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HL Bio > 9.1 transport in the xylem of plants > Flashcards

9.1 transport in the xylem of plants Flashcards

1
Q

almost all plants are …. p- a-

A

photosynthetic autotrophs

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2
Q

vascular plants have …

A

two types of transport tissue – xylem and phloem

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3
Q

what is transpiration?

A

the loss of water vapour thru leaves, stems, and other (above ground) parts of plant

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4
Q

transpiration is the consequence of…

A

gas exchange in the leaf

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5
Q

where does transpiration occur through

A

mainly through open stomata

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6
Q

how is transpirtation connected to photosynthesis

A

A tension is created in the plant due to transpiration and this acts as a driving force for the uptake of water from the soil and the movement of water to the shoots.
water required by photosynthesis

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7
Q

adaptations of leaves for gas exchange (2)

A
  1. stomata
    tiny pores, opening and closing controlled by 2 guard cells
  2. lower tissue layer (spongy mesophyll)
    provides large surface area and moist surface neccesary for gas exchange
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8
Q

how to plants transport water from roots to leaves (to replace losses from transpiration) 4

A
  1. co2 conc drops = co2 from air spaces dissolve, diffuse into cells
  2. air conc drops = net movement of co2 molecules into leaf thru stomata
  3. O2 diffuses out leaf cells into int. air spaces (then into atmos thru stomata)
  4. transpiration: water vapour diffuses out of leaf into atmos
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9
Q

function of xylem vessels

A

transports water and dissolved minerals
- from roots to all parts of plant

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10
Q

structure of xylem vessels (that allow transport under tension) 3

A
  • long continuous tubules (from roots thru stems)
  • hollow: dead at maturity, cell mem. + int. structures + horizontal cell walls break down
  • walls strengthened with lignin (binds with cellulose – provides great strength and rigidity)
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11
Q

what to note when drawing structure of pri xylem vessels

A
  1. continuous tubule
  2. xylem wall should have gaps (pits) – enable water molc exchange
  3. lignin represented via spiral/rings
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12
Q

cohesive property of water 2 factors, briefly

A
  1. cohesion
    - water molc form weak hydrogen bonds
  2. adhesion
    - polarity of water (interacts with hydrophillic cellulose in cell walls)
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13
Q

cohesive property of water: cohesion

A

water molecules form weak hydrogen bonds (bc of polarity)
= transpirational pull can extend thru long columns of water

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14
Q

cohesive property of water: adhesion

A

polarity interacts with hydrophilic cellulose in cell walls = create pull to draw water out xylem into cells

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15
Q

transpirational pull 4 steps `

A
  1. cellulose in mesophyll (leaf) cell walls is hydrophilic – water adheres = film of water on cell surface
  2. water vapour diffuses out stomata = internal air spaces less humid = water evaps from moise mesophyll cell walls into air spaces
  3. when eavaporates = pulling force on water molecules within cell (cohesion)
  4. tension caued by pull of evap – draws water from xylem into leaf cells
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16
Q

adaptations of root hairs for mineral ion uptake

A

active uptake = high demand for atp
- plasma membrane of root hairs – many protein pumps –> AT of mineral ions from water into cytoplasm of cell
- high rate of cellular respiration, many mitochondria, high o2 gas demand

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17
Q

how does uptake of mineral ions cause absorption of water

A

high conc of mineral ions in cytoplasm = low water potential = osmosis of water in

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18
Q

water potential of pure water

A

0.0MPa

19
Q

what are Xerophytes

A

plants that adapted to live in conditions where liquid water is hard to obtain (eg deserts)
- some have special tissues for water storage, some adapt to reduce water loss thru transpiration

20
Q

10 adaptations of desert plants for water conservation + xerophyts too

A
  1. thick waxy cuticle on leaf/stem: reduces non-stomatal transpiration rate
  2. fewer stomata: reduces transpiration rate
  3. stomata in sunken pits: maintains humidity – decr. transp.
  4. fine hairs on leaf underside: maintains layer of moisture near stomata – decr transp.
  5. CAM physiology – stomata close during day
  6. reduced air spaces in leaf mesophyll: decr surface area
  7. few/small leaves/ photosynthesis in stem: red. surface area
  8. curled/rolled leaves: reduced surface area + incr humidity
  9. deep, highly branched roots: incr ability to take up water
21
Q

adaptations of saguaro cactus 6

A
  • thick waxy cuticle on stem
  • one tap root + highly branched system
  • stores water in stem
  • reduced S.A. (p.sis in stem)
  • leaves reduced to spines
  • CAM photosynthesis (stomata closed in day)
22
Q

adaptations of Marram grass 4

A
  • thick outer cuticle
  • rolled shape
  • few stomata
  • hair like structures
23
Q

what are halophytes

A

plants that have adapted to areas with high salinity (Eg ocean shorline)
– makes establishment of higher conc of ions in roots more difficult
- some have adaptations to secrete salt, some establish high concs of other solutes, some conserve water in the plant

24
Q

adaptations of halophytes 6

A
  1. salt storage in vacuoles: compartmentalizes, protects organelles and enzymes from damage
  2. high conc of organic solutes: incr osmolarity = water can still enter
  3. salt storage glands in leaf: accumulates salt in limited area, release thru crystals
  4. leaf abscission: breaking off leaves with toxic levels of salt
  5. selectively permeable membrane (in roots): excluses salt by having no ion channels to allow passage of Na/Cl / has AT pumps to remove
  6. xerophytic adaptations: few stomata, water storage, thick cuticle etc
25
Q

adaptations of mangrove trees

A
  • salt glands that excrete salt crystals (grey mangrove)
  • root cell membranes that mostly exclude salt ions (red)
  • store salt in vacuoles, keeping cell turgid (red)
26
Q

internal factors affecting rate of transpiration 4

A
  1. root to shoot ratio
  2. surface area of leaves
  3. number of stomata per unit leaf area
  4. leaf struture eg presence of hair
27
Q

external factors affecting rate of transpiration

A
  1. light
  2. wind
  3. temperature
  4. humidity
  5. water availiablity
28
Q

how does temp affect rate of transpiration

A

temp incr = transpiration incr
- incr temp = incr energy for water evaporation + decr humidity
(but if temp too high for enzymes, stomata close, transp. rate falls)

29
Q

how does humidity affect transpiration rate

A

incr humidity = decr transpiration
- concentration gradient for diffusion of water vapour between air spaces and atmosphere: more/less steep

30
Q

how does light affect transpiration rate

A

light intensity incr = transpiration incr
- stomata closed in dark; incr LI = open stomata, water escapes
- photons provide energy for evaporation

31
Q

how does wind affect transpiration rate

A

wind velocity incr = transpiration incr
- low wind = incr humidity = decr water vapour conc gradient = decr transpiration

32
Q

using a porous pot, how is cohesion-tension due to evaporation demonstated via a model

A
  • water saturates the porous pot, evaporates into surrounding air
  • cohesion tension extends down tubing into beaker, water drawn up
33
Q

using filter paper, how is cohesion-tension due to capillary action demonstated via a model

A

cohesion of water + adhesion to cellulose fibres in paper draws water up

34
Q

what are potometers used for

A

indirect measurement of water loss = rate of transpirationmeasurement of water uptake via water level/ movement of air bubbles

35
Q

measuring transpiration rates using mass

A

measuring decr in mass from plant in sealed container
- BUT does not account for mass incr due to photosynthesis

36
Q

struture of stomata

A
  • structure: 2 elongated guard cells, attached to epidermal cells
  • pore appears when they seperate
37
Q

how do stomata open and close

A

due to turgor pressure of guard cells

water absorbed by guard cells = push epidermal cells beside them = pore develops

  • closes when water is lost and guard cells become flaccid
38
Q

what are root hairs

A

extensions of individual epidermal cells, relatively short lived

39
Q

3 possible routes for water movement thru plant cells and tissues

A
  1. mass flow (apoplast pathway)
    - occurs thru interconnecting free spaces betw cellulose fibres of cell walls (incl xylem)
  2. diffusion (symplast pathway)
    - occurs thru cytoplasm and via cytoplasmic connections betw cells (organelles = resistance)
  3. osmosis
    - from vacuole to vacuole, driven my osmotic pressure gradient
    - AT of mineral ions in roots = absorption of water via osmosis
    - not as significant pathyway for across plant transport
40
Q

how active uptake is achieved – movement of water and ions from roots to xylem by structure

A
  1. vascular tissue in roots contained by endodermis
  2. Casparian strip at endodermis: waxy strip in radial walls – blocks water passage momentarily
  3. water passes thru endodermis via osmosis
  4. HENCE cytoplasm of endodermal cells AT ions from cortex to endodermis
41
Q

outline ion uptake

A
  • by active transport
  • highly selective process – reflects needs of the plant
  • involves protein pumps – needs ATP + specific
42
Q

how do ions reach the cell membranes during active uptake of ions in roots

A
  1. mass flow of water thru free spaces = delivers fresh soil solution to root hair cell plasma membranes
  2. active uptake of selected ions
  3. ions diffuse from higher conc outside apoplast –> lower conc adjacent to protein pumps
  4. mutualistic r/s with soil-inhabiting fungi: fungal hyphae receive supply of sugar from plant root cells, in exchange they release ions + death & decay also releases ions
43
Q

active uptake of ions in soil but mnore chemistry

A
  • neg charged clay particles – pos charge ions attach
  • minerals needed: Mg2+, nitrates, Na+, K+, PO43-
  • AT uploading into roots
  • root cells have protein pumps – expel H+ ions into soil = displaces pos mineral ions

HL Bio (19 decks)

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