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AS biology > 3.3 plant transport > Flashcards

3.3 plant transport Flashcards

1
Q

why do multicellular plants need a transport system

A
  1. need water, sugar, mnierals to live and need to get rid of waste substances
  2. Low SA:V, but are realtively big w a high metabolic rate
  3. direct diffusion would be too slow to met their needs
  4. so need transport systems to move substances to and from individual cells quickly
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2
Q

whatis transported in xylem adn how

A

water and soluble mineral ions UPWARDS

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3
Q

whatis transported in phloem and how

A

assimilates (Eg sugars) UP AND DOWN

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4
Q

Dicotyledonous plants

A

2 seed leaves
branching pattern of veins in the leaves

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5
Q

vascular bundle

A

where the xylem and phloem are found together
- contains other type of tissue

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6
Q

vascular bundle labelled

A

outer layer of circle (endodermis)
x shaped star in the middle (xylem)
little triangles between the star arms (phloem)
other inner region (medulle)

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7
Q

why is the phloem found within the arms of the xylem

A

provides strength to withstand the puling forces to which roots are exposed

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8
Q

meristem cells

A
  • cells which retain their ability to divide
  • inside the endodermis
    called PERICYCLE
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9
Q

Cambium

A
  • in between xylem and phloem
  • layer of meristem that divide to produce new xylem and phloem
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10
Q

why dont plants need to transport gases like o2 in their trnaport system

A

not very metabolically active
respiratiion rate low
low o2 demand met by simple diffusion

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11
Q

ring of vascular bundle arrangement advantage

A

provides strength and flexibility to withstand the BENDING forces to whicih stems and branches are exposed

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12
Q

xylem tissue consists of:

A
  • vessels to carry the water and dissolved mineral ions
  • fibres to help support the plant
  • LIVING PARENCHYMA CELLS - packing tissue to separate and support the vessels
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13
Q

lignin in xylem

A
  • impregnates walls
  • makes the walls waterproof and kills the cells
  • continuous column of dead cells with no contents
    PURPOSE:
  • strenghtens vessel walls and prevents vessel from collapsing
  • keeps vessel open even at times where water is in short supply
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14
Q

bordered pits

A
  • incomplete lignification
  • the bordered pits in 2 adjacent vessles are aligned to allow water to leave one vessel and pass into the next
  • also allow water to leave xylem and pass into the living parts of the cell
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15
Q

how does lignin look within

A

spiral of lignin
- important as allows the xylem to stretch while the plant grows
- and allows stem/branch to bend

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16
Q

xylem adaptations(4)

A
  1. dead cells aligned end to end to form a continuous column
  2. narrow tubes. water column doesnt break easily
  3. BORDERED PITS allow water to move sideways from one xylem cell to the next and out of the xylem to the living tissues
  4. lignin impregnates the walls in a spiral to allow xylem to STRETCH as the plant grows and can bend
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17
Q

in what form is sucrose trnasported

A

dissolved in water to form sap

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18
Q

phloem tissue consits of…

A

SIEVE TUBES
- made of sieve tube elements and companion cells

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19
Q

sieve tube elements

A
  • no nucleus, little cytoplasm, allowing space for mass flow of sap to occur
  • at the end of the sieve tube element are PERFORATED CROSS WALLS called sieve plats. perforations allow movement of sap from one element to the next
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20
Q

sieve tubes in dissection

A

v thin
5/6 sided

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21
Q

companion cells

A
  • in between sieve tubes
  • large nucleus+dense cytoplasm
  • NUMEROUS mitochondria to produce ATP
  • carry out metabolic processes needed to load assimilated actively into the sieve tubes
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22
Q

plasmodesmata

A

gaps in the cell wall containing cytoplasm that connects 2 cells

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23
Q

are cellulose cell walls water permeable

A

yes

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24
Q

2 types of pathways taken by water through a plant

A

apoplast
symplast

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25
Q

apoplast pathway

A
  • passes through INTERCELLULAR spaces
  • doesnt pass through any plasma membranes
  • MASS FLOW
  • so dissolved mineral ions and salts can also be carried
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26
Q

drawing apoplast pathway

A

in between cracks of cell

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27
Q

symplast pathway

A
  • enters through plasma membrane to the cell cytoplasm
  • passes through plasmodesmata from one cell to the next
    OSMOSIS
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28
Q

drawing synplast pathway

A
  • through first cell wall
  • through gaps in between the cells (plasmodesmata)
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29
Q

cytoplasm water potential

A

ALWAYS VERY NEGATIVE
- contains mineral ions and solutes which reduce water potential

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30
Q

turgid

A
  • water has entered the cell by osmosis from a higher water potential to a lower water potential
  • water exerts pressure on the cell wall (pressure potential). as it builds, it reduces the influx of water
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31
Q

plasmolysis

A

water leaves cell by osmosis from a higher water potential to a lower water potential
- plasma membrane pulls away from cell wall

32
Q

what is transpiration

A

loss of water VAPOUR from the aieral parts of the plant, mainly the stomata in the leaves

33
Q

why is most water vapour lost during the day

A
  • stomata are open when there is light
  • to allow gas exchange for photosynthesis
  • water evaporates
34
Q

transpiration pathway

A
  • water enters the leaf through xylem. moves by osmosis into the cells of the spongy mesophyll. may also pass along cell walls via apoplast pathway
  • water evaporates from cell walls of the spongy mesophyll
  • water diffuses out of the leaf through the open stomata, due to the water vapour potential gradient
35
Q

importance of transpiration (4)

A
  • transports useful mineral ions up the plant
  • maintains cell turgidity
  • supplies water for growth, cell elongation, photosynthesis
  • as water evaporates, cools the plant on a hot day
36
Q

LI effect on transpiration

A
  • stomata open for gaseous exchange for photosynthesis
  • ↑ LI, ↑ photosynthesis
37
Q

temperature effect on transpiration

A
  1. increases rate of evaporation from cell surfaces so WVP in leaf rises (steeper conc grad)
  2. increases rate of diffusion out through stomata bc water molecules have more kinetic energy
  3. decrease WVP in air; more rapid diffusion of molecules out of leaf
    OVERALL AS TEMP ↑ , TRANSPIRATION ↑
38
Q

relative humidity of air effect on transpiration

A
  • as humidity ↑ , transpiration ↓
  • smaller WVP gradient between air inside leaf and air outside
39
Q

air movement effect on transpiration

A
  • as air movement ↑ , transpiration↑
  • air movement outside leaf carries away water vapour that has just diffused out of the leaf
  • maintains a steep WVP gradient
40
Q

water availability effect on transpiration

A
  • if there is LITTLE water avilability in the soil, the plant cant replace any water lost
  • so stomata close, leaves wilt
41
Q

what does a potometer ACTUALLY measure

A
  • rate of water uptake by a leafy shoot
  • assuming cells are turgid, and most water taken up is lost by transpiration, we can use it to estimate
42
Q

name of tube in potometer

A

capillary tube

43
Q

how to set up potometer for valid results:

A
  1. set up potometer under water so no air in apparatus
  2. cut shoot under water to make sure no air in xylem
  3. healthy shoot
  4. cut stem AT AN ANGLE to provide a large surface area in contact w water
  5. dry the leaves
44
Q

how to get a rate from a potometer

A
  • distance moved by bubble
  • πr2d/t
45
Q

adhesion

A

attraction between water molecules and the walls of the xylem vessel

46
Q

cohesion

A

attraction between water molecules caused by hydrogen bonds

47
Q

where are root hair cells fuond

A

epidermis (outermost layer of cells)

48
Q

movement of water ACROSS THE ROOT

A
  • mineral ions ACTIVE TRANSPORTLY absorbed from soil into root hair cell. decreases WP of cytoplasm
  • decreased WP → water enters root hair cell by osmosis
  • water moves across cortex by apoplast (intracellular spaces) UNTIL it reaches CASPARIAN STRIP, so needs to do synplast
  • mineral ions are actively transported into medulla (plasma membrane carrier proteins), making WP more negative so water will osmosis
49
Q

endodermis
evidence of energy used

A

layer of cells surrounding medulla and xylem
- STARCH SHEATH, contains granules of starch (shows that energy is being used)

50
Q

casparian strip…

A

blocks apoplast pathway between root cortex and medulla
- ensures that water and dissolved mineral ions have to go through plasma membranes and into cytoplasm
- carrier proteins/channel proteins in the plasma membrane will then pump the ions into medulla and xylem
- decreases WP of medulla and xylem, so water will osmosis from root cortex cells into medula and xylem
- and once its there, water cant go back into the cortex, because the apoplast pathway is BLOCKED by the casparian strip

51
Q

mechanism of movement of water up xylem

A

mass flow

52
Q

3 processes that help the mass flow of water up the stem

A
  1. root pressure
  2. transpiration pull
    3, capillary action
53
Q

root pressure

A
  • action of the endodermis moving minerals into the medulla and xylem by active transport draws water into the medulla by osmosis due to the lowered water potential
  • pressure in the root medulla builds up and forces water into the xylem, pushing the water up.
54
Q

transpiration pull (cohesion tension theory)

A
  • loss of water by evaporation from the leaves must be replaced by water coming up the xylem
  • water molecules are attracted to each other by cohesion, forces which hold the molecule together in one column
  • as molecules are lost at the top of the column, the whole column is pulled up as one chain
  • the LOSS OF WATER above creates LOW HYDROSTATIC PRESSURE and thus tension in the column of water. this is why the xylem vessels must be strengthened by lignin; to prevent the vessel collapsing
55
Q

what does the cohesion tension theory rely on

A
  • the maintaining of an unbrokwn column of water all the way up the xylem. if the water column is broken in one xylem vessel, it can be maintained through another vessel via the bordered pits
56
Q

capillary action

A
  • adhesion of water molecules to the side of the xylem vessek
  • because the vessels are very narrow, the forces of attraction can pull water up the sides of the vessel
57
Q

how does water leave the leaf

A
  • evaporates from cell walls of spongy mesophyll
  • evaporates out of stomata from the cells lining the cavity immediately above the guard cells
  • this lowers the WP in the cells, causing water to enter them by osmosis from neighboruing cells, so water is drawn from the xylem in the leaf by osmosis
58
Q

hydrophyte

A

a plant adapted to living in water or very wet conditions

59
Q

xerophyte

A

a plant adapted to living in dry conditions

60
Q

general terrestrial plant adaptations

A
  1. waxy cuticle on leaf → reduces water loss due to evaporation
  2. stomata on the under surface of leaves → reduces evaporation due to direct heating by the sun
  3. stomata closed at night, no light for photosynthesis
  4. deciduous plants lose their leaves in winter when ground is frozen (no water) and temperatures too low for photosynthesis
61
Q

marram grass

A
  • live on sand dunes
  • xerophyte
  • leaf rolled longitudinally → air trapped inside → air becomes humid, reducing water loss. rolls tighter the drier it is
  • thick waxy cuticle on upper epidermis → reduce evaporation
  • stomata on the inner side of the rolled leaf → protected by enclosed air space
  • stomata in PITS in the lower epidermis which is folded and covered by hairs → reduce air movement
  • VERY dense spongy mesophyll → less SA for evaporation of water
62
Q

Cacti

A
  • SUCCULENTS: store water in stems which become fleshy/swollen. stem ribbed and fluted to allow for expansion when water avilable
  • leaves reduced to spines → reduces SA so less water lost
  • green stem fr photosynthesis
  • roots are v widespread → take advantage of any rainfall
63
Q

other genral xerophytic features

A
  • close stomata when water availability low → reduce water losos
  • low WP inside leaf cells by maintaining a high salt concentration. lowers WVP gradient so reduces evaporation of water
  • very long tap root → reaches water deep underground
64
Q

hydrophyte issue

A

getting oxygen and keeping afloat

65
Q

water lily adaptations

A
  1. large air spaces → keeps them afloat so they can get sunlighy
  2. stomata on upper epidermis → exposed to air to allow for gas exchange
  3. stem has many large air spaces → buoyancy AND allows o2 to quickly diffuse to roots for respiration
66
Q

how do hydrophytes transpiration

A
  • have HYDATHODES at the tips of their leaves
  • release water droplets which then evaporate from the leaf surface
67
Q

source

A

actively loads assimilates into the phloem

68
Q

sink

A

part of the plant where the assimilates are removed from the transport system [phloem]

69
Q

GENERALL, who is the source and hwo is the sink

A

source = leaves
sink = roots

70
Q

examples of assimilates moves in the phloem

A

sucrose + amino acids

71
Q

active loading

A
  • companion cells use ATP to actively transport H+ ions out of themselves
    -increases conc outside, and reduces inside, creating a concentration gradient
  • COTRANSPORT: h+ ions facilitated diffuse back into the companion cells using cotransport proteins in plasma membrane, which only let H+ diffuse if accompanied by sucrose molecules
  • now, conc of sucrose in companion cell increases, so can diffuse through plasmodesmata in sieve tube
72
Q

how does sucrose move along the phloem

A

MASS FLOW OF SAP

73
Q

how does the mass flow of sap along the phloem work

A
  • after the sucrose is actively loaded into sieve tube element, WP decreases. so water moves in by osmosis at the source, increasing hydrostatic pressure
  • the sap moves down the sieve tube from a HIGHER hydrostatic pressure to a lower hydrostatic pressure at the sink
74
Q

why are the leaves a source

A
  • sugars made during photosynthesis are converted to sucrose and loaded into the phloem sieve tubes
    HAPPENS WHEN THE LEAVESA RE GREEN
75
Q

what happens to the sucrose transported in the phloem

A
  • used for respiration and growth in meristem
  • or starch for storage in a root
  • DIFFUSES OUT OF THE SIEVE TUBE VIA PLASMODESMATA/ACTIVE TRANSPORT
76
Q

after mass flow of sap across phloem, when its removes

A
  • diffuses out of plasmodesmata to meristem or active transport
  • increases the water potential inside the phloem
  • water moves out of phloem by osmosis, reducing the hydrostatic pressur
77
Q

upper epidermis adaptation

A
  • transparent
  • allows light to pass through for photosynthesis in the undelrying cells

AS biology (14 decks)

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