potential gradient in the symplast pathway
- solute concentration in cytoplasm of endodermal cells is dilute compared to cells in xylem
- endodermal cells move mineral ions into the xylem by active transport
- water potential in xylem cells is lower than endodermal cells
55
once in vascular bundle what pathway can water return to
- apoplast
- it can enter xylem
- and move up plant
56
how does root pressure occur in the xylem
- active pumping of minerals
- produces movement of water by osmosis
- root pressure is independent of any effects of transpiration
57
root pressure
- gives a push up the xylem
- but isn’t the major factor in the movement of water from roots to leaves
58
evidence for role of active transport in root pressure
- some poisons affect mitochondria and prevent production of ATP = i’d applied to root cells no energy supply so root pressure stops
- root pressure increases with a rise in temperature = chemical reactions
- if levels of oxygen or respiratory substrates fall, root pressure falls
- guttation
59
guttation
- xylem sap may exude from cut ends of stems at certain times
- xylem sap is forced out of special pores at the ends of leaves in some conditions
60
photosynthesis
- process by which green plants make their own food
- occurs in the leaves
61
Carbon dioxide and Water
- needed for photosynthesis
- must be transported from roots
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waxy cuticle - leaves
makes leaves waterproof
63
large sa - leaves
- capturing sunlight
64
how does carbon dioxide and oxygen move in and out of the leaf
- by diffusion
- down concentration gradients
- through stomata
65
what controls opening and closing of stomata
guard cells
66
when stomata is open for carbon dioxide and oxygen to be exchanged, what else moves out of the leaf
- water vapor
- by diffusion
67
transpiration
loss of water vapor from leaves and stems of plants
68
when is most stomata closed
- at night
- as no oxygen is being produced by photosynthesis
- so prevents water loss
69
why do some stomata always need to be open
- to take in oxygen for cellular respiration
70
Transpiration stream - step by step
- water molecules evaporate from surface of mesophyll cells into air spaces in leaf
- move out of stomata into surrounding air by diffusion down concentration gradient
- loss of water by evaporation from a mesophyll cell lowers the water potential of the cell
- water move into the cell from an adjacent cell by osmosis along both pathways
- this is repeated across the leaf to the xylem
- water moves out of the xylem by osmosis into the cells of the leaf
- water molecules form hydrogen bonds with carbohydrates in walls of xylem vessels = adhesion
- water molecules form H bonds with each other = cohesion
- water moves up across roots from soil
71
what do the combined effects of adhesion and cohesion result in
- capillary action
72
capillary action
- water can rise up narrow tube
- against force of gravity
- water is drawn up xylem in a continuous stream
- replacing water lost by evaporation
- transpiration pull
73
transpiration pull
- causes tension across xylem
- helps move water across roots from soil
- cohesion tension theory
74
cohesion tension theory
- water moving from soil in continuous stream up xylem in leaf
75
evidence for cohesion tension theory
- changes in diameter of trees
- xylem vessel broken
76
changes in diameter of trees
- when transpiration is high
- tension in xylem is high
- tree shrinks in diameter
- vice versa
- tested by measuring circumference of tree at different times of the day
77
xylem vessels broken
- air is drawn into water
- water doesn’t leak out
- plant can’t move water up stem
- as continuous stream of water molecules held by cohesion is broken
78
transpiration role - summary
- delivers water and mineral ions
- to cells where they’re needed
- evaporation or water from leaf surfaces help cool lead down
- preventing heat damage
79
why is water loss by transpiration a problem
- amount of water available is often limited
- in high intensity sunlight there is a high rate of gas exchange
- stomata will be open
- plant may lose lots of water through transpiration
- so supply won’t meet demand
80
what process controls opening and closing of stomata
- turgor driven process
81
low turgor - stomata
- asymmetric configuration of guard cell walls closes pore
82
guard cells - stomata - environmental conditions are favorable
- guard cells pump in solutes by active transport
- increasing their turgor
83
cellulose hoops
- prevent guard cells swelling in width
- they extend lengthways
84
at optimum conditions how does the guard cell change shape
- inner wall which is more flexible causes bean shape
85
when water becomes scarce what happens to guard cells
- hormonal signals from roots trigger turgor loss from GC
- closing stomatal pore
- conserving water
86
factors affecting transpiration
- light
- humidity
- temperature
- air movement
- soil water availability
87
light affecting transpiration
- needed for photosynthesis
- in dark most stomata close
- lighter = more stomata open
- increasing rate of water vapour moving out
- increasing evaporation
- increasing transpiration
88
humidity
- a measure of the amount of water vapour in air compared to total concentration of water the air can hold
89
humidity affecting transpiration
- high humidity lowers transpiration
- due to reduced water water vapour potential gradient
- between the inside of the leaf and outside air
90
temperature affecting transpiration
- increases kinetic energy of water molecules
- increasing evaporation from spongy mesophyll cells into air spaces of the leaf
- increases concentration of water vapour that external air can hold before it becomes saturated
- increasing diffusion gradient between air inside and outside leaf
- increasing rate of transpiration
91
air movement in leaf
- each leaf is a layer of still air around it
- trapped by shape of leaf and features on the surface,
eg hairs
- decreasing air movement close to leaf
92
air movement affecting transpiration
- water vapour that diffuses out of leaf accumulates in still air around leaf
- water potential gradient around stomata increases
- diffusion gradient decreases
- air movement increased rate of transpiration
- period of still air decreases transpiration
93
soil water availability
- if plant is dry
- plant under water stress
- rate of transpiration reduces
94
in translocation where do organic compounds in the phloem move from and to
- sources to sinks
95
type of process - translocation
active
96
assimilates
- products of photosynthesis that are transported
97
what is the main assimilate
sucrose
98
sources
- green leaves and green stems
- storage organs eg tubers
- food stores in seeds when they germinate
99
sinks
- roots that are growing
- meristems which are actively dividing
- any part of the plant that are laying down food stores
100
stages of translocation
- phloem loading
- symplast route
- apoplast route
- phloem unloading
101
phloem loading
- products of photosynthesis are moved into the phloem from sources
102
why is sucrose transported instead of glucose
- it isn’t used in metabolism as readily
- less likely to be metabolized during transport
103
2 types of phloem loading
- apoplast route
- symplast route
104
symplast route - translocation
- sucrose moved through cytoplasm of mesophyll cells and into sieve tubes
- through diffusion through plasmodesmata
- mainly passive route
- sucrose ends up in siege elements
- water follows by osmosis creating a pressure of water that moves sucrose through phloem by mass flow
105
apoplast route - translocation
- sucrose travels through cells walls and inter cell spaces to companion cells and sieve elements
- by diffusion
- along concentration gradient
106
apoplast route - translocation - how is a concentration gradient of sucrose maintained
- removing sucrose into phloem vessels
107
apoplast route - translocation PROCESS
- sucrose is moved to cytoplasm in companion cells across cell membrane in active process
- hydrogen ions are actively pumped out of the companion cells into surrounding tissues using ATP
- hydrogen ions return to companion cell down a concentration gradient via co transporter protein
- sucrose is co transported with H+ ions
- increasing sucrose concentration in companion cells and in the sieve elements through many plasmodesmata between 2 cells
108
companion cells - adapted for translocation
- many infoldings in cell membranes
- giving increased surface area for active transport
- many mitochondria to supply ATP needed for transport pumps
109
translocation - what happens to build up of sucrose in companion cell and sieve tube element
- water moves in by osmosis
- leads to build up of turgor pressure due to cell walls
- water carrying assimilates move into sieve tube elements
- reducing pressure in companion cells
- water moves up or down plant by mass flow to areas of low pressure (sinks)
110
what happens when solutes accumulate in the source phloem lead to
- increase in turgor pressure
- forcing sap to regions of lower pressure
111
phloem unloading
- diffusion of sucrose from phloem into surrounding cells
- moves from cell to cell by diffusion
- or converted into another substance eg glucose
112
what do pressure differences in plant allow - translocation
- transport solutes rapidly
- over many meters
- up or down plant
113
when does phloem unloading occur
- at any point
- into cells which need it
114
why is phloem unloading important
- concentration gradient of sucrose is maintained
- between contents of phloem and surrounding cells
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what does a loss of solutes from the phloem lead to for water ( translocation )
- rise in water potential
- water moves into surrounding cells by osmosis
- some is drawn into transpiration stream into xylem
116
evidence for translocation
- microscopy = adaptations of companion cells for active transport
- mitochondria in companion cells poisoned = translocation stops
- flow of sugars is about 10,000 faster than diffusion alone = active transport drives mass flow
- aphids
117
how do aphids show evidence for translocation
- there’s a positive pressure in the phloem that forces sap out through stylet
- pressure and therefore flow rate in phloem is closer to the sink than the source
- concentration of sucrose in phloem sap is also higher near to the source than near the sink
118
translocation - evidence negatives
- not all solutes in phloem move out at same rate
- however sucrose always seems to move at same rate regardless of concentration at sink
- role of sieve plates is uncertain
119
xerophytes
- plants in dry habitats which have evolved a wide range of adaptations that enable them to live and reproduce in places where water availability is low
120
example of a xerophyte
- conifers
- marram grass
- cacti
121
features of xerophytes
- thick waxy cuticle
- sunken stomata
- reduced numbers of stomata
- reduced leaves
- hairy leaves
- curled leaves
- succulents
- leaf loss
- root adaptations
- avoiding the problem
122
thick waxy cuticle
- minimizes water loss by evaporation
123
sunken stomata
- stomata located in pits
- reduce air movement
- produce microclimate of moist air
- reduces water vapour potential gradient
- reduces transpiration
124
reduced leaves
- reduce leaf area
- water loss reduced
- reduced sa:v r
- minimizing water loss by evaporation
125
hairy leaves
- create a microclimate of still humid air
- reducing water potential gradient
- minimising loss of water vapour by transpiration from surface of the leaf
126
curled leaves
- reduces water loss by transpiration
- confines all of the stomata within a microenvironment of still, humid air
- reducing diffusion of water vapour from the stomata
127
succulents
- store water in specialised parenchyma tissue in stems and roots
- water is stored when it is in plentiful supply then used in times of drought
128
leaf loss
- plants prevent water loss by losing their leaves when water is unavailable
129
root adaptations
- helps plants get as much water as possible from soil
- long tap roots growing deep into the ground which can penetrate serveral metres
- so the roots can can access water that is a long way below the surface
- a mass of widespread shallow roots with a large surface area can absorb any available water before a rain shower evaporates
130
root adaptations - marram grass
- has long vertical roots which penetrates metres into the sand
- have a mat of horizontal rhizomes from which many more roots develop to form an extensive network
- helps to change their environment
- enables sand to hold more water
131
avoiding the problems
- plants may lose leaves
- become dormant
- may die entirely, leaving seeds behind to germinate and grow rapidly when rain walls again
- surviving as storage organs
- some plants withstand complete dehydration and recover then plant becomes turgid and green again and begins to photosynthesise
132
how can some plants survive dehydrated then recover
- disaccharide trehalose
- which appears to enable the cells to survive unharmed
133
storage organs example
- bulbs (onions)
- corms (crocuses)
- tubers (potatoes)
134
hydrophytes
- plants that actually live in water
- need special adaptations to cope with growing in water or in permanently saturated soil
135
how do hydrophytes live in water
- submerged
- on the surface
- the edges of bodies of water
136
examples of hydrophytes
- water lilies
- water cress
- duckweeds
- marginals
- yellow iris
137
why is it important that surface water plant leaves float
- so they are near the surface of the water
- so they get the light needed for photosynthesis
138
what is a common issues hydrophytes face
- water logging
- the air spaces of hydrophytes need to be full of air in order to survive
139
adaptations of hydrophytes
- very thin/no waxy cuticle
- many open stomata on upper surfaces
- reduced structure to the plant
- wide, flat leaves
- small roots
- large surface area of stems and roots underwater
- air sacs
- arenchyma
140
very thin / no waxy cuticle
- hydrophytes do not need to conserve water
- so water loss by transpiration is not an issue
141
many open stomata on upper surface
- maximise number of stomata maximises gas exchange
- as there is no risk to turgor loss
- as water is plentiful
142
why do stomata need to be on the upper surface of floating leaves
- so they are in contact with air
143
reduced plant structure
-water supports the leaves and flowers
- no need for strong supporting structures
144
wide flat leaves
- spread across water surface
- to capture as much light as possible
145
small roots
- water can diffuse directly into stem and leaf tissue
- less need for uptake by roots
146
large surface area of stems and roots underwater
- maximises area for photosynthesis
- for oxygen to diffuse into submerged plants
147
air sacs
- to enable leaves/flowers to float to water surface
148
aerenchyma
- specialised parenchyma tissue forms in leaves, roots, stems of hydrophytes
- has many large air spaces
149
how is aerenchyma formed
- by apoptosis in normal parenchyma
150
functions - aerenchyma
- making leaves/stems more buoyant
- forming a low resistance internal pathway for the movement of substances such as oxygen to tissues below the water
- this allows the plants to cope with anoxic conditions in the mud by transporting oxygen to different tissues
151
what does the aerenchyma low resistance pathway do
- methane produced by rice plants
- can be vented into atmosphere
152
why is aerenchyma tissue allowing methane into the atmosphere bad
- greenhouse gas
- climate change
153
in situations with lots of water and less air, roots can become waterlogged, how are roots specialised
- special ariel roots = pneumatophores
- grow upwards int the air
- have many lenticels allowing entry of air into tissue
