3.2 Transport in plants Flashcards
1
Q
word equation for photosynthesis
A
carbon dioxide + water —–> glucose + oxygen
2
Q
how many transport systems do plants have
A
2
3
Q
what tissue are water and mineral ions transported in
A
xylem
4
Q
what tissues are photosynthates transported in
A
phloem
5
Q
what are the products of photosynthesis called
A
photosynthates
6
Q
what movement does the phloem use
A
bi-directional
7
Q
what direction is transport in the xylem
A
upwards
8
Q
where in the stem are vascular bundles
A
the periphery
9
Q
where in the root are vascular tissues
A
the centre
10
Q
explain the uptake of water and minerals ions by the root
A
minerals are actively transported from soil into root hair cells. This lowers the. water potential in the root hair cells and so water enters by osmosis
11
Q
why do waterlogged soils struggle with ion uptake
A
oxygen is required for aerobic respiration to provide ATP for active transport. oxygen can only enter aerated soil
12
Q
apoplast pathway
A
the pathway by which water and dissolved mineral ions move through the cell walls by cohesion and adhesion
13
Q
symplast pathway
A
the pathway by which water and dissolved mineral ions diffuse through the cytoplasm and plasmodesmata
14
Q
vacuolar pathway
A
water can move via the cytoplasm and vacuoles
15
Q
casparian strip
A
an impermeable barrier in the endodermis formed from Suberin which blocks the apolast pathway
16
Q
why does the plant need to control entry of mineral ions into the xylem
A
selective uptake of mineral ions into the xylem sets up a water potential gradient for water uptake by osmosis
17
Q
how does the plant ensure toxic ions cannot enter its cells
A
there are no carrier proteins specific to these ions on the membrane so these ions cannot enter by facilitated diffusion
18
Q
why do plants need to absorb nitrates from the soil
A
required for synthesis of amino acids, proteins, DNA, RNA, ATP, nucleotides, nitrogenous bases
19
Q
why is K+ required
A
for stomatal opening
20
Q
why is mg2+ required
A
constituent of chlorophyll
21
Q
why is PO43- required
A
synthesis of phospholipids and a constituent of ATP
22
Q
what are two adaptations of root hair cells
A
- large surface area for absorption of water and mineral ions
- large amount of mitochondria (ATP required for active transport of ions)
23
Q
transpiration
A
the evaporation of water from inside the leaves, through the stomata and into the atmosphere
24
Q
cohesion
A
water molecules attracted to each other by hydrogen bonds
25
adhesion
water molecules are attracted to the hydrophilic lining of the lignified xylem vessel walls
26
the cohesion-tension theory
water diffuses out of the stomata of the leaf by transpiration.
water molecules drawn up to replace those lost, and drawn across leaf and up the xylem.
cohesion and adhesion make this possible.
the upward movement creates tension on the xylem walls.
27
capillarity
the tendency of a liquid in a fine tube to rise or fall as a result of surface tension
28
what two other processes help water move up the xylem
capillarity
| root pressure
29
why is capillarity not useful in large trees
it will be opposed by the downward force of gravity
30
root pressure
hydrostatic pressure in the root due to active transport of ions (and water flowing by osmosis) which forces water upwards
31
what 4 factors affect rate of transpiration
temperature
wind
humidity
light intensity
32
what does a potometer measure
the uptake of water
33
why is the uptake in a potometer only and estimate of transpiration rate
the water is used as a reactant in photosynthesis and will be used to keep the cells turgid
34
how would you calculate the volume of water in the capillary tube of a potometer
Pi r2 h
h= distance moved by bubble
r= internal radius of capillary tube
35
how could you improve the reliability of a potometer experiment
repeat the experiment 3x to allow calculation of a mean result
36
how does temperature increase affect rate of transpiration
rise in temperature increases the kinetic energy of the water molecules, which increases the rate of evaporation and diffusion of water vapour.
The water potential of the atmosphere is also lower in higher temperatures which increases the water potential gradient.
37
how does wind speed affect the rate of transpiration
still air forms a layer of water vapour around the stomata (diffusion shell).
This reduces the water potential gradient between the inside and outside of the leaf.
Air movement blows away the diffusion shell and increases the rate of transpiration
38
how does increase humidity affect the rate of transpiration
when there is more water vapour in the atmosphere the water potential gradient between inside and outside of leaf decreases.
39
how does light intensity affect the rate of transpiration
light causes the stomata to open to allows gas exchange for photosynthesis
40
what 4 different cells is the xylem tissue composed of
vessels
tracheas
fibres
xylem parenchyma
41
xylem vessels
a continuous column of dead cells arranged end to end with completely dissolved cross walls.
their walls are thickened with lignin which stops them collapsing under pressure
42
tracheids
similar to vessels but more elongated and with tapering ends.
their cell walls are also thickened with lignin
43
why is it important that vessel walls are impermeable to water and solutes
so water keeps moving upwards to the leaves in one unbroken stream
44
lignin is hydrophilic. why is this important for xylem function
water molecules are attracted to the lignified walls of the xylem, so adhesion can take place
45
what are pits function
allow movement of water between adjacent vessels.
| in tracheids they are involved in movement of water to nearby living tissue
46
function of the phloem
transports sucrose and amino acids
47
what 4 types of cells is the phloem made up of
sieve tubes
companion cells
phloem fibres
phloem parenchyma
48
what direction does the phloem transport
bi-directional
49
sieve tube
transport sucrose and amino acids (photosynthates) up and down the plant stem
50
companion cells
connect to sieve tubes vie plasmodesmata.
| They supply the sieve tubes with ATP
51
phloem fibres
for support
52
are phloem cells dead of alive
alive
53
sieve plates
allow cytoplasm to run from cell to cell
54
what are 3 ways that sieve tubes are adapted to their function
very few organelles - more space to transport solutes.
have companion cells - with organelles that supply ATP
end walls perforated (sieve plates) - allow passage of dissolved solutes
55
translocation
the transport of soluble organic materials produced by photosynthesis (e.g. sucrose and amino acids) in the phloem
56
what kind of movement is translocation
bi- directional
57
source
the region where photosynthates are produced and exported
58
sink
the region where photosynthates are stored or used for growth
59
source examples
leaf
60
sink examples
roots, shoot tips, flower, fruits, seeds
61
ringing experiment
ring of bark removed from tree, removes the phloem
62
what is seen in the ringing experiment
bulge seen above where ring removed. Accumulated phloem sap cannot move any further down
63
what does the ringing experiment result show
that the phloem is responsible for the transport of sucrose/ amino acids up and down the plant. Transport downwards was prevented by the removal of the ring, so the photosynthates accumulated above it.
64
explain the aphid experiment
small insects use stylets to collect phloem sap. aphid anaesthetised with CO2 and the stylet is cut off to collect pure phloem sap for analysis.
65
why is the aphid experiment more accurate than collecting sap with a needle
aphids enzymes ensure the stylet doesn't get blocked
66
mass flow
passive flow of sugars from areas of high concentration in the leaf (source) to areas of low concentration (sink) down a pressure gradient
67
describe how the mass flow hypothesis works
1. sucrose actively transported into the sieve tubes, lowering the water potential in the phloem
2. water potential in the xylem is higher so water enters the sieve tubes along a water potential gradient by osmosis.
3. pressure in sieve tubes increases and sucrose moves down the pressure gradient towards the sink.
4. sucrose actively transported into sink cells
5. water potential is now higher in the phloem so water moves by osmosis back into the xylem.
68
mesophyte
plants that grow in temperate regions
69
hydrophyte
plants adapted to grow either fully or partially submerged in water
70
xerophyte
plants adapted to grow in very dry environments
71
what are some arguments against the mass flow hypothesis
1. no explanation of sieve plates which seem to act as barriers, hindering flow
2. sucrose and amino acids have been observed moving at different rates and in different directions
3. companion cells are found all the way along the sieve tubes, if companion cells purely load and unload photosynthates they would not be needed anywhere else other than sources and sinks
72
what are some alternative theories of mass flow
1. streaming in the cytoplasm of sieve tubes could be responsible for bi-directional movements
2. protein filaments have been observed passing through the sieve pores, suggesting different solutes are transported by different filaments
73
how are mesophytes adapted to their environment
1. deciduous trees shed leaves In autumn to survive unfavourable conditions in winter, new leaves grow in spring
2. bulbs are produced by non-woody plants to survive underground over winter
3. annual plants produce seeds and die in the same year, seeds survive winter frost and germinate the next spring when conditions are more favourable
74
5 ways hydrophytes are adapated to their environment
1. stomata on upper epidermis, allow gas exchange with the air above
2. large air spaces, provide buoyancy for the leaves and acts as a reservoir of O2 and CO2
3. thin/ no waxy cuticle, no need to reduce water loss as they live in or on water
4. poorly developed xylem tissue, no need to transport large quantities of water as plant is aquatic
5. little lignin, water is a supportive medium and so little lignin is required to support xylem tissue
75
5 adaptations of xerophytes to their environment
1. reduced leaf size, reduces surface area from which transpiration can occur
2. rolled leaves, stomata are less exposed. Water vapour also trapped so water potential gradient decreases so less water lost through transpiration
3. thick cuticle, reduces water loss from the epidermis
4. sunken stomata in pits, water vapour trapped in pits. This decreases water potential gradient and less water lost through transpiration
5. hairs on leaf, water vapour trapped between hair. This decreases water potential gradient so less water lost through transpiration
