Chapter 9 - Transport In Plants Flashcards
1
Q
Need for transport system
A
- long distance from external surface to cells
- small SA:V = diffusion not fast enough/efficient
- metabolic rate = low metabolic activity = oxygen can be obtained from diffusion but they require lots of sugar and water = can’t get from diffusion
2
Q
Procedure to observe position of xylem vessels in leaf stalks
A
Put stalks in stain
Cut transversely
3
Q
Similarities between xylem and phloem
A
- made up of cells joined end to end
- complex tissues
- both use mass flow
4
Q
Differences between xylem and phloem
A
Xylem = lignified phloem = not lignified
Xylem = wide lumen phloem = small lumen
Xylem = no sieve plates phloem = sieve plates
Phloem carries carbs and xylem doesn’t
5
Q
Precautions when using a potometer
A
- cut shoot = prevents air lock
- keep light intensity constant = affects rate of transpiration
- keep screw clip closed = prevents entry of water whilst measuring
6
Q
Plan an investigation into rate of transpiration
A
- measure distance moved by bubble at regular intervals
- repeat experiment at least 3 times = can identify anomalies + take mean
- plot graph to compare results visually (time on x and distance moved on y)
- control light intensity using a lamp and wind movement using a fan
7
Q
Precautions whne setting up potometer
A
- cut stem underwater = no air can enter stem
- insert stem under water = air could block xylem
- joint must be sealed tight = air could block xylem
8
Q
Precautions when using potometer 2
A
- use syringe to move bubble = so same bubble can be reused
- don’t allow bubble to move too far = so it doesn’t enter xylem
9
Q
Translocation 3 stages
A
Phloem loading
Mass flow
Phloem unloading
10
Q
Phloem loading
A
- glucose converted to an assimilate
- apoplast route
- active process = proton pump in companion cells pump out H+ = H+ concentration gradient
- cotransport of H+ and sucrose into companion cell
- entry of solutes decreases water potential of phloem
- water enters phloem from surrounding cells
- results in higher hydrostatic pressure
11
Q
Structural adaptations of companion cells
A
Many mitochondria
Increase surface area of cell surface membrane
12
Q
Mass flow
A
- bulk transport of sucrose caused by pressure difference
- assimilates enter sieve tube elements = lowers water potential = water enters by osmosis = increases hydrostatic pressure
- Sugars leave the sieve tube = increases w.p. in sieve tube. Water leaves sieve tube by osmosis which lowers the hydrostatic pressure
- movement from source to sink
- sugar moves from high to low hydrostatic pressure
13
Q
Phloem unloading
A
- diffusion of sucrose from phloem to surrounding cells
- sucrose converted back to glucose
- glucose used for respiration
- converted to start for storage
- concentration gradient of sucrose maintained between phloem and cells
- loss of sucrose increases w.p. Of phloem = water leaves phloem to surrounding cells = lowers hydrostatic pressure
14
Q
Why are carbs transported as sucrose
A
Soluble = can be transported in sap
Metabolically inactive so not used during transport
15
Q
How do some plants of the plant act as a source and sink
A
- certain parts can store and release carbohydrates when needed
- e.g. root can act as a sink or source at diff times of year
16
Q
Vascular tissues
A
Xylem and phloem
17
Q
Xylem function
A
Transports water and minerals up the plant
18
Q
Phloem function
A
Transports sugars and other assimilates up or down the plant
19
Q
Pericycle
A
Many meristem cells inside the endodermis
20
Q
Diagram of roots (transversely cut)
A
21
Q
Stem diagram (transversely cut)
A
22
Q
Packaging tissues
A
Sclerenchyma and collenchyma
23
Q
Function of packaging tissues
A
Mechanical support
- facilitate the transport of water and nutrients throughout the plants
24
Q
Cambium
A
Layer between xylem and phloem which is a layer of stem cells
25
Plant leaf transverse section diagram
Xylem on top, phloem at bottomn
26
Ways a plant can be cut
longitudinally (front layer and back layer) or transversely (top layer and bottom layer)
27
Xylem structure
- hollow in the middle
- Made up of dead cells = lignin present on the walls which causes the cells to die = makes them waterproof
- Continuous column
28
Function of lignin
- adds strength which prevents the walls from collapsing good because xylem needs to withstand pressure
- makes cell walls impermeable to water
29
Ways lignin can thicken walls
- added in spirals, rings (annular), reticulate (broken/half rings)
30
Pits
Some parts of the xylem don’t have lignin = lateral movement of water
31
Adaptations of xylem
No top and bottom walls between cells to form continuous hollow tubes through which water is drawn upwards towards the leaves by transpiration
o Cells are essentially dead, without organelles or cytoplasm, to allow free movement of water
o Outer walls are thickened with a substance called lignin, strengthening the tubes, which helps support the plant
32
Adaptations of xylem
o No top and bottom walls between cells to form continuous hollow tubes through which water is drawn upwards towards the leaves by transpiration
o Cells are essentially dead, without organelles or cytoplasm, to allow free movement of water
o Outer walls are thickened with a substance called lignin, strengthening the tubes, which helps support the plant
33
Adaptations of phloem
Made of living cells which are supported by companion cells
o joined end-to-end and contain holes in the end cell walls (sieve plates) forming tubes that allow sugars and amino acids to flow easily through (by translocation)
o have very few subcellular structures to aid the flow of materials
34
Phloem components
Sieve tube and companion cells
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Sieve tube
made up of individual cells = sieve tube elements = don’t have a nucleus = very little cytoplasm = not good at performing things = sieve tube elements are connected to eachother through sieve plates
36
Companion cells
large nucleus, large cytoplasm, all the main organelles to perform all the metabolic tasks of a cell
37
3 pathways of water moving through a plant
Apoplast
Symplast
Vacuolar
38
Apoplast pathway
water can move through spaces in the cell walls
39
Symplast pathway
water can move through the cell’s cytoplasm and through the plasmodesmatas (gaps in the cell wall)
40
Vacuolar pathway
water goes through the cytoplasm and specifically through the vacuole
41
Transpiration
loss of water vapour from the upper parts of the plant, specifically the stomata
42
Movement of water in root
Water moved across root cortex by osmosis until it reaches the endodermis, which has a casparian strip (impervious to water = blocks the apoplast pathway) forces water and minerals to pass through the cytoplasm which allows all the minerals and water to get into the cell. To get into the xylem, the mineral ions are actively transported into the medulla of the xylem and water follows through osmosis.
43
Transpiration stream
Going from bottom to top of stem
44
Cohesion
Hydrogen bonds pull molecules towards each other // moves as one mass as molecules are attracted to each other
45
Adhesion
Attraction of water molecules to the impermeable walls of xylem tissue
46
Transpiration stream
Bottom = high hydrostatic pressure
- gradient maintained at top as water diffuses out of stomata
- to be able to evaporate, water relies on the water vapour potential gradient. If the outside has a higher water vapour potential than the inside, the water won’t leave
- water vapour travels from high to low hydrostatic pressure
- cohesion pulls all of the water molecules to the top
- adhesion gives water molecules support to be dragged up
- opening and closing of the stomata are controlled by the guard cells
47
Importance of transpiration
- supplies water to the cells = needed for growth, cell elongation, photosynthesis
- Maintains cell turgidity
- Transports useful mineral ions up the plant
- Supplies water that, as it evaporates, can keep the plant cool on a hot day
48
How to set up potometer
- has to be set up underwater because you don’t want any other air bubbles other than the meniscus in the tube
- Shoot has to be healthy
- Stem has to be cut underwater
- Stem has to be cut at an angle to increase the surface area exposed to water
- When the potometer is taken out of water, dry the leaves to maintain a regular water vapour potential gradient.
49
Limitation of using a potometer
only 95% of water taken up by a plant is used for transpiration - actually only measuring the water uptake
50
What does a potometer do
Time transpiration and see the distance moved by the bubble for the length = water taken up for transpiration. The volume of water taken up by the plant/time = rate of transpiration
Volume = pi x r^2 x L
51
Another name for the air bubble in the potometer
Meniscus
52
Factors affecting transpiration
Light intensity
Temperature
Humidity
Air move,ent
Water availability
53
Affect of light intensity on transpiration
increase light intensity, increase transpiration because there is an increase in photosynthesis, which requires gas exchange so the stomatas open up, which means that more water vapour is lost.
54
Affect of temperature on transpiration
increase temperature, increase transpiration because it’ll increase the rate of diffusion through the stomatas because the water molecules have a high kinetic energy. It’ll also increase the rate of evaporation from the surface of the cells, so the water vapour potential in the leaves will increase
55
Affect of humidity on transpiration
decrease transpiration because it will decrease the rate of water vapour potential gradient as the gradient won’t be as steep.
56
Affect of air movement on transpiration
increase air movement, increase transpiration because it’ll maintain a steep water vapour potential gradient by pushing away water molecules constantly
57
Affect of water availability on transpiration
if there’s little water in the soil, the plant won’t be able to replace the water so naturally the stomatas will close therefore transpiration can’t happen
58
Affect of waxy cuticle on transpiration rate
Reduces transpiration by acting as a barrier that limits water loss
59
Terrestrial plants
- want to conserve water so they reduce transpiration rate
- Have a waxy cuticle and stomatas will be found on the lower surface of the leaf ( stomatas won’t open as a response to light)
- Most stomatas are closed at night
- Plants lose their leaves in winter
60
Xerophyte
Lives in dry place
61
Marram grass
terrestrial plants) xerophyte = lives in dry place
- leaves are rolled so that air is trapped inside which increases humidity and reduces transpiration rate
- Thick, waxy cuticle
- Deep long root to absorb more water
- Stomatas on lower surface
62
Cactus
terrestrial plants)
- succulent = store water in the stem
- Have spines which reduces the surface area of the leaves = less surface area = less transpiration
- Stem is green for photosynthesis, so most of the photosynthesis happens at the stem
- Roots are widespread and long
63
Hydrophytes
= live in water
- large air spaces, allow them to float in water so that they can absorb light
- Stomata are on the upper epidermis, allowing them to capture as much light as possible
- Leaves have large air spaces for buoyancy
64
Translocation
movement of assimilates and sucrose throughout the plant
65
Source
Part where sucrose enters phloem
66
Sink
Part where sucrose leaves phloem
67
Source and sink in summer
the source is the leaves because of photosynthesis and the sink is the cells at the bottom e.g. roots
68
Source and sink in winter
the source can be the roots because that’s where sucrose was stored all summer and the sink is the leaves
69
Units to compare rate of transpiration using potometer
Mm3cm^-2min^-1
70
B
71
B
72
A
73
C
74
B
75
Explain why large multicellular plants need a transport system.
76
Explain the benefit to plants of internal transport systems.
77
Sodium chloride in solution dissociates into Na* and CI.
Explain how the Casparian strip prevents these ions from reaching the xylem of the plant by the apoplast pathway.
78
Soluble mineral ions are present in soil.
Explain why water molecules can form hydrogen bonds with nitrate (NO3) ions.
79
80
81
data for 'fan off' are, more spread out about the mean / less precise v
82
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84
85
Describe how a potometer can be used to calculate a more accurate rate of transpiration.
86
The students concluded that there is a positive correlation between distance of the tree from the river and mean leaf hair density.
Suggest reasons for this positive correlation.
further away from the river less water (available) / ORA V
transpiration causes water loss
bi hairs, trap water vapour / reduce
transpiration / reduce loss of water (vapour)v
reduced water (vapour) potential gradient from inside to outside leaf v
87
For this investigation, the students randomly selected leaves from ten downy birch trees at varying distances from the river.
Suggest three ways in which the students could improve the validity of their sampling method.
88
89
Suggest how water is being lost from the cut stem when all the leaves have been treated with petroleum jelly.
evaporation (1)
from upper leaf surfaces (1)
90
Suggest two possible sources of error in this investigation. > potometer
not all lower leaf surface covered (1)
leaks in apparatus (1)
shoot not cut under water (1)
error in reading position of meniscus (1)
91
92
Suggest a reason for the reading that you identified as anomalous in (i).
Potometer
93
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95
96
97
98
99
100
101
102
103
What else to mention for water moving up xylem vessels
- hydrogen bonds between water molecules allow cohesion
- Hydrogen bonds between the water molecules and the lining of the xylem allows adhesion
- This allows a continuous column of waste to be created
- Transpiration pool = water diffusing out at the top of the xylem
