Transport in Plants Flashcards
1
Q
Why do plants need transport systems?
A
Metabolic demands- Need oxygen and glucose and waste products removed.
Size- Be able to move substances up and down long distances
Small surface area to volume ratio- cannot rely on diffusion alone
2
Q
What is are dicots?
A
Dicotyledonous plants
3
Q
What are cotyledons?
A
Organs that act as food stores for developing embryo plant and form the first leaves when the seed germinates.
4
Q
What sort of seeds to dicots make?
A
Seeds which contain two cotyledons.
5
Q
What are herbaceous dicots?
A
Soft tissue
Short life cycle
6
Q
What are woody/ arborescent dicots?
A
Hard lignified tissue and a long life cycle.
7
Q
What is the vascular system?
A
Series of transport vessels running through the stem, roots and leaves.
8
Q
What is the vascular system made up of herbaceous dicots?
A
Xylem
Phloem
9
Q
How are the transport tissues arranged?
A
In vascular bundles.
10
Q
In a stem, …
A
… the vascular bundles are around the edge to give strength and support (phloem further outside than xylem)
11
Q
In the roots, …
A
… vascular bundles are in the middle to help plants withstand tugging strains that result as the stems and leaves are blown in the wind.
12
Q
In the leaves, …
A
… the midrib of a dicot leaf is the main vein carrying the vascular tissue through the organ.
13
Q
What are the functions of the xylem?
A
Transport water and mineral and support.
14
Q
What is the direction of flow in the xylem?
A
From roots to leaves.
15
Q
What sort of cells make up the xylem?
A
Dead
16
Q
What is the structure of the xylem?
A
Long, hollow structures.
Made by several columns of cells fusing together end to end.
17
Q
What are the other tissues associated with the xylem in herbaceous dicots?
A
Parenchyma
Lignin
18
Q
What is parenchyma?
A
Thick walled.
Around xylem, stores foods, contains tannins deposits.
19
Q
What is lignin?
A
Provide extra mechanical strength. Can be laid down in several ways, it can form rings, spirals or solid tubes with lots of small unlignified areas called border pits.
20
Q
What happens at border pits?
A
Water leaves xylem
21
Q
What is the phloem?
A
Living tissue that transport food in the form of organic solutes.
22
Q
What is the direction of flow in the phloem?
A
Both
23
Q
What are the main transporting vessels of the phloem?
A
Sieve tube elements
24
Q
How is the structures of xylem and phloem different?
A
Phloem does not have lignin.
25
How is the structures of xylem and phloem similar?
Made up of many cells joined end to end to form a long, hollow structure.
26
In the phloem what perforates the walls?
Sieve plates
27
What don't mature phloem have?
Nucleus
28
What is the phloem filled with?
Phloem sap
29
How are companion cells linked with sieve tube elements?
Plasmodesmata
30
What are plasmodesmata?
Microscopic channels through the cellulose cells walls linking the cytoplasm to adjacent cells.
31
What do companion cells maintain?
Nucleus and organelles.
32
What supporting tissues does the phloem contain?
Fibres
| Sclereids (cells with thick walls)
33
How is water important to the structure of plants?
Turgor pressure, loss of water by evaporation keeps plants cool
34
How is water important for metabolism in plants?
Raw material for photosynthesis
35
What is the exchange surface in plants where water is taken into the plant?
Root hair cells
36
How are root hairs adapted as exchange surfaces?
Large SA:V ratio
Thin surface layer
Microscopic size means they can penetrate between soil particles
Concentration of solutes in the cytoplasm of root hair cells maintains a water potential gradient between the soil water and the cell.
37
Does soil water have a high or low water potential?
High
38
Why does soil water have a very high water potential?
Has a low concentration of dissolved minerals.
39
Is the water potential higher in soil water or root hair cytoplasm?
Soil water so water moves into root hair vacuolar sap and cytoplasm by osmosis.
40
What are the two pathways in which water can move across the root to the xylem?
Symplast
| Apoplast
41
What is symplast?
Continuous cytoplasm of living plant cells that is connected through the plasmosdesmata.
42
How does water move through the symplast?
Root hair cell has a higher water potential than the cell next to it so water moves by osmosis. This continues from cell to cell until the xylem is reached.
43
What is the apoplast?
The cell walls and the intercellular spaces.
44
How does water move through the apoplast?
Water fills spaces between the loose, open network of fibres in the cellulose cell wall. As water molecules move into the xylem, more water molecules are pulled through the apoplast behind them due to cohesive forces between the water molecules. The pull from water moving into the xylem and up the plant along with the cohesive forces between the water molecules creates a tension that means there is a continuous flow of water through the open structure of the cellulose wall, which offers little resistance.
45
What is the endodermis?
Layer of cells surrounding the vascular tissue of the roots?
46
What are the vascular tissues?
Xylem and phloem
47
Why is the endodermis particularly noticeable in the roots?
Because of the effect on the Casparian stip.
48
What is the Casparian strip?
Band of waxy material that runs around each of the endodermal cells forming a waterproof layer.
49
What is the band of waxy material around each andodermal cell called?
Suberin
50
How does water move from endodermis to the xylem?
At the casparian strip water in the apoplast pathway can go no further and is forced into the cytoplasm of the cell, joining the water in the symplast pathway. The cytoplasm of the endodermal cells is dilute compared to the cells in the xylem and there is active transport of minerals into the xylem from the endodermal cells. This increases the rate of water movement into the xylem through the symplast pathway.
51
What does water do once inside the vascular bundle?
Water returns to the apoplast pathway to enter the xylem itself and move up the plant.
52
What does the AT of minerals into the xylem create?
Root pressure
53
What does root pressure do to the xylem?
Gives water a push up the xylem.
54
Give some evidence supporting the role of AT in root pressure.
- If levels of oxygen or respiratory substrates fall, root pressure falls.
- Some poisons affect mitochondria and prevent the prediction of ATP. If applied to root cells, root pressure disappears.
- Root pressure increase with a rise in temperature and falls with a fall in temperature, suggesting chemical reaction are involved.
55
What are xerophytes?
Plants which have evolved a wide range of adaptions that enable them to live in and reproduce in place where water availability is very low.
56
Give an example of a xerophyte.
Cacti
57
Give 5 ways xerophytes conserve water.
1) Reduced number of stomata - to reduce water loss by transpiration.
2) Curled leaves - cofines stomata in a microenvironment of still, humid air reducing the water potential gradient.
3) Thick waxy cuticle - minimise water loss
4) Reduced leaves (thin needles) - reduces the SA:V ratio, reducing water loss by transpiration.
5) Root adaptions - long deep roots
58
What are hydrophytes?
Plants which live in water and need to adapt to cope with growing in water or in permanently saturated soil.
59
Give an example of a hydrophyte.
Water lilies
60
What is a major problem for hydrophytes?
Water logging. The air spaces of a plant need to be full of air, not water.
61
Give 5 adaptations of hydrophytes.
1) Stomata on upper layer open - maximises gaseous exchange
2) Wide flat leaves - capture as much light as possible
3) Air sacs - enable leaves to float
4) Large SA of stems and roots under water - maximises the area for photosynthesis and for oxygen to diffuse into submerged plants
5) Aerenchyma - specialised parenchyma tissue forms in the leaves, stems and roots. Makes leaves and stems buoyant and forms a low resistance internal pathway for the movement of substances to tissues below the water. Allow plants to cope with anoxic.
62
What is parenchyma?
Packing tissue
63
What is anoxic?
Extreme low oxygen conditions e.g. mud.
64
Give an example of where Aerenchyma is found and why it provides a low resistance pathway.
Rice
Provides a low resistant pathway by which methane produced by rice plants can be vented into the atmosphere, this contributes to the greenhouse effect.
65
What are pneumatophores?
Aerial roots which grow upwards into the air, they have many lenticles which allow the entry of air into woody tissue.
66
Give 3 pieces of evidence for translocation.
- If mitochondria in companion cells are poisoned, translocation stops.
- Microscopy allows us to see adaptions of companion cells for AT.
- Aphid studies show there is a positive pressure in the phloem that forces sap out through the stylet. So the pressure and therefore the flow rate in the phloem is lower closer to the sink than the source.
67
Give 3 pieces of evidence for the cohesion-tension theory.
- Diameter of tree is lowest when the transpiration is at its highest during the day as xylem is under tension.
- When a xylem vessel is broken, air in drawn in rather than air leaking out.
- If xylem is broken plant can no longer move water up as the continuous column of water is broken.
68
What is the cohesion-tension theory?
1) Water evaporates from mesophyll cells into air spaces in the leaf.
2) This lowers the water potential of the cell. So water moves in along both the symplast and apoplast pathways.
3) This is repeated across the leaf to the xylem.
4) Water molecules form H bonds with the carbohydrates in the walls of xylem vessels (Adhesion) and water molecules form H bonds with each other (Cohesion). This results in capillary action. This creates a continuous stream of water to replace water lost by evaporation (transpiration pull).
5) Transpiration pull results in tension in the xylem.
69
What is capillary action?
Process by which water can rise up a narrow tube against gravity.
70
What is transpiration?
Loss of water vapour from leaves and stems of plants.
71
Why do some stomata need to be open at all times?
During the day CO2 needs to be taken in for photosynthesis. At night O2 is needed as none is being produced by photosynthesis.
72
How does a transpiration prevent heat damage?
Cools leaf down as water evaporates
73
How do you measure transpiration?
Potometer- measures rate of water uptake
74
Why is difficult to directly measure transpiration?
The practical difficulties with condensing and collecting all of the water that evaporates from the leaves and stems without also collecting water that evaporates from the soil surface.
75
What can be measured to measure transpiration?
Uptake of water
76
Why can uptake of water be a measure of rate of transpiration?
Almost all water taken up is lost by transpiration.
77
How can you calculate the rate of water uptake using a photometer?
Distance moved by air bubble / time taken for air bubble to move that distance
78
What are the units for rate of water uptake?
cm/s
79
What prevents cells from swelling in width and so they extend lengthways?
Cellulose hoops
80
Is the inner layer or outer layer more flexible?
Outer layer
81
What is an example of a turgor driven process?
Transpiration
82
Why is transpiration a turgor driven process?
It is controlled by the opening and closer of stomata.
83
Give 5 factors affecting the rate of transpiration.
```
Light
Relative humidity
Temperature
Air movement
Soil/ water availability
```
84
How does light affect transpiration?
Light is needed for photosynthesis. In the light, stomata open for gas exchange. In the dark most stomata close. Increased light intensity increases the number of stomata open, increasing rate of water vapour diffusing out, increasing evaporation from the leaf. So, greater light intensity leads to greater transpiration.
85
How does humidity affect transpiration rate?
A higher relative humidity will lower the rate of transpiration because of the reduced water potential gradient between the leaf and the air. Very dry air will increase the rate of transpiration.
86
What is humidity?
Measure in the amount of water vapour un the air compared to total concentration of water the air can hold.
87
How does temperature affect the rate of transpiration?
- An increase in temperature increases the kinetic energy of water molecules which increases the rate of evaporation from the spongy mesophyll cells into the air spaces of the leaf.
- An increase in temperature increases the concentration of water vapour that the external air can hold before it becomes saturated, so decreases its humidity and its water potential.
- Both increase the diffusion gradient between the air inside and outside the leaf, thus increasing the rate of transpiration.
88
How does air movement effect the rate of transpiration?
Each leaf has a layer of still air around it trapped by the shape of the leaf and features on the surface of the leaf which decrease air movement close to the leaf. Water vapour that diffuses out of the leaf accumulates here and so the water potential around the stomata increases, in turn reduces the diffusion gradient. This reduces transpiration.
Air movement or wind will increase the rate of transpiration.
89
How does soil/ water availability affect transpiration?
If soil is very dry the plant will be under water stress and the arte of transpiration will be reduced.
90
What is glucose converted to for storage?
Sucrose
91
What happens when sucrose reaches the cells where it is needed?
Converted back to glucose for respiration or starch for storage or to produce amino acids.
92
What is translocation?
Movement of organic compounds from sources to sink.
93
What are the products of photosynthesis that are transported known as?
Assimilates
94
What is the main assimilate?
Sucrose
95
What are the main sources of assimilates in a plant?
Green leaves and stems
Storage organs
Food stores
96
What are the storage organs of a plant?
Tubers, tap roots
97
What are the main sinks in a plant?
Roots
Meristems
Any part laying down food stores
98
What are the two ways in which plants load assimilates into the phloem?
Symplast route and apoplast route.
99
What is the apoplast route in phloem loading?
1) Sucrose from source travels through cell walls and inter-cell spaces to the companion cells and sieve elements by diffusion down a concentration gradient.
2) In companion cells sucrose is moved into the cytoplasm across the cell membrane in an active process.
3) H+ are AT out of the companion cell into the surrounding tissue using ATP.
4) H+ return to the companion cells down a concentration gradient by a co-transport protein.
5) Sucrose is co-transported which increases sucrose concentration in the companion cells and the sieve elements through the many plasmodesmata between the two linked cells.
6) This lowers the water potential, so water moves in by osmosis. This builds up turgor pressure.
7) Water carrying the assimilates moves into the sieve elements and moves up and down the plant by mass flow.
100
What is phloem unloading?
Diffusion of sucrose from phloem into other cells.
