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Biology > mass transport in plants > Flashcards

mass transport in plants Flashcards

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1
Q

root structure

A
  • water enters root hair cells via epidermis
  • passes cells of cortex, across endodermis into xylem
  • xylem passes water up the plant to the leaves
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2
Q

root adaptations

A
  • extensions to increase SA to increase uptake of water
  • thin cell wall so shorter diffusion distance
  • RHC actively tranport ions from soil across membranes via carrier proteins
  • water potential becomes more negative
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3
Q

xylem

A

transports water and mineral ions

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4
Q

phloem

A

transports sugars and organic substances from where formed via PS to where needed (eg: shoots, flowers, fruits)

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5
Q

explain how water enters the xylem from tge endodermis in the root and is then transported to the leaves

A

ROOT
- casparian strip blocks apoplast pathway
- active transport by endodermis
- of ions into xylem
- lower water potential in xylem

XYLEM TO LEAF
- transpiration from leaves
- creates cohesion between water molecules
- adhesion between water molecule and wall of xylem
- creates a continuous column of water

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6
Q

symplastic pathway

A
  • slower, resistance to movement of water
  • via cytoplasm and membranes by OSMOSIS
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7
Q

apoplastic pathway

A
  • faster, larger gaps between cellulose molecules so less resistance
  • along cellulose cell walls by DIFFUSION until reaches casparian strip (in endodermis)
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8
Q

vascular bundle

A

zylem and phloem tissue together
xylem always inside

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9
Q

xylem adaptations

A
  • dead hollow tubes so allows easier water flow
  • cell walls strengthened with lignin so rigid, withstands tension and waterproof
  • end walls break down to form a continuous tube with no end walls so continous column
  • thick walls to withstand hydrostatic pressure
  • narrow to enable capillary action
  • pits enable water to move laterally between xylem vessels
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10
Q

root pressure moves water through the xylem. describe what causes root pressure.

A
  • active transport by endodermis
  • of ions into xylem
  • lowers water potential of xylem
  • water enters by osmosis
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11
Q

transpiration

A

loss of water from the leaf due to evaporation

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12
Q

cohesion-tension theory and transpiration

A
  • transpiration from leaves
  • lowers water potential of mesophyll cells, so water moves by osmosis into these cells
  • creates a water potential gradient across leaf between mesophyll cells and air spaces
  • water from xylem enters leaf
  • continuous column of water formed
  • cohesion of water molecules
  • adhesion between water and xylem
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13
Q

why does the diameter of a tree trunk decrease?

A
  • movement of water makes xylem more narrower
  • negative tension
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14
Q

describe how a high pressure is produced in the leaves

A
  • water potential becomes more negative
  • as sugar enters phloem
  • water enters phloem by osmosis
  • increased volume of water = increased pressure
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15
Q

name a factor that can affect the rate of transpiration

A
  1. light intensity
  2. temperature = rate of diffusion increases, increases KE
  3. humidity = greater difference = greater rate of diffusion down a water potential graident
  4. air movement = increases water potetial gradient
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16
Q

a leafy shoot is cut diagonally under water

A

stops xylem sealing

17
Q

care is taken to prevent water getting on leaves. wy?

A

prevents stomata being blocked by water

18
Q

the potometer is filled completely with water making sure there are no air bubbles. why?

A

might get into xylem
and disrupt the continuous column of water

19
Q

potometer is removed from under the water and all joints are sealed with waterproof jelly. why?

A

stops air from getting in and water escaping potometer

20
Q

limitations of potometer:

A
  • vol of water taken up doesnt always equal vol of water lost via transpiration. may also be used for: respiration, photosynthesis, support
  • potometer measures uptake via stem and not roots of a normal plant
21
Q

give 2 precaustions taken when setting up a potometer to get the most accurate results possible

A
  • seal joints/ ensure airtight
  • cut shoot under water
  • cut shoot at a slant
  • dry off leaves
  • shut tap
  • insert into apparatus under water
  • ensure no air bubles
22
Q

xerophytic plant adaptations to reduce transpiration

A
  • reduced no of stomata
  • stomata in pits
  • hairs to trap water
  • rolled leaves
  • leaves reducied into spines
  • thick waxy cuticle
23
Q

solutes

A

dissolved substances

24
Q

phloem structure

A
  • transport organic solutes (eg: sucrose) around plants
  • have sieve tubes. no nucleus, living cells
  • have companion cells, carry out living functions for sieve cells
  • companion cells have mitochondria to synthesise ATP via aerobic respiration for active transport of solutes
25
Q

translocation

A
  • movement of solutes/ assimilates (eg: amino acids, sucrose) to where needed.
  • requires energy
  • from sources (where produced) to sinks (where used)
  • enzymes at sink convert solutes into storage molecules (eg: starch) to maintain a concentration gradient
  • always a lower concentration at sink than source
26
Q

describe the mass flow hypothesis for the mechanism of translocation in plants

A

i- n source, sugars are actively transported into phloem
- by companion cells
- lowers water potential of sieve tube
- water enters by osmosis (increase in volume = increase in pressure)
- increase in prsssure causes mass movement towards sink
- sugars in sink converted for respiration for storage

27
Q

evidence FOR mass flow hypothesis

A
  • ring of bark removed from stem then bulge above ring
  • fluid of bulge higher conc of sugars than fluid below: evidence for DOWNWARD flow
  • aphids pierce phloem and sap flows quicker near leaves than stem: evience of PRESSURE GRADIENT
  • autoradiography where radioactive tracer can be tracked during translocation from source to sink
28
Q

evidence AGAINST mass flow

A
  • sugar transported to many different sinks, not just to the one with highest water potential as model suggests
  • sieve plates would be abarrier for mass flow
  • a lot of pressure required to get solutes through at a reasonable rate

Biology (29 decks)

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