Mass Transport In Plants Flashcards

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1
Q

XYLEM function

A
  • transports water and mineral ions through the stem up the plant and to the leaves
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2
Q

XYLEM adaptions related to its function

A
  • cells joined with no end walls forming a long continuous tube => so enables water to flow as a continuous column
  • cells contain no cytoplasm/nucleus so easier water flow/no instructions
  • thick cell walls containing lignin so provides support/ withstands tension
  • pits inside walls allow later water movements
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3
Q

Transpiration

A
  • the loss of water vapour from plant leaves by evaporation through the stomata
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4
Q

Cohesion tension theory

A
  • how water moves up the xylem against gravity via the transpiration stream
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5
Q

Cohesion tension theory process

A
  1. water is lost from the leaf via transpiration
    - water evaporates from the mesophyll cells to the air spaces and diffuses though open stomata
  2. this lowers the water potential in mesophyll cells
  3. so water is drawn out of the xylem down a water potential gradient
  4. this creates upwards tension on the column of water in the xylem vessels
  5. Hydrogen bonds result in cohesion between the water molecules
  6. So water is pulled up as a continuous column
  7. Water also adheres to the walls of the xylem
  8. The whole column of water moves up and more water enter the roots via osmosis
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6
Q

Factors affecting transpiration rate

A
  • light intensity
  • temperature
  • wind intensity
  • humidity
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7
Q

Light intensity

A
  • Increasing light intensity increase transpiration rate
  • this is because more stomata open in the light to let in CO2 for photosynthesis
  • allowing more water to evaporate faster
  • stomata close when it’s dark due to low transpiration rate
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8
Q

Temperature

A
  • increasing temperature increases the rate of transpiration
  • this is because water molecules have more kinetic energy as temp increase - so water evaporates faster
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9
Q

Wind intensity

A
  • increasing wind intensity increases the rate of transpiration
  • this is because wind blows away water molecules surrounding the stomata
  • decreasing water potential of air around the stomata
  • therefore increasing the water potential gradient so water evaporates faster
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10
Q

Humidity

A
  • increasing humidity ( moisture/water in the air) decrease rate of transpiration
  • there is more water in the air so it has a higher water potential
  • this reduces water potential gradient from leaf to air
  • so water evaporates slower
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11
Q

Photometer

A

Estimates transpiration rate by measuring water uptake

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12
Q

Photometer limitations

A
  • does not truly measure transpiration rate as rate of water uptake might not be the same as transpiration rate
  • water is used for support/turgidity of plant cells
  • water is used in photosynthesis
  • water is produced during respiration
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13
Q

Phloem

A
  • transports organic substances eg. Sucrose in plants
  • contains two keys cells:
  • seive tube elements
  • companion cells
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14
Q

Structure of phloem

A
  • contains seive tube elements which have no nucleus/few organelles to allow easier flow of organic substances
  • also contain end walls called seive plates which allow solutes to pass through
  • companion cells are next to seive tube elements and contain lots of mitochondria due to high rate of respiration to produce ATP for active transport of solutes/sucrose
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15
Q

Translocation

A
  • is the movement of solutes from source to sink through the phloem vessels
  • requires energy from ATP
  • source : where the solute is made e.g sucrose is made at leaves
  • sink : where the solute is used up/converted e.g sucrose is converted to starch by enzymes for storage
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16
Q

Mass flow hypothesis

A

sucrose/ solutes move down a pressure gradient from source to sink

17
Q

Mass flow (AT SOURCE)

A
  • sucrose is actively transported from companion cells to seive tubes
  • lowering water potential in seive tubes
  • thus water enters phloem from xylem/companion cells via osmosis
  • increasing hydrostatic pressure in seive tubes near source
18
Q

Mass flow (AT SINK)

A
  • sucrose is removed to be used up or stored
  • increasing water potential in sieve tubes
  • so water leave phloem via osmosis
  • lowering hydrostatic pressure in seive tubes near sink