2.3b adaptations for transport in plants

Question 1

what is the role of the xylem in the vascular bundle?

Answer 1

responsible for transport of water and mineral ions as well as providing support

Question 2

what is the role of the phloem in the vascular bundle?

Answer 2

responsible for translocation of organic solutes eg sucrose and amino acids

Question 3

describe the arrangement of the vascular bundle in the roots.
what is the purpose of this?

Answer 3

xylem arranged centrally into star shape w/phloem outside it
helps anchor plant into soil, resisting pulling forces

Question 4

from outside in list what comprises the vascular bundle in the roots

Answer 4

root hair
epidermis
cortex
endodermis
pericycle
phloem
xylem

Question 5

describe the arrangement of the vascular bundle in the stem.
what is its purpose?

Answer 5

arranged towards periphery in a ring
provides flexible support to resist bending

Question 6

list from the outside in all that comprises the stem

Answer 6

epidermis
colenchyma
cortex
fibres of phloem and xylem
medulla

Question 7

describe the arrangement of the vascular bundle in the leaf.
what is its purpose?

Answer 7

arranged in the midrib giving both resistance to tearing and flexibility

Question 8

list from the outside in all that comprises the leaf

Answer 8

adaxial surface (upper surface)
collenchyma
vascular bundle in leaf vein
compacted parenchyma
phloem and xylem
abaxial surface (facing away from central axis of plant)

Question 9

what are the main cell types in the xylem?

Answer 9

vessels and tracheids

Question 10

describe how the vessel is made in the xylem and its characteristics

Answer 10

only occurs in angiosperms, as lignin builds up in cell walls, contents die leaving empty space - lumen, end walls break down making a long hollow tube (drainpipe like)
characteristic lignin pattern is a spiral, unlike cellulose of phloem cell walls
stains red so xylem easily identifiable

Question 11

where are tracheids found?

Answer 11

occurs in ferns, conifers and angiosperms but not mosses as mosses have no water-conducting tissue therefore poorer at transporting water and can’t grow as tall

Question 12

describe the structure of tracheid cell walls

Answer 12

contain lignin which is hard, strong and waterproof
tracheids are spindle shaped so water travels in a twisting, rather than straight, path up the plant

Question 13

what are the two functions of the xylem?

Answer 13

1. transports water and dissolved minerals
2. providing mechanical strength and support

Question 14

what is the more efficient movement of water up a plant?

Answer 14

straight rather than twisting path through tracheids

Question 15

where is the region of greatest water uptake?

Answer 15

root hair zone, where SA is increased by the presence of root hairs and water uptake enhanced by their thin cell walls

Question 16

how does water move into the root hair cells?

Answer 16

by osmosis down water potential as soil has dilute solution of minerals and high water potential while vacuole and cytoplasm of root hair cell have conc solution of solutes and lower more negative water potential

Question 17

what are the three movements of water through the root?

Answer 17

1. apoplast pathway
2. symplast pathway
3. vacuolar pathway

Question 18

describe the water movement through the apoplast pathway

Answer 18

water moves in cell walls, cellulose fibres are separated by spaces through which water moves

Question 19

describe the movement through the symplast pathway

Answer 19

water moves through cytoplasm and plasmodesmata

Question 20

describe the movement through the vacuolar pathway

Answer 20

water moves from vacuole to vacuole

Question 21

where is there a water potential, why?

Answer 21

water potential across root cortex, highest in root hair cells and lowest in the xylem so water moves down conc gradient across root

Question 22

what is the endodermis?

Answer 22

single layer of cells around pericycle and vascular tissue of root

Question 23

what does each cell have?

Answer 23

each cell has an impermeable waterproof, suberin, barrier in cell wall

Question 24

how can water pass into xylem?

Answer 24

only from symplast or vacuolar pathway

Question 25

what is the casparian strip? and what does it do

Answer 25

impermeable suberin in cell walls of endodermal cells, blocking movement of water in apoplast so moves into cytoplasm

Question 26

what are the two explanations for the movement of water from root endodermis into xylem across cell membranes?

Answer 26

increase in hydrostatic pressure in root endodermal cells decrease of water potential in xylem

Question 27

how does the increase in hydrostatic pressure in root endodermal cells move water from root into xylem?

Answer 27

pushes water into xylem hydrostatic pressure is increased by AT of ions into endodermal cells which decrease water potential, drawing in more water by osmosis diversion of water into endodermal cells by apoplast pathway by Casparian Strip

Question 28

how does a decrease in water potential move water into the xylem?

Answer 28

decrease in water potentials below endodermal cells draws water in by osmosis across endodermal cell membranes water potential decreases by water being diverted into endodermal cells by CS AT of mineral salts from endodermis and pericycle

Question 29

how are minerals taken up?

Answer 29

absorbed into cytoplasm by AT against conc grad as minerals present in v low conditions in soil water they mover across apoplast pathway in solution and when reach endodermis, the CS prevents further movement of ions enter cytoplasm by AT and tissue or are AT into xylem

Question 30

describe the movement of water from roots to leaves

Answer 30

water always moves down conc grad, air has v low water potential and soil water has v high water potential so water moves from soil, through plant into air

Question 31

what are the 3 mechanisms of movement of water from roots to leaves?

Answer 31

1. cohesion-tension 2. capillarity 3. root pressure

Question 32

describe the mechanism of cohesion-tension theory.

Answer 32

water movement up in xylem by combination of adhesion of water molecules and tension in water column resulting from their cohesion as water molecules leave the xylem cells in leaf (transpiration) they pull up other water molecules behind them in the xylem, water molecules move together bc they show cohesion

Question 33

how does adhesion contributes to water movement up the xylem?

Answer 33

charges on water molecules also cause attraction to hydrophobic lining of vessels

Question 34

describe the capillarity theory

Answer 34

movement of water up narrow tubes (xylem) by capillary action cohesion between water molecules generates surface tension and this, combined w/adhesion, draws water up but only over a short distance

Question 35

describe the root pressure theory

Answer 35

over short distance is consequence of movement of water from the endodermal cells into xylem, pushing water already there further up caused by osmatic movement of water down water potential gradient, across root and into base of xylem

Question 36

what is transpiration?

Answer 36

the evaporation of water vapour from leaves and other above ground parts of the plant out through stomata and into atmosphere

Question 37

what happens if plants don't balance water uptake?

Answer 37

if they lose more than they absorb, leaves wilt if excessive volume of water lost, plants cannot regain turgor after wilting and dies

Question 38

what are the harmful aspects of transpiration? useful?

Answer 38

water loss water uptake, water distribution, ion distribution, evaporative cooling

Question 39

what factors affect rate of transpiration?

Answer 39

genetic factors - controlling number and distribution and size of stomata environmental factors - temperature, humidity and air movement, light intensity

Question 40

how does temperature affect transpiration rate?

Answer 40

as temperature increases, water potential of atmosphere decreases as it increases the KE of water molecules increasing their rate of evaporation from walls of mesophyll cells

Question 41

how does humidity affect transpiration rate?

Answer 41

air inside leaf is saturated with water vapour, so relative humidity is 100% water potential gradient between leaf and atmosphere and when stomata open, water vapour diffuses out of leaf down gradient the transpiration in air still results in accumulation of a layer of saturated air at the surface of leaves, water vapour gradually diffuses away leving concentric rings of decreasing humidity the further from the leaf you go.

Question 42

how does air speed surrounding affect transpiration rate?

Answer 42

movement of air bows away layer of humid air at the leaf surface the faster the air is moving the faster the concentric cells of water vapour get blown away the faster transpiration occurs

Question 43

how does light intensity affect transpiration rate?

Answer 43

stomata opens wider as light intensity increases, increasing rate of transpiration and therefore stomata tend to open widest in the middle of the day

Question 44

how do you measure rates of transpiration using a potometer?

Answer 44

measures rate of water uptake in a shoot, but since most water taken up by leafy shoot is lost through transpiration, rate of uptake is almost the same as rate of transpiration

Question 45

what happens if cells are turgid?

Answer 45

rate of uptake is equal to rate of transpiration, less small volumes lost through cuticle and used in metabolic activity.

Question 46

what is a mesophyte?

Answer 46

plants that have evolved in conditions of adequate water supply, neither wet not dry environments

Question 47

what happens if a mesophyte looses too much water, explain.

Answer 47

it wilts and leaves droop bc stomata close to reduce water loss and leaf surface area available for absorbing light is reduced so photosynthesis becomes less efficient

Question 48

how is the loss of excess water prevented in mesophytes? give some examples of mesophytes

Answer 48

stomata generally close at night when dark maize, potato, tomato

Question 49

what are the adaptations of mesophytes for their environments?

Answer 49

- broad flat leaves and green which can be easily shed before winter so they don't loose water by transpiration when liquid water may be scarce - extensive fibrous root system to absorb water - many aerial parts of non-woody plants die off in winter so they're not exposed to fast or cold winds - most annual mesophytes winter as dormant seeds with such a low metabolic rate that almost no water is required.

Question 50

what is the definition of a xerophyte?

Answer 50

plants that have adapted to environments with little liquid water available

Question 51

give some examples of xeorphytes

Answer 51

marram grass, cacti

Question 52

what are the adaptations of xerophytes their environments?

Answer 52

rolled leaves sunken stomata hairs thick cuticle sclerenchyma fibres

Question 53

describe the adaptation of xerophytes of rolled leaves

Answer 53

large thin-wlled epidermal cells called hinge cells, at the bases of grooves become plasmolysed when they loose water from excessive transpiration and the leaf rolls with its adaxial surface inwards, this reduces the leaf area exposed to air, and so reduces transpiration

Question 54

describe the adaptation of xerophytes of sunken stomata

Answer 54

stomata are in pits or depressions and humid air is trapped in the pit, outside the stomata, this reduces water potential gradient between inside of leaf and outside and so reduces rate of diffusion of water out through stomata

Question 55

describe the adaptation of xerophytes of hairs

Answer 55

stiff, interlocking hairs trap water vapour and reduce water potential gradient between inside of leaf and outside

Question 56

describe the adaptation of xerophytes of thick cuticle

Answer 56

wax is waterproof and so reduces water loss, the thicker the cuticle, the lower the rate of transpiration through cuticle

Question 57

describe the adaptation of xerophytes of sclerennchyma fibres

Answer 57

stiff fibres so lead shape maintained even when cells become flaccid

Question 58

define hydrophytes give three examples

Answer 58

plants adapted to living in an aquatic environment water lily, water lettuce, pond weed

Question 59

what are the adaptations in hydrophytes?

Answer 59

water supportive so have little lignified support tissue surrounded by water so little need for transport tissue so xylem poorly developed leaves have little/no cuticle bc no need to reduce water loss stomata on upper surface of floating leaves bc lower surface in water stems and leaves have large air spaces down to root frming reveroir of O2 + CO2, providing buoyancy

Question 60

what is translocation?

Answer 60

the transport of soluble products of photosynthesis eg sucrose and amino acids, through the phloem from sources to sinks

Question 61

what happens after the translocation to 'sinks'?

Answer 61

then used for growth or storage

Question 62

what direction does xylem transport? what does it transport?

Answer 62

up and down water and dissolved minerals

Question 63

what direction does phloem transport? what does it transport?

Answer 63

sideways to wherever products of photosynthesis are needed

Question 64

what is the phloem and what cells is made up of?

Answer 64

living tissue consisting of several types of cells, eg sieve tubes and companion cells

Question 65

what are sieve tubes?

Answer 65

only components of phloem obviously adapted for flow of material

Question 66

what are the elements of sieve tubes?

Answer 66

component of phloem, lacking nucleus but with cellulose cell walls perforated by sieve plates, through which products of photosynthesis are conducted up, down, or sideways

Question 67

why do sieve tubes loose nucleus and most of their organelles?

Answer 67

allows space for transporting materials

Question 68

how is metabolism controlled?

Answer 68

by companion cells, they're biochemically active, indicated by a large nucleus, dense cytoplasm containing much rough endoplasmic reticulum and many mitochondria

Question 69

how are companion cells connected to sieve tubes?

Answer 69

by plasmodesmata

Question 70

what are the experimental techniques that shows organic subtsances that are translocated through the phloem

Answer 70

ringing experiments radioactive tracers and autoradiography aphid experiments aphids and radioactive tracers

Question 71

what are ringing experiments? what is the evidence in ringing experiments?

Answer 71

cylinders of outer bark tissue were removed from all the way around a woody stem, in a ring, removing the phloem. after leaving the plant for some it, white it photosynthesised, the phloem contents above and below the ring were analysed evidence: above the ring there was a lot of sucrose, translocated in the phloem, below ring, no sucrose, suggesting it had been used by plant tissues but not replaced bc ring prevented from being moved downwards

Question 72

what are radioactive tracers and autoradiography? what is the evidence?

Answer 72

plant photosynthesises in presence of radioactive isotopes, eg 14C in 14CO2, stem section is placed on photographic film which is fogged, if there is radioation source, producing an autoradiograph. position of fogging and therefore radioactivity coincides with position of phloem, indiciating that it is phloem that translocates the sucrose in photosynthesis

Question 73

what are aphid experiments? what is the evidence?

Answer 73

stylet inserted into sieve tube and phloem contents, sap, exude under pressure into aphid's stylet aphid is anaesthetised and removed, stylet remained embedded in phloem, as sap in phloem under pressure, it seeps out of stylet and is collected and analysis shows presence of sucrose

Question 74

what is the mass flow hypothesis?

Answer 74

suggests there is a pssive mass flow of sugars from the phloem of leaf where there is highest conc to other areas sch as growing tissues, where there is lower conc (sink)

Question 75

describe how the mass flow model works in the whole plant

Answer 75

source cell, eg mesophyll cell of leaf where sucrose is formed has high hydrostatic press bc dissolved sucrose reduces water potential and draws in water by osmosis sugar loads into sieve tube elements sugar flows long sieve tube elements from high to low hydrostatic press to the sink cell, eg starch storage cell water uptake in root hair causes low hydrostatic pressure bc sucrose is converted into insoluble starch so water pot is higher so water lost by osmosis transpiration stream moves up xylem back into source cell, some water lost of evaporation

Question 76

is the mass flow theory a passive process? what must you take into account?

Answer 76

yes translocation in phloem is ab 10000times faster than if subtsances moved via diffusion phloem translocates solutes to tops of trees, but echanism descrived does not allow enough pressure to be developed to transfer material that high phloem has high O2 consumption and translocation slowed at low temps or if respiratory poisons applied, suggests active process may be involved sucrose and amino acids move at diff rates in same tissue