9.1 Xylem transport Flashcards

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1
Q

Define transpiration

A

TRANSPIRATION: loss of water vapour thrpugh the stems and leaves of a plant

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2
Q

Explain process of transpiration

A

Some light E converted into heat - water in spongy mesophyll into vapour - evaporate through stomata - new water is _absorbed by root_s from soil creating different pressure gradients in roots (high) and leaves (low) - water is pulled via xylem along the pressure gradient (in transpiration stream by transpiration pull)

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3
Q

Define stomata

A

STOMATA: pores on the underside of the leaf which facilitate gas exchange needed for photosynthesis

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4
Q

Leaf anatomy

A
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5
Q

Stem anatomy

A
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6
Q

Root anatomy

A
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7
Q

What influences rate of transpiration?

A
  • opening of stomata (levels of photosynthesis - gas exchnage)
  • humidity of the environment
  • wind
  • light intensity
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8
Q

How stomata regulate water loss?

A

Stomata open/close:

  • dehydrated cells release plant hromone abscisic acid ABA - triggers efflux of K+ from guard cells - decrease water pressure (lose turgor) - stomata close
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9
Q

What makes transpiration stream possible?

A

Water adhesive (xylem polar - intermolecular associations - additional tension) and cohesive (H bonds - continuous stream) peroperties

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10
Q

Explain xylem

A
  • from tracheids (exchange water via pits) and vessels (main traspiration stream)
  • tubes composed of dead cells
  • water movement passive
  • many pores - pits - water transferred to cells
  • walls thicker cellulose and lignin - strength as water creates tension
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11
Q

Way in which lignin may be deposited

A
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12
Q

Adaptation of roots

A

Roots - very branched off - root hairs - increase SA by which minerals, ions and water can be taken up

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13
Q

Tissues in roots

A
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14
Q

Explain mineral uptake by roots

A

Needed to take up: Mg2+, K+, Na+, NO3-, PO4-

Can be taken up by diffusion or active transport - root cells contain ion pumps that expel H+ - displace the cations in soil (indirect active transport) - diffusion along a gradient - anions may bind with H+ and reabsorbed

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15
Q

Explain water uptake by roots

A

Via osmosis to higher solute conc - by aquaporins - once inside the cell will move into xylem:

  • symplastic route: via cytoplasm, water moves continuously between cells and plasmodesmata,
  • apoplastic route: via cell wall, cannot pass Capsarian strip - run through cytoplasm of endodermis
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16
Q

Explain water conservation adaptations by two types of plants

A

Xerophytes: tolerate dry conditions: reduced SA, exposure of stomata for water loss, thickened cuticle, CAm open stomata at night

Halophytes: tolerate salty conditions: can isolate toxins, salts in vacuoles and cell walls, abscission, salt glands, flowering at humid seasons

17
Q

Experiments modelling the movement of water up the xylem

A
  • capillary tubing: traspiration pull/stream, adhesion + cohesion
  • filter paper: movement up xylem, adhesion + cohesion - paper and xylem from cellulose
  • porous pots: loss of water through pores similar to trasnpiartion
18
Q

Explain potometer

A

POTOMETER: device that is used to estimate transpiration rates by measuring rate of water loss/uptake

Plant fixed to a potometer - water uptake assesed by movement of a air buble along a ruler - important to remember that not all water is lost due to transpiration - some used for metabolism

19
Q

Controlled variables of experiment with potometer

A
  • temperature
  • humidity
  • wind
  • light intensity