mass transport in plants Flashcards

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1
Q

what is the xylem tissues role

A

transports water and mineral ions through stem up to leaves

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2
Q

how is xylem tissue adapted for its function

A

cells joined with no end walls forming continuous tube —> water can flow as continuous column

cells contain no cytoplasm —> easier water flow no obstruction

thick cell walls with lignin —> support to withstand tension and prevent water loss

pits in side walls —> allows lateral water movement

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3
Q

what is cohesion theory

A

how water moves up xylem against gravity via transportation system

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4
Q

what is transpiration

A

loss of water vapour from plant leaves by evaporation through stomata

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5
Q

describe the process of transpiration

A

leaf
1. water lost by transpiration water evaporated from mesophyll cells into air spaced and water vapour diffuses through stomata
2. reducing water potential of mesophyll
3. water drawn out of xylem down water potential gradient

xylem
4. creating tension in xylem
5. hydrogen bonds result in cohesion
6. water pulled as continuous column
7. water also adheres to walls

root
8. water lost entered the roots via osmosis

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6
Q

what is the phloem tissue

A

transports organic substances eg. sucrose in plants

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7
Q

what 2 cells are in the phloem and their adaptations

A

sieve tube elements
- no nucleus —> easier flow
- end walls between cells perforated

companion cells
- many mitochondria- ATP for active transport

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8
Q

what is translocation

A

movement of absolutes from sources to sinks by mass flow

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9
Q

describe the process of translocation

A

at the source
- active transport loads solutes from companion cells
- lowering water potential in sieve prices
- so water entered by osmosis from xylem
- increasing hydrostatic pressure

at the sink
- solutes removed to used or stored
- increasing water potential in sieve plates
- water leaves by osmosis
- lowing hydrostatic pressure

mass flow
- pressure gradient form source to sink pushed solutes

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10
Q

how would you use tracer experiments to investigate transport in plants

A

leaf supplied with radioactive tracer
radioactive carbon incorporated into organic substances during photosynthesis
these move around by translocation
movement tracked using Geiger counter

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11
Q

how would you use ringing experiments to investigate transport in plants

A

remove and kill phloem eg. remove ring of bark
bulge formed in source side of ring
fluid from bulge has higher conc. of sugars than below
tissues bellow ring due as cannot get organic substances

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12
Q

how to interpret evidence form tracer and ring experiments and to evaluate evidence for and against mass flow hypothesis

A

is there evidence to suggest phloem is involved
is there evidence to suggest respiration/ active transport involved
is there evidence to show movement from source to sink - what are these
is there evidence to suggest movement from high to low hydrostatic pressure
could movement be due to another factor

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13
Q

how would you investigate transpiration

A

potometers

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14
Q

how to set up a potometer

A
  1. cut a shoot underwater at a slant to prevent air entering
  2. assemble potometer with capillary tube end submerged in beaker of water
  3. insert shoot underwater
  4. ensure apparatus is watertight
  5. dry leaves and allow time for shoot to acclimatise
  6. shut tap to reservoir
  7. form an air bubble - quickly remove end of capillary tube from water
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15
Q

how to use a potometer to investigate the effect of a named environment variable on rate of transpiration

A
  1. record position of air bubble
  2. use stop watch to record time
  3. record distance moved in time
  4. calculate volume of water uptake
    - use radius of capillary tube to calculate cross sectional area (pie x radius squared)
    - multiply by distance moved
  5. calculate rate of water uptake
    - divide volume by time
  6. change one variable (wind, humidity, light, temperature )
  7. keeps all other variables constant
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16
Q

what are the limitations of using a potometer

A

doesn’t truly measure tater of transpiration - rate of water uptake not the same as transpiration
• water used for support
• water used in photosynthesis
• water produced during respiration

rate of movement through shoot in potometer may not be same as rate of movement through shoot of whole plane
• shoot in potometer has no roots
• xylem cell’s very narrow

17
Q

how does increasing light intensity affect transpiration rate

A

increases rate

stomata open in light to let CO2 in for photosynthesis
allowing more water to evaporate faster
stomata close when it’s dark so low transpiration rate

18
Q

how does increasing temperature affect transpiration rate

A

increases

water molecules gain kinetic energy
so water evaporates faster

19
Q

how does increasing wind intensity affect transpiration rate

A

increases

wind blows away water molecules from around stomata
decreasing water potential of air around stomata
increasing water potential gradients so water evaporates faster

20
Q

how does increasing humidity affect transpiration rate

A

decreasss

more water in air so higher water potential
decreasing water potential gradient from leaf to air
water evaporates slower