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OCR A-Level Biology > Chap 9 - Transport in plants > Flashcards

Chap 9 - Transport in plants Flashcards

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1
Q

Define herbaceous plants

A

plants that have non-woody items

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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

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3
Q

Define vascular system (in plants)

A

system of transport vessels running through stem, roots and leaves

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4
Q

Define vascular bundles

A

vascular system of herbaceous dicots made of xylem and phloem tissue

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5
Q

Name 2 types of transport vessels in vascular bundles

A

xylem, phloem

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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
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7
Q

Define assimilate

A

products of photosynthesis

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8
Q

Describe the structure of xylem

A
  • composed of xylem vessel elements and parenchyma cells
  • long hollow tubes
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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
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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
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11
Q

Define sieve tube element

A

main cells of phloem that have greatly reduced living content and sieve plates between cells

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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

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13
Q

Define companion cell

A

active cells found next to sieve tube elements that supply phloem vessles with their metabolic needs

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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
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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
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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
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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
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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
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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
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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

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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

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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
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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
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24
Q

Define stomata

A

pores in surface of a leaf or stem that may be opened and closed by guard cells

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25
Q

Define guard cells

A

cells that can open/close stomatal pores, controlling gaseous exhange and water loss in plants

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26
Q

Explain how transpiration results in water moving through the plant (cohesion-tension theory).

A
  • 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
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27
Q

Describe 3 sources of evidence for cohesion-tension theory.

A
  • 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
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28
Q

Explain how guard cells can open/close stomata.

A
  • 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
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29
Q

State 5 env factors that can affect the rate of transpiration and for each explain how they have their effect.

A
  • 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
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30
Q

Show how a potometer can measure transpiration rate.

A
  • 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
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31
Q

Explain precautions that must be taken when setting up potometer.

A
  • 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
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32
Q

Describe 5 functions of water in plants.

A
  • 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
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33
Q

Describe 4 ways that the root hairs of root hair cells are adapted as exchange surfaces,

A
  • 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
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34
Q

Explain why water moves from the soil into root hair cells.

A
  • 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
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35
Q

Name the two pathways by which water travels across the root to the xylem.

A
  • symplast
  • apoplast
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36
Q

Describe the symplast pathway of water movement.

A
  • 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
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37
Q

Explain the importance of water potential gradients for movement of water thru a plant.

A

Allow passive movement of water thru plants

38
Q

Describe the apoplast pathway of water movement.

A
  • 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
Q

Define endodermis

A

layer of cells surrounding vascular tissue of roots

40
Q

Define casparian strip

A

band of waxy material (suberin) that runs around each endodermal cell forming a waterproof layer

41
Q

Define root pressure

A

active pumping of minerals into xylem by root cells that produces a movement of water into xylem by osmosis

42
Q

Describe the function of the Casparian strip.

A
  • 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
Q

Explain the role of active transport by endodermal cells for the movement of water.

A
  • 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
Q

Describe evidence for role of active transport in moving water from root endodermis into xylem.

A
  • 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
Q

Define xerophytes

A

plants with adaptations that enable them to survive in dry habitats or habitats where water is in short supply in the environment

46
Q

Define hydrophytes

A

plants with adaptations that enable them to survive in very wet habitats or submerged or at surface of water

47
Q

State 3 examples of xerophytes.

A
  • cacti
  • marram grass
  • conifers
48
Q

State 3 examples of hydrophytes.

A
  • water lilies
  • duckweeds
  • bulrushes
49
Q

State 3 ways most plants conserve water or gain better access to water.

A
  • 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
Q

Describe environmental conditions where water loss, or water access may become a real problem for plant species.

A
  • hot, dry and breezy conditions - water evaporates rapidly
  • cold, icy conditions - water in ground is not freely available bc frozen
51
Q

List 10 examples of adaptations xerophytes have for conserving, storing or accessing water.

A
  • thick waxy cuticle
  • sunken stomata
  • reduced number of stomata
  • reduced leaves
  • hairy leaves
  • curled leaves
  • succulents
  • leaf loss
  • root adaptations
52
Q

Explain how thick waxy cuticle helps xerophytes.

A

hydrophobic layer that minimises loss by transpiration by larger degree th an normal waxy cuticle

53
Q

Explain how sunken stomata help xerophytes.

A

located in pits which reduce air movement, trapping moist air, reducing water vapour potential gradient and therefore transpiration

54
Q

Explain how reduced numbers of stomata help xerophytes.

A

less water lost by transpiration

55
Q

Explain how reduced leaves helps xerophytes.

A

lower leaf area maeans lower SA:V ratio, minimising diffusion rate and therefore rate of transpiration

56
Q

Explain how hairy leaves helps xerophytes.

A

trap humid air reducing water potential gradient and minimising loss of water by transpiration

57
Q

Explain how curled leaves helps xerophytes

A

confines stomata within microenvironment of still humid air to reduce diffusion of water from stomata

58
Q

Explain how being a succulent helps some xerophytes.

A

plants that store water in specialised parenchyma tissue in stems/roots - water stored in plentiful supply and used when drought

59
Q

Explain how leaf loss helps xerophytes.

A

lose leaves when water not available - prevent transpiration & water loss

60
Q

Explain how root adaptations help xerophytes.

A

long tap roots growing deep into ground penetrate several meters and access water that is far from surface

61
Q

Describe two problems faced by hydrophytes.

A
  • water logging - air spaces must be full of air not water for plant survival
  • water current may damage plant body
62
Q

List 8 adaptations of hydrophytes.

A
  • 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
Q

How does having thin/no waxy cuticle help hydrophytes?

A

no need to conserve water as they have access to a lot of water

64
Q

How do always-open stomata help hydrophytes?

A

maximises gas exhange bc no risk of loss of turgor bc abundance of water available

65
Q

How does reduced structure help hydrophytes?

A

water supports the entire plant so no need for strong supporting structures

66
Q

How do wide, flat leaves help hydrophytes?

A

capture as much light as possible, maximise photosynthesis rate

67
Q

How do small roots help hydrophytes?

A

water diffuses directly into stem and leaf tissue, no need for uptake by roots

68
Q

How do large surface areas of stems and roots under water help hydrophytes?

A

maximises area for photosynthesis and for oxygen to diffuse into submerged plants

69
Q

How do air sacs help hydrophytes?

A

enable buoyancy

70
Q

How do aerenchyma help hydrophytes?

A
  • 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
Q

State the form in which carbs are transported in plants.

A

sucrose

72
Q

Define translocation.

A

mass flow of assimilates in the phloem between sources and sinks

73
Q

Define source.

A
  • part of plant that loads assimialtes into phloem
  • storage cells, photosynthesising cells
74
Q

Define sink.

A
  • part of plant where assimilates are being removed from phloem
    -storage cells, growth regions
75
Q

Give 3 examples of sources.

A
  • green leaves and stems
  • storage organs - tubers and tap roots
  • food stores in seeds when they germinate
76
Q

Give 3 examples of sinks.

A
  • roots that are growing/actively absorbing ions
  • meristems
  • parts of plant that are laying down food stores - developing seeds, fruits or storage organs
77
Q

Define phloem loading.

A

process by which assimilates are selectively and actively taken up by sieve tubes

78
Q

State two ways phloem loading occurs.

A
  • actively by apoplast route
  • largely passively by symplast route
79
Q

Describe the symplast route for phloem loading and explain how it occurs

A
  • 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
Q

Describe the apoplast route for phloem loading.

A
  • 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
Q

Explain how apoplast route for phloem loading occurs.

A
  • 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
Q

Describe how companion cells are adapted for their function.

A
  • 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
Q

Describe how water and assimilates in phloem move from source to sink.

A
  • 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
Q

Describe the process of phloem unloading and explain how a conc gradient is maintained from the phloem into cells requiring sucrose.

A
  • 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
Q

Give 3 examples of what sucrose can be converted into.

A
  • glucose for respiration
  • starch for storage
  • used to produce amino acids and other compounds
86
Q

Describe and explain 4 sources of evidence for processes involved in translocation.

A
  • 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
Q

Compare the substances transported in translocation and transpiration

A

translocation: assimilates
transpiration: water, ions

88
Q

Compare where substances come from in translocation and transcription

A

translocation: photosynthesising cells, storage cells
transcription: soil water

89
Q

Compare where the substances are being transported to in translocation and transpiration

A

translocation: storage cells, growth regions
transpiration: photosynthesising cells, growth regions

90
Q

Compare the main transporting cell type in translocation and transpiration

A

translocation: sieve tube elements
transpiration: xylem vessel elements

91
Q

Compare how the substances move in translocation and transpiration

A

translocation: mass flow
transpiration: mass flow, diffusion, osmosis

92
Q

Compare what drives the movement of substances in translocation and transpiration

A

translocation: active transport
transpiration: transpiration pull, root pressure, capillary action

OCR A-Level Biology (16 decks)

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