Chapter 7: transport in plants Flashcards

1
Q

how are xylem vessels adapted to their function?

A
  • cells are joined end-to-end to form tubes
  • the cells are dead
  • cell walls thickened with lignin
  • non-lignified areas (pits) allow water to move between cells
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2
Q

how are phloem sieve tube elements adapted to their function?

A
  • made of living cells
  • elongated elements are joined end-to-end
  • sieve elements do not contain a nucleus or ribosomes
  • sieve plates at the end walls have pores to allow the movement of liquids
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3
Q

how are companion cells adapted for their function?

A
  • structured like a ‘normal’ plant cell
  • more mitochondria and ribosomes because the cell is aerobically active
  • plasmodesmata link cells to the sieve element
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4
Q

what is water potential?

A

a measure of the ability of water to move freely in solution

eg high water potential is pure water

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5
Q

what direction does water move (relating to water potential)?

A

DOWN the water potential gradient

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6
Q

what is ‘mass flow’?

A

the movement of water and nutrients from the roots to all other areas of the plant

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7
Q

define ‘cohesion’

A

the sticking together of water molecules

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8
Q

define ‘adhesion’

A

the attraction of water molecules to the cellulose and lignin in the walls of the xylem vessels

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9
Q

describe the apoplast pathway

A
  • water only travels through cell walls

- it moves due to cohesion

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10
Q

describe the symplast pathway

A
  • water moves into the cytoplasm/ vacuoles of the xylem vessels by osmosis
  • it moves through the xylem through plasmodesmata
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11
Q

what is the casparian strip?

A
  • forms an impenetrable barrier to water in the endodermis
  • the apoplast pathway is blocked
  • endodermis cells have suberin in their walls
  • water is forced into the cytoplasm
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12
Q

define transpiration

A

the loss of water from a plant to its environment, by diffusion down a water potential gradient

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13
Q

why is transpiration an inevitable consequence of gas exchange?

A

opening stomata for gas exchange leads to water loss by transpiration

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14
Q

what are xerophytes?

A

plants that live in places where water is in short supply

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15
Q

give three examples of adaptations of xerophytes

A
  • cuticle contains a waxy substance called cutin
  • stomata only found in the upper epidermis
  • hairs that reduce the steepness of the diffusion gradient
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16
Q

how is sucrose loaded into companion/ sieve elements?

A

by active transport