🔺🔥2.4 Adaptions For Transport -plants Flashcards
(112 cards)
1
Q
What is the name of the external tissue around the root of a dicotyledon?
What does it contain?
A
The epidermis
Many root hair cells
2
Q
What is the name for the bulk of the root of a dicotyledon
A
Cortex tissue
3
Q
What is the name for the middle of the dicotyledon root?
What surrounds the stele?
What is found inside the stele?
A
Stele
The epidermis
Vascular tissues including the xylem and phloem
4
Q
Where in the stele is the xylem cell normally located?
A
In the centre often in a cross or star shape
5
Q
Where is the phloem found in the stele
A
In the arms (surrounding) the xylem
6
Q
Name an advantage of the arrangement of vascular tissues in the stele
A
Resists vertical stresses (pull) and anchors the plant In the soil
7
Q
Where is the vascular tissue located in stems, reference xylem and phloem location
A
In stems vascular bundles are in a ring at the periphery (outside circumference of stem)
Xylem = towards centre
Phloem = towards outside
8
Q
What is a benefit of the location of vascular bundles in the stem
A
Makes them flexible and resists bending
9
Q
Where is the vascular tissue located in leaves?
A
In the midrib and in a network of veins
10
Q
What is the benefit for the location of vascular tissue in leaves?
A
Makes them flexible strength and resistance to tearing
11
Q
Learn the locations of these in Leaf: Phloem Xylem Vascular bundle Upper and lower epidermis Adaxial surface Abaxial surface Collenchyma Compacted parenchyma
A
Learn on pg 201/202
12
Q
What are the main cells present in the xylem
A
Xylem vessels and tracheids
13
Q
Where do tracheids occur in plants?
A
In ferns, conifers and angiosperms (flowering plants) but not Moses
14
Q
Why are Moses poor at conducting water?
A
Poor because they have no water-conducting tissue (xylem cells) and therefore are poor at transporting water and can’t grow as tall as other plants
15
Q
Where to xylem vessels occur
A
Only in angiosperms
16
Q
What builds up xylem cell walls?
What patten does lignin grow in?
What colour does it stain?
A
Lignin
It has a characteristic spiral pattern
It stains red so is easy to identify
17
Q
What’s found in the centre of the xylem? Why?
A
Lumen
As lignin builds up in xylem cell walls the contents die creating the empty space called the lumen
18
Q
How is the xylem structured like a hollow tube
A
As tissues develop the end walls of the cell break down creating a hollow tube
19
Q
Why is the hollow tube essential in the xylem vessel
A
It allows water the climb straight up the plant
20
Q
Why is the water transport in xylem vessels more efficient than in tracheids?
A
In xylem vessels water moves straight up whereas in tracheids there is a twisting path
21
Q
What are the 2 main functions of the xylem
A
- Transport of water and dissolved minerals
2. Provides mechanical strength and support
22
Q
Why does water need to constantly be replenished in a terrestrial plant?
A
Plants risk dehydration due to water loss in transpiration via the stomata of a plant. :: loss must be replaced by water from soil
23
Q
Name 2 uses for water in a plant
A
Required for photosynthesis
Maintains turgidity in a plant and :: won’t wilt
24
Q
Where is the location of greatest water uptake into a plant?
Why?
A
The root hair zone
- Because the surface area of the root is increased by root hairs
- uptake is enhanced by thin cell walls
- large vacuole to absorb water quickly
25
Why is there a fast rate of osmosis in the root hair cell?
Because the soil has a very dilute solute potential and the root hair cell contains a concentrated solute potential, more negative water potential :: osmosis occurs rapidly down a water potential gradient
26
What are the 3 different ways that water can travel to the xylem across the root cortex?
The apoplast pathway
The symplast pathway
The vacuolar pathway
27
What happens to water in the apoplast pathway?
Water moves in the cell walls. Cellulose fibres in the cell wall are separated by spaces through which the water moves
28
What happens to water in the symplast pathway
Water moves trough the cytoplasm and plasmodesmata.
29
What is the plasmodesmata?
Strands of cytoplasm through pits in the cell wall joining adjacent cells so the symplast is a continual pathway across the root cortex
30
What happens to water in the vacuolar pathway?
Water moves from vacuole to vacuole
31
Which is the most efficient pathway and :: the most likely to be questioned
The apoplast pathway, also frequently question symplast pathway
32
Define the term endodermis
A single layer of cells around the pericycle and vascular tissue of the root. Each cell has an impermeable waterproof barrier in its cell wall
33
Define casparian strip
The impermeable band of Suberin in the cell walls of endodermal cells, blocking the movement of water in the apoplast driving it into the cytoplasm
34
What are the parts of the root cortex
Root hair
Epidermis
Endodermis
Casparian strip
35
Where does water move from the root endodermis?
From the root endodermis into the xylem by osmosis across the endodermal cell membrane
36
How is the water potential gradient between the root endodermis and xylem maintained for osmosis
- water potential of the endodermis is raised by water being driven in by the casparian strip
- the water potential of the xylem is decreased by active transport of mineral salts, mainly sodium ions from the endodermis and pericycle into the xylem
37
How does water leave the xylem?
Water moves into the xylem via osmosis, which generates an upwards push known as the root pressure on the water already in the xylem
38
How are the minerals from the soil absorbed into the cytoplasm of a root hair cell?
By active transport against a concentration gradient as the soil has a higher water potential than the root hair cell
39
Describe how mineral ions enter the xylem
1. Mineral ions move alone the apoplast pathway in solution until they reach the endodermis
2. At endodermis the casparian strip prevents further movement in cell walls
3. Minerals enter cytoplasm by active transport
4. Then diffuse or are actively transported in the xylem
40
Why is active transport at the endodermis an advantage?
Because it allows the plant to absorb ions (such as nitrogen or ammonium ions) selectively
41
Why is oxygen essential for the root?
Because it allows cells to produce ATP in aerobic respiration which provides energy for active transport of ions etc
42
What evidence is there that a tree doesn’t necessarily need to be alive to transport water
Dead trees can transport some water upwards
43
Brief movement of water location?
Soil water (high water potential)
Plant
Air (low water potential)
44
What are the 3 mechanisms for the movement of water from roots to the leaves
1. Cohesion tension
2. capillarity
3. root pressure
45
Define cohesion
Attraction is water molecules for each other, seen as hydrogen bonds, resulting from dipole structure of the water
46
Describe how cohesion tensions allows water to move up a plants stem to the Leaf
1- water vapour evaporates from Leaf to cells in the air spaces
2- it then diffuses out through the stomata into the atmosphere
3- this draws water across the cells of the leaf in the apoplast, symplast and vacuolar pathways
4- as water molecules leave the xylem cells they pull up other water molecules behind them
5-water molecules all move because they show cohesion producing water tension in the water column
47
What else contributes towards cohesion theory in the pulling of water up a plants stem in the leaf
The charges on the water molecules cause attraction to the hydrophilic lining of the vessels called adhesion
48
Describe how capillarity contributes towards how the water is pulled up the stem
It is the movement of water up narrow tubes by capillary action, only small contribution to water movement in plants more than a few centimetres
49
What limitation does capillarity action have on the movement of water up a stem?
Therefore in what plant is it effective?
- It only operates over short distances (around a meter)
| - Moses
50
Describe how root pressure can draw water up the stem of a plant
Caused by the osmotic movement of water down the water potential gradient across the root and into the base of the xylem pushing prior water upwards
51
What is a limitation of the root pressure in propelling water upwards in the stem
Only operates over short distances in living plants
52
How is water drawn up the plant in a transpiration stream (2)
- the cohesive force between water molechles
| - the adhesive forces between the water molecules and the hydrophilic lining of the xylem vessels
53
Define transpiration.
The evaporation of water vapour from the leaves or other above ground parts of the plant, out through stomata into the atmosphere
54
What happens if a plant loses more water by transpiration than they absorb
They will wilt and die if an excessive volume is lost as it can’t regain turgor
55
Name the hatful, and useful aspects of transpiration
Harmful= water loss
Useful= water uptake; water distribution; ion distribution; evaporative cooling
56
What factors does the transpiration rate depend on?
1- genetic factors such as those controlling the number, distribution and size of the stomata
2-environmental factors such as temperature, humidity and air movement
3-light intensity
57
Why do environmental factors such as temperature, humidity and air movement affect transpiration?
They affect the water potential gradient between the water vapour in the leaf and the atmosphere
58
Describe in detail how temperature affects the rate of transpiration.
- A temperature increase lowers the water potential of the atmosphere
- increase KE of water molecules accelerating their rate of evaporation from the walls of the mesophyll cells and if stomata open diffusion out into the atmosphere
59
How does temperature affect the water potential gradient and therefore rate of transpiration
Higher temperatures cause the water molecules around the leaf to diffuse away more quickly, reducing water potential around leaf
60
Describe in detail how the humidity affects the rate of transpiration.
- Air inside a leaf is saturated with water vapour so humidity is 100%
- humidity of the atmosphere surrounding a leaf is never >100%
- water potential gradient between leaf and atmosphere
- when stomata are open water vapour diffuses out of the leaf down a concentration gradient
61
What happens to transpiration In still Air?
There is an accumulation of saturated air at the surfaces of leaves. The water vapour gradually diffuses away leaving concentric rings of decreasing humidity.
62
Describe in detail how Air movement can affect the rate of transpiration
Movement of surrounding air blows away the layer of humid air at the leaf surface. The water potential gradient between the inside and the outside of the leaf increases. The faster the air is moving the faster the concentric shells of water vapour get blown away, the faster transpiration occurs
63
How does air movement affect diffusion out of the stomata
The more air movement the faster the concentric shells of water vapour get blown away the quicker water vapour diffuses out through the stomata
64
Describe how light intensity can affect the rate of transpiration
It controls the degree of the stomatal opening. The stomata open wider as light intensity increases, increasing the rate of transpiration.
65
How do you set up a potometer
1. Cut a leafy shoot under water so no air enters xylem
2. Under water fill the potometer with water, ensuring there is no air bubbles
3. Fit the leafy shoot to the potometer with rubber tubing Uber the water, to prevent air bubbles forming
4. Remove the potometer and shoot from the water, seal joints with Vaseline
5. Introduce an air bubble into capillary tube
6. measure distance the air bubble moves in a given time
7. Use the water reservoir to bring the air bubble back to the start point + repeat
66
- What does the potometer measure
| - if the cells are fully turgid what is this equal to
- The rate of water uptake into a shoot
| - when turgid this is equal to the rate of transpiration
67
What is a meophyte
A plant that lives in conditions of adequate water supplies
68
What is a xerophyte
A plant that lives in conditions where water is scarce
69
What is a hydrophyte
Water plants, these can be partly of wholly submerged in water e.g water lily/elodea
70
What are more land plants growing in temperate regions and crop plants
Mesophytes
71
What happens when a plant looses top much water
| -reference stomata and photosynthesis
It wilts and the leaves drop, the stomata close and leaf surface area available for absorbing light is reduced so photosynthesis becomes less efficient
72
Name 3 adaptations of mesophytes in bad conditions e.g when ground is frozen or liquid water not available
1) many shed leaves before winter so they don’t loose water by transpiration
2) aerial parts of non-woody plants die in winter so they are not exposed to frost or cold winds, but underground organs such as bulbs survive
3) annual mesophytes become dormant seeds over winter, with such a low metabolic rate that almost no water is required
73
What type of plants are most likely to live in extreme conditions e.g desert region, low water, cold regions
Xerophytes e.g Marram grass
74
What is found inside marram grass? (6/7)
- Thick cuticle
- Abaxial epidermis
- Hinge cells
- Sclerenchyma fibres
- Interlocking hairs trapping water vapour inside adaxial epidermis with sunken stomata
- vascular bundle
75
Name some of the environmental challenges marram grass faces (5)
Colonises in sand dunes :: no soil, rainwater drains say, High wind speeds, salt spray and lack of sun shade
76
List the modifications of marram grass
```
1- rolled leaves
2- sunken stomata
3- hairs
4- thick cuticle
5- thick fibres of sclerenchyma
```
77
Describe how rolled leaves occur and why they are an advantage in marram grass
Occur= hinge cells (large thin-walled epidermal cells) at the bases of grooves become plasmolysed due to transcription and the Leaf rolls with its upper adaxial surface inwards
Benefit= this reduced the leaf area exposed to air so reduces transcription
78
Describe how a sunken stomata is a benefit for marram grass
Occur= stomata occur in grooves on the adaxial surface but not on a facial surface. Humid air is trapped in pits outside stomata
Benefit= reduces water loss by reducing water potential gradient between the inside of leaf and outside :: slower rate of diffusion out of stomata
79
Describe how hairs in marram grass reduce water loss
Stiff interlocking hairs trap water vapour and reduce water potential gradient between inside and outside of the leaf.
80
Why is the thick cuticle of marram grass a benefit?
- Waxy cuticle is waterproof so reduces water loss
| - Thicker the cuticle the lower the rate of transcription through cuticle
81
How are hydrophytes adapted
- water is a supportive medium :: little lignified support tissues
- little need for transport tissue :: xylem is poorly developed
- leaves have little or no cuticle
- stomata are on the upper surface
- stems and leaves have large air spaces down to their roots
82
What is the advantage of hydrophytes having little/no cuticle?
No need to prevent water loss as submerged in water
83
What is the advantage of hydrophytes having stomata on the upper surface
Because the lower surface is in the water
84
What is the advantage of hydrophytes having continuous air spaces down to their roots?
It forms a reservoir of oxygen and carbon dioxide which provide buoyancy
85
Describe the stomata on the upper (adaxial surface) in mesophytes, xerophytes and hydrophytes
```
Mesophytes = few
Xerophyte= many
Hydrophyte= many
```
86
Describe the stomata on the lower (abaxial surface) in mesophytes, xerophytes and hydrophytes
```
Mesophytes = many
Xerophytes = few
Hydrophytes = none
```
87
Describe the upper (adaxial surface) cuticle of mesophytes, xerophytes and hydrophytes
```
Mesophytes = thick
Xerophytes = thin on rolled leaves, thick on flat leaves and needles
Hydrophytes = none
```
88
Describe the lower (abaxial surface) cuticle of mesophytes, xerophytes and hydrophytes
```
Mesophytes = thin
Xerophytes = thick
Hydrophytes = none
```
89
Define translocation
The movement of the soluble products of photosynthesis, such as sucrose and amino acids through the phloem from sources to sink
90
Define phloem
Plant tissue containing sieve tube elements and companion cells, translocating the sucrose and amino acids from the leaves to the rest of the plant
91
Where are sucrose/amino acids translocated from/ to
Translocated away from the site of photosynthesis in the leaves to all other parts of the plant ‘sinks’ where they are used for growth or storage
92
In which location can phloem translocate substances
Up down and sideways, wherever the products of photosynthesis are needed
93
Describe the sieve tubes in the phloem
- comprise ems-to-end cells called sieve tube elements
- the end walls do not break down as they do in xylem vessels
- instead the end walls (sometimes side walls) are perforated at the sieve plates
94
Where are the cytoplasmic filaments located in the phloem
Cytoplasmic filaments containing phloem protein extend from one sieve tube to the next through pores in the sieve plate
95
How are sieve tube element cells adapted in the phloem
They lose their nucleus and other organelles during their development allowing space for transporting materials
96
What is the metabolism of sieve tube elements controlled by?
At least one neighbouring companion cell
97
How do we know that companion cells are highly metabolically active?
Because they have large nuclei, dense cytoplasm containing much RER and mitochondria.
98
How are companion cells connected to sieve tube elements
By plasmodesmata
99
Name 4 experiments which provide evidence of organic substances being translocated through the phloem
- ringing experiments
- radioactive traces and autoradiography
- aphid experiments
- aphids and radioactive tracers
100
Describe how ringing experiments are conducted
- outer bark tissue were removed from all the way around a woody stem (in a ring)
- this removes the phloem
- after time (leaving plant to photosynthesis) the phloem contents should be analysed
101
Describe the expected results of a ringing experiment for above and below the ring
Above the ring= accumulation of sucrose :: it had been translocated in the phloem
Below the ring= no sucrose :: it has been used by plant tissues but not replaced because the ring prevented it moving downwards
102
Why does the bark above the ring in the ringing experiment swell?
Because solutes were accumulating and couldn’t move downwards
103
Why is glucose (product of photosynthesis) converted to starch for transport?
1. Less chemically reactive
2. Insoluble so no osmotic effect
3. Can’t diffuse out of the cell
4. Carries lots of energy in c-h and c-c bonds
104
Describe how radioactive tracers and autoradiography provide evidence for translocation
-plant photosynthesises in presence of radioisotope e.g C14 in carbon dioxide
-stem is place on photographic film exposed to radiation producing autoradiograph
-position of exposure coincides with position of the phloem
-this indicates that the phloem translocates the sucrose made from 14Co2 in photosynthesis
(Look at diagram on pg 213)
105
Describe how aphid experiments provide evidence for translocation
- aphids have mouthpart called a stylet
- they insert this into sieve tube and the phloem contents (sap) exude into aphids stylet
- aphid then removed whilst stylet remained embedded in the phloem
- sap in phloem collected in the stylet was analysed showing presence of sucrose
106
Describe how aphids and radioactive tracers provide evidence for translocation
- aphid sap collected from plants that had been photosynthesising with 14CO2
- showed radioactivity (sucrose made in photosynthesis) moves at a speed of 0.5-1 (h-1)
- this is much faster than diffusion alone so an additional mechanism was present
107
When was the mass flow hypothesis proposed to explain translocation?
What did it suggest?
1937
-suggested that there is a passive mass flow of sugars from the phloem of the leaf (highest concentration; source) to other areas e.g growing tissue (lower concentration; sink)
LEARN MASS FLOW DIAGRAM ON PAGE 214!!!!!!!!!!!
108
What does mass flow hypothesis not explain about translocation (5)
1- rate if phloem transport is 10,000x faster than if it was moved by diffusion
2- doesn’t account for sieve plates
3-sucrose and amino acids Travel at different rates in different directions in the same tissue
4-phloem has a High oxygen consumption and translocation is slowed/stopped at low temperatures/respiratory inhibitors applied
5-companion cells are biochemically active, mass flow hypothesis does not suggest a role for them
109
Name 3 other theories about translocation
Translocation involves:
A) an active process
B) Protein filaments
C) Cytoplasmic streaming
110
Why do some argue that translocation is an active process?
Because respiratory inhibitors and low temperatures inhibit translocation indicating energy generated by respiration is used
111
Why do some argue protein filaments are used in translocation
Because protein filaments pass through sieve pores so maybe different solutes are carried along routes through the same sieve tube element
112
Why do some argue that cytoplasmic streaming is responsible for translocation
Could be responsible for the movement in different directions in individual sieve tube elements, as lone as there’s a mechanism to transport solutes thrive sieve plates
(CHECK DIAGRAM PAGE 215)
