Chap 9 - Transport in plants Flashcards
1
Q
Define herbaceous plants
A
plants that have non-woody items
2
Q
Define dicotyledonous plants
A
produce seeds containing two cotyledons which act as food stores for the developing embryo and form the first leaves when the seed germinates
3
Q
Define vascular system (in plants)
A
system of transport vessels running through stem, roots and leaves
4
Q
Define vascular bundles
A
vascular system of herbaceous dicots made of xylem and phloem tissue
5
Q
Name 2 types of transport vessels in vascular bundles
A
xylem, phloem
6
Q
State the function of xylem and phloem
A
- xylem: transport of water, minerals + support
- phloem: transport of assimilates to all cells of plant
7
Q
Define assimilate
A
products of photosynthesis
8
Q
Describe the structure of xylem
A
- composed of xylem vessel elements and parenchyma cells
- long hollow tubes
9
Q
Describe how xylem is adapted to its function
A
- no cytoplasm (dead cells) - hollow tube for water and ion flow
- no end walls - less resistance to mass flow
- long - greater distance per element - more efficient and simpler transport
- pits in cell walls - water and minerals can flow from one vessel into another - good if vessel blocked to divert and allow movement
- narrow - aid capillary action of water
- lignified - extra mechanical strength(prevent collapse), adhesive with water so aid capillary action, precent vessles from collapsing under transpiration pull
10
Q
Describe patterns of lignification in xylem and state its function.
A
- rings, spirals or solid tubes with small unlignified areas - bordered pits
- support to withstand pressure changes as water moves thru plant
11
Q
Define sieve tube element
A
main cells of phloem that have greatly reduced living content and sieve plates between cells
12
Q
Define sieve tube
A
areas between cells of phloem where walls become perforated giving many gaps and a sieve-like appearance that allows phloem contents to flow thru
13
Q
Define companion cell
A
active cells found next to sieve tube elements that supply phloem vessles with their metabolic needs
14
Q
Describe the structure of phloem.
A
- long hollow tubes made of living cells
- consist of sieve tube elements and companion cells
- sieve tube elements form tube to transport assimilates
- sieve plates found in between sieve tube elements
- companion cells are linked to sieve tube elements by plasmodesmata, fulfill metabolic needs ot sieve tube elements as they have lost normal cell functions and have no nucleus
15
Q
Describe the adaptations of phloem.
A
- sieve tube elements - no nucleus & no/small amount cytoplasm to allow transport of assimilates more easily
- sieve plates allow assimilates to pass thru phloem tubes
- lots of plasmodesmata between companion cells, lots of mitochondria & dense cytoplasm in companion cells, to allow them to fulfill sieve tube elements with metabolic needs
16
Q
Compare similarities in structure & function of xylem and phloem.
A
- both transport materials around plant
- both made up of cells joined end to end forming long hollow structures
17
Q
Compare differences in structure & function of xylem and phloem
A
- xylem largely non-living tissue, phloem living
- xylem transports water & mineral ions, phloem transports organic solutes around plant
- xylem flow of materials from roots to shoots and leaves, phloem flow of material up and down
- xylem cell walls lignified, phloem cell walls not
18
Q
Describe how to produce stained sections of plant stems for viewing under microscope.
A
- put plant material into water containing strongly colored dye for 24 hours
- remove plant from dye rinse it
- make clean transverse cuts across stem with sharp blade on white tile
- make clean longitudinal cut thru region where vascular bundles would be expected to be
- put on slide and carry out wet mount if observing living tissue
19
Q
Define transpiration
A
- loss of water vapour from the leaves of a plant as result of evaporation of water from cell surfaces inside leaf,
- diffusion down a concentration gradient out of the stomata
20
Q
Define transpiration stream
A
movement of water through a a plant from the roots until it is lost by evaporation from the leaves
21
Q
Define transpiration pull
A
the force which aids in drawing the water upward from roots to leaves in order to replace water lost by evaporation
22
Q
Explain why water loss is inevitable for plants.
A
- CO2 moves in and O2 moves out of leaf by diffusion thru stomata
- when stomata are open to allow gas exhange, water vapour also moves out by diffusion and is lost - transpiration
- stomata open/close to control amount of water lost, during the day must be open for photosynthesis but during night closed
23
Q
Outline the route water takes through a plant.
A
- absorbed by roots
- travels thru xylem to leaves where it diffuses out thru stomata
24
Q
Define stomata
A
pores in surface of a leaf or stem that may be opened and closed by guard cells
25
Define guard cells
cells that can open/close stomatal pores, controlling gaseous exhange and water loss in plants
26
Explain how transpiration results in water moving through the plant (cohesion-tension theory).
- water molecules evaporate from surface of mesophyll cells into air spaces in leaf and move out of stomata into surrounding air by diffusion down conc gradient
- loss of water lowers water potential of mesophyll cell so water moves into it from an adjacent cell by osmosis along both pathways
- repeated across leaf to xylem, water moves out of xylem by osmosis into cells of leaf
- water mols form hydrogen bonds with carbs in walls of xylem vessels - adhesion, they also form them with each other - cohesion resulting in combined effect - capillary action allowing water to move against force of gravity
- water is drawn up xylem in continuous stream to replace water lost by evaporation - transpiration pull
- transpiration pull results in tension in xylem helping to move water across roots from the soil
27
Describe 3 sources of evidence for cohesion-tension theory.
- poisons - if cut shoot is placed in cyanide water, uptake and transpiration continues as usual showing that transpiration does not rely on live cells and therefore isnt an active process
- dyes - if leafy shoot is cut and dipped into dye the dye will visibly be taken into the xylem vessels supporting that major water pathway is thru xylem
- diameter of tree trunk over 24 hour period is narrowest at midday and widest at midnight - cohesive forces in xylem cause negative pressure that draws tissues in and reduces diameter bc highest rate of photosynthesis is at midday & lowest around midnight
28
Explain how guard cells can open/close stomata.
- when turgor is low, asymmetric configuration of guard cell walls closes the pore
- when env conditions favorable, guard cells pump in solutes by active transport, increasing turgor, opening the pore
29
State 5 env factors that can affect the rate of transpiration and for each explain how they have their effect.
- light - required for photosynthesis so stomata will open when there is light - higher rate of transpiration
- relative humidity - high humidity lowers rate of transpiration bc reduced water vapour potential gradient between inside leaf and outside
- temperature - increases kinetic energy of water mols so it increases rate of evaporation, also increases conc of water vapor that external air can hold before it becomes saturated - decreaes relative humidity and water potential
- air movement - water vapor that diffuses out accumulates at leaf, air movement ventialtes and increases diffusion
- soil water availability - dry soil means plant will draw less water and therefore lower rate of transpiration
30
Show how a potometer can measure transpiration rate.
- measures rate of water uptake
- measure distance moved by air bubble and divide by time taken to get rate of water uptake
- 99% of water taken up is lost by transpiration, by measuring factors that affect rate of water uptake we measure factors that affect rate of transpiration
31
Explain precautions that must be taken when setting up potometer.
- leafy shoot should be cut and inserted into potometer under water - only water is in xylem so it is not clogged
- once set up, leave apparatus for some time before taking measurements - acclimatise the plant for new conditions
- all joints must be sealed with waterproof jelly to make sure that any water loss measured is a result of transpiration from stem and leaves
32
Describe 5 functions of water in plants.
- turgor pressure as result of osmosis provides hydrostatic skeleton that supports stem and leaves
- turgor drives cell expansion - enables plant roots to force their way thru terrain
- transpiration helps cool plants down
- mineral ions and assimilates are transported in aq solutions
- raw material for photosynthesis
33
Describe 4 ways that the root hairs of root hair cells are adapted as exchange surfaces,
- microscopic size - penetrate easily between soil particles
- large SA:V ratio, lots of them on each root tip
- thin surface layer - short diffusion distances
- conc of solutes in cytoplasm maintains water potential gradient between soil water and the cell
34
Explain why water moves from the soil into root hair cells.
- soil water has low conc of dissolved minerals - high water potential
- cytoplasm and vacuolar sap of root hair cell has many solutes - low water potential
- water moves into root hair cells by osmosis
35
Name the two pathways by which water travels across the root to the xylem.
- symplast
- apoplast
36
Describe the symplast pathway of water movement.
- water moves thru continuous cytoplasm of living plant cells connected thru plasmodesmata (symplast)
- root hair cell has higher water potential than next cell bc water diffused into it making it more dilute
- water moves from root hair cell to adjacent cell by osmosis, continues cell to cell until xylem reached
37
Explain the importance of water potential gradients for movement of water thru a plant.
Allow passive movement of water thru plants
38
Describe the apoplast pathway of water movement.
- water moves thru the cell walls and intercellular spaces (apoplast)
- as water moves into xylem, more water mols pulled thru apoplast behind them due to cohesion between water mols
- pull from water moving into xylem and up plant along with cohesive forces creates tension meaning continuous flow of water thru cell walls
39
Define endodermis
layer of cells surrounding vascular tissue of roots
40
Define casparian strip
band of waxy material (suberin) that runs around each endodermal cell forming a waterproof layer
41
Define root pressure
active pumping of minerals into xylem by root cells that produces a movement of water into xylem by osmosis
42
Describe the function of the Casparian strip.
- blocks apoplast pathway and forces it into cytoplasm of the cell, joining water in symplast
- water must pass thru selectively permeable CSM - prevents potentially toxic solutes in soil water from entering living tissues
43
Explain the role of active transport by endodermal cells for the movement of water.
- they move mineral ions into xylem by active transport
- this means xylem cells water potential is lower than endodermal cell water potential
- water mols follow minerals by osmosis creating higher hydrostatic pressure in root xylem
- this push - root pressure that contributes to mass flow of water thru plant
44
Describe evidence for role of active transport in moving water from root endodermis into xylem.
- poisons - affect mitochondria, prevent ATP production - root cells have no energy supply - root pressure disappears
- root pressure increases with rise in temp - suggests chemical reations involved
- if levels of oxygen/respiratory substrates fall, root pressure falls - it relies on energy
45
Define xerophytes
plants with adaptations that enable them to survive in dry habitats or habitats where water is in short supply in the environment
46
Define hydrophytes
plants with adaptations that enable them to survive in very wet habitats or submerged or at surface of water
47
State 3 examples of xerophytes.
- cacti
- marram grass
- conifers
48
State 3 examples of hydrophytes.
- water lilies
- duckweeds
- bulrushes
49
State 3 ways most plants conserve water or gain better access to water.
- waxy cuticle - reduces transpiration
- stomata on underside & can be closed - not exposed to abundance of light - too much water loss
- roots grow down to water in soil
50
Describe environmental conditions where water loss, or water access may become a real problem for plant species.
- hot, dry and breezy conditions - water evaporates rapidly
- cold, icy conditions - water in ground is not freely available bc frozen
51
List 10 examples of adaptations xerophytes have for conserving, storing or accessing water.
- thick waxy cuticle
- sunken stomata
- reduced number of stomata
- reduced leaves
- hairy leaves
- curled leaves
- succulents
- leaf loss
- root adaptations
52
Explain how thick waxy cuticle helps xerophytes.
hydrophobic layer that minimises loss by transpiration by larger degree th an normal waxy cuticle
53
Explain how sunken stomata help xerophytes.
located in pits which reduce air movement, trapping moist air, reducing water vapour potential gradient and therefore transpiration
54
Explain how reduced numbers of stomata help xerophytes.
less water lost by transpiration
55
Explain how reduced leaves helps xerophytes.
lower leaf area maeans lower SA:V ratio, minimising diffusion rate and therefore rate of transpiration
56
Explain how hairy leaves helps xerophytes.
trap humid air reducing water potential gradient and minimising loss of water by transpiration
57
Explain how curled leaves helps xerophytes
confines stomata within microenvironment of still humid air to reduce diffusion of water from stomata
58
Explain how being a succulent helps some xerophytes.
plants that store water in specialised parenchyma tissue in stems/roots - water stored in plentiful supply and used when drought
59
Explain how leaf loss helps xerophytes.
lose leaves when water not available - prevent transpiration & water loss
60
Explain how root adaptations help xerophytes.
long tap roots growing deep into ground penetrate several meters and access water that is far from surface
61
Describe two problems faced by hydrophytes.
- water logging - air spaces must be full of air not water for plant survival
- water current may damage plant body
62
List 8 adaptations of hydrophytes.
- thin/no waxy cuticle
- always-open stomata
- reduced structure
- wide, flat leaves
- small roots
- large surface area of stems and roots under water
- air sacs
- arenchyma
63
How does having thin/no waxy cuticle help hydrophytes?
no need to conserve water as they have access to a lot of water
64
How do always-open stomata help hydrophytes?
maximises gas exhange bc no risk of loss of turgor bc abundance of water available
65
How does reduced structure help hydrophytes?
water supports the entire plant so no need for strong supporting structures
66
How do wide, flat leaves help hydrophytes?
capture as much light as possible, maximise photosynthesis rate
67
How do small roots help hydrophytes?
water diffuses directly into stem and leaf tissue, no need for uptake by roots
68
How do large surface areas of stems and roots under water help hydrophytes?
maximises area for photosynthesis and for oxygen to diffuse into submerged plants
69
How do air sacs help hydrophytes?
enable buoyancy
70
How do aerenchyma help hydrophytes?
- specialised parenchyma tissue in leaves, stems and roots that has many large air spaces that:
- makes leaves more buoyant
- forms low-resistance internal pathway for movement of oxygen to tissues below water helping plant to cope with anoxic conditions in mud
71
State the form in which carbs are transported in plants.
sucrose
72
Define translocation.
mass flow of assimilates in the phloem between sources and sinks
73
Define source.
- part of plant that loads assimialtes into phloem
- storage cells, photosynthesising cells
74
Define sink.
- part of plant where assimilates are being removed from phloem
-storage cells, growth regions
75
Give 3 examples of sources.
- green leaves and stems
- storage organs - tubers and tap roots
- food stores in seeds when they germinate
76
Give 3 examples of sinks.
- roots that are growing/actively absorbing ions
- meristems
- parts of plant that are laying down food stores - developing seeds, fruits or storage organs
77
Define phloem loading.
process by which assimilates are selectively and actively taken up by sieve tubes
78
State two ways phloem loading occurs.
- actively by apoplast route
- largely passively by symplast route
79
Describe the symplast route for phloem loading and explain how it occurs
- sucrose moves thru cytoplasm of mesophyll cells into sieve tubes by diffusion thru plasmodesmata
- sucrose ends up in sieve elements and water follows by osmosis
- hydrostatic pressure created that moves sucrose thru phloem by mass flow
80
Describe the apoplast route for phloem loading.
- sucrose travels thru cell walls and intercellular spaces to companion cells and sieve elements
- happens by diffusion down gradient maintained by removal of sucrose into phloem vessels
81
Explain how apoplast route for phloem loading occurs.
- protons are actively transported out of companion cells
- proton gradient into companion cells created
- protons diffuse back into companion cells via co-transport carrier protein
- this allows co-transport of sucrose with protons into the companion cell from source cells
- sucrose can then diffuse into sieve tube elements down conc gradient
82
Describe how companion cells are adapted for their function.
- many infoldings in cell membranes give increased surface area for active transport of sucrose into cell cytoplasm
- many mitochondria to supply ATP to transport pumps
83
Describe how water and assimilates in phloem move from source to sink.
- as result of buildup of sucrose in companion cell and sieve tube element, water moves in by osmosis
- buildup of turgor pressure due to rigid cell walls
- water carrying assimilates moves into tubes of sieve elements
- this reduces pressure in companion cells
- water carrying assimilates moves up/down the plant by mass flow to areas of lower hydrostatic pressure (sinks)
84
Describe the process of phloem unloading and explain how a conc gradient is maintained from the phloem into cells requiring sucrose.
- sucrose diffuses from phloem into surrounding cells at any point into cells that need it
- sucrose rapidly moves into other cells by diffusion/converted into another substance so that conc gradient is maintained
- loss of solutes causes rise in water potential of phloem - water moves out into surrounding cells by osmosis, some drawn into transpiration stream
85
Give 3 examples of what sucrose can be converted into.
- glucose for respiration
- starch for storage
- used to produce amino acids and other compounds
86
Describe and explain 4 sources of evidence for processes involved in translocation.
- microscopy - adaptations of companion cells for active transport
- poison - if mitochondria of companion cells are poisoned, translocation stops - active process
- flow 10k times faster than it would be by diffusion - active process driving mass flow
- aphids - sap continues to exude from proboscis of aphid - evidence for pressure driven mass flow bc aphids dont have to suck
87
Compare the substances transported in translocation and transpiration
translocation: assimilates
transpiration: water, ions
88
Compare where substances come from in translocation and transcription
translocation: photosynthesising cells, storage cells
transcription: soil water
89
Compare where the substances are being transported to in translocation and transpiration
translocation: storage cells, growth regions
transpiration: photosynthesising cells, growth regions
90
Compare the main transporting cell type in translocation and transpiration
translocation: sieve tube elements
transpiration: xylem vessel elements
91
Compare how the substances move in translocation and transpiration
translocation: mass flow
transpiration: mass flow, diffusion, osmosis
92
Compare what drives the movement of substances in translocation and transpiration
translocation: active transport
transpiration: transpiration pull, root pressure, capillary action
