Chapter 9 - Transport in Plants Flashcards
1
Q
Suggest and explain 3 reasons why multicellular plants need transport systems
A
- Metabolic demands, many underground and internal parts of plant can’t make own food etc. O2 and glucose needs to be transported to them and waste products removed
- Size, plants continue to grow * need effective transport system to move substances up and down tip of roots
- SA:VOL ratio, leaves are adapted to have large SA:VOL for GE, but still have a small SA:VOL bc of trunk, stem etc * cannot rely on diffusion alone
2
Q
What are dicotyledonous plants?
A
-make seeds that contain two cotyledons (food stores for developing plant and forms the first leaf in germination)
3
Q
Describe the two types of dicotyledonous plants
A
Herbaceous dicots - soft tissue and short life cycle
Woody dicots - hard lignified tissues + long life cycle
4
Q
Name the parts of the vascular bundle
A
Xylem
Phloem
Cambium
5
Q
Draw and label a diagram of the stem of a plant
A
- epidermis
- cortex
- phloem
- xylem
- vascular bundle
- parenchyma
6
Q
Explain the function of the xylem in plants
A
- Transport of water and mineral ions
- Support the plant
7
Q
Describe the structure of the xylem
A
Xylem vessels- long hollow structures made of long column cells
Thick-walled xylem parenchyma - packs around xylem vessels storing food, contains tannin (bitter chemical to protect plant)
Fibres- long cells with lignified secondary walls that provide extra mechanical strength but don’t transport water
8
Q
How is lignin adapted in the xylem for maximum support?
A
Laid in spirals, rings or tubes w unlignified areas (boarded pits)
9
Q
Suggest the role of the phloem
A
Living tissue that transports food in form of organic solutes around plant from the leaves, supplies cells w sugars and aa needed for cellular respiration
10
Q
What are the phloems main transport vessels?
A
Sieve tube element cells, cells joined end to end to form long hollow structure
11
Q
Are phloem tubes lignified?
A
No
12
Q
What forms in between the cells in phloem tissue?
A
Walls become perforated to form sieve plates, let phloem contents through * tube is filled with phloem sap
13
Q
What structures break down in the phloem because of the large pores?
A
Cell walls, tonoplast (vacuole membrane), nucleus and other organelles
14
Q
What are companion cells?
A
Cells that link to the sieve tube elements by many plasmodesmata
-function of life support for sieve TEC which have lost most of its OG function
15
Q
Why do plants need water?
A
- Turgor pressure (hydrostatic pre) bc of osmosis in plant cells provides hydrostatic skeleton to support stems and leaves
- Turgor drives cell expansion, the force enables plant to grow through tarmac
- Loss of water by evaporation helps keep plant cool
- Mineral ions and products of photosynthesis are transported in aq sol
- Raw material for photosynthesis
16
Q
Suggest how RHC are adapted to carry out its function (5 marks)
A
Function: to take up water from soil into plant
- Microscopic size-> can penetrate easily through soil particles
- Each hair large SA:VOL
- large SA bc there are so many
- Each hair thin surface layer so diff and osmosis is rapid
- Conc of solutes in cytoplasm of RHC maintains a water potential gradient between soil water and cell
17
Q
Explain how water moves into the RHC from the soil
A
- Soil has low conc of dissolved minerals * high wp
- Cytoplasm and vacuolar sap of RHC has many solvents (aa, sugars) so wp low
- Water moves into RHC via osmosis
18
Q
Name the 3 ways water can move across the root
A
Symplast pathway
Apoplast
Vacuolar
19
Q
Describe the mechanism when water moves through the symplast across the root
A
Through the cell
-RHC has higher wp than the next cell along -> water diffuses from into cell from soil
- Makes the cytoplasm more dilute (higher wp) so water moves into next cell via osmosis
- As water leaves RHC by osmosis, wp of cytoplasm falls again, maintains a step water potential grad to ensure max water is moved
20
Q
Explain how water moves across the root via apoplast pathway
A
Water moves across cells walls and intercellular spaces, fills spaces btwn loose open network of fibres in cellulose cell wall
- As water moves towards the xylem more water mol. are drawn due to the cohesion of water mol.
- The pull creates tension meaning there is a continuous flow of water through open structure of the cellulose cell wall
- Cellulose cell wall offers little resistance
21
Q
Describe the movement of water into the xylem (6 marks)
A
Water diffuses across root via symplast and apoplast pathways
- Until it reaches the endodermis (cells surrounding vascular bun)
- Reaches casparian strip
- Due to the ability of the casparian strip to be waterproof
- The water travelling through the apoplast pathway is forces out into cytoplasm
22
Q
What is the casparian strip?
A
A band of waxy material (suberin) that runs around each of the endodermal cells forming a waterproof layer
23
Q
What is the function of the casparian strip?
A
Filters the water as it has to pass the selective permeability cell surface membrane, it removes any toxic solutes
24
Q
What increases the rate of water moving into xylem by osmosis?
A
- Solute conc in cytoplasm of endodermal cells is more dilute compared to cells in xylem
- and the endodermal cells move mineral ions into xylem by active transport
- wp of xylem cells is lower than the wp of the endodermal cells
- Increasing the rate of water moving into xylem by osmosis down a water potential grad from the endodermis through the symplast pathway
25
What happens to the water once it's inside the vascular bundle?
Water returns to the apoplast pathway to enter the xylem and move up the plant
26
What causes root pressure?
Active pumping of minerals into xylem to produce movement of water by osmosis causes root pressure
27
What is the function of root pressure?
Gives water a push up the xylem, but isn't the biggest factor in movement of water
28
Suggest and explain evidence for the role of active transport in root pressure
1. Poisons, e.g. cyanide (affects mitochondria and prevents production of ATP), so no energy supplied root pressure disappears
2. Root pressure increases w incr in temp and walls w drop, suggesting chemical reactions are involved
3. If levels of oxygen fall, root pressure falls
4. Xylem sap may exclude from the cut end of stems at certain times (e.g. overnight)
29
Define transpiration
The loss of water vapour by diffusion out of the plant via the stomata
30
Why is transpiration inevitable?
Bc of the GE in stomata
31
What is the transpiration stream?
Movement of water through a plant from the roots until its lost by evaporation through the leaves
32
Describe the process of transpiration in the plant cell
1. Water evaporates from mesophyll cells into air spaces and move out of stomata into surrounding air by diffusion
2. wp in mesophyll cells is lower than surrounding cells so water will diffuse out of xylem into mesophyll cell via osmosis
3. Water can hydrogen bond to itself giving it a cohesive force
4. Hydrogen bonds also forms between water and the carbohydrates in the wall of the xylem (adhesion)
5. Results in capillary action- so H2O can move up against gravity
33
What is transpiration pull?
Water is drawn up xylem in a continuous stream to replace water lost by evaporation
Results in tension in the xylem which helps move water across roots from soil
34
Suggest pieces of evidence to support the cohesion theory
- Changes in diameter of trees decr in day bc transpiration at its peak and incr a night bc transpiration low
- When xylem vessel is broken air is drawn in to the xylem rather than water leaking out
- When broken plant can't move water up stem anymore because the continuous stream of water is broken
35
What is mass flow with water?
The overall water movement from high pressure at root end to low pressure at leaf end
36
Opening and closing the stomata is what type of process?
Turgor-driven process
37
Explain the function of the stomata
When turgor is low the asymmetric configuration of the guard cells walls close the pores as the stomata swells up
Conditions are good= guard cells pump solutes in by active transport increasing their turgor
When water becomes scarce hormones from roots trigger turgor loss from guard cells which close pores
38
Describe the adaptations of the stomata to minimize transpiration loss
Cellulose hoops to prevent the cells from swelling in width
Inner wall of guard cells is less flexible than outer wall cell becomes bean shaped and open pore
39
Describe factors affecting transpiration
- Light, needed for photo w light stomata opens up, incr light intensity incr n. of stomata open so incr loss of wv
- Humidity, high humidity will lower rate of transpiration bc of reduced water vapour potential btwn inside of leave and outside air
-Temperature, incre KE + incr rate of evaporation from spongy mesophyll cells into air space
o also increases the conc of water vapour that air can hold before it saturated
- Air movement, lot of air movement increases rate of trnpr, when low the diffused water vapour will accumulate
- Soil water availability, v dry plant= under water stress so less transpiration
40
Describe an experiment to measure the amount of water taken up by a plant
- potometer
1. Cut shoot under water to prevent air entering the xylem, cut at slant to increase SA:VOL
2. Insert shoot underwater into potometer
3. Use petroleum jelly to seal the ends
4. Dry the leaves of the plant to ensure no water is lost on the leaf
5. Allow time for plant to acclimatise
6. Allow one bubble into the tube
7. Record starting point of bubble and start stopwatch
8. Record finishing point
Rate= distance/time
41
Define translocation
The movement of dissolved substances (e.g. sucrose) o where they are needed
-Energy requiring process that happens in phloem
42
What is the source?
The source of a substance where its made by photosynthesis
43
What is the sink?
The area where substances are required to supply metabolic needs
44
What are assimilates?
Products of photosynthesis that are transported (mainly sucrose)
45
Suggest the main sources of assimilates
Green leaves and stems
Storage organs (e.g. tubers)
Food stores in seeds when they germinate
46
Suggest the main sinks in a plant
Roots that are growing or actively absorbing mineral
Meristems that are actively dividing
Any part of plant that are laying down food stored (e.g. developing seeds)
47
Describe and explain the process of translocation ( 6 marks)
1. Hydrogen ions are actively transported out of companion cell
2. Meaning there are more H+ ions outside cell than inside cell creating a hydrogen ion conc gradient
3. Hydrogen ions move down the conc gradient into cell by FACILITATED DIFFUSION through a CO-TRANSPORT PROTEIN associated w SUCROSE
4. . Sucrose moves in w H+ ion, sucrose transported against the sucrose conc grad
5. Sucrose diffuses through the plasmodesmata from the companion cell into sieve tube element cell
48
What is the evidence for translocation?
- Using microscope to see the adaptations of the companion cell for active transport
- If mitochondria of compan c. is poisoned the translocation stops
- Flow of sugars is faster than w diffuse
- Aphids show that the concentration of the sucrose in the phloem is higher near to the source than sink
49
How does translocation happen in the symplast route?
The source moves through the cytoplasm of the mesophyll cells and into the sieve tubes by diffusion through the plasmodesmata
Passive process
Sucrose ends up in sieve elements and water follows by osmosis
50
what are xerophytes? and give example
Live in areas where water lost via transpiration is greater than taken up by roots
-Cacti
51
Suggest how xerophytes are adapted to live in dry and hot environments ( 7 marks )
- Thick waxy cuticle to minimise water loss
- Reduced n. of stomata to reduce transpiration (e.g. marram grass)
- Sunken stomata, reduced air movement, producing a microclimate of still humid air reduces wp grad so less trans
- Reduced leaves to decre leaf area where water can be lost
- Hairy leaves, traps a pocket of air creating a high humidity reducing water vapour gradient * minimising the transpi loss
- Mircrohairs such a marram grass in sunken stomatal pits
- Curled leaves, confines all of the stomata within a microenvironment of still, humid air to reduce diffusion of wv from stomata
- Some parts of plants can store water in different areas (e.g. swollen stem of cacti)
- Leaf loss, so reduce SA for transpiration
52
Suggest how roots of xerophytes are adapted to their extreme climate
- Long strong roots so that they can penetrate several meters to access water
- Wide spread shallow roots to maximise SA:VOL for max uptake of water
- Adapted to avoid problems (e.g. lose leaves or become dormant)
53
What are hydrophytes?
Plants that live in water (eg. lillies)
54
Suggest adaptation of hydrophytes which allows them to survive in water ( 7 marks)
- Very thin or no waxy cuticle
- Many open stomata to maximise GE
- Reduced structure of plant, water supports the leaves
- Wide flat leaves, to spread across the water to maximise SA for photo
- Small roots, water can diffuse directly into stem and leaf tissue so there is less need for uptake by roots
- Incr SA:VOL of stems and roots underwater max area for photo
- Air sacs to enable plants to float
-Aerenchyma (specialised parenchyma) forms in stems, leaves and roots
Function:
o Make leaves in stem more buoyant
o Form low resistance pathway for movement of substances
55
Describe how guard cells surrounding the leaf pores are adapted to their role
- Unevenly thickened cell wall, wall is thicker on one side
- Inner wall is thicker than outer
- Able to change shape
- Transports proteins
- In the presence of chloroplast to provide ATP
56
Name one other part of the leaf from which water may be lost
Cuticle
57
Use the cohesion theory to explain how water moves from the roots to the leaves
- Evaporation at the top of plant creates tension in the xylem
- Water molecules stick together
- Allows chain of water to be pulled up by tension
58
Suggest what adaptations could be seen on companion cells
- Many large plasmodesmata
- Many ribosomes
- Many large mitochondria
59
Distinguish between transpiration and transpiration stream
Transpiration- loss of water vapour through stomata
Transpiration stream- movement of water up xylem from roots to leaves
60
State two adaptations of sieve tubes that enables mass flow to occur
- Elongated elements
- Joined end to end to form
- Sieve plates
- Little cytoplasm
- No nucleus
61
Describe the features of the xylem that enable the steam to pass from one end of the stem to another
- Cells joined end to end
- Hollow
- Walls are lignified
- Bordered pits in walls
62
Describe and explain how transpiration contributes to the mechanism of water transport up the stem ( 6 marks )
- Water lost from the leaf is replaced
- Via apoplast or symplast pathway
- Water is replaced by the xylem
- Loss of water in the xylem creates a water pressure
- Water moves from high pressure to low pressure by MASS FLOW
- Cohesion
63
Suggest why a bunch of flowers may survive longer if the ends of the stems are removed immediately before placed in water
- Removes the bubbles in the air blocking the xylem
| - To restore the continuous flow of water
64
Where is the casparian strip located?
In the endodermis
65
Describe 4 steps the student should take when setting up the potometer
- Shoot is healthy
- Cut shoot underwater
- Cut at least 2-3 cm
- Check there are no air bubbles
- Water tight
- Leaves dry
