3.1.3 Transport in plants Flashcards
1
Q
why do plants require transport systems?
A
-metabolic demands
-size
-surface area to volume ratio
2
Q
why do plants require transport systems for their metabolic demands?
A
glucose and oxygen are produced in photosynthesis, but not all areas of a plant photosynthesis, ions and hormones also need to be transported
3
Q
why do plants require transport systems due to their size?
A
plants grow throughout their lives, transport from root to stem tip in large plants
4
Q
why do plants require transport systems due to their surface area to volume ratio?
A
leaves have a large SA:V ratio for gas exchange and the absorption of light, but stems and trunks have relatively small SA: ratio, so diffusion is in inefficient
5
Q
what do plants need to survive?
A
-CO2, oxygen from air or photosynthetic cells
-organic nutrients, products of photosynthesis
-inorganic ions, taken in by roots
-water
6
Q
define xylem
A
transports water and inorganic ions from the root to the rest of the plant as a result of physical forces
7
Q
define phloem
A
transports assimilates from leaves to all other parts of the plant
8
Q
what is the vascular bundle system of a herbaceous dicot made up of?
A
made up of xylem and phloem tissue
9
Q
what are monocotyledons?
A
single leafed plants
10
Q
what are some examples of monocotyledons?
A
grasses, rice and wheat
11
Q
what are dicotyledons?
A
makes seeds that contain two cotyledons
12
Q
what are some examples of dicotyledons?
A
all flowering plants
13
Q
what are herbaceous dicots?
A
soft tissues and relatively short life cycle (leaves and stems die at the end of the growing season)
14
Q
label a diagram of a flower
A
see paper flashcard
15
Q
label a diagram of a cross section of a leaf
A
see paper flashcard
16
Q
what’s the function of a waxy cuticle?
A
prevent water loss and protects against infection, allows light through
17
Q
what’s the function of the upper epidermis?
A
small cells that are transparent to allow light through
18
Q
what’s the function of the palisade mesophyll?
A
contains lots of chloroplasts for photosynthesis
19
Q
what’s the function of the air space in the spongy mesophyll?
A
provide gases needed for diffusion
20
Q
what’s the function of the lower epidermis?
A
protection- prevents entry to air spaces
21
Q
what’s the function of the stomata?
A
to allow entrance and exit of gases for diffusion (CO2)
22
Q
what’s the function of the guard cell?
A
to control opening and closing of stomata
23
Q
draw and label a cross section of a dicot stem
A
see paper flashcard
24
Q
draw and label a cross section of a dicot root
A
“see paper flashcard*
25
draw and label a cross section of a dicot leaf
*see paper flashcard*
26
what does the xylem vessel transport?
transports water and minerals
27
is the phloem made of living or dead cells?
living cells
28
describe the thickness of the phloem cell wall
thin cell wall
29
is the xylem made of living or dead cells?
made of dead cells
30
what does the phloem transport?
carries assimilates to growing parts and storage organs
31
describe the thickness of the xylem cell wall
thick cell wall
32
describe the composition of the phloem
-tissue has companion cells
-has sieve plates
33
are the xylem cell walls permeable or impermeable?
impermeable cell walls
34
what are the phloem cell walls made of?
cell walls are made of cellulos
35
does the xylem have cytoplasm?
no cytoplasm
36
are there sieve plates in the xylem?
sieve plates are absent
37
what is the direction of the flow in the phloem?
flow is upwards and downward
38
what is the direction of the flow in the xylem?
flow is upward
39
what does the xylem carry?
carries water and minerals to the leaves
40
what do the xylem tissues contain?
also contains fibres
41
what are the cells in the phloem lined with?
cytoplasm strands
42
what are the cell walls in xylem made from?
lignin
43
are the cell walls in the phloem permeable or impermeable?
permeable
44
what are parachyma?
unspecialised cells
45
what are collenchyma?
thickened cells with cellulose in cells walls for support and protection
46
what is the role of water in plants?
-turgor pressure (hydrostatic skeleton to support stems and leaves)
-cell expansion
-evaporation to cool plants
-transport mineral ions
-reactant for photosynthesis
47
describe the process by which water is take in by root hair cells
1. mineral ions are transported into root hair cells via active transport
2. this lowers water potential in root hair cells
3. water moves into root hair cells via osmosis
48
what type of cells are root hair cells?
epidermal cells
49
draw and label a cross section of a root (how does water move across it?)
*see paper flashcard*
50
how does water move from root hair cell to xylem vessel?
water crosses the cortex and enters the xylem in the centre of the root due to a water potential gradient
51
what are the two different pathways that water can cross the cortex?
-apoplast
-symplast
52
what is the apoplast pathway?
through cell walls and intracellular spaces and as the water moves into the xylem, the water molecules pull more water along due to cohesion
53
what is the symplast pathway?
through the cytoplasm and vacuoles, via plasmodesmata
54
what are plasmodesmata?
gap in cell wall through which the cytoplasm is linked
55
draw the routes of the symplast and apoplast pathways
*see paper flashcard*
56
what happens to water once it's gone through the cortex?
-apoplast pathway is blocked by casparian strip as suberin builds up
-only path available is through cytoplasm (symplast pathway)
57
as cells get older what happens to the amount of suberin in them?
as cells get older, suberin deposits increase except in the passage cells
58
why do we have a casparian strip?
-thought to exclude potentially harmful/toxic solutes from entering xylem
-gives some control over inorganic ions entering xylem
59
what role does active transport have in root pressure?
active transport decreases water potential gradient into xylem so water will move in by osmosis resulting in root pressure
60
what is some evidence for active transport being involved in root pressure?
-cyanide affects mitochondria (therefore ATP production) and root pressure disappears
-root pressure rises and falls with increase/decrease in temperature
-low oxygen concentration causes a decrease in root pressure
61
what are the adaptations of root hair cells?
-large surface area to volume ratio
-lots of mitochondria for active transport
-long, thin extension
-can penetrate soil particles
-thin surface for quick osmosis and diffusion
-fast growth rate
62
what do pits in xylem allow?
allow lateral movement between vessels
63
draw and label the cellular structure of a root
*see paper flashcard*
64
what type of cells is the outer layer of the stele?
endodermis cells
65
what is the stele?
central structure containing vascular bundle
66
what is suberin?
a water proof chemical
67
what are the function of pits in the xylem?
pits allow water to reach the other tissues in the plant
68
describe the pathways and mechanisms by which the water passes from the soil to the xylem vessels in the root (6 marks)
Water moves into the root through the epidermis cells which have adapted into root hair cells. The water and soluble minerals such as potassium, move into the root hair cell by osmosis and active transport. They are able to do this as they move down the concentration gradient from a region of low concentration to an area of high concentration. The most negative end of the water potential gradient is in the xylem vessel. The sugar is then able to move through the cells by 2 different routes. The first is the symplast pathway, this is when the water moves through the cytoplasm and vacuole of the cells. It is able to do this by moving through plasmodesmata. The other pathway is the apoplast pathway, water moves through the cell walls until it reaches the endodermis cells called the casparian strip. The strip blocks the apoplast pathway and the symplast pathway continues through passage cells. The water then has to cross the pericycle membrane and enter the xylem vessel through pits.
69
what are the two main functions of the xylem?
-the transport of water and mineral ions
-support
70
what makes up the xylem?
-xylem vessels
-parenchyma packs around the xylem vessels
-tannin deposits
-lignified walls
-pits
71
what are the xylem vessles?
they are long, hollow structures made by several columns of cells fusing together end to end
72
what are parenchyma packs?
these are thick walled packs around the xylem vessels, storing food and containing tannin deposits
73
what is tannin?
a bitter, astringent-tasting chemical that protects plant tissues from attack by herbivores
74
what are the different ways that lignin can be laid down?
it can form rings, spirals or relatively solid tubes with lots of small unlignified areas called bordered pits
75
what do pits do in the xylem vessle?
this is where water leaves the xylem and moves into other cells of the plant
76
what makes up the phloem?
-sieve tube elements
-sieve plates
-companion cells
-supporting tissues
77
what are the main transporting vessels in the phloem?
the sieve tube elements
78
what are the phloem sieve tubes made up of?
many cells joined end to end to forma long, hollow structure- they are not lignified
79
what forms in the areas between sieve tube cells in the phloem?
the walls become perforated to form sieve plates
80
what do sieve plates in the phloem do?
they let the phloem contents through
81
what happens as the large pores appear in the sieve tube elements to form sieve plates?
the tonoplast, the nucleus and some of the other organelles break down, the phloem becomes a tube filled with phloem sap and the mature phloem cells have no nucleus
82
what forms with the sieve tube elements?
companion cells
83
what are companion cells linked to the sieve tube elements by?
by many plasmodesmata
84
what are the plasmodesmata?
microscopic channels through the cellulose cell walls linking the cytoplasm of adjacent cells
85
what are companion cells?
they are very active cells and they function as a 'life support system' for the sieve tube cells
86
what does the supporting tissues that phloem contains include?
fibres and sclereids, cells with extremely thick cell walls
87
how do the stomata open?
Potassium pump transports potassium into the guard cell by active transport. This lowers the water potential of the cell and water moves in by osmosis- the influx of water causes the guard cells to become turgid asymmetrically as the inner region of cell wall is thicker. This causes the stomata to open.
88
how do the stomata close?
Potassium pump transports potassium out the guard cell by active transport. This increases the water potential of the cell and water moves out by osmosis- the loss of water causes the guard cell to become flaccid and the stomata is no longer open.
89
how would you predict the number and position of the stomata may vary between xerophytes and normal plants?
There would be less stomata as they would want to limit water loss. They also may have pitted stomata that create pockets of localised humidity.
90
suggest why it is difficult to investigate stomata of cacti, even though they are effective xerophytes
Cacti are covered in spikes so they don't have leaves that we can comfortably look at. Also due to the fact the stomatas are pitted we wouldn't see them on the first layer of cells (it would just be empty space)
91
why is the plant stem in a potometer cut at a slant?
to increase the surface area
92
describe the procedure of using a potometer
1. lay the capillary tube and rubber connector under water and fill both parts
2. carefully select a leafy shoot which has a stem as close in diameter to that of the rubber connector as possible, keep the end of the shoot under water whilst you select and trim if necessary with a knife
3. quickly insert the shoot into the rubber connector making sure the fit is as tight as possible- carry this step out under water
4. now firmly clamp the capillary tube to the stand with the shoot at the top end, place the bottom end of the capillary tube into the beaker of water, two people may need to carry out this step to avoid the leafy shoot becoming detached
5. smear vaseline around the join between shoot and rubber connector to ensure an airtight seal
6. leave the apparatus for five minutes to allow water to be drawn up into the end of the capillary tube and form a small air bubble
7. if there is no air bubble, the tube can quickly be removed from the water and a piece of paper towel used to soak a little water from the open end, when the tube is replaced into the beaker of water a small air bubble should be visible
8. time the movement of this air bubble along the capillary tube for a set distance
9. reset the air bubble to the start by repeating steps 7 and 8
10. repeat the readings using different environmental conditions
93
why is it important not to get water on the leaves of the shoot that you are using for your potometer?
because otherwise you would be measuring evaporation of the extra water before transpiration even occurs
94
why is it important to put the capillary tube and rubber connector from the potometer together under water?
to prevent extra air bubbles from getting in
95
why is it important to smear vaseline around the join between shoot and rubber connecter in the potometer?
to prevent evaporation occuring
96
why do you time the movement of an air bubble in a potometer?
because as the plant transpires the air bubble will move along the tube
97
what is needed to be able to calculate the rate of transpiration?
-potometer
-ruler
-timer
98
what is transpiration?
the loss of water vapour from the stems and leaves of a plant as a result of evaporation from cell surfaces inside of the leaf and diffusion down a concentration gradient
99
how does transpiration work?
-water molecules evaporate from the surface of mesophyll cells into the air spaces in the leaf and diffuse out of the stomata into the surrounding air by diffusion, down a concentration gradient
-the loss of water by evaporation from a mesophyll cell lowers the water potential of the cell, so water moves in from the adjacent cell by osmosis (along both the apoplast and symplast pathways)
-this is repeated across the leaf to the xylem, water moves out of the xylem by osmosis
100
what does the removal of water from the top of the xylem do?
it reduces the hydrostatic pressure which means the gradient allows water to move upwards
101
what do the lignin walls do to the xylem during transpiration?
prevent the xylem vessel from collapsing under tension
102
what is the transpiration pull?
the combined forces of adhesion and cohesion in the xylem, result in water exhibiting capillary action- this is how water can move in xylem vessels against gravity and is called the transpiration pull
103
define cohesion
water molecules stick together and move together
104
define adhesion
water molecules stick to carbohydrates in the xylem wall
105
what is cohesion-tension theory?
the model of water moving through the soil in a continuous stream up the stem and across the leaf
106
what does the transpiration pull result in?
results in a tension in the xylem which helps to move water across the roots from the soil
107
what is some evidence for cohesion tension theory?
-changes in the diameter of trees
-broken xylem vessels
-air entering the xylem
108
how is changes in the diameter of trees evidence for cohesion tension theory?
increase in transpiration in the day correlated with an increase in tension and therefore, decrease in diameter
109
how is broken xylem vessels evidence for cohesion tension theory?
when you cut flower stems to put them in water, air is drawn in but water does not leak out
110
how is air entering the xylem evidence for cohesion tension theory?
if air enters the xylem, cohesive forces become broken and the plant can no longer move water molecules up the stem
111
what are the factors that affect the rate of transpiration?
-stomata density
-light intensity
-relative humidity
-temperature
-air movement
-soil water availability
112
how does a high light intensity effect the water movement in transpiration?
when it is light the stomata are open= this increases the rate of water evaporating and diffusing out of the leaf= increase in transpiration
113
how does a low light intensity effect the water movement in transpiration?
when it is dark the stomata are closed= this decreases the rate of diffusion and therefore transpiration
114
what is relative humidity?
measure of the amount of water vapour in the air
115
how does a high humidity effect the water movement in transpiration?
less of a water potential gradient between inside and outside of leaf lowering rate of transpiration
116
how does a low humidity effect the water movement in transpiration?
dry air= steep water potential gradient between inside and outside of leaf increasing the rate of transpiration
117
how does a high temperature effect the water movement in transpiration?
-increased kinetic energy of water molecules
-increases evaporation from cells into air spaces
-increases concentration of water vapour in air spaces increases water potential gradient between inside and outside of leaf
-increase in rate of transpiration
118
what is air movement?
each leaf had a layer of air trapped around it where water vapour accumulates
119
how does a high wind speed effect the water movement in transpiration?
moves this water vapour away increasing water potential gradient and therefore transpiration
120
how does a low wind speed effect the water movement in transpiration?
results in the water vapour not being disturbed as regularly reducing transpiration
121
how does a low soil water availability effect the water movement in transpiration?
if the soil is dry the plant is under water stress and this causes a decrease in transpiration
122
what is the role of the guard cell?
they help to regulate the rate of transpiration by opening and closing the stomata
123
why do stomata open and close during the day?
at high light intensity the stomata open to allow CO2 to diffuse into the leaf, at low light intensity they close to conserve water
124
what moves into the stomata during the day?
carbon dioxide
125
what moves out of the stomata during the day?
oxygen and water vapour
126
when can transpiration and therefore the stomata being open be a problem for the plant?
if the temperature gets too high it can cause excess water loss
127
why do guard cells not change shape symetrically?
cellulose prevent the cells from swelling in width, so they extend lengthways
128
how do stomata help in controlling the rate of transpiration?
stomata open so that water vapour diffuses out of the leaf
129
what happens when water becomes scarce?
the stomata close
130
what are hydrophytes?
they are plants that live in water and need special adaptations to cope with growing in water
131
what are xerophytes?
plants found in dry habitats that have evolved a wide range of adaptations that enable them to live and reproduce in places where water availability is very low
132
what are the different adaptations of hydrophytes?
-very thin or no waxy cuticle
-many, always open stomata
-reduced structure to the plant
-wide, flat leaves
-small roots
-large surface area of stems and roots under water
-air sacs
-aerenchyma
-pneumatophores
133
what is guttation?
the loss of water from leaves during times of low transpiration (often overnight)
134
what is root pressure?
upwards pressure maintained by movement of water into root hair cells by osmosis and active transport of mineral ions into the xylem
135
how does the adaptation of very thin or no waxy cuticle aid survival of hydrophytes?
they do not need to conserve water as there is always plenty available so water loss by transpiration is not an issue
136
how does the adaptation of many, always open stomata aid survival of hydrophytes?
this maximises gaseous exchange
137
how does the adaptation of reduced structure to the plant aid survival of hydrophytes?
the water supports the leaves and flowers so there is no need for strong supporting structures
138
how does the adaptation of wide, flat leaves aid survival of hydrophytes?
to capture as much sunlight as possible
139
how does the adaptation of small roots aid survival of hydrophytes?
water can diffuse directly into stem and leaf tissue so there is less need for uptake by roots
140
how does the adaptation of large surface area of stems ad roots under water aid survival of hydrophytes?
this maximises the area for photosynthesis and for oxygen to diffuse into submerged plants
141
how does the adaptation of air sacs aid survival of hydrophytes?
to enable leaves to float
142
what is aerenchyma?
specialised parenchyma tissue forms in the leaves, stems and roots- it has many large air spaces
143
what is the function of aerenchyma?
- making the leaves and stems more buoyant
-forming a low resistance internal pathway for the movement of substances
144
how does the adaptation of pneumatophores aid survival of hydrophytes?
special aerial roots grow upwards into the air, they have many lenticels which allow the entry of air into the waxy tissue
145
which of the hydrophyte adaptations are specific to water lilies?
-many, always open stomata
-wide, flat leaves
146
how does the adaptation of thick waxy cuticle aid survival of xerophytes?
helps minimise water loss- helps them survive hot dry summers and cold winters
147
what are the adaptations of xerophytes?
-thick waxy cuticle
-sunken stomata
-reduced number of stomata
-reduced leaves
-hairy leaves
-curled leaves
-succulents
-leaf loss
-root adaptations
-avoiding the problems
148
how does the adaptation of sunken stomata aid survival of xerophytes?
this reduces air movement, producing a microclimate of still, humid air that reduces the water vapour potential gradient and so reduces transpiration
149
how does the adaptation of reduced numbers of stomata aid survival of xerophytes?
this reduces their water loss by transpiration but also reduce their gas exchange capabilities
150
how does the adaptation of reduced leaves aid survival of xerophytes?
water loss can be greatly reduced
151
how does the adaptation of hairy leaves aid survival of xerophytes?
creates a microclimate of still, humid air, reducing the water vapour potential gradient and minimising the loss of water by transpiration from the surface of the leaf
152
how does the adaptation of curled leaves aid survival of xerophytes?
this confines all of the stomata within a microenvironment of still, humid air to reduce diffusion of water vapour from the stomata
153
how does the adaptation of succulents aid survival of xerophytes?
store water in specialised parenchyma tissue in their stems and roots- water is stored when it is in plentiful supply and then used in times of drought
154
how does the adaptation of leaf loss aid survival of xerophytes?
some plants prevent water loss through their leaves by simply losing their leaves when water is not availabile
155
how does the adaptation of root adaptations aid survival of xerophytes?
help them to get as much water as possible from the soil- the long roots can penetrate deep into the ground
156
how does the adaptation of avoiding the problems aid survival of xerophytes?
some plants are adapted to cope with the problems of low water availability by avoiding the situation entirely, many plants become dormant
157
which of the adaptations of xerophytes are specific to cacti?
sunken stomata, hair leaves and succulents
158
which of the adaptations of xerophytes are specific to marram grass?
sunken stomata and curled leaves
159
what do plants transform the glucose molecules they get from photosynthesis into? why?
plants transform their glucose molecule into sucrose, this is because sucrose is not metabolised as easily as glucose so it is more likely to be transported
160
draw and label the parts of a xylem vessel
*see paper flashcard*
161
draw and label the parts of a phloem vessel
*see paper flashcard*
162
define translocation
the transport of assimilates (e.g. sucrose) through phloem tissue requiring the input of metabolic energy
163
where does translocation always transport assimilates from and to?
translocation always transports assimilates from sources, where it is made to, sinks, where it can be used
164
what are the main sources of assimilates?
-green leaves and stems
-storage organs (e.g. tubers)
-food stores in germinating seeds
165
what are the main sources of sinks?
-actively growing roots
-meristems that are actively dividing
-plant food stores (e.g. fruits)
166
what are the methods of translocation?
-symplast route
-apoplast route
167
describe the symplast route for translocation
the passive process by which sucrose moves through the cytoplasm of mesophyll cells (via plasmodesmata) by diffusion- this process travels straight into the sieve tubes
168
describe the apoplast route for translocation
the passive process through the cells wall and intracellular space to companion cells, this is followed by the active transport of sucrose into companion cells (active loading)
169
which translocation route requires active loading of sucrose?
the apoplast route
170
describe the active loading of sucrose into the phloem
1. H+ ions are actively transported out of the companion cells using ATP
2. excess H+ ions build up outside of the companion cell
3. H+ ions are transported back into the cell down a concentration gradient by facilitated diffusion through a co-transport protein and sucrose is taken with it
4. sucrose then moves into the sieve element (through plasmodesmata) by diffusion
171
draw and label the process of active loading into the phloem
*see paper flashcard*
172
what are the different types of co-transport proteins?
-symport
-antiport
173
define symport
a type of co-transport protein that allows two different molecules to move across it in the same direction
174
define antiport
a type of co-transport protein that allows two different molecules to move across it in different directions
175
describe the role of turgor pressure in transport in the phloem
-sucrose entering the companion cells and sieve tube elements lowers the water potential and water moves in by osmosis from the xylem
-this leads to a build up of pressure to rigid cell walls and water carrying assimilates moves into the sieve tube elements
-water moves up or down the plant by mass flow to areas of lower pressure
176
describe how the phloem unloads to sinks
The plant actively loads sucrose into the sieve tube element from the source. Sucrose lowers the water potential of the sap so water moves into the sieve element by osmosis. When sucrose is removed from the phloem is increases the water potential. Water leaves the sieve element down a water potential gradient to the sink.
177
how does root pressure occur in the xylem?
cells in the endodermis use active transport to pump mineral ions into the xylem, this lowers the xylems water potential triggering water to move into the xylem vessels by osmosis which creates root pressure
178
what is the evidence for translocation in plants?
-advances in microscopy allow us to see the adaptations of the companion cells for active transport
-if the mitochondria of the companion cells are poisoned, translocation stops
-the flow of sugars in the phloem is about 10,000 times faster than it would be by diffusion alone, suggesting an active process is driving the mass flow
-aphids can be used to demonstrate the translocation of organic solutes in the phloem, using evidence from aphid studies it has been shown that there is a positive pressure in the phloem that forces the sap out through the stylet, the pressure and therefor the flow rate in the phloem is lower closer to the sink than it is near the source
