Unit 2.3b - Adaptations for transport in plants Flashcards
1
Q
What do plants need to transport?
A
Inorganic ions and water
2
Q
Where do plants need to transport inorganic ions and water?
A
From the soil to where they’re synthesising new compounds, which is in the leaves (photosynthesis)
3
Q
What’s the name of the transport system used to transport inorganic ions in plants?
A
The transpiration system
4
Q
Transpiration
A
The loss of water vapour through the stomata of plants
5
Q
What’s the first step of the transpiration system?
A
Inorganic ions are dissolved in water and carried up to the leaves to be used in the plants metabolism
6
Q
Name some inorganic ions that are transported in a plant
A
Mg2+
NO3^2-
PO4^3-
7
Q
Where is water “pulled up” in a plant?
A
The xylem vessels
8
Q
How is water pulled up the xylem vessels?
A
Cohesion tension
Adhesion
9
Q
Cohesion tension
A
Hydrogen bonding between H and O between different water molecules
10
Q
Adhesion
A
The polar nature of water giving them an attraction to the cellulose in the walls of the xylem vessels - capillarity
11
Q
What’s the name of the other transport system used in plants as opposed to the transpiration system?
A
Translocation
12
Q
Translocation
A
The process of moving the products of photosynthesis from where they’re mad or stored to other parts of the plant
13
Q
From where is large quantities of water lost from a plant and how?
A
Through the stomata
Via the transpiration stream
14
Q
Why must water be replaced in the soil?
A
Large quantities of water are lost through the stomata via the transpiration stream
15
Q
How is water replaced into a plant?
A
A specialised region of root - the root hair zone - absorbs water (and inorganic ions)
16
Q
Which part of a plant is responsible for absorbing water from the soil?
A
The root hair zone - a specialised region of root
17
Q
How does the root hair zone of root absorb water?
A
Via osmosis
18
Q
How does the root hair zone of root absorb inorganic ions?
A
Via active transport or fascilitated diffusion
19
Q
Root hair cell
A
Epidermal cells with the extension - the root hair zone
20
Q
Root hair cells adaptations to their function
A
Large surface area for the absorption of water by osmosis
Thin cell walls for a short diffusion pathway
21
Q
Draw and label the transverse section of the root of a plant
A
(See notes)
22
Q
Where are root hairs on the root?
A
On the upper epidermis layer
23
Q
What does xylem tissue do?
A
Transports water and minerals throughout the plant
24
Q
Where is xylem tissue found?
A
At the centre of the root
25
What is xylem tissue surrounded by?
A single layer of cells - the endodermis
26
What does the endodermis surround?
Xylem tissue
27
What does the stele of a root contain?
Vascular tissue
28
Where is the stele of a root?
The central part of the stem
And
In the root
29
Draw and label a stem transection
(See notes)
30
Draw and label a high power view of the stele
(See notes)
31
Endodermis
A single layer of cells around the stele
32
What is the endodermis important for?
Absorbing water and inorganic ions into the plant
33
What does endodermis include and what does this do?
Water proof Casparian strip which stops transport via the apoplast route
34
What does Phloem do?
Transports the products of photosynthesis e.g - sucrose and amino acids
35
What does Xylem do?
Transports water and minerals
36
How are xylem tissues fit for their purpose?
They’re dead cells with thickened cell walls so the middle is empty for transporting water and inorganic ions
37
What makes up the vascular bundle?
Xylem
Cambium
Phloem
38
What do the xylem, cambium and phloem make up?
The vascular bundle
39
What chemical do two parts of the stem both have and what does this mean?
Xylem and schlerenchyma have lignin
Stain the same colour
40
Chemical of xylem and schlerenchyma
Lignin
41
What’s the schlerenchyma of the vascular bundle also known as?
Fibres
42
Fibres of the vascular bundle
Schlerenchyma
43
What do all 3 routes of transporting water and minerals in the root start with?
Water enters the root hairs on the epidermis via osmosis (water potential gradient from the soil into root hair cell)
Inorganic ions dissolved in water enter the root hair cells via facilitated diffusion or active transport
44
Where do the 3 routes for transport of water and minerals in the root go to and from?
From epidermis
To cortex
To the vascular tissue of the steel in the centre of the root
45
What are the 3 possible routes for the transport of water and minerals in the root?
Symplastic route
Apoplastic route
Vacuolar route
46
Symplastic route
Water and dissolved ions are absorbed into the cytoplasm of the root hair by osmosis active transport and fascilitated diffusion
Then move through the root tissues via the cytoplasm and plasmodesmata of adjacent cells
47
What are the symplastic, apoplastic and vacuolar routes all routs for?
The transport of water and minerals in the root
48
Apoplastic route
Water and dissolved ions move through the root tissues via the cell walls of adjacent cells (it doesn’t actually enter the cells)
There is no restriction to flow until the endodermis is reached
49
Why are water and dissolved ions able to move through the root tissues via the cell walls when taking the apoplasic route?
Cellulose cell walls and permeable to water and ions
50
At which point in the apoplastic route is there a restriction to the flow of water and why?
The endodermis
The endodermis contains a band of waterproof tissue known as the casparian strip which prevents water from going through the apoplast route
51
Where is the casparian strip?
The endodermis
52
What’s the purpose of the casparian strip in the endodermis?
To prevent water from going through the apoplast route
53
Vacuolar route
Water and dissolved ions move through the tissues of the root from the vacuole of one cell to the vacuole of the neck cell down a water potential gradient
54
Sketch the vacuolar route
(They look like coffee beans)
55
Sketch the symplastic route
(Nodiadau)
56
Sketch the apolastic route
(Nodiadau)
57
Draw a diagram to represent the transport of water and minerals in the route down both the apoplastic and symplastic route
Yes
58
How are inorganic ions taken from the soil solution?
Active transport
59
Ho do inorganic ions move through the plant once they’ve been absorbed?
Move along the apoplastic pathway (carried in solution by the water) in the transpiration system
60
How are inorganic ions carried in the transpiration stream?
In solution by the water
61
What happens when minerals reach the casparian strip?
It prevents further movement via the apoplast
62
What’s the casparian strip formed from?
Waterproof Suberin
63
What happens to minerals once they’ve been restricted by the casparian strip?
They must enter the cytoplasm and are transported from cell to cell via diffusion or active transport
64
How does nitrate enter a plant?
As nitrate or ammonium ions
65
Why do plants need nitrates?
To make amino acids
66
How do nitrate ions enter the apoplastic pathway?
Diffuse along a concentration gradient
67
How do inorganic ions travel from the apoplastic to the symplastic pathway when restricted by the casparian strip in the endodermis?
By active transport against the concentration gradient, through the selectively permeable cell membrane into the cytoplasm
68
What must ions do at the endodermis and why?
Enter the symplastic pathway by active transport to bypass the casparian strip
69
Is the apoplastic pathway living or non-living?
Non-living
70
Is the symplastic pathway living or non-living?
Living
71
How does the casparian strip actually help? How?
Allows the plant to selectively take up ions
When ions have to travel from the apoplastic to the symplastic pathway, they have to travel into the cytoplasm to get into it, through the selectively permeable membrane
72
How does the casparian strip in the endodermis allow a plant to selectively take up ions?
Inorganic ions have to travel from the apoplastic to the symplastic pathway, and to do this they need to travel into the cell’s cytoplasm, and to do THIS they need to travel through the selectively permeable membrane
73
What does root pressure do?
Helps move water up the plant
(Although not to the same extent as cohesion tension)
74
What IS the casparian strip?
A layer of Suberin within the cell walls of the endodermal cells
75
How is root pressure formed? [5]
The Suberin of the casparian strip is water proof and stops water and dissolved ions form following the apoplast root through the endodermis, forcing them to cross the cel membrane and enter the symplastic route
Transport proteins in the membrane of the endodermis cells actively transport dissolved ions/salts across the endodermis and into the xylem vessels
This lowers the water potential within the xylem vessels and water moves into the xylem by osmosis from the root cortex
The movement of water into the xylem creates a hydrostatic pressure which forces the xylem contents upwards - this is root pressure
76
What creates hydrostatic pressure in the roots and what does this cause?
The movement of water into the xylem, which forces the xylem contents upwards (root pressure)
77
Where does water move into the xylem by osmosis from to form root pressure?
The root cortex
78
What is the ultimate cause of root pressure?
The casparian strip forcing inorganic ions to cross the cell membranes and enter the symplastic route
79
What’s an experiment that we can do to test for root pressure?
Cut the plant close to the soil to leave a stump
Tightly seal to an s-shaped tube half filled with mercury, half filled with water
Over time, the mercury will be pushed to the top of the tube due to the hydrostatic pressure
Measure pressure of the liquid using a manometer
80
How can we measure the pressure of a liquid?
Manometer
81
Where are the vascular bundles in stems?
Around the periphery
82
Why are the vascular bundles around the periphery in stems?
Gives flexible support and resistance to bending strain due to the tough xylem cells - fibres
83
What gives flexible support and resistance to a stem?
Tough xylem cells - fibres
84
Draw and label the vascular bundle in a stem
(See notes)
85
What does the phloem contain?
Living material (e.g - nucleus, cytoplasm)
86
Which 2 tissues in vascular bundles contain lignin and what does this lead to?
Fibres
Xylem
Both stain red
87
Compare lignin to cellulose
Lignin is harder
88
What gives a plant the texture of wood?
Xylem vessels with lignin
89
What does lignin give plants?
Rigidity
90
What are the 4 types of xylem cells?
Vessels
Tracheids
Fibres
Parenchyma
91
What are vessels, tracheids, fibres and parenchyma all examples of?
Xylem cells
92
What happens when a xylem cell matures?
Gets thicker and fills with lignin
93
Is lignin permeable to water?
No
94
Why are xylem cells dead cells?
As they mature, the cell walls get thicker and fill with lignin
Lignin is impermeable to water and stronger than cellulose
Therefore, water can’t easily get in, so the cell contents die away
95
How does lignin lead to the dead of a xylem cell?
Impermeable to water and stronger than cellulose - water can’t get in easily, cell contents die away
96
What type of cells are xylem cells?
Dead
97
Why are xylem cells important?
Form tubes to carry water and dissolved ions
Provide mechanical strength to support the plant
98
Why is it useful that xylem cells are dead?
Form tubes to carry water and dissolved ions
99
Xylem function
Transports water and mineral salts from the root to the leaves
100
Phloem function
Transports soluble produce of photosynthesis (sucrose and amino acids) from the leaves to other parts of the plant
101
How are the functions of the xylem and phloem different?
Xylem - transports water and mineral salts from the root to the leaves
Phloem - transports soluble products of photosynthesis (sucrose and amino acids) from the leaves to other parts of the plant
102
Where does the phloem carry the products of photosynthesis to and from?
From the leaves to other parts of the plant
103
Where does xylem transport water and mineral salts/inorganic ions to and from?
From the root to the leaves
104
Describe tracheid xylem tissues
Longer, slender cell with an empty lumen to transport water and inorganic ions
Thick to support the plant
105
Describe the fibre xylem tissues
Specialised for support
Has almost no central cavity when the cell dies at maturity
Thickened cell walls
Lots of lignin
106
Describe the vessel xylem tissues
Specialised for water transport
Has a wide lumen to reduce the resistance to water flow through the tissue
Shorter and wider
No end walls between vessel elements (cells) that make up a vessel
107
Describe the parenchyma xylem tissue
Live cells that develop to form the other types of xylem cells
Contain cytoplasm, nuclei…
Cell walls thicken as they develop
108
Which xylem cells are the live cells that develop to form the other types?
Parenchyma
109
What are fibrous xylem tissues specialised for?
Support
110
What are tracheid xylem tissues specialised for?
Transporting water and inorganic ions
111
What are vessel xylem tissues specialised for?
Water transport
112
What would happen eventually when testing for root pressure and why?
There would be no more upward movement of mercury due to gravity resisting this movement
113
Describe the steps involved in transporting water FROM the xylem in the leaf
1. Water arrives in the leaf through xylem vessels
2. Water leaves the xylem vessels through the pits in the walls and travel through the living spongey mesophyll cells down a water potential gradient via osmosis
3. Water evaporates from the surface of mesophyll cells into the sub stomatal air chamber
4. When the stomata is open (sufficient light intensity), water vapour escapes - transpiration
The water potential of the cells near the stomata has now lowered
114
Where does water evaporate from the surface of mesophyll cells into?
The sub stomatal air chamber
115
How does water leave the xylem vessels and where does it go to?
Through the pits in the walls
Travels through the living spongey mesophyll cells
116
How does water move from the xylem vessels through the living spongey mesophyll cells?
Down a water potential gradient via osmosis
117
What is the route taken when water is transported FROM the xylem in the leaf?
The same as for the transport of water and minerals in the root…
Symplastic
Apoplastic
Vacuolar
118
How does water travel in the xylem to the leaves?
Via the apoplast, symplastic and vacuolar pathways
119
What happens to most of the water as it travels from the xylem through the leaf?
Most is lost as it evaporates from the internal leaf surface and passes out as water vapour into the atmosphere
120
Transpiration
Water loss from the surface of leaves by the evaporation through the stomata
121
Why does transpiration happen at all?
Most of the water travelling in the apoplast, symplastic and Vacuolar pathways from the xylem throughout the leaf is lost as it evaporates from the internal leaf surface
122
Transpiration pull
As water molecules leave xylem cells in the leaf, they pull up other water molecules - this pulling effect is known as the transpiration pull
123
What is the name for the effect caused when other water molecules are pulled up when water molecules leave xylem cells in the leaf?
The transpiration pull
124
What are the factors that effect transpiration rate?
Temperature
Humidity
Air movement
Light intensity
125
Describe how temperature can effect transpiration rate
Rise in temperature = additional kinetic energy for the movement of water molecules = increased rate of evaporation from the walls of the mesophyll cells
Also, if the stomata are open, this speeds up the rate of diffusion of water vapour into the surrounding air
Also, the water potential of the air becomes lower as its temperature is raised as it can hold more moisture
126
What happens to the water potential of the air as the temperature is raised and what does this mean?
It become lower
Can hold more moisture
127
Humidity
The amount of water vapour in the air
128
How much water vapour is there in the air inside the leaf?
Saturated with water vapour
129
Which part of a leaf has a high humidity and why?
The sub-stomatal air chamber as it’s saturated with water vapour
130
Relationship between humidity and rate of transpiration
Greater humidity = lower rate of transpiration
131
Relationship between rate of transpiration and temperature
Increased temperature = increased transpiration rate
132
Describe how humidity effects transpiration rate
Sub-stomatal air chamber has a very high humidity as it’s saturated with water vapour, giving it a high water potential
The humidity of the air surrounding a leaf varies (rarely exceeds 70% in Britain)
Therefore, a water potential gradient is always present between the leaf and the air
When the stomata open, water vapour rapidly diffuses out of the leaf from a high to low water potential
So, the greater the humidity, the lower the rate of transpiration
133
Describe the rate of transpiration in still air
Water vapour accumulates around the leaf surface
This decreases the water potential gradient between the leaf and air
This decreases the rate of transpiration
134
Describe the rate of transpiration in moving air (wind)
Removes the layer of saturated air
Increases the water potential gradient between the leaf and air
Increases the rate of transpiration
135
Is it still or moving air that increases the rate of transpiration? Why?
Moving (windy conditions)
Removes the layer of saturated air, increasing the water potential gradient between the leaf and air
136
What’s the relationship between the rate of transpiration and light intensity?
The higher the light intensity, the higher the rate of transpiration
137
Describe how light intensity effects the rate of transpiration
Controls the degree of stomatal opening
Higher light intensity = greater number of open stomata
Increases the rate of transpiration
138
What is the primary purpose of stomata?
To allow CO2 to enter for photosynthesis (but when it opens, water vapour DOES get released)
139
Potometer
Apparatus used to measure the rate of uptake of water by a leafy shoot
140
Apparatus used to measure the rate of uptake of water by a leafy shoot
Potometer
141
How do we use a Potometer?
Cut stem from plant
Plug to Potometer
Plant continues to transpire
Air bubble moves to indicate the volume of water taken up by he shoot in a certain period of time
142
How does a Potometer actually measure the rate of uptake of water by a leafy shoot?
Air bubble moves to indicate the volume of water taken up by the shoot in a certain period of time
143
Draw the set up of a Potometer
(See notes)
144
How must we cut the shoot of the plant to attach to a Potometer and why?
Cut it under water
To prevent air bubbles forming in the xylem. If air gets in, it’ll break the water column and break the cohesion tension
145
What are 4 precautions to take when setting up a Potometer?
Cut the shoot under water
Keep the leaves dry
Set up apparatus under water
Ensure all joints are airtight
146
Why is it important to keep the leaves dry when using a Potometer?
If there’s water vapour on the leaves, it’ll prevent water from leaving via transpiration
147
How do we setup the apparatus of a Potometer and why?
Under water to prevent air bubbles
148
How could we ensure that all joints are airtight on a Potometer and why is this important?
Use Vaseline to seal joints
Prevents air bubbles
149
What does using a Potometer NOT measure and why?
The rate of transpiration
Not all the water taken up by the plant and drawn over the leaf goes through the stomata - the purpose of water being there is to photosynthesise, so some is used for this
150
As well as measuring the rate of uptake of water by a leafy shoot, what else can we use a Potometer to measure? Give examples
Measure the factors that effect transpiration rate
e.g - lamp (light intensity)
Fan (air movement)
151
What are the different types of plants depending on their different environments?
Mesophytes
Hydrophytes
Xerophytes
152
What does the availability of for plants change depending on where they live?
The availability for water
153
Mesophytes
Plants that live in habitats where there is sufficient water available for their survival
154
Plants that live in habitats where there is sufficient water available for their survival
Mesophytes
155
Which type of plants don’t really have any special adaptations to avoid water loss and why?
Mesophytes - they live in habitats where there is sufficient water available for their survival
156
What are the general adaptations of mesophytes to avoid water loss?
Closing stomata (+ most on the base for slower water evaporation)
Waxy cuticle to prevent water from evaporating from the surface
157
Why is it important that Mesophytes have a waxy cuticle?
They would otherwise lose a lot of water due to their large surface area
158
What type of plants are most of those around us?
Mesophytes
159
Hydrophytes
Plants that live in or on water and have a plentiful supply of water at all times
160
Plants that live in or on water and have a plentiful supply of water at all times
Hydrophytes
161
Which types of plants don’t have any specific adaptations to avoid water loss and why?
Hydrophytes - they have a plentiful supply of water at all times
162
Xerophyte
Plants that live in areas of low water availability (e.g - deserts, sand dunes, tundra (frozen soil))
163
Examples of areas of low water availability
Deserts, sad dunes, tundra (frozen soil)
164
What type of plant is a lily pad an example of?
Hydrophyte
165
Hydrophyte example
lily pad
166
Why do sand dunes have low water availability?
Sand dries up quickly
Sea water is salty = drier air
167
Draw and label a hydrophyte transection
(See notes)
168
Which tissue do we observe when looking at a hydrophyte transection and where is this?
Specialised tissue - aerenchyma
Underneath the palisade layer
169
What are the adaptations of a hydrophyte?
Large air spaces
Stomata on the upper epidermis
Thin or absent cuticle
Lack of supporting tissues
Less organised vascular tissue
Increased surface area
Roots usually reduced in size
170
Why do hydrophytes have large air spaces?
Gives leaves buoyancy to float on the water surface
Reservoirs of O2 and CO2
171
Why is the stomata on the upper epidermis of a hydrophyte?
Allows gas exchange with the air above from the floating leaf
172
Why does the hydrophyte have a thin or absent cuticle?
Do not need to reduce water loss
173
Why do hydrophytes have a lack of supporting tissues?
High density of water gives support to the submerged leaves and stems
174
Name some supporting tissues that a hydrophyte lacks
Fibres
Collenchyma
Sclerenchyma
175
What is the vascular tissue less organised in hydrophytes compared to?
Compared to the midrib in mesophytes
176
Why is the vascular tissue of hydrophytes less organised than the midrib of mesophytes?
Don’t need a good supply of water
177
Why do hydrophytes have a large surface area?
Increases the surface area for gas exchange and photosynthesis
178
Why are the roots of hydrophytes usually reduced in size?
They act mainly to anchor the plant as water absorption can take place over the whole surface of the plant
179
What type of specialised roots have some hydrophytes developed and why?
Roots that extend into the air and can absorb oxygen
(If anchored in mud at the bottom of water and they don’t receive sufficient oxygen)
180
Pneumaphores
Specialised roots in hydrophytes that extend into the air to absorb oxygen as the roots would otherwise be anchored in mud at the bottom of water with insufficient oxygen
181
Specialised roots in hydrophytes that extend into the air to absorb oxygen as the roots would otherwise be anchored in mud at the bottom of water with insufficient oxygen
Pneumaphores
182
Draw and label a xerophute transection
(See notes)
183
Name a xerophyte
Ammophila leaf
184
What is an ammophila leaf an example of?
A xerophyte
185
What are the adaptations of xerophytes?
Rolled leaves
Hairs
Thick waxy cuticle
Sunken stomata in pits
Hinge cells
Succulent (thick) leaves
White leaves/spines
Reduced number of stomata
CAM photosynthesis
186
What causes the leaves of xerophytes to roll up?
Large, thin walled epidermal cells at the bases of the grooves shrink when they lose water from excessive transpiration, causing the leaf to roll inwards
187
Why are xerophyte leaves rolled up?
It reduced the leaf area exposed to air, and so reduces transpiration
188
Name for the hairs of xerophytes
Trichomes
189
Trichomes
Hairs of xerophytes
190
Why do xerophytes have Trichomes (hairs)?
Stiff, interlocking hairs trap water vapour and reduce the water potential gradient, thus reducing the rate of transpiration
191
Why do xerophytes have a thick waxy cuticle?
Reduced water loss by evaporation from the epidermal tissue as they’re waterproof
192
Why do xerophytes have sunken stomata in pits?
A more humid microenvironment is created, as they allow water vapour to accumulate above the stomatal pore
+ wind can’t blow the water vapour away (rolled leaf) - this decreases the water potential gradient between the inside of the leaf and the gas chamber, reducing transpiration rate
193
What do hinge cells in xerophytes do and why is this important?
Absorb water from the surroundings to become turgid and open when it’s not too dry to increase the surface area for photosynthesis
194
Why do xerophytes have succulent (thick) leaves?
To store water
195
Why do xerophytes have white leaves/spines?
Light colours reflect light and heat, thereby cooling the plant
196
Why do xerophytes have a reduced number of stomata?
Fewer gaps for water to evaporate out through
197
What is CAM photosynthesis and why is it used by xerophytes?
Stomata open when it’s cooler at night
CO2 is fixed so that it can be used during the day for photosynthesis without having to open the stomata
198
Draw and label the transection of a pine leaf
(See notes)
199
Give an example of a xerophyte
Pine leaf
200
What is a pine leaf an example of?
A xerophyte
201
How do we improve the accuracy of the experiment with the Potometer?
Use a capillary tube with smaller graduations
Time over a greater distance
202
What implies more reliable data with range bars?
If they do not overlap
If they’re smaller
203
Translocation
The transport of the products of photosynthesis from source to sink in the plant
204
Source for translocation
The site of photosynthesis in the leaves
205
Sink in translocation
Areas that use the materials of photosynthesis for growth, respiration, storage and other metabolic processes
206
Products of photosynthesis
Soluble organic materials, sucrose and amino acids
207
Are the products of photosynthesis transported with inorganic ions and water?
No, they’re transported separately in the phloem
208
Where are the products of photosynthesis carried to and from in the phloem?
From the source to the sink
209
How is sucrose a product of photosynthesis?
Glucose (made during photosynthesis) + fructose —> sucrose
210
What are the types of cell in phloem tissue?
Sieve tubes
Companion cells
Phloem fibres
Phloem parenchyma
211
What is a sieve tube made up of?
Sieve cells/ sieve element
212
Function of sieve tubes
Transport organic materials such as sucrose and amino acids (the products of photosynthesis)
213
What are the cells of sieve tubes called?
Sieve elements
214
Where are the sieve elements in sieve tubes?
End to end
215
Sieve plates
The ends of the walls of each sieve cell do not break down, but are perforated by pores at either side, called sieve plates
216
What’s the name for the pores at the ends of the walls of sieve cells?
Sieve plates
217
Draw and label a sieve tube and it’s surroundings
(See notes)
218
Describe sieve cells
Long, columnar
Not completely empty like xylem - contain living material such as a thin cytoplasm and a few organelles
219
Adaptations of sieve cells/elements for their function
Sieve plates containing pores allow bidirectional flow form element to element throughout the plant
Thin cytoplasm with no large organelles, which allows the products of photosynthesis to flow without obstruction
Plasmodesmata are present in the walls, which allow the transport of ATP and other molecules from the companion cell to the sieve tube cell/element
No nucleus, and most of the other cell organelles disintegrate during sieve tube development
Cytoplasmic filaments contains phloem protein extend from one sieve cell to the next through the pores in the sieve plate
220
Which part of sieve tubes contain pores and why?
Sieve plates
Allow bidirectional flow from element to element throughout the plant
221
Describe and explain the cytoplasm of sieve cells/elements
Thin cytoplasm with no large organelles
Allow the products of photosynthesis to flow without obstruction
222
Where are plasmodesmata present in sieve tubes and why?
In the walls of sieve tube cells/elements
Allow the transport of ATP and other molecules from the companion cell into the sieve tube cell/element
223
Why do sieve cells/elements not have most of their organelles?
They disintegrate during sieve tube development
224
What do cytoplasmic filaments contain in sieve tubes?
Phloem Protein
225
What contain phloem protein in sieve tubes?
Cytoplasmic filaments
226
How do cytoplasmic filaments extend from one sieve cell to the next?
Through the pores in the sieve plate
227
Describe companion cells
Dense cytoplasm
Centrally placed large nuclei
Many mitochondria
Rough endoplasmic reticulum
Golgi body
Connected to the sieve tube elements by plasmodesmata
Make proteins and ATP for the sieve tube cells/elements
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What do companion cells make and for what?
Proteins and ATP for the sieve tube cells/elements
229
How are companion cells connected to the sieve tube elements?
By plasmodesmata
230
Where in sieve tubes is where metabolic activity takes place?
Companion cell
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What takes place in companion cells?
Metabolic activity
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How is a companion cell different to a sieve cell/element?
Contain a lot more material and a relatively small vacuole
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Wha are the 3 experiments for evidence for translocation?
Ringing experiments
Phloem sampling
Radioactive labelling
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What do ringing experiments support the idea of?
Translocation in the phloem
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How are ringing experiments done to provide evidence for translocation?
Cylinders of outer bark tissue are removed from all the way around a woody stem, in a ring
The phloem is removed when doing this (located towards the periphery), leaving the xylem (further in the stem)
236
What are the results from the ringing experiment to provide evidence for translocation? Explain this
Sucrose (a product of photosynthesis) accumulated above the cut ring
Lowers the tissue’s water potential
Water moves into the cell via osmosis
Swells as water enters the cells
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What does the ringing experiment provide evidence for?
That sucrose was transported to this region of the stem by translocation in the phloem
238
Why are too many aphids bad for a plant?
Take the nutrients from a plant
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What’s the name of the mouthpart of an aphid? Describe this
Stylet
Hollow and needle-like
240
What does an aphid do with its stylet?
Inserts it directly into the sieve tube, allowing the aphid to feed on the sugary sap of the phloem
241
Which part of a plant does an aphid insert its stylet and why?
The sieve tube of the phloem
To feed on the sugary sap
242
What happens during phloem sampling?
The stylet of aphids is cut off using a laser, leaving it attached to the plant, forming a useful micro pipette
Sap exudes from the stylet after being cut - the contents of the phloem must be under pressure for it to be pushed up like this
Upon collection and analysis of this sap, it contains high levels of sucrose and amino acids - the products of photosynthesis
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How do we extract sap from the phloem of a plant?
Cut of the stylet of an aphid to use it as a micropipette
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How does phloem sampling give evidence for translation?
Upon collection and analysis of the sap from the stylet, it contains high levels of sucrose and amino acids - the products of photosynthesis
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What additional concept is proved by phloem sampling and why?
That the contents of the phloem are under pressure, a sap exudes from the stylet after being cut
246
What happens during radioactive labelling to provide evidence for transpiration?
Carbon dioxide labelled with a radioactive carbon isotope (14C) is supplied to an illuminated plant leaf
247
Which carbon isotope is supplies to a plant leaf dung radioactive labelling and why?
14C
Radioactive
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What’s the method of using radioactive labelling to provide evidence or translocation using aphids?
Aphids feed on the contents of phloem
Upon cutting the stylet, we can analyse the sap that exudes for radioactivity
249
How is the radioactive carbon isotope transported to other parts of the plant to make radioactive labelling possible?
The radioactive carbon becomes fixed in the sucrose produced by photosynthesis and is translocated to other parts of the plant
250
What’s the alternative method to using aphids to using radioactive labelling to provide evidence for translocation? Describe this
Trace the radioactive carbon in the sucrose using autoradiography
Source leaf and sink tissues are places firmly on photographic film in the dark for 24 hours
When the film is developed, the presence of radioactivity in parts of the plant tissue show up as fogging of the negatives
251
What has radioactive labelling showed specifically about translocation in the phloem?
That sucrose is transported both upwards and downwards
252
How did radioactive labelling prove that sucrose is transported both upwards and downwards during translocation ?
Radioactivity was observed both where products have been used for growth and in the roots, as most plants store carbohydrates in the form of starch in the roots
253
What’s the most widely accepted theory for translocation?
The mass-flow hypothesis
254
The mass-flow hypothesis
The most widely accepted theory for translocation
255
When was the mass flow hypothesis proposed?
1937
256
Summarise what the mass-flow hypothesis suggests
There’s a passive mass flow of sugars from the phloem of the source leaf, which has the highest concentration of sugar, to other areas of the plant, such as growing tissues, which have a lower sugar concentration
257
Where does translocation occur to and from according to the mass-flow hypothesis?
From source to sink
258
Source in the mass-flow hypothesis
Site of photosynthesis in the leaves
259
Sink in the mass flow hypothesis
Roots and regions of growth
260
Draw a diagram to represent the mass flow hypothesis
(See notes)
261
Describe, in detail, the steps of the mass-flow hypothesis
1. When sugar is made at the source, the water potential becomes more negative and water passes into the metabolically active source cells by osmosis
2. As water enters the source cells, hydrostatic pressure increases, forcing sugars and other products of photosynthesis into the sieve tubes via active transport - phloem sieve tubes are loaded
3. Mass flow occurs along the sieve tubes to the sink, the products if photosynthesis are forces along by the flow of water form a high to a low hydrostatic pressure
4. Hydrostatic pressure will be lower at the sink because sugars are stored as starch or are used for respiration - this reduces the water potential
5. Water passes form the sink cells to the xylem to be returned to the source
262
Why is the hydrostatic pressure lower at the sink (mass flow hypothesis)?
Sugars are stored as starch or are used for respiration
263
How are the products of photosynthesis forced along during mass flow-hypothesis along the sieve tubes to the sink?
The flow of water from a high to a low hydrostatic pressure
264
Why does water move from the xylem to the phloem i the mass-flow hypothesis?
When the phloem sieve tubes are loaded with sugars and other products of photosynthesis, water moves via osmosis from a high to a low water potential
265
What causes an increase in the phloem’s hydrostatic pressure?
Water moving from the xylem to the phloem via osmosis due to the sugars and products of photosynthesis in the phloem giving it a low water potential
266
What explains the rising sap in the aphid experiment?
The increase in the phloem’s hydrostatic pressure when water moves form the xylem to the phloem via osmosis
267
What creates a pressure gradient in the phloem?
The movement of water from the xylem to the phloem
268
Why is the pressure gradient in the phloem important?
Contents of phloem move down a pressure gradient from source to sink
269
Why does water move from the phloem to the xylem?
At the same time, sucrose is taken out of the phloem into sink cells, increasing the water potential in the phloem
Water moves from the phloem back into the xylem due to the water potential gradient
270
What are the different arguments against the mass-flow theory?
1. The rate of translocation is 10,000x faster than it would be if the substances were moving along by diffusion
2. Sieve plates with tiny pores act as a barrier impeding flow
3. Sucrose and amino acids move at different rates and in different directions in the same phloem tissue
4. Phloem tissue has a high rate of oxygen consumption, and translocation is stopped when a respiratory position such as potassium cyanide enters the phloem
5. Companion cells contain numerous mitochondria and produce ATP, but the mass flow hypothesis fails to suggest a role for the companion cells
271
Describe the rate of translocation compared to substances moving by diffusion
10,000x faster
272
How do we know the rate of translocation?
Can use radio labelling experiments to measure the rate of flow
273
Why is the fact that sieve plates have tiny pores that act as a barrier impeding flow an argument against the mass-flow theory?
Would be expected that plants would evolve away from them - there may be an unexplained reason for them
274
Why is glucose converted into sucrose in plants?
Too reactive for transport
275
Bidirectional movement or organic molecules in a plant
Transported both upwards and downwards
276
Name for the fact that organic molecules in a plant are tranported both upwards and downwards
Bidirectional
277
What does xylem show a similar pattern of support material to?
That seen in an insects trachae
278
What shows a similar pattern of support material to that seen in an insects trachae?
Xylem
279
What do the Xylem vessels NOT transport?
Nutrients
280
How many directions does mass-flow occur in?
1
281
What other hypothesis could be used instead of the mass flow hypothesis if flow is bidirectional?
Active transport or diffusion
282
If flow is bidirectional, what is it NOT and why?
Mass-flow, as this is unidirectional
283
When could active transport or diffusion be used as a hypothesis for the movement of materials as opposed to mass-flow and why?
When it’s bidirectional, as mass flow is unidirectional
284
What’s the importance of lignin in the xylem?
Mechanical support to the xylem and prevents it from collapsing
285
What do all three of the apoplastic, symplastic and vacuolar routes rely on?
Osmosis
286
Why is having the stomata sunken in pits beneficial to xerophytes?
Less air movement
287
What’s closest to the stele in a root? The endodermis or pericycle?
Pericycle
288
The transport of what are we talking about when discussing the apoplastic and symplastic routes with the casparian strip?
Mineral ions
289
What do we always need to refine when discussing translocation?
Sources and sinks
290
What is the main leaf tissue where 14C is incorporated into organic molecules? (Radioactive labelling as evidence for translocation)
Palisade mesophyll
