3.3 plant transport Flashcards
(80 cards)
1
Q
why do multicellular plants need a transport system
A
- need water, sugar, mnierals to live and need to get rid of waste substances
- Low SA:V
- DISTANCE TOO LONG
- direct diffusion would be too slow to met their needs
- so need transport systems to move substances to and from individual cells quickly
2
Q
whatis transported in xylem adn how
A
water and soluble mineral ions UPWARDS
3
Q
whatis transported in phloem and how
A
assimilates (Eg sugars) UP AND DOWN
4
Q
Dicotyledonous plants
A
2 seed leaves
branching pattern of veins in the leaves
5
Q
vascular bundle
A
where the xylem and phloem are found together
- contains other type of tissue
6
Q
vascular bundle labelled in a root
A
outer layer of circle (endodermis)
x shaped star in the middle (xylem)
little triangles between the star arms (phloem)
other inner region (medulla)
7
Q
why is the phloem found within the arms of the xylem in the root
A
provides strength to withstand the puling forces to which roots are exposed
8
Q
meristem cells
A
- cells which retain their ability to divide
- inside the endodermis
called PERICYCLE
9
Q
Cambium
A
- in between xylem and phloem
- layer of meristem that divide to produce new xylem and phloem
10
Q
why dont plants need to transport o2 in their trnaport system
A
not very metabolically active
respiratiion rate low
low o2 demand met by simple diffusion
11
Q
ring of vascular bundle arrangement advantage
A
provides strength and flexibility to withstand the BENDING forces to whicih stems and branches are exposed
12
Q
xylem tissue consists of:
A
- vessels to carry the water and dissolved mineral ions
- fibres to help support the plant
- LIVING PARENCHYMA CELLS - packing tissue to separate and support the vessels
13
Q
lignin in xylem
A
- impregnates walls
- makes the walls waterproof and kills the cells
- continuous column of dead cells with no contents
PURPOSE: - strenghtens vessel walls and prevents vessel from collapsing
- keeps vessel open even at times where water is in short supply
14
Q
bordered pits
A
- incomplete lignification
- the bordered pits in 2 adjacent vessles are aligned to allow water to leave one vessel and pass into the next
- also allow water to leave xylem and pass into the living parts of the cell
15
Q
how does lignin look within
A
spiral of lignin
- important as allows the xylem to stretch while the plant grows
- and allows stem/branch to bend
16
Q
xylem adaptations(4)
A
- lignin in walls => waterproofs
- spiral of lignin => flexibility
- no end walls =>continuous column of water
- narrow tubes. water column doesnt break easily
- BORDERED PITS allow water to move sideways from one xylem cell to the next and out of the xylem to the living tissues
17
Q
in what form is sucrose trnasported
A
dissolved in water to form sap
18
Q
phloem tissue consits of…
A
SIEVE TUBES
- made of sieve tube elements and companion cells
19
Q
sieve tube elements
A
- no nucleus, little cytoplasm, allowing space for mass flow of sap to occur
- at the end of the sieve tube element are PERFORATED CROSS WALLS called sieve plats. perforations allow movement of sap from one element to the next
20
Q
sieve tubes in dissection
A
v thin
5/6 sided
21
Q
companion cells
A
- in between sieve tubes
- large nucleus+dense cytoplasm
- NUMEROUS mitochondria to produce ATP
- carry out metabolic processes needed to load assimilated actively into the sieve tubes
22
Q
plasmodesmata
A
gaps in the cell wall containing cytoplasm that connects 2 cells
23
Q
are cellulose cell walls water permeable
A
yes
24
Q
2 types of pathways taken by water through a plant
A
apoplast
symplast
25
apoplast pathway
- passes through INTERCELLULAR spaces
- doesnt pass through any plasma membranes
- MASS FLOW
- so dissolved mineral ions and salts can also be carried
26
drawing apoplast pathway
in between cracks of cell
27
symplast pathway
- enters through plasma membrane to the cell cytoplasm
- passes through plasmodesmata from one cell to the next
OSMOSIS
28
drawing synplast pathway
- through first cell wall
- through gaps in between the cells (plasmodesmata)
29
cytoplasm water potential
ALWAYS VERY NEGATIVE
- contains mineral ions and solutes which reduce water potential
30
turgid
- water has entered the cell by osmosis from a higher water potential to a lower water potential
- water exerts pressure on the cell wall (pressure potential). as it builds, it reduces the influx of water
31
plasmolysis
water leaves cell by osmosis from a higher water potential to a lower water potential
- plasma membrane pulls away from cell wall
32
what is transpiration
loss of water VAPOUR from the aieral parts of the plant, mainly the stomata in the leaves
33
why is most water vapour lost during the day
- stomata are open when there is light
- to allow gas exchange for photosynthesis
- water evaporates
34
transpiration pathway
- water enters the leaf through xylem. moves by osmosis into the cells of the spongy mesophyll. may also pass along cell walls via apoplast pathway
- water evaporates from cell walls of the spongy mesophyll
- water diffuses out of the leaf through the open stomata, due to the water vapour potential gradient
35
importance of transpiration (4)
- transports useful mineral ions up the plant
- maintains cell turgidity
- supplies water for growth, cell elongation, photosynthesis
- as water evaporates, cools the plant on a hot day
36
LI effect on transpiration
- stomata open for gaseous exchange for photosynthesis
- ↑ LI, ↑ photosynthesis
37
temperature effect on transpiration
1. increases rate of evaporation from cell surfaces so WVP in leaf rises (steeper conc grad)
2. increases rate of diffusion out through stomata bc water molecules have more kinetic energy
3. decrease WVP in air; more rapid diffusion of molecules out of leaf
OVERALL AS TEMP ↑ , TRANSPIRATION ↑
38
relative humidity of air effect on transpiration
- as humidity ↑ , transpiration ↓
- smaller WVP gradient between air inside leaf and air outside
39
air movement effect on transpiration
- as air movement ↑ , transpiration↑
- air movement outside leaf carries away water vapour that has just diffused out of the leaf
- maintains a steep WVP gradient
40
water availability effect on transpiration
- if there is LITTLE water avilability in the soil, the plant cant replace any water lost
- so stomata close, leaves wilt
41
what does a potometer ACTUALLY measure
- rate of water uptake by a leafy shoot
- assuming cells are turgid, and most water taken up is lost by transpiration, we can use it to estimate
42
name of tube in potometer
capillary tube
43
how to set up potometer for valid results:
1. set up potometer under water so no air in apparatus
2. cut shoot under water to make sure no air in xylem
3. healthy shoot
4. cut stem AT AN ANGLE to provide a large surface area in contact w water
5. dry the leaves
44
how to get a rate from a potometer
- distance moved by bubble
- πr2d/t
45
adhesion
attraction between water molecules and the walls of the xylem vessel
46
cohesion
attraction between water molecules caused by hydrogen bonds
47
where are root hair cells fuond
epidermis (outermost layer of cells)
48
movement of water ACROSS THE ROOT
- RHC actively transports mineral ions in from soil, decreasing its WP
- water enters root hair cell by osmosis
- water moves across cortex by apoplast + symplast
- UNTIL it reaches CASPARIAN STRIP at the endodermis, blocks apoplast and forces water to do symplast
- mineral ions are actively transported into xylem (plasma membrane carrier proteins), making WP more negative so water will osmosis into xylem
49
endodermis
evidence of energy used
layer of cells surrounding medulla and xylem
- STARCH SHEATH, contains granules of starch (shows that energy is being used)
50
casparian strip...
blocks apoplast pathway between root cortex and medulla
- ensures that water and dissolved mineral ions have to go through plasma membranes and into cytoplasm
- carrier proteins/channel proteins in the plasma membrane will then pump the ions into medulla and xylem
- decreases WP of medulla and xylem, so water will osmosis from root cortex cells into medula and xylem
- and once its there, water cant go back into the cortex, because the apoplast pathway is BLOCKED by the casparian strip
51
mechanism of movement of water up xylem
mass flow
52
transpiration pull (cohesion tension theory)
- transpiration occurs when water evaporates out of spongy mesophyll and diffuses out of stomata
- lowers water potential in the leaf, water moves by osmosis into mesophyll cells
- LOW HYDROSTATIC PRESSURE and thus tension at the top of the column
- water molecules H bond so are attracted to each other by cohesion, and H bond to the walls of the xylem so ADHESION
- water drawn up as one continuous column
53
what does the cohesion tension theory rely on
- the maintaining of an unbrokwn column of water all the way up the xylem. if the water column is broken in one xylem vessel, it can be maintained through another vessel via the bordered pits
54
capillary action
- adhesion of water molecules to the side of the xylem vessek, and cohesion of the water molecules to each other
- because the vessels are very narrow, the forces of attraction can pull water up the sides of the vessel
55
how does water leave the leaf
- water moves into leaf from xylem by osmosis into spongy mesophyll cells
- evaporates out of spongy mesophyll into air spaces
- diffuses out of stomata
- this lowers the WP in the cells, causing water to enter them by osmosis from neighboruing cells, so water is drawn from the xylem in the leaf by osmosis
56
hydrophyte
a plant adapted to living in water or very wet conditions
57
xerophyte
a plant adapted to living in dry conditions
58
general terrestrial plant adaptations
1. waxy cuticle on leaf → reduces water loss due to evaporation
2. stomata on the under surface of leaves → reduces evaporation due to direct heating by the sun
3. stomata closed at night, no light for photosynthesis
4. deciduous plants lose their leaves in winter when ground is frozen (no water) and temperatures too low for photosynthesis
59
xerophytic adaptations
- rolled leaves → air trapped inside → air becomes more humid, reducing water loss. rolls tighter the drier it is
- thick waxy cuticle on upper epidermis → reduce evaporation, prevent water loos
- stomata in PITS → trap moist air
- hairy leaves → trap moist air
- leaves reduced to spines → reduces SA for less transpiration
- roots very widesperead → take advatnage of any rainfall
60
hydrophyte issue
getting oxygen and keeping afloat
61
hydrophyte adaptations
1. large air spaces → buyoancy to keep them afloat so they can get sunlight
2. stomata on upper epidermis only → exposed to air to allow for gas exchange
3. thin or no waxy cuticle → water is not a limiting factor so would be a. waste of resources
62
source
actively loads assimilates into the phloem
63
sink
part of the plant where the assimilates are removed from the transport system [phloem]
64
GENERALL, who is the source and hwo is the sink
source = leaves
sink = roots
65
examples of assimilates moves in the phloem
sucrose + amino acids
66
active loading
- companion cells use ATP to actively transport H+ ions out of cell
- increases [h+] outside, and reduces inside, creating a concentration gradient
- COTRANSPORT: h+ ions facilitated diffuse back into the companion cells using cotransport proteins in plasma membrane, with sucrose molecules
- now, [sucrose] in companion cell increases, CG created, so can diffuse through plasmodesmata into sieve tube
67
how does sucrose move along the phloem
MASS FLOW OF SAP
68
how does the mass flow of sap along the phloem work
- after the sucrose is actively loaded into sieve tube element, WP decreases. so water moves in by osmosis at the source, increasing hydrostatic pressure
- the sap moves down the sieve tube from a HIGHER hydrostatic pressure to a lower hydrostatic pressure at the sink
69
why are the leaves a source
- sugars made during photosynthesis are converted to sucrose and loaded into the phloem sieve tubes
HAPPENS WHEN THE LEAVESA RE GREEN
70
what happens to the sucrose transported in the phloem
- used for respiration and growth in meristem
- or starch for storage in a root
- DIFFUSES OUT OF THE SIEVE TUBE VIA PLASMODESMATA/ACTIVE TRANSPORT
71
after mass flow of sap across phloem, when its removes
- diffuses out of plasmodesmata to meristem or active transport
- increases the water potential inside the phloem
- water moves out of phloem by osmosis, reducing the hydrostatic pressur
72
upper epidermis adaptation
- transparent
- allows light to pass through for photosynthesis in the undelrying cells
73
do guard cells photosynthesise
yes
- have chloroplasts
74
2 mark practical to observe xylem
- add dye
- cut TRANSVERSE and microscope on low power
75
underwater plants have .... lignin
LESS
- flexible leaves and stems to prevent damage by water currents
- water keeps it buoyant and supportted
76
guard cell adaptation
- uneven thickness of cell wall
- able to change shape
- transport proteins in pm
- lots of mitochondria
77
why is sucrose good, and why better than glucose
- soluble
- less REACTIVE
78
2 routes of sucrose going from photosynthesising cells to the companion cells
1. apoplast
2. symplast
79
when using potometer considerations:
- bubble doesnt go too far, or could enter xylem and break continuous column
- place open end in water so no air introduced
- keep shoot still to avoid breaking water column
80
what do sieve tubes lack
- nucleus
- and very little cytoplasm
