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Biology > Transport in plants > Flashcards

Transport in plants Flashcards

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1
Q

why do plants need transport systems?

A
  • they are large so have a small SA:V ratio - can’t rely on diffusion alone for transport of molecules
  • underground parts eg. root tissues can’t photosynthesise so absorb nutrients by active transport - high rate of metabolic reactions so sugars must be transported to them
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2
Q

dicotyledenous plant

A
  • two cotyledons
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3
Q

structure of phloem

A
  • sieve tube elements - most of living organelles lost to make room for phloem sap - separated by sieve plates - allow sap to pass between cells
  • companion cell attached to each sieve tube element with channels called plasmodestmata - ATP and proteins can move into sieve tube element cells
  • contain fibres (long and narrow) and sclereids (variety of shapes) which have thickened cell walls containing lignin
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4
Q

structure of xylem vessels

A
  • walls made of lignin arranged in spirals or rings - impermeable to prevent substances passing through walls, help maintain structure and allow flexibility under transpiration pull
  • regions of cell wall free of lignin - pits allow water and dissolved substances to pass between vessels
  • made of dead cells - living contents die and end walls between cells break down
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5
Q

structure of xylem fibres

A
  • very large amounts of lignin
  • interior contents die
  • provide mechanical support for plant
  • do not transport water or mineral ions
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6
Q

xylem function

A

carries water and mineral ions from the roots of the plant through the stem to the leaves

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7
Q

phloem function

A

transports organic molecules such as sugars produced by photosynthesis in the leaves - up or down the plant

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8
Q

vascular bundle in the root

A
  • epidermis on outside of root
  • cortex - thick layer of cells containing parenchyma cells
  • vascular bundle surrounded by endodermis
  • xylem in centre - strong - prevents plant being pulled out of soil
  • phloem surrounding xylem
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9
Q

vascular bundle in stem

A
  • vascular bundles arranged in a ring on outside of stem - helps withstand bending from wind
  • centre of stem called pith - contains parenchyma cells
  • around edge is epidermis and cortex
  • phloem on outside, xylem on inside
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10
Q

vascular bundle in leaf

A
  • xylem at upper part, phloem at lower part
  • photosynthesis takes place in palisade mesophyll - upper part of leaf
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11
Q

adaptations of root hair cells

A
  • densely packed - large SA:V ratio
  • surface consists of only cell wall and cell membrane - thin
  • soil contains Mg ions - lower con. in soil than root hair so uses active transport to move them into cells
  • water potential lower in root hair cell than soil - contains dissolved minerals - water moves in by osmosis
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12
Q

how does water move from root hair cells to xylem?

A
  • moves through root cortex to xylem by symplast or apoplast pathway
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13
Q

symplast pathway

A
  • water moves from cytoplasm of one cell to cytoplasm of another through plasmodesmata linking cells
    driven by water potential gradient between root hair cells and xylem - water continually moving into root hair cells so high water pot. than cortex cells
  • slow - obstructed by organelles
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14
Q

apoplast pathway

A
  • water moves through cell walls and spaces between cells
  • cell walls have relatively open structure so water can move easily between cellulose fibres
  • as water is carried away in xylem, more water moves along apoplast pathway due to cohesion
  • less resistance than symplast
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15
Q

casparian strip

A
  • made of waterproof material - suberin
  • water can no longer move through apoplast pathway
  • instead water moves through cell membrane and into cytoplasm - symplast
  • forcing all water into cytoplasm - cell membrane can control which substances entering xylem
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16
Q

root pressure and how to stop it

A
  • cells in endodermis get mineral ions into xylem by active transport - lowers water potential, causing more water to move into xylem vessels by osmosis
  • active process requiring respiration
  • inhibit respiration using cyanide - root pressure stops
  • exclude oxygen and stop aerobic respiration - root pressure stops
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17
Q

function of waxy cuticle

A

reduce water loss from surface of leaf by evaporation

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18
Q

how does CO2 get into leaf?

A

diffuses from external air through stomata

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19
Q

why are cells in the leaf covered in thin layer of water?

A
  • water evaporates from surface of cells
  • internal leaf spaces have high conc water vapour
  • water vapour conc in external air is low so water vapour diffuses out of leaf
  • this is transpiration
  • water pot. of cells in leaf decreases - causes water to move from adjacent cells into leaf cells
    , water pot of adjacent cells decreases and water moves into them from the xylem
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20
Q

tension

A
  • water pot. of cells in leaf decreases because of transpiration
  • causes water to move from adjacent cells into leaf cells
  • water pot. of adjacent cells decreases and water moves into them from the xylem
21
Q

transpiration stream

A

movement of water into the roots, up the stem and out of the leaf

22
Q

adhesion

A

water forms hydrogen bonds with molecules in xylem vessel walls eg. carbohydrates

23
Q

capillary action

A
  • water can move up very thin tubes against the force of gravity by cohesion and adhesion
24
Q

transpiration pull

A
  • when water is removed from top of xylem vessels due to transpiration, more water moves up xylem vessels by capillary action to take its place
25
Q

cohesion-tension theory

A
  • whole process of how water moves into roots, up stem, out of leaves
  • root pressure, tension, adhesion, cohesion, capillary action, transpiration pull
26
Q

evidence for cohesion-tension theory

A
  • if plant stem is cut, air sucked into xylem - under tension
  • diameter of tree trunk reduces when transpiration is at maximum - transpiration pull creates tension in xylem
27
Q

how do you calculate rate of water uptake from a potometer?

A
  • measure how far air bubble move in certain time
  • mm/min
28
Q

weaknesses of potometer

A
  • only measures water uptake - not all used it transpiration - some used in photosynthesis
29
Q

precautions of potometer

A
  • air taken up into xylem when stem is cut so cut underwater
  • set up potometer under water to prevent air gaps
  • smear vaseline around connection between stem and tube
  • allow plant to adapt to surroundings for 10 mins before starting experiment
30
Q

mass potometer

A
  • place plant of scales and see how much mass is lost
  • prevent water evaporating from soil by covering soil with plastic wrap
  • directly measures rate of transpiration, not water uptake
  • much less disruptive to plant - don’t cut stem
31
Q

how do guard cells open?

A
  • open stomata in light - solutes eg. K+ transferred into guard cells lowering wtaer pot. of interior, water moves in by osmosis causing them to become tugid
  • close stomata in dark - reduce water loss
  • cell wall of inner side is thicker than rest of cell - prevents them expanding evenly and creates curved shape allowing stomata to open
  • come cellulose microfibrils in cell wall are ring shaped - prevents guard cells from expanding width wise
32
Q

what happens to guard cells in a drought?

A
  • hormonal signal sent to leaves from roots causing guard cells to lose tugidity and stomata to close
  • reduces water loss
33
Q

effect of light intensity on rate of transpiration

A
  • graph is diagonal line up then flat
  • light causes stomata to open and allow water vapour to diffuse out of leaf
  • at high light intensities rate of transpiration no longer increases because almost all stomata are open
34
Q

effect of humidity on transpiration

A

high humidity - smaller conc. grad. between inside of leaf and outside, slower transpiration rate

35
Q

effect of temperature on transpiration

A
  • at high temps water molecules have more kinetic energy and diffuse out of leaf faster
  • at high temps humidity of outside air decreases - high conc grad
36
Q

effect of air movement on transpiration

A
  • water vapour can build up around external surface of leaf - reduces conc grad and rate of transpiration
  • aire movement removes water vapour from external surface of leaf
37
Q

effect of water availability on transpiration

A
  • drought conditions - hormonal response causes stomata to close - reducing transpiration
38
Q

adaptations of cacti - spines

A
  • spines replace leaves reducing SA:V ratio and reducing water loss - photosynthesis takes place in stem, trap moist air reducing transpiration eg. cacti
39
Q

adaptations of xerophytes - thick waxy cuticle

A
  • reduces water loss by evaporation
40
Q

adaptations of cacti - sunken stomata

A
  • traps layer of moist air around stomata reducing transpiration rate
  • cacti only open stomata at night to absorb CO2 when conditions are cool -reduces water loss - and use it in day during photosynthesis
41
Q

adaptations of cacti - shallow roots/deep roots

A
  • shallow - absorb water from a rain shower before it evaporates
  • deep - access water from lower levels of soil
42
Q

marram grass adaptations

A
  • stomata on inside of leaves trapping water on inside rather than being blown away
  • sunken stomata
  • fine hairs projecting inwards - moist air is trapped around stomata
  • thick waxy cuticle
  • long roots to find water deep into sand
  • shallow roots to retain water
43
Q

why is glucose converted into sucrose in leaves?

A

less reactive than glucose

44
Q

sources

A

where assimilates are produced
- leaves, storage organs

45
Q

sinks

A

regions where assimilates are required
- roots (active transport so high respiration rate), shoots (dividing meristem), storage organs

46
Q

phloem loading

A
  • active process
  • protein on cell membrane of companion cell uses ATP to pump H+ out cytoplasm into spaces of cell wall (active transport)
  • (ATP produced by lots of mitochondria in companion cell)
  • this creates conc. grad.
  • H+ co-transports sucrose back into companion cell
  • foldings on cell membrane creates large SA for more proteins involved
  • sucrose diffuses through plasmodesmata from companion cells into sieve tube element cells
  • low water pot. in sieve tube elements so water moves into them by osmosis from xylem vessels
  • increased hydrostatic pressure in sieve tube element - phloem sap moves towards the sink - mass flow
47
Q

phloem unloading

A
  • sucrose diffuses out sieve tube element at sink and is converted into glucose for respiration or is converted into starch
  • increases water pot. in sieve tube element - water moves out by osmosis - can go back to xylem and join transpiration stream
48
Q

evidence for active model of translocation

A
  • rate of flow of sucrose in phloem is much faster than could take place by diffusion alone
  • if companion cell mitochondria is inhibited, translocation stops

Biology (17 decks)

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