Water Transport In Plants Flashcards

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1
Q

mass transport in plants

A

water = transpiration (via xylem)
organic substances = translocation (via phloem)

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2
Q

describe the process of transpiration

A
  • transpiration is the evaporation of water from a leaf
  • water exits the leaves by evaporation via the stomata
  • water is transported through hollow, thick-walled tubes called xylem vessels
  • water enters the root through root hair cells via osmosis
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3
Q

describe water transport in plants

A
  • the main force that pulls water through the xylem vessels in the stem of a plant is the evaporation of water.
  • the energy supplied for this is heat from the sun, therefore the process is passive (no metabolic energy)
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4
Q

describe evaporation of water from the leaves

A

the humidity of the atmosphere is less than that of the air spaces next to the stomata
this means:
- the atmosphere has a lower water potential than the air space
- there is a water potential gradient from the air spaces to the air surrounding stomata
- therefore is stomata are open then water diffuses out of the air spaces into the surrounding air down a water potential gradient

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5
Q

describe movement of water across the leaves from the xylem

A
  • water lost from mesophyll cells via evaporation, this lowers the water potential inside these cells
  • therefore water enters these cells via osmosis from neighbouring cells down a water potential gradient
  • this in turn decreases the water potential of these neighbouring cells
  • hence a water potential gradient is established that pulls water from the xylem, across the mesophyll cells, into the air space and finally out through the stomata into the atmosphere
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6
Q

describe cohesion-tension

A

cohesion = water molecules form hydrogen bonds between one another and therefore stick together, this is known as cohesion. this means water forms a continuous, unbroken column all the way up the xylem

tension = as water evaporates from the mesophyll cells into air spaces, more molecules are drawn up behind as a result of cohesion. as column of water is pulled up, transpirational pull. transpirational pull puts the xylem under tension

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7
Q

how is the xylem tissue adapted for its function?

A
  • end walls of cells break down so they form unbroken tubes , this allows continuous columns of water to be pulled up
  • no cytoplasm or organelles, this allows no obstructions for the flowing water
  • walls contain lignin, this provides support/withstands tension
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8
Q

what are the 4 factors which can affect transpiration?

A
  • temperature
  • light
  • wind
  • humidity
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9
Q

describe how temperature can affect transpiration?

A

increasing temperature causes water molecules to have more kinetic energy, therefore faster diffusion out of stomata + faster evaporation of water from cells to airspace
so increases transpiration rate

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10
Q

describe how light can affect transpiration?

A

increasing light causes more stomata to open so greater surface area from which water vapour can diffuse out
so increases transpiration rate

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11
Q

describe how wind can affect transpiration?

A

increases windspeed removes water vapour from around leaf outside stomata more quickly so increases water potential gradient between airspace and atmosphere
so increases transpiration rate

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12
Q

describe how humidity can affect transpiration?

A

increasing humidity means more water vapour in the air so reduced water potential gradient between airspace and atmosphere
so decreases transpiration rate

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13
Q

how do you measure rate of transpiration?

A

with a potometer
- attach a shoot of plant with its end in contact with the water inside the tubing
- linked to an airwater meniscus

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14
Q

how would you measure the rate of uptake using a potometer?

A
  • measure the distance the waters moved
  • calculate the volume by multiplying the distance by pir^2
  • divide by the time taken
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