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transport in plants Flashcards

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1
Q

what substances do plants need to transport over long distances?
why?

A

water and minerals from roots to leaves for turgor, p/s, cooling, and nutrients
sucrose and amino acids from source to sink
diffusion is not sufficient bc distances too long

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2
Q

what substances do plants need to transport over short distances?

A

O2 and CO2
can rely on diffusion alone bc leaves are thin so short diffusion distance and plants have a lower metabolic rate than animals so lower demand for O2 (not v active). in general, leaves and roots are adapted for gas exchange

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3
Q

what are the 4 types of cells in xylem tissue

A

xylem vessels
xylem tracheids
fibres
parenchyma

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4
Q

are the 4 types of cells in xylem tissue dead or living?

A

all dead (xylem vessels, xylem tracheids, fibres) except parenchyma, which is living

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5
Q

xylem vessels structure and function

A

long, tubular structures formed by water conducting cells end to end, who’s transverse cell wall has broken down to form a continuous tube
transport water and minerals from roots to leaves
thick walls have lignin so have structural support function (impermeable to water and solutes)
mature xylem vessels are dead and the protoplasm has disintegrated leaving hollow tubes

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6
Q

xylem tracheids structure and function

A

water conducting cells
transport water and minerals from roots to leaves
have lignin so have structural support function

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7
Q

fibres in xylem structure and function

A

elongated cells
lignified
support function only

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8
Q

parenchyma structure and function

A

packing tissue
support function only

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9
Q

xylem vessels vs xylem tracheids differences

A

vessels are shorter and wider, tracheids are longer and thinner
vessels are continuous tubes with no end walls, tracheids have tapered ends with perforations in end walls
vessels are more efficient at water conduction, tracheids are less efficient at water conduction (used for water storage)

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10
Q

xylem vessels and xylem tracheids similarities in structure

A

both dead
both have pits
both water conducting cells
both have lignin

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11
Q

functions of xylem

A

transport water and minerals
provide mechanical support (lignification of cellulose cell wall)

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12
Q

why is the lumen of xylem vessels hollow

A

less/no resistance to flow of water

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13
Q

why are xylem vessels fairly narrow

A

the column of water doesn’t break easily

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14
Q

why are the walls of xylem vessels lignified

A

lignin adds strength and rigidity so prevents collapse under the large tension/negative pressure/transpiration pull
lignin is waterproof so impermeable to water so that it doesn’t leak out of the xylem

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15
Q

what part of a xylem vessel doesn’t contain lignin

A

pits

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16
Q

why don’t pits in xylem vessels contain lignin

A

allow lateral flow of water between xylem vessels
allows water to leave xylem or bypass blockage

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17
Q

types of lignified cell wall thickenings

A

spiral
annular
reticulate
pitted

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18
Q

why is lignin arranged in spirals around the lumen of the xylem

A

more flexibility
prevents stem breakage during growth/movement

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19
Q

components of phloem

A

sieve tube elements
companion cells

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20
Q

components of companion cells in phloem

A

small vacuoles
Golgi
cellulose cell wall
lots of ribosomes
large nucleus
RER
plasmodesma
mitochondria

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21
Q

function of plasmodesmata in companion cells of phloem

A

connect companion cells and sieve tube elements
facilitate movement of substances between the cells e.g. sucrose
enables cell signalling

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22
Q

why do companion cells have many mitochondria

A

because they are very metabolically active

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23
Q

companion cells brief function

A

service and maintain sieve tube element

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24
Q

components of sieve tube element

A

few small mitochondria
endoplasmic reticulum
amyloplasts (starch grains)
cytoplasm
sieve plate with sieve pores
NO NUCELUS RIBOSOMES GOLGI OR VACUOLE

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25
Q

location of cytoplasm in sieve tube element
why

A

pushed up to the sides so there is only a thin peripheral layer
less resistance to flow of assimilates (sucrose and amino acids)

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26
Q

why do sieve tube elements not have a nucleus, ribosomes, Golgi or vacuole

A

would take up too much space and impede the flow

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27
Q

function of sieve plate

A

may be to help keep STE open
allows for blocking with callose as a defence mechanism

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28
Q

sieve pores function

A

sap can easily pass from cell to cell (STE to STE)

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29
Q

parenchyma cells in phloem function

A

support and storage
act as packing tissue
(living cells)

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30
Q

evidence that transport of organic material occurs in the phloem?

A

removal of all the tissues external to the xylem: when the phloem is cut away the sieve elements respond by rapidly blocking the sieve pores and sucrose accumulates above the ring of bark cut away
aphids can be used to collect sap from plants. if the aphid is cut away, the exuding sap is collected in a capillary tube. when the stem is sectioned, the send of the aphids stylet is found in the phloem

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31
Q

features which distinguish sieve tubes from xylem vessels

A

sieve plates
no pits
xylem vessels are hollow
xylem vessels have lignin

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32
Q

components in TS section through leaf

A

waxy cuticle
upper epidermis
palisade mesophyll
spongy mesophyll
lateral vein
xylem (above)
phloem (below)
vascular bundle/midrib
air spaces
lower epidermis

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33
Q

function of waxy cuticle

A

waterproof to prevent water loss/ fungal disease

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34
Q

lower epidermis function

A

has stomata/guard cells for gas exchange

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35
Q

upper epidermis function

A

transparent to allow light to pass through

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36
Q

air spaces in leaf function

A

maintain concentration gradient

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37
Q

label diagram

A

A- from outside to inside: cuticle, epidermis, collenchyma
B-pith of parenchyma
C-sclerenchyma tissues (bundle cap)
D-phloem
E-xylem
LINE=CAMBIUM

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38
Q

function of collenchyma in stem

A

provides some support

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39
Q

function of cortex of parenchyma in stem

A

storage and supporting function

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40
Q

function of pith of parenchyma in stem

A

storage and supporting

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41
Q

function of sclerenchyma tissue in stem

A

support

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42
Q

label diagram

A

A-endodermis
B-conjunctive tissue
C/D/F- xylem
E-phloem
pericycle inside endodermis
cortex outside endodermis

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43
Q

meristem definition

A

area of undifferentiated cells which can divide and differentiate into other cell types

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44
Q

where is meristem found

A

root and shoot tips
in cambium of vascular bundles
pericycle cells in root

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45
Q

features of meristematic cells

A

have thin cell walls containing little cellulose
do not have a vacuole
do not have chloroplasts

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46
Q

where are new cells formed in plants
what do some differentiate into

A

in cambium region by mitosis
xylem vessels or phloem sieve tubes/companion cells

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47
Q

how do cells differentiate into xylem vessels

A

lignin deposited in walls (cells die and lose cell contents)
end walls break down (xylem forms continuous column)

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48
Q

how do cells differentiate into sieve tube elements

A

lose most of their organelles and develop sieve plates

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49
Q

how do cells differentiate into companion cells

A

retain organelles
increase number of mitochondria

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50
Q

compare cell walls of xylem vessels and phloem sieve tubes

A

xylem: cellulose and lignin (impermeable)
phloem: cellulose, fully permeable, plasmodesmata

51
Q

compare cells of xylem vessels and phloem sieve tubes

A

xylem: stacked end to end, dead
phloem:stacked end to end, living

52
Q

compare end walls of xylem vessels and phloem sieve tubes

A

xylem: absent
phloem: present. sieve plates and sieve pores

53
Q

compare diameter of xylem vessels and phloem sieve tubes

A

xylem: larger
phloem: smaller

54
Q

compare cell contents of xylem vessels and phloem sieve tubes

A

xylem: no cell contents, hollow
phloem: peripheral cytoplasm, no nucleus, golgi, vacuole, ribosomes

55
Q

compare transported substances of xylem vessels and phloem sieve tubes

A

xylem:mineral ions and water
phloem: sucrose and amino acids (assimilates)

56
Q

compare loading and unloading of xylem vessels and phloem sieve tubes

A

xylem: water is absorbed in the roots and unloaded via pits into leaves
phloem: active loading at the source and passive unloading at the sink

57
Q

compare direction of transport in xylem vessels and phloem sieve tubes

A

xylem: upwards (single direction)
phloem: bidirectional

58
Q

compare method of transport in xylem vessels and phloem sieve tubes

A

xylem: mass flow (passive), driven by transpiration pull, cohesion and adhesion. active= root pressure
phloem: mass flow and active loading

59
Q

importance of water in plants

A

evaporative water loss cools plants bc high latent heat of vaporisation
mineral ions and photosynthetic products transported in aqueous solution
water is a raw material for photosynthesis
osmosis in plant cells results in turgor pressure, providing a hydrostatic skeleton to support stems and leaves
turgor drives cell expansion

60
Q

root hair cells: structure of hairs

A

large surface area
thin surface layer (just cell plasma membrane and cell wall) so short diffusion distance

61
Q

why do root hair cells contain many mitochondria

A

provide ATP for active transport of minerals

62
Q

root hair cells solute concentration

A

high bc maintains water potential gradient between soil water and the cell
cytoplasm and vacuole sap of root hair cell contain many diff solutes, lowering water potential so water moves in by osmosis
(soil water has a v low conc of dissolved minerals so v high water potential)

63
Q

2 pathways that water molecules take between cells in roots

A

apoplast pathway
symplast pathway

64
Q

apoplast pathway:
cells
movement method

A

cell walls and intercellular spaces
mass flow

65
Q

symplast pathway:
cells
movement method

A

cell membrane, cytoplasm, plasmodesmata
osmosis

66
Q

what is the endodermis

A

a layer of cells surrounding vascular tissue

67
Q

what is the Casparian strip

A

a band of waxy material called Suberin
runs around each of the endodermal cells, forming a waterproof layer

68
Q

what does the casparian strip do

A

prevents water moving across the root any further in the apoplast pathway, so it transfers to the symplast pathway, when it is forced into the cytoplasm

69
Q

diversion form apoplast to symplast pathway: what happens

A

significant diversion: water passes through a selectively permeable cell surface membrane, excluding toxic soil solutes from living tissue, as carrier proteins for toxins are lackign

70
Q

solute concentration in cytoplasm of endodermal cells vs xylem cells

A

dilute in cytoplasm compares to xylem cells so endodermal cells move mineral ions into the xylem by active transport

71
Q

what does AT of mineral ions into xylem cause

A

water potential of xylem cells is much lower than that of endodermal cells, so rate of water movement into xylem by osmosis down the water potential gradient increases from endodermis through symplast

72
Q

can water return to the apoplast pathway inside vascular bundle?

A

yes: to enter xylem and move up plant

73
Q

what results in root pressure?

A

active pumping. of minerals into xylem produces water movement by osmosis
(independent of transpiration effects)

74
Q

what does root pressure do?

A

gives water a push up the xylem, but isn’t a major factor in vertical movement

75
Q

why is the transpiration stream important

A

carries water for p/s to the palisade cells in the leaves
the water carries essential mineral salts in solution
evaporation from the leaves has a cooling effect

76
Q

what is transpiration a consequence of

A

gaseous exchange

77
Q

mechanism of stomata opening

A

stomata allow gaseous exchange: surrounded by guard cells (contain chloroplasts for p/s and to produce ATP)
ATP is used to drive AT ion pumps
to open guard cells pump ions into cell, lowering WP
water enters by osmosis, causing cells to become turgid and bend apart, thus opening the stoma

78
Q

3 processes involved in moving water up the stem

A

transpiration pull
capillary action
root pressure

79
Q

how does transpiration pull aid in moving water up the stem

A

air flow around leaf takes humid air away, maintaining a diffusion gradient
water evaporates & diffuses out of leaf mesophyll cells into air spaces, lowering WP in spongy mesophyll cells so water moves into them from xylem down WP gradient
as H2O leaves the whole column of water behind is pulled up due to cohesive forces
this is called transpiration pull/shoot tension/negative pressure

80
Q

how does capillary action aid movement water up stem

A

(COHESION TENSION THEORY)
columns of water in xylem are held together by cohesion (H2O molecules hydrogen bond with each other)
also adhesion (attraction between water molecules and sides of xylem)
collectively these forces are known as capillarity/capillary action
water is moving by mass flow

81
Q

evidence that water is carried in dead cells (xylem)

A

a tree trunk with a steam jacket still transpires (steam kills living cells but plant still transpires so water must be carried in dead cells: the xylem)
cut stem placed in picnic acid poison will still transpire: so transport is in dead cells

82
Q

evidence that water is carried in xylem

A

cut stem placed in dye & later sectioning reveals dye in the xylem
if plants allowed to draw up fatty substances then the lumen of the xylem vessels becomes blocked (suggests xylem can take up substances but not designed to transport fat)
ringing experiments which involved removing the phloem do not affect water transport: if xylem removed, plant would wilt bc no transport to leaves

83
Q

evidence for role of root pressure in water transport in xylem

A

plants poisoned with cyanide cannot respire so no ATP produced so no AT can take place so not root pressure. this is proven to affect transpiration
if oxygen level falls, root pressure falls
if temp increases then root pressure increases, and if decrease in temp then root pressure decreases (proves respiration reactions are important for supplying ATP for root pressure)

84
Q

evidence for cohesion tension theory

A

changes in tree diameter can be detected: it is smallest when rate of transp is greater (tension created narrows vessels, and lignin prevents vessel from collapsing under tension created)
at night, transp rates fall and tension is at lowest, so diameter increases
if air gets into xylem transpiration stops (column of water broken so no forces of cohesion)
coloured water will rise up narrow tube to a height greater than the level of the liquid it is stood in (capillarity evidence)

85
Q

how does number of leaves affect rate of transpiration

A

more stomata so faster rate

86
Q

how does number and position of stomata affect rate of transpiration

A

leaves with more stomata lose more water vapour than those w fewer
open stomata increase rate of transpiration
larger stomata means water vapour lost more quickly
more stomata on lower epidermis than upper decreases rate bc shaded

87
Q

how does the presence of a cuticle affect rate of transpiration

A

thicker layer= less water vapour lost (decreased rate)
young leaves and shade plants have thinner cuticles

88
Q

how does light intensity affect rate of transpiration

A

in light, stomata open up to allow gaseous exchange for p/s
higher light intensity increases rate of transp

89
Q

how does temperature affect rate of transpiration

A

higher temp increases rate of transpiration bc:
increased rate of evaporation from cell surfaces (water vapour potential in leaf increases)
increased rate of diffusion through stomata bc water molecules have more KE
lower relative water vapour potential in air so more rapid diffusion of molecules out of leaf (steeper conc grad)

90
Q
A
91
Q

how does relative humidity affect rate of transpiration

A

increased relative humidity in air decreases rate of water loss bc smaller water vapour potential gradient between the air spaces in the leaf and the air outside

92
Q

how does air movement/wind affect rate of transpiration

A

air moving outside the leaf will carry away water vapour that has just diffused out of the leaf
this maintains high water vapour potential gradient

93
Q

how does water availability affect rate of transpiration

A

if there is little water in the soil, plant cannot replace the water that is lost
if there is insufficient water in the soil, then the stomata will close and the leaves wilt (cells surrounding stomata lose turgidity)

94
Q

what does a photometer measure

A

the rate of uptake of water
assumed that this is equal to the water lost by transpiration

95
Q

why is rate of uptake of water not always equal to water lost by transpiration?

A

water issued in p/s and support (turgor pressure)
at night stomata are closed so decreased rate
some plants e.g. xerophytes have adaptations to decrease rate of transpiration

96
Q

examples of xerophytes

A

cacti
marram grass

97
Q

cacti adaptations to reduce water loss

A

thick waxy cuticle on epidermis reduces water loss by evap. some have waxy cuticle on upper and lower leaves
spines instead of leaves reduces SA for water loss. p/s occurs in stem
stomata closed at hottest times of day when transp rates would be highest
crassulacean acid metabolism (CAM) ensures CO2 taken in at night can be sued for p/s during day
succulents store water in stem/leaves
shallow, extensive root system or long tap root

98
Q

marram grass adaptations to reduce transpiration rate

A

curled/rolled leaves to minimise SA of moist tissue exposed to air & protects leaves from wind & funnels water to roots
stomata buried in pits, shattered from wind. layer of hairs on epidermis. both cause moist air to be trapped in pits, slowing transp by lowering WP gradient
thick waxy layer on epidermis reduces water loss by evap

99
Q

example of hydrophyte

A

waterlilies

100
Q

waterlilies adaptations

A

found in aquatic habitats so don’t need to reduce water loss, but need to cope with low O2
air spaces in tissues helps float, also O2 storage for respiration.
floating increases light received, whilst root/stem air spaces allow O2 movement from leaf to underwater parts
stomata only present on upper surface to maximise gas exchange
flexible leaves and stems, supported by water around them.
no need for rigid stem: this reduces damage by water currents

101
Q

why do waterlilies have reduced structure
why do they have more/larger air spaces

A

water provides support
makes stem and leave buoyant

102
Q

why do substances move from source to sink in translocation?

A

sugars are produced in the leaves during p/s. respiration in plants depends upon these products of p/s, which are frequently some distance away for those areas of the plant needing to release the chemical energy in these products.
at highest conc at source, lower at sink

103
Q

what is translocation

A

the movement of dissolved solutes like sucrose and amino acids to where they are needed in the plant.

104
Q

what are assimilates

A

dissolved substances that are transported and become incorporated into plant tissue

105
Q

what is the main transported assimilate
why is it not used up during transport?

A

sucrose
it is soluble and metabolically inactive, so not used up during transport

106
Q

examples of translocation sources

A

green leaves
stems
food stores in roots, seeds, tubers (begin unloading stores at beginning of growing period)

107
Q

main sinks in translocation

A

actively dividing meristems
parts laying down food stores e.g. developing seeds and fruits
metabolically active tissues e.g. those actively absorbing mineral ions in roots

108
Q

3 stages of translocation and are they active or passive

A

phloem loading (active)
pressure flow/ mass flow (passive: bulk movement due to a pressure gradient)
phloem unloading (passive: facilitated diffusion)

109
Q

what is active loading in translocation

A

AT is used to load sucrose against concentration gradient at the source

110
Q

stages of active loading in translocation

A

ATP hydrolysis supplies energy to pump H+ ions out of companion cell into leaf mesophyll cells
this sets up an electrochemical gradient for H+ ions
H+ ions and sucrose bind to co-transporter protein
both are co-transported by facilitated diffusion (secondary AT) into the companion cell
sucrose then diffuses via plasmodesmata into the sieve tube element at the source

111
Q

what is pressure flow in translocation?

A

mass flow: sucrose is moved from source to sink

112
Q

stages of pressure flow in translocation

A

sucrose conc has increased in the sieve tube element at the source
this decreases WP so water moves in down WP gradient by osmosis from xylem
hydrostatic pressure increases in sieve tube element near the source
assimilates move from high to low HP

113
Q

what is phloem unloading in translocation?

A

sucrose is unloaded at any point where it is needed (sink)

114
Q

stages of phloem unloading in translocation

A

sucrose moves into sink cells via facilitated diffusion (passive)
WP increases in sieve tube element near sink so water moves out of sieve tube element into xylem by osmosis
HP decreases at sink so gradient for mass flow is maintained
sucrose used by source cells to maintain concentration gradients e.g. converted to glucose and used in respiration

115
Q

evidence for translocation

A

cyanide poisons mitochondria, stopping translocation as active processes require energy as ATP from respiration, needed for translocation
sucrose flow 10,000x faster than diffusion alone, providing evidence for mass flow (can be proven using aphids to collect sap and measure rate)

116
Q

what do you call parts of the cellulose cell wall of a xylem vessel element where no lignin has been deposited

A

pits

117
Q

does water enter the cytoplasm through the cell surface membrane in the apoplast or symplast pathway?

A

symplast

118
Q

does water enter vacuoles in the apoplast or symplast pathway?

A

symplast

119
Q

does water move from cell to cell through plasmodesmata in the symplast or apoplast pathway?

A

symplast

120
Q

does water move from cell to cell through intercellular spaces in the apoplast or symplast pathway?

A

apoplast

121
Q

how does water move from the xylem in the root to the leaf (one word)

A

transpiration pull

122
Q

how does water move from mesophyll cell walls to intercellular air spaces (one word)

A

evaporation

123
Q

how does water vapour move from intercellular air spaces to the atmosphere outside the leaf (one word)

A

diffusion

124
Q
A

biology (27 decks)

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