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Biology module 3 > 3.3 transport in plants > Flashcards

3.3 transport in plants Flashcards

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1
Q

what does a multicellular plant need a supply of

A

oxygen, water, nutrients and minerals

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2
Q

why do plants need a transport system

A

to move water and minerals from roots up to leaves

to move sugars from leaves to the rest of the plant

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3
Q

what does the transport system in plants consist of

A

specialised vascular tissue:

  • water and soluble mineral ions travel up xylem tissue
  • assimilates (sugars) travel up or down phloem tissue
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4
Q

define dicotyledonous plants

A

plants with two seed leaves and a branching pattern of veins in the leaf

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5
Q

how are the xylem and phloem found

A

in vascular bundles

may also contain other tissues (collenchyma and sclerenchyma) that give strength and support plant

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6
Q

how can you identify the xylem and phloem in a young root

A

xylem is in the centre of a young root in the shape of an X

phloem is found in between the armies of the X-shaped xylem tissue

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7
Q

what can be found around the vascular bundle in a young root

A

endodermis and just inside it is a layer of meristem cells

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8
Q

where can the vascular bundles be found in the stem

A

near the outer edge of the stem
xylem is found towards the inside of each vascular bundle
phloem is found towards the outside of each vascular bundle
in between xylem and phloem there is a layer of cambium
cambium is layer of meristem cells which divide to produce new xylem and phloem

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9
Q

how can you find the xylem and phloem in a leaf

A

vascular bundles form the midrib and veins of a leaf

the xylem is located on top of the phloem

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10
Q

define companion cells

A

cells that help load sucrose into sieve tubes

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11
Q

define sieve tube elements

A

make up tubes in phloem tissue that carry sap up and down plant- they are separated by sieve plates

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12
Q

what does the xylem tissue consist of

A

vessels to carry the water and dissolved ions
fibres to help support the plant
living parenchyma cells which act as packing tissue to separate and support vessels

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13
Q

how do xylem vessels develop

A
  • lignin impregnates walls of cells making them waterproof which kills the cells
  • the cell walls and contents decay leaving a long column of no content
  • lignin strengthens the cells walls and prevents collapsing
  • the lignin thickening forms a pattern which prevents the vessel from being too rigid and allows some flexibility
  • in some places, lignification is not complete forming bordered pits which allow water to leave one vessel and pass into the next
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14
Q

how is the xylem adapted to its function

A
  • forms continuous column
  • tubes are narrow so water column doesn’t break easily
  • bordered pits allow water to move from one vessel to another
  • lignin deposited in walls in spiral allows it to stretch as the plant grows
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15
Q

why is the flow of water in the xylem not impeded

A
  • there are no cross walls
  • there are no cell contents
  • lignin thickening prevents the wall from collapsing
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16
Q

what is the structure of the phloem

A

consists of sieve tubes which are made up of sieve tube elements and companion cells

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17
Q

describe sieve tube elements

A

they are lined up end to end to form sieve tubes
at the end of sieve tube elements there are sieve plates-keep lumen open
the perforations in the sieve plate allow. movement of sap from one element to the next
have very thin walls

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18
Q

describe companion cells

A

small cells, w large nucleus and dense cytoplasm
numerous mitochondria to produce ATP needed for active processes
they carry out metabolic processes needed to load assimilates actively into the sieve tubes

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19
Q

define plasmodesmata

A

gaps in the cell wall containing cytoplasm that connects two cells

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20
Q

what are the 3 pathways taken by water

A

apoplast pathway

symplast pathway

vacuolar pathway

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21
Q

describe the apoplast pathway

A

water passes through the spaces in the cell walls between the cells

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22
Q

describe the symplast pathway

A

plasma membrane —-> cytoplasm —–> plasmodesmata from one cell to the next

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23
Q

describe the vacuolar pathway

A

plasma membrane —-> cytoplasm —-> Vacuole—–> cytoplasm—–> plasmodesmata to next cell

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24
Q

define transpiration

A

the loss of water vapour from the aerial parts of a plant

25
Q

what is a potometer

A

device that can measure the rate of water uptake as leafy stem transpires

26
Q

what is water loss in transpiration limited by

A

waxy cuticle

27
Q

describe the process of transpiration

A
  • water enters leaf through xylem
  • water moves into the cells of the spongey mesophyll by osmosis
  • water evaporates from the cell walls of the spongy mesophyll
  • water moves by diffusion out of the leaf by the open stomata-relies on water vapour potential gradient
28
Q

why is transpiration important

A
  • transports useful mineral ions up the plant
  • maintains cell turgidity
  • supplies water for growth, cell elongation and photosynthesis
  • supples water that can keep the plant cool on a hot day
29
Q

how does light intensity affect transpiration

A

higher light intensity increases transpiration rate

30
Q

how does temperature affect transpiration

A
  • increases rate of evaporation- water vapour potential in leaf rises
  • increase rate of diffusion- more kinetic energy
  • decrease relative water vapour potential In air- rapid diffusion of molecules out leaf
31
Q

how does humidity affect transpiration

A

decreases rate of water loss- smaller water vapour potential gradient

32
Q

how does wind affect transpiration

A

air moving outside leaf will carry away water vapour that just diffused out leaf
maintain high water vapour potential gradient

33
Q

how does water availability affect transpiration

A

insufficient water will cause the stomata to close and the leaves to wilt

34
Q

define adhesion

A

the attraction between water molecules and the walls of the xylem vessel

35
Q

define cohesion

A

the attraction between water molecules caused by hydrogen bonds

36
Q

describe water uptake and movement across the root

A
  • epidermis contains root hair cells which increase SA of root, they absorb mineral ions and water from soil through osmosis
  • water moves across root cortex by osmosis via apoplast pathway
  • water is forced into symplast pathway as casparian strip blocks apoplast path
  • mineral ions actively transported into medulla by osmosis
37
Q

describe the role of the epidermis

A
  • movement of water across the root is driven by an active process that occurs at the epidermis
  • casparian strip blocks apoloplast path between cortex and medulla which ensures mineral ions pass into cytoplasm
  • plasma membranes contain transporter proteins which actively pump mineral ions from cytoplasm in cortex into medulla and xylem
  • water cant pass back into cortex bc its blocked by casparian strip
38
Q

why is root pressure useful in transpiration

A

it forces water into the xylem and pushes it up the xylem

39
Q

describe the transpiration stream

A
  • minerals are actively transported into the xylem which lowers water potential so water follows in by osmosis
  • cohesion of water molecules enabled water to move up by mass flow
  • movement of water out of xylem creates low hydrostatic pressure
  • osmosis moves water across the leaf
  • water from cell surface evaporates
  • water vapour diffuses out of leaf
40
Q

define hydrophyte

A

a plant adapted to living in water or where ground is very wet

41
Q

define xerophyte

A

a plant adapted to living in dry conditions

42
Q

what do plants living on land have to be adapted to

A

reducing this loss of water

replacing the water that is lost

43
Q

what structural and behavioural adaptation do terrestrial plants have to reduce water losses

A
  • waxy cuticles on leaves reduce water loss from evaporation
  • the stomata is on the bottom of the leaves and reduces evaporation
  • stomata is closed at night when there’s no light for photosynthesis
44
Q

marram grass is xerophyte. what are its adaptations

A
  • leaf is rolled so air his trapped inside, makes air humid and reduces water loss
  • thick waxy cuticle on outer side of rolled leaf to reduce evaporation
  • stomata are on inside of rolled leaf
  • stomata are in pits in lower epidermis which is folded and covered in hairs
  • spongey mesophyll is very dense with few air spaces
45
Q

what adaptations do cacti have

A
  • they are succulents (store water in stems)
  • leaves are reduced to spines, lower SA, less water lost in transpiration
  • stem is green for photosynthesis
  • roots are widespread to take advantage of any rain that does fall
46
Q

list other xerophytic features

A
  • close stomata when water availability is low
  • have a low water potential inside their leaf cells
  • very long root that can reach water deep underground
47
Q

what issues do hydrophytes face

A

getting oxygen to their submerged tissues and keeping afloat- need to keep leaves in sunlight for photosynthesis

48
Q

what adaptations do water Lillys have

A
  • many large air spaces in the leaf- keeps it afloat and can absorb sunlight
  • stomata is on upper epidermis- exposed to air and allows gaseous exchange
  • leaf stem has many large air spaces- helps buoyancy and oxygen to diffuse quickly
49
Q

how do hydrophytes transpire

A

they have hydathodes which are structures that can release water droplets so they can evaporate from the leaf surfaces

50
Q

define translocation

A

the transport of assimilates through the plant

51
Q

define assimilates

A

substances that have become part of the plant

52
Q

what is the first step of translocation

A

phloem loading

53
Q

describe phloem loading

A
  • ATP is hydrolysed and H+ ions are pumped out
  • H+ ions return to companion cell by special cotransporter proteins with sucrose by facilitated diffusion (against conc. gradient)
  • Conc. of sucrose in companion cells increases so it diffuses through plasmodesmata into sieve tube element
54
Q

what is cotransport

A

when H+ ions are only allowed back in the cell if they’re accompanied by sucrose

55
Q

what does the mass flow hypothesis describe

A

the movement of sucrose along the phloem

56
Q

what is the source in translocation

A

where sucroses is produced (leaf)

57
Q

what is the sink in translocation

A

it is where the sucrose is used (root)

58
Q

describe the mass flow hypothesis

A
  • sucrose is actively loaded into the phloem which reduces water potential
  • water flows in phloem from xylem by osmosis +increases hydrostatic pressure
  • sucrose moves down phloem from high hydrostatic pressure at source to lower hydrostatic pressure at sink
  • sucrose diffuses into companion cell and increases water potential in sieve tube element
  • water moves out phloem into xylem by osmosis and reduces hydrostatic pressure

Biology module 3 (3 decks)

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