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Mass Transport (pack 8) > mass transport in plants > Flashcards

mass transport in plants Flashcards

1
Q

transpiration

A

evaporation of water from leaves
movement of water from stomata
due to diffusion

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2
Q

what makes guard cells open

A

during light, K+ actively pumped into guard cells then water moves in my osmosis.. The turgid cells buckle as they have uneven thickening of their cell walls.

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3
Q

movement of water out of the stomata

A
  • lower water potential outside stomata
  • {{ gradient between the inside and outside of the leaf
  • diffusion of water out of the leaf through open stomata
  • water evaporates from surface of mesophyll cells to replace that lost in air spaces
  • rate of transpiration controlled by size and number of stomata stores
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4
Q

movement of water across cells of the leaf

A
  • mesophyll cells lose water by evaporation from surface due to heat from the sun
  • cells now have lower water potential
  • water enters cell from neighbouring cells by osmosis
  • loss of water from neighbouring cells lower their water potential
  • water enters these cells from their neighbours by osmosis
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5
Q

cell wall pathway (apoplastic)
by which process will movemnt of water occur

A

diffusion
water not passing through membrane so not osmosis

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6
Q

cytoplasmic pathway (symplastic)
by which process does this occur

A

osmosis as water passes through membrane to enter cytoplasm

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7
Q

what final canals does water move into other cells through

A

plasmodesma (plural plasmodesmata)

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8
Q

the main type of xylem vessel

A

pitted vessel

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9
Q

during pitted vessels differentiation they

A

lose their cytoplasm and nucleus
become thickened by lignin in certain areas

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10
Q

at maturity the cells in xylem vessels are what

A

dead

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11
Q

why does the cellulose cell wall of xylem vessels not prevent water movement

A

it is fully permeable

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12
Q

what is the role of the pits in xylem vessels

A

to allow lateral diffusion of water in air bubble
stops movement of water

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13
Q

what is transpiration pull

A

water being pulled up the xylem as a result of transpiration

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14
Q

how many ways could water move from the xylem to the sub stomatal cavity

A

2

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15
Q

sub stomatal cavities

A

apoplast and symplast

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16
Q

which stomatal cavity is most important

A

apoplast as its faster

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17
Q

what do stomatal cavities rely on

A

water potential gradient between xylem vessel and exterior of leaf

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18
Q

what evidence is there which supports the cohesion tension theory

A
  • change in diameter of plant stems according to the rate of transpiration
  • if a xylem vessel id broken and air enters water can no longer be drawn up as the continuous colum of water is broken
  • if a plant stem is cut off water does not drip out. Instead air is drawn up stem
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19
Q

criticisms of cohesion- tension theory

A

for it to work you need a continuous flow of water up the xylem
strength of xylem vessels

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20
Q

steps to measure transpiration using a potometer

A
  1. Cut a shoot under water (so no air gets into xylem).
  2. Assemble apparatus under water.
  3. Remove and dry apparatus and shoot.
  4. Vaseline bungs to make water tight.
  5. If no air bubble is present, introduce one.
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21
Q

what is the reservoir for?
transpiration using a potometer

A

allows the bubble to be reset so further repeats/ experiments using the same shoot can be carried out

22
Q

how could you calculate the rate?
transpiration using a potometer

A

divide the distance moved by the bubble by time

23
Q

What is the photometer used for?
transpiration using a potometer

A

comparing how different conditions affect transpiration rate

24
Q

what precautions must be made when setting up a potometer

A
  • seal joints
  • cut shoot under water
  • cut shoot at a slant
  • dry off leaves
  • insert into apparatus under water
  • ensure no air bubbles are present
  • shut tap
  • move bubble to the start position
25
Q

what does a potometer really measure

A

water uptake accounts for
- transpiration
- leaks
- respiration
- photosynthesis
- water used for support

26
Q
A
27
Q

Translocation definition

A

The process by which organic molecules and some mineral ions are transported from one part of a plant to another

28
Q

Source translocation

A

Site of sugar production during photosynthesis

29
Q

Sink translocation

A

Site where sugars will be relocated for immediate use of storage
Can be either above or below the source

30
Q

What is the phloem made up of

A

Sieve tube elements

31
Q

How are sieve tube elements adapted for mass transport

A
  • Stacked one on top of another
  • end walls (sieve plates) have large pores
  • during maturation they lose their nuclei and much of their cytoplasm
32
Q

Features of companion cells

A
  • nucleus and rough endoplasmic reticulum
  • relatively large numbers of mitochondria
  • many plasmodesmata in the lateral walls of the companion cells and their associated sieve tube elements
33
Q

In which direction does transport in the sieve tube elements of phloem take place?

A

Transports in both directions

34
Q

What is transported in the phloem

A
  • organic molecules
  • inorganic molecules
  • dissolved in water
35
Q

In which direction does transport in the xylem take place?

A

Up forms roots towards leaves

36
Q

What is transported in the xylem?

A

Water and dissolved ions

37
Q

three phrases of mass flow theory relating to transport of sucrose in sieve tube elements

A
  • transfer of sucrose into sieve tube elements from photosynthesising tissue
  • mass flow through sieve tube elements
  • transfer of sucrose from the sieve tube elements into storage of other sink cells
38
Q

what is sucrose manufactured from

A

products of photosynthesis in source cells

39
Q

what is the route taken through the cytoplasm of the companion cells called

A

symplast

40
Q

describe the apoplast route

A

along and through cell walls

41
Q

sucrose is contransported with what into sieve cells by active transport

A

hydrogen ions
from a high proton concentration to a low proton concentration

42
Q

what happens to water potential in the sieve tubes when sucrose id transported in

A

has a lower water potential than the neighbouring xylem

43
Q

what happens to sucrose in the sink cell

A

used for respiration or converted to starch

44
Q

how does sucrose move into the sink cell from the sieve tube

A

via companion cell by active transport

45
Q

how does mass flow occur

A
  • sucrose
  • region of high hysdrostatic pressure
  • to a region of low hysdrostatic pressure
  • down a hydrostatic pressure gradient
46
Q

evidence supporting mass flow theory

A
  • pressure in sieve tube- sap released when cut
  • concentration of sucrose is higher in leaves than roots
47
Q

evidence questioning mass flow theory

A
  • not all solutes move at same speed- should do if mass transport
  • sucrose delivered at same rate to all regions- should vary
48
Q

what is sometimes observed after ringing a plant

A

a bulge above the ring

49
Q

why is CO2 containing the isotope 14C used in tracer experiments

A

incorporated into sucrose in photosynthesis as it can be traced using x ray film

50
Q

is sucrose transported in xylem or phloem

A

phloem

51
Q
A

Mass Transport (pack 8) (2 decks)

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