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AS Biology > 7) Transport in Plants > Flashcards

7) Transport in Plants Flashcards

1
Q

what is adhesion ?

A

the formation of hydrogen bonds between carbohydrates in the xylem vessel walls and water molecules

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2
Q

what is cohesion ?

A
  • formation of hydrogen bonds between water molecules.
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3
Q

what is the apoplastic pathway ?

A

water moves through the intercellular spaces between cellulose molecules in the cell wall

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4
Q

what is the casparian strip ?

A

waterproof strip surrounding endodermal cells of the root that blocks the apoplastic pathway, forcing water through the symplast route.

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5
Q

what is the symplastic pathway ?

A
  • water enters the cytoplasm through the plasma membrane and moves between adjacent cells via plasmodesmata.
  • water diffuses down its water potential gradient by osmosis.
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6
Q

what is the function of the xylem

A
  • carries dissolved minerals and water up the plant
  • structural support
  • food storage
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7
Q

what is the function of phloem

A

transport organic compounds (sucrose) from source to the sink

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8
Q

where is xylem and phloem in the roots

A

xylem : centre of vascular bundle
phloem : on the edges of the centre

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9
Q

where is xylem and phloem in the stems

A

xylem : inside (closest to centre of stem)
phloem : outside (closest to epidermis)

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10
Q

where is xylem and phloem in the leaves

A

xylem : upper side (closest to upper epidermis)
phloem : lower side (closest to lower epidermis)

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11
Q

phloem sieve tube adaptations

A

-cell membranes that retain sucrose & other assimilates within cells
- few cell contents to reduce resistance to flow of phloem sap
- sieve plates to hold sieve tubes together/resist internal pressure
- sieve pores to allow ease of flow between sieve tube elements

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12
Q

adaptations of companion cell

A
  • many mitochondria to provide energy to move solutions into sieve tubes
  • many plasmodesmata to allow easy movement of phloem sap into/out of sieve tubes
  • pump & co-transporter proteins in cell membranes for absorption of sucrose (from apoplast pathway from mesophyll cells)
  • some plasmodesmata shared with mesophyll cells for transport of sucrose via symplast pathway
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13
Q

how is xylem vessel suited to their function

A
  • transport of water & mineral ions
  • elongated cells / tubes for transport
  • hollow/ no cytoplasm or contents SO more space for greater volume for flow
  • cellulose lining SO adhesion of water molecules
  • lignified walls to prevent collapse
  • lignified walls SO waterproof/prevents loss of water
  • pits to allow sideways movement
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14
Q

how does sieve tube element help translocation

A
  • little cytoplasm/no vacuole/no tonoplast
  • pores in sieve plate provide little resistance
  • sieve plate prevents cell collapsing
  • plasmodesmata allows loading
  • cellulose walls prevent tm expansion
  • mitochondria for ATP for repair
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15
Q

how do companion cells help in translocation

A
  • assimilates (sucrose/amino acids) loaded/pumped
  • pumping H+
  • co-transport (H+ carry sucrose with them)
  • mitochondria provide ATP for active transport
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16
Q

describe the apoplastic pathway

A
  • water enters cell wall
  • water moves through the cell wall
  • water may move from cell wall to cell wall through intracellular spaces OR directly
17
Q

describe the symplastic pathway

A
  • water enters cytoplasm by osmosis through cell membrane
  • water moves into the sap in the vacuole through tonoplast by osmosis
  • water may move from cell to cell through plasmodesmata OR adjacent cell membrane/walls
18
Q

5 features of xerophytic plants + their effects

A
  1. thick cuticle to leaf epidermis : prevents water loss thru external wall of epidermis.
  2. layer of hairs on epidermis : traps moist air over leaf & reduces diffusion.
  3. reduction in no of stomata : reduces outlets through which moist air can diffuse.
  4. stomata in pits/groves : moist air trapped outside stomata, reducing diffusion.
  5. leaf rolled/folded : reduces area from which transpiration can occur.
19
Q

Suggest how the permeability of the tonoplast changes and explain how this change
could result in the rupture of the tonoplast

A
  • increased permeability to water
  • increased protein channels (in the tonoplast)
  • water potential in vacuole is lower than that of cytoplasm
  • more water enters (vacuole) by osmosis
  • vacuole increases, in volume / pressure (until it bursts)
20
Q

why is water the main component of xylem sap and phloem sap

A
  • solvent for assimilates / mineral ions
  • hydrogen bonds for cohesion & adhesion (xylem)
  • to build up hydrostatic pressure for mass flow/translocation (phloem)
21
Q

Explain how water moves up xylem vessels in the trunks of trees

A
  • diff in water potential
  • continuous columns of water
  • transpiration pull/ cohesion tension
  • hydrogen bonding between molecules / cohesion
  • adhesion
22
Q

role of cotransporter proteins in companion cells

A
  1. movement of sucrose with, protons / H+ ions, into companion cells.
  2. (sucrose moved) from, apoplast / cell wall / mesophyll cell ;
  3. sucrose moves against its concentration gradient (into companion cell) ;
  4. (needs cotransporter protein because) sucrose is polar so cannot pass through membrane
23
Q

Suggest why mineral ions are found within phloem sieve tubes and state how they are
transported within phloem sieve tubes

A
  • they enter from xylem through plasmodesmata from companion cells
  • dissolved in water
  • transported as part of mass flow in phloem
24
Q

Suggest and explain how the presence of mineral ions in the root hair cell can increase
the absorption of water by the root hair cells

A
  • mineral ions dissolve in water
  • they decrease w.p in cytoplasm
  • w.p gradient steep
  • water enters by osmosis
25
Q

how is sucrose transported into phloem sieve tubes

A
  • mass flow
  • from companion cell
  • sucrose dissolved in water/lowers w.p
  • transport from high hydrostatic pressure to low
26
Q

roles of hydrogen bonding in the movement of water through xylem vessels

A
  • gives adhesion between water molecules and cellulose = formation of continuous column
  • gives cohesion between water molecules
  • transpiration pull
27
Q

how is tension created in the xylem vessels

A
  • transpiration pull
  • water lost during transpiration
  • cohesion & adhesion
28
Q

why are lignified walls in the xylem important ?

A
  • prevents collapse
  • thickening for support
  • waterproofing properties
  • allows formation of hollow cells
  • maintains column of water (adhesion of water to hydrophilic groups in lignin)
29
Q

Describe and explain the mechanism that is responsible for the movement of phloem sap in sieve tubes

A
  • diffuse into phloem sieve tube by plasmodesmata.
  • w.p in sieve tube decreases.
  • water enters by osmosis
  • hydrostatic pressure increases
  • mass flow
  • unloading at sink decreases hydrostatic pressure

AS Biology (11 decks)

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