Chapter 9 - Transport In Plants Flashcards
1
Q
Why do large organisms need transport systems
A
o Increasing transport distances
o Surface area: volume ratio
o Increasing levels of activity
2
Q
Why do small organisms not need transport systems
A
o due to their large surface area: volume ratio
o diffusion or transport distance in these organisms are also very small so essential nutrients or molecules are able to reach the necessary parts of the cell efficiently
o Smaller organisms tend to have lower levels of activity and so smaller metabolic demands
3
Q
Why do plants need specialised transport system
A
-to remove products of photosynthesis + water + oxygen
- large organisms = huge distances to transport
- SA:V ratio = small
4
Q
Define vascular system
A
A system of transport vessels in plants or animals
5
Q
Define herbaceous
A
Having fleshy / soft stem
6
Q
What is the impact of large transport systems
A
makes simple diffusion a non-viable method for transporting substances all the way from the exchange site to the rest of the organism
7
Q
If the organism is small
A
Large SA:V ratio
8
Q
Define dicotyledonous
A
Plants that produce two seed leaves
9
Q
Adaptations of plants to increase SA : V
A
• Plants have a branching body shape
Leaves are flat and thin
Roots have root hairs
10
Q
How does increasing levels of activity effect oxygen demand
A
• Larger organisms are not only more physically active but they also contain more cells than smaller organisms
• A larger number of cells results in a higher level of metabolic activity
o As a result, the demand for oxygen and nutrients is greater and more waste is produced
11
Q
What is mass flow
A
bulk movement of materials.
12
Q
Advantages / functions of mass transport
A
o Bring substances quickly from one exchange site to another
o Maintain the diffusion gradients at exchange sites and between cells and their fluid surroundings
o Ensure effective cell activity by keeping the immediate fluid environment of cells within a suitable metabolic range
13
Q
What does the xylem transport
A
water + mineral ions
14
Q
What does the phloem transport
A
sucrose + other nutrients = assimilates
15
Q
Do plants have specialised transport system for oxygen + carbon dioxide
A
NO
16
Q
Why don’t they have a specialised transport system for oxygen and carbon dioxide
A
They don’t need one
17
Q
Why don’t they need a specialised transport system for oxygen and carbon dioxide
A
o They have adaptations that give them a high SA: V ratio for the absorption and diffusion of gases
o The leaves and stems possess chloroplasts which produce oxygen and use up carbon dioxide
o There is a low demand for oxygen due to plant tissues having a low metabolic rate
18
Q
Why do plants need water - 5
A
- maintain turgidity of cells
- transport nutrients around the plants
- create an aqueous environment for reactions to occur
- to cool plants by evaporation
- for photosynthesis
19
Q
From the inside to the outside what tissues are present in a root dissection
A
Xylem
Phloem
Pericycle
Endodermis
Cortex
Epidermis = root hair cells
20
Q
Functions of the xylem
A
carries dissolved minerals and water up the plant
o Structural support
o Food storage
21
Q
What type of tissue is the xylem
A
Vascular
22
Q
Where is the xylem found
A
in vascular bundles with phloem
23
Q
Where is the vascular bundle found in the roots
A
the centre and t he centre core of this is xylem tissue.
24
Q
Advantages of the vascular bundle in the centre of the roots
A
helps the roots withstand the pulling strains they are subjected to as the plant transports water upwards and grows
25
Where is the vascular bundle found in the stem
located around the outside and the xylem tissue is found on the inside (closest to the centre of the stem)
= CONCENTRIC RINGS
26
Why is the vascular found in concentric rings at the stem
Help support the plant
27
Where is the vascular bundle found in the leaves
the midrib and veins and therefore spread from the centre of the leaf in a parallel line.
The xylem tissue is found on the upper side of the bundles (closest to the upper epidermis)
28
Function of the phloem
o Transport organic compounds, particularly sucrose, from the source (eg. leaf) to the sink (eg. roots).
29
Is the phloem two way
Yes
30
What is the phloem made of
Sieve tube elements
Companion cells
parenchyma
Sclerenchyma
31
Key difference in place of vascular bundles
In roots and stem, the xylem tissue is found on the inside – however, in leaves, xylem is found above phloem tissue.
32
What is the xylem made of
Tracheids
Vessel elements
Xylem parenchyma
Sclerenchyma
33
What are tracheids
Long narrowed tapered cells with pits
34
What are vessel elements
Larger cells with thickened cell walls and no end plates ( when matured )
35
What is common about tracheids and vessel elements
both types of water-conducting cell
36
Function of lignified cell walls in xylem
37
Features of the xylem
Lignified cell walls
No end plates
No protoplasm
Pits
Small diameter of vessels
38
Function of no end plates in mature xylem cells
39
Function of no protoplasm in mature xylem cells
40
Function of pits
41
Function of small diameter of vessels
42
Components of the phloem
• Sieve tube elements
• Companion cells
• Parenchyma
• Sclerenchyma
• Living cells
43
Features of sieve tube elements
Sieve plates + sieve pores
Cellulose cell wall
No nucleus / vacuole / ribosomes
Thin cytoplasm
44
Function if seive plates + seive pores
45
Function of cellulose cell wall
46
Function of no nucleus / vacuole / ribosomes
Maximises space for translocation of the assimilates
47
What is sometimes present in seive tube elements
ER + mitochondria
48
Function of thin cytoplasm
49
Function of companion cells
- control metabolism of seive tube elements
- loading + unloading of sugars
50
Key features of companion cells
- nucleus + other organelles present
- transport proteins in plasma membrane
- large numbers of mitochondria
- plasmodesmata
51
Function of nucleus + other organelles present in companion cells
52
Function of transport proteins in plasma membrane of companion cells
53
Function of a lot of mitochondria in companion cells
54
Function of plasmodesmata in companion cells
55
Xylem vs phloem : living cells (mature)
Xylem - no living cells
Phloem - yes = companion cells
56
Xylem vs phloem : transported substances
Xylem - water + mineral ions
Phloem - organic compounds / assimilates
57
Xylem vs phloem : process of transportation
Xylem - transpiration
Phloem - translocation
58
Xylem vs phloem : direction of flow
Xylem - one way / roots to leaves
Phloem - two way = source to sink
59
Xylem vs phloem : presence of end walls
Xylem - no
Phloem = yes = sieve plates with sieve pores
60
Xylem vs phloem : cell wall material
Xylem = lignin + cellulose
Phloem = cellulose
61
Features of Dicotyledonous (dicots) plants
o Seeds that contain two cotyledons (seed leaves)
o Network of veins
o Leaves that typically have broad blades (leaf surface) and petioles (stalks)
o Tap root with lateral branches
62
Why do plants need transport systems
- meet metabolic demands
- move substances around the plant
- compensate for small SA:V ratio
63
What does the palisade mesophyll contain
Parenchyma cells
64
From top to bottom of a leaf - name structures
Upper epidermis
Palisade mesophyll
Xylem
Phloem
Spongy mesophyll
Lower epidermis
65
Define transpiration
• he tloss of water vapour from a plant to its environment by evaporation and diffusion
66
What’s transpiration a consequence of
• gaseous exchange at the stomata
67
Advantages of transpiration
• provides a means of cooling the plant via evaporative cooling
• The transpiration stream is helpful in the uptake of mineral ions
• The turgor pressure of the cells (due to the presence of water as it moves up the plant) provides support to leaves (enabling an increased surface area of the leaf blade) and the stem of non-woody plants
68
Define transpiration stream
• the movement of water from the roots to the leaves
69
What causes the movement of water through a plants xylem
evaporation of water vapour from the leaves and the cohesive and adhesive properties exhibited by water molecules
70
Describe the transpiration stream = beginning of the stream at the leaves
71
Factors effecting rate of transpiration
• Air movement / light intensity / temperature / humidity
72
How does air movement effect rate of transpiration
• When the air is relatively still water molecules can accumulate near the leaf surface. This creates a local area of high humidity which lowers the concentration gradient and the rate of transpiration
• Air currents can sweep water molecules away from the leaf surface, maintaining the concentration gradient and increasing the rate of transpiration
73
How does temperature effect rate of transpiration
= increase temp = increase KE = rate of transportation will increase
74
What happens if the temp gets too high in relation to transpiration
• the stomata close to prevent excess water loss.
dramatically reduces the rate of transpiration
75
How does light intensity effect rate of transpiration
• Stomata close in the dark, their closure greatly reduces the rate of transpiration
• When the light is sufficient for the stomata to open, the rate of transpiration increases
• Once the stomata are open any increase in light intensity has no effect on the rate of transpiration
• Stomata will remain open at relatively low light intensities
76
How does humidity effect rate of transpiration
• If the humidity is high that means there is a large concentration of water molecules in the airsurrounding the leaf surface
• This reduces the concentration gradient between inside the leaf and the outside air which causes the rate of transpiration to decrease
77
What happens at a certain level of humidity
• an equilibrium is reached; there is no concentration gradient and so there is no net loss of water vapour from the leaves
78
Draw graph for rate of transportation against temp
79
Draw graph for rate of transportation against humidity
80
Draw graph for rate of transportation against air movement
81
Draw graph for rate of transportation against light intensity
82
What occurs via osmosis in transpiration
Uptake of water to the roots
83
What occurs by active transport in transportation
Uptake of mineral ions in the roots
84
How does the plant ensure that the water potential of the root is more negative than the soil
Ions from the soil are ACTIVELY pumped into the root
85
What does active pumping mean
Energy required for movement
86
What pathway is taken by the water to go from the soil to the xylem
Root hair cell
Cortex
Endodermis
Pericycle
Xylem
87
What are the two different routes the water can take to the xylem
Apoplast + symplast
88
What’s the function of the pericycle
It is meristematic + produces the lateral roots
89
What is the function of the endodermis
Contains a ring of Suberin which is impermeable to water
90
What is the function of the cortex
Stores a large amount of starch
91
What path does most water travel through
Apoplastic
92
What is the apoplast pathway
Water travels through cellulose cell walls
93
How does the water move in the apolast pathway
- moved by diffusion = as it is not crossing partially permeable membrane
94
What’s the problem with the apoplast pathway
• When the water reaches the endodermis the presence of a thick, waterproof, waxy band of suberin within the cell wall blocks the apoplastic pathway
95
What is the band of Suberin called
the Casparian strip
96
Key property of the casparian strop
Impermeable to water
97
What happens to the water when it reaches the casparian strip
- they must take the symplast pathway
98
Advantages of apoplast pathway
- much quicker
- offers path of least resistance
99
What is the function of the Casparian strip
• help the plant control which mineral ions reach the xylem and generate root pressure
100
As the plant ages, what happens to the casparian strip
Thickens
101
How does water enter the xylem from the endodermis
- endoderm cells actively pump salts into the xylem
- makes water potential of the xylem more negative than the endodermal cells
- this means water enters the xylem via osmosis
- ensures water potential gradient is maintained
102
Where is the casparian strip located
In the endodermal cells
103
How do endodermal cells move ions into the xylem
Active transport
104
Once water has entered the xylem how does it move
As a continuous stream
105
What force is created by the bonds between water molecules
Cohesion
106
What force is created by the interaction between water molecules + vessel
Adhesion
107
How is the continuous streak created
Cohesion + adhesion
108
What’s another way water can enter to the xylem
Symplast
109
What is symplast
Water travels through the cytoplasm + from cell to cell via the plasmodesmata
110
What three processes are involved in the movement of water up the stem + through the leaves
- root pressure
- capillarity
- cohesion - tension theory
111
What causes root pressure
- endodermal cells actively pump ions into the xylem vessel
- water potential gradient formed + water enters the xylem
- pressure in the xylem increases = forcing water upwards
112
What is the evidence for root pressure
- if cyanide is added to the root = sap is no longer exuded
- root pressure replies on the active pumping of ions which requires ATP
- if there is no ATP = no pumping = no water potential gradient
- therefore no water entering xylem
- no root pressure
113
What causes capillarity
- adhesive forces between xylem vessels + water molecules
- pulls water molecule up
- due to cohesive forces = other molecules are pulled up with it
114
Why is the xylem a bundle of very narrow vessels rather than one wide vessels
- greater heights of liquid are achieved in thinner tubes due to capillarity
- with smaller tubes = greater contact with vessel wall compared with the volume of water at the Center
- so greater cohesive + adhesive forces
115
What is transpiration = Howard definition
Loss of WATER VAPOUR from leaves + stem as a result of evaporation from cell surfaces inside the leaf and diffusion down a conc gradient out through stomata
116
Why is transpiration pull referred to as the cohesion - tension theory
- cohesive force between water molecules pulls other molecules up = continuous stream
- puts pressure on the column of water
- inward pressure is called tension
117
What effect does tension have on the column of water
Produces narrower column of water
118
Water happens if a xylem vessel is broken
The continuous stream of water is broken so no water can be taken up
119
If a xylem vessel becomes blocked can water still reach the leaves
Yes
120
Why can water still reach the leaves if a xylem vessel becomes blocked
The pits in the xylem allows for the movement of water
121
How does the water move through leaves
122
What is the role of the stomata in transpiration
• Transpiration is mainly controlled by the pairs of guard cells that surround stomata (plural, stoma is singular)
123
Label the parts of the leaf
124
Method to investigate rate of transpiration
• Cut a shoot underwater
• Place the shoot in the tube
• Set up the apparatus
• Make sure it is airtight, using vaseline to seal any gaps
• Dry the leaves of the shoot
• Remove the capillary tube from the beaker of water to allow a single air bubble to form and place the tube back into the water
• Set up the environmental factor you are investigating
• Allow the plant to adapt to the new environment for 5 minutes
• Record the starting location of the air bubble
• Leave for a set period of time
• Record the end location of the air bubble
• Change the light intensity or wind speed or level of humidity or temperature
• Reset the bubble by opening the tap below the reservoir
• Repeat the experiment
125
How to analyse result from transpiration experiment
The further the bubble travels in the same time period, the faster transpiration is occurring and vice versa
126
Apparatus for transpiration experiment
127
Why do we cut the shoot underwater
o prevent air from entering the xylem
128
Why do we make sure it is airtight
o If air enters the apparatus the readings will be affected
129
Why do we dry the leaves
o Any moisture present on the leaves will affect the rate of transpiration
130
How to investigate airflow
Hairdryer / fan
131
How to investigate humidity
Spray water in a plastic bag + wrap around the plant
132
How to investigate light intensity
Change the distance of a light source from the plant
133
How to investigate temperature
Temp of room
134
What makes up the vascular bundle
Xylem
Cambium
Phloem
Sclerenchyma
135
What is the function of the cambium
It is meristematic + differentiates to form xylem + phloem as the plant grows
136
What is the advantage of xylem vessels not being fully lignified
Allows stem to flex + move = Pits
137
Example for what is glucose used for
Aerobic respiration
138
Example of what plants use lipids for
Cell membrane
139
Example of what plant uses proteins for
Enzymes
140
Example of what plants use nucleic acids for
DNA replication
141
Define assimilates
Products of photosynthesis/ respiration
142
What is translocation
• transport of assimilates from source to sink and requires the input of metabolic energy (ATP)
143
What is the liquid called that’s being transported in translocation
Phloem sap
144
Direction of translocation
Source to sink
145
Examples of sources
• Green leaves and green stem (photosynthesis produces glucose which is transported as sucrose, as sucrose has less of an osmotic effect than glucose)
• Storage organs eg. tubers and tap roots (unloading their stored substances at the beginning of a growth period)
• Food stores in seeds (which are germinating)
146
Examples of sinks
• Meristems (apical or lateral) that are actively dividing
• Roots that are growing and / or actively absorbing mineral ions
• Any part of the plant where the assimilates are being stored (eg. developing seeds, fruits or storage organs)
147
Can loading + unloading be stopped
Yes
148
How can loading + unloading be stopped
• can be slowed down or even stopped at high temperatures or by respiratory inhibitors
149
Evidence for translocation
• Collecting and studying the sap from plants with 'clotting' sap (eg. castor oil plants)
• Using aphids to collect the sap – after the aphid inserts its stylet (tubular mouthpart) scientists remove the aphids head and collect the sap that continues to flow
• Using radioactively labelled metabolites (eg. Carbon-14 labelled sugars) which can be traced during translocation
• Advances in microscopes enabling the adaptations of companion cells to be seen
150
How is carbohydrates transported
In the form of sucrose
151
Why is carbohydrates transported in the form of sucrose
o allows for efficient energy transfer and increased energy storage (sucrose is a disaccharide and therefore contains more energy)
o It is less reactive than glucose as it is a non-reducing sugar and therefore no intermediate reactions occur as it is being transported
152
How are assimilates loaded
• modified companion cells pump hydrogen ions out of the cytoplasm via a proton pump and into their cell walls / source = active
• The large concentration of hydrogen ions in the cell wall of the companion cell / source results in the hydrogen ions moving down the concentration gradient back to the cytoplasm of the companion cell
• But cant diffuse back due to phospholipid bilayer = polar crap = Therefore moves through cotransporter protein.
• While transporting the hydrogen ions = also carries sucrose molecules into the companion cell against the concentration gradient for sucrose
• The sucrose molecules then move into the sieve tubes via the plasmodesmata from the companion cells
153
How does sucrose move down the phloem
• now sucrose in sieve tube elements
• Decreases water potential
• As xylem vessels right next to phloem = water moves into phloem down water potential gradient = pits
• Now very high hydrostatic pressure in sieve tube
- sink = very low hydrostatic pressure = down conc gradient
154
Unloading at sink
• When sucrose goes into sink = converted into starch = to maintain concentration gradient
• Low concentration of sucrose in sink
• Therefore starch goes from sieve tube elements to companion cells to sink = through plasmodesmata
• All down concentration gradient = passive
• Therefore this increases water potential in sieve tube elements as sucrose in sink now
• Now low hydrostatic pressure = ultimately assimilates gone from high to low hydrostatic pressure
• Water goes from phloem back to xylem = follows water potential gradient
155
What do plant cells use sucrose for
- convert into starch for storage
- respiration
156
Advantage of the mass flow hypothesis
• moves the organic solutes faster than diffusion
157
How is the pressure difference created in the mass flow of assimilates
• by actively loading sucrose into the sieve elements at the source(usually a photosynthesising leaf or storage organ) which lowers the water potential in the sap
• This results in water moving into the sieve elements as it travels down the water potential gradient by osmosis
158
What actually causes mass flow
Hydrostatic pressure differences
159
Summaries translocation = steps
160
How do guard cells differ from the lower epidermal cells
- they contain chloroplasts
- have extra cellulose thickening on the inner side of cell
161
Outline how guard cells open
- cells surrounding guard cells actively pump K+ ions into the guard cells, making their water potential more negative
- water enters by osmosis as water potential of guard cells more negative than surrounding p
-guard cells swell but because inner wall thicker than outer wall = as cell swells a pore opens
162
What is crucial about the cell walls of guard cells
The inner wall is thicker than the outer wall
163
Outline how guard cells close
K+ ions diffuse out of the guard cells + back into epidermal cells
No longer more negative water potential
Guard cells become flaccid
164
Give 4 ways plants generally conserve water
- waxy cuticle
- stomata on underside of leaf
- closable stomata
- roots that grow down to the water in the soil
165
What is a xerophyte
• plants that are adapted to dry and arid conditions
166
Give two examples of xerophytes
Conifers + marram grass
167
Examples of xerophyte adaptations
- fleshy succulent leaves
- hinge cells shrink when flaccid
- spines / needles
- sunken stomata
-less stomata
- thick waxy cuticle
168
Effect of fleshy succulent leaves
Water stores for times of low availability
169
Effect of hinge cels shrinking when flaccid
Causes leaves to roll = exposing thick waterproof cuticle to air + creates a humid space in the middle of the rolled leaves
170
Effects of spines / needles
Reduces transpiration rate due to reduces surface area
171
Effect of sunken stomata
Water loss is minimised by trapping moist air close to the area of water loss = reducing diffusion gradient
172
Effect of less stomata
Less water loss due to fewer pores
173
Effect of thick waxy cuticle
Water loss reduced via the cuticle
174
How do sunken stomata help to adapt a plant to hot + dry conditions
- reduce air movement
- create microclimate of still, humid air
- reduces gradient = reduces transpiration rate
175
What is a downside of reduced number of stomata
Reduces gas exchange capillaries
176
How do hairy leaves adapt xerophytes
- create microclimate of still, humid air
- reduces water vapour potential gradient
177
How do curled leaves adapt xerophytes
- confine all stomata within a microenvironment of still, humid air
- reduce diffusion gradient
178
How are succulents adapted to their environment
- contain specialist parenchyma tissue in stems + roots
- stores water there - used in times of draught
179
How can losing leaves adapt a xerophyte
- leaves lost when water is not available
- reduces water loss by transpiration
- trunk + branches turn green + photosynthesis
180
How do xerophytes have roots adapted for their environment
- long tap roots grow deep into the ground below surface
- mass widespread shallow roots with large surface area are able to absorb water before a rain shower evaporates
181
Why is a hydrophyte
Plants that are adapted to living in freshwater
182
State two examples of hydrophytes
Water lilies + water cress
183
Problems faced by hydrophytes
- water logging = air spaces of plants need to be full or air not water
- Important that leaves float on the water to enable photosynthesis
- receiving enough carbon dioxide during the day + neigh oxygen during the night = water contains less oxygen + carbon dioxide then air
184
Adaptations of hydrophytes
- floating leaves
- air sacs
- wide flat leaves
- think waterproof waxy cuticle
- stomata on upper surface of the leaves
- reduced root system
- reduced veins in the leaves
- permentantly open stomata
185
Why is excess water uptake not a major concern for hydrophytes
Cell wall prevents too much water being absorbed
186
How does having thin / no waxy cuticle adapt hydrophytes
Allows water to be lost via transpiration
187
How does having many stomata /permanently open adapt hydrophytes
Maximises gas exchange
188
Why do hydrophytes have reduced structural support
Water supports leaves + flowers
189
How does having wide flat leaves adapt hydrophytes
Spread across surface of water = maximise light absorption
190
Why do hydrophytes have small roots
Water + nutrients can diffuse directly into stem + leaf tissue = less need for uptake via roots
191
How do air sacs adapt hydrophytes
Enable leaves to float
192
How does floating leaves adapt hydrophytes
Keeps them close to surface of water = maximise light
193
How does stomata located on upper surface of leaves in hydrophytes adapt
Allows gas exchange with air not water
194
Effect of reduced veins in the leaves of hydrophytes
Xylem is significantly reduces = less / no need to transport water
195
What are aerenchyma
Specialised parenchyma tissue which has many large air spaces
196
How do aerenchyma adapt hydrophytes
- makes leaves + stems more Buoyant
- form low resistance pathway for the movement of substances = e.g oxygen = to tissues below water
- help plant cope with extreme low oxygen conditions
197
Differnces between tracheids + vessel elements
198
199
200
DNA
201
202
203
204
205
206
207
208
209
210
211
Describe how a potometer can be used to calculate a more accurate rate of transpiration.
212
213
B
214
215
216
Less uncertainty
