9.1 transport in the xylem of plants

Question 1

almost all plants are …. p- a-

Answer 1

photosynthetic autotrophs

Question 2

What 2 types of transport tissue do vascular plants have

Answer 2

xylem and phloem

Question 3

what is transpiration?

Answer 3

the loss of water vapour thru leaves, stems, and other (above ground) parts of plant

Question 4

transpiration is the consequence of…

Answer 4

gas exchange in the leaf

Question 5

where does transpiration occur through

Answer 5

mainly through open stomata

Question 6

how is transpirtation connected to photosynthesis

Answer 6

A tension is created in the plant due to transpiration and this acts as a driving force for the uptake of water from the soil and the movement of water to the shoots.
water required by photosynthesis

Question 7

adaptations of leaves for gas exchange (2)

Answer 7

1. stomata
   tiny pores, opening and closing controlled by 2 guard cells
2. lower tissue layer (spongy mesophyll)
   provides large surface area and moist surface neccesary for gas exchange

Question 8

describe the exchange of gases in the leaf leading to transpiration 4

Answer 8

1. co2 conc drops = co2 from air spaces dissolve, diffuse into cells
2. air conc drops = net movement of co2 molecules into leaf thru stomata
3. O2 diffuses out leaf cells into int. air spaces (then into atmos thru stomata)
4. transpiration: water vapour diffuses out of leaf into atmos

Question 9

function of xylem vessels

Answer 9

transports water and dissolved minerals
- from roots to all parts of plant

Question 10

structure of xylem vessels (that allow transport under tension) 3

Answer 10

• long continuous tubules (from roots thru stems)
• hollow: dead at maturity, cell mem. + int. structures + horizontal cell walls break down
• walls strengthened with lignin (binds with cellulose – provides great strength and rigidity)

Question 11

what to note when drawing structure of pri xylem vessels

Answer 11

1. continuous tubule
2. xylem wall should have gaps (pits) – enable exchange of water molc
3. lignin represented via spiral/rings

Question 12

cohesive property of water 2 factors, briefly

Answer 12

1. cohesion
   - water molc form weak hydrogen bonds
2. adhesion
   - polarity of water (interacts with hydrophillic cellulose in cell walls)

Question 13

cohesive property of water: cohesion

Answer 13

water molecules form weak hydrogen bonds (bc of polarity)
= transpirational pull can extend thru long columns of water

Question 14

cohesive property of water: adhesion

Answer 14

polarity interacts with hydrophilic cellulose in cell walls = create pull to draw water out xylem into cells

Question 15

transpirational pull 4 steps `

Answer 15

1. cellulose in mesophyll (leaf) cell walls is hydrophilic – water adheres = film of water on cell surface
2. water vapour diffuses out stomata = internal air spaces less humid = water evaps from moist mesophyll cell walls into air spaces
3. when evaporates = pulling force on water molecules within cell (cohesion)
4. tension caused by pull of evap – draws water from xylem into leaf cells

Question 16

adaptations of root hairs for mineral ion uptake (2, related to energy demands)

Answer 16

active uptake = high demand for atp
- plasma membrane of root hairs – many protein pumps –> AT of mineral ions from water into cytoplasm of cell
- high rate of cellular respiration, many mitochondria, high o2 gas demand

Question 17

how does uptake of mineral ions cause absorption of water

Answer 17

high conc of mineral ions in cytoplasm = low water potential = osmosis of water in

Question 18

water potential of pure water

Answer 18

0.0MPa

Question 19

what are Xerophytes

Answer 19

plants that adapted to live in conditions where liquid water is hard to obtain (eg deserts)
- some have special tissues for water storage, some adapt to reduce water loss thru transpiration

Question 20

10 adaptations of desert plants for water conservation + xerophytes too

Answer 20

1. thick waxy cuticle on leaf/stem: reduces non-stomatal transpiration rate
2. fewer stomata: reduces transpiration rate
3. stomata in sunken pits: maintains humidity – decr. transp.
4. fine hairs on leaf underside: maintains layer of moisture near stomata – decr transp.
5. CAM physiology – stomata close during day
6. reduced air spaces in leaf mesophyll: decr surface area
7. few/small leaves/ photosynthesis in stem: red. surface area
8. curled/rolled leaves: reduced surface area + incr humidity
9. deep, highly branched roots: incr ability to take up water

Question 21

adaptations of saguaro cactus 6

Answer 21

• thick waxy cuticle on stem
• one tap root + highly branched system
• stores water in stem
• reduced S.A. (p.sis in stem)
• leaves reduced to spines
• CAM photosynthesis (stomata closed in day)

Question 22

adaptations of Marram grass 4

Answer 22

• thick outer cuticle
• rolled shape
• few stomata
• hair like structures

Question 23

what are halophytes

Answer 23

plants that have adapted to areas with high salinity (Eg ocean shoreline)
– makes establishment of higher conc of ions in roots more difficult
- some have adaptations to secrete salt, some establish high concs of other solutes, some conserve water in the plant

Question 24

adaptations of halophytes 6

Answer 24

1. salt storage in vacuoles: compartmentalizes, protects organelles and enzymes from damage
2. high conc of organic solutes: incr osmolarity = water can still enter
3. salt storage glands in leaf: accumulates salt in limited area, release thru crystals
4. leaf abscission: breaking off leaves with toxic levels of salt
5. selectively permeable membrane (in roots): excluses salt by having no ion channels to allow passage of Na/Cl / has AT pumps to remove
6. xerophytic adaptations: few stomata, water storage, thick cuticle etc

Question 25

adaptations of mangrove trees

Answer 25

- salt glands that excrete salt crystals (grey mangrove) - root cell membranes that mostly exclude salt ions (red) - store salt in vacuoles, keeping cell turgid (red)

Question 26

internal factors affecting rate of transpiration 4

Answer 26

1. root to shoot ratio 2. surface area of leaves 3. number of stomata per unit leaf area 4. leaf struture eg presence of hair

Question 27

external factors affecting rate of transpiration

Answer 27

1. light 2. wind 3. temperature 4. humidity 5. water availiablity

Question 28

how does temp affect rate of transpiration

Answer 28

temp incr = transpiration incr - incr temp = incr energy for water evaporation + decr humidity (but if temp too high for enzymes, stomata close, transp. rate falls)

Question 29

how does humidity affect transpiration rate

Answer 29

incr humidity = decr transpiration - concentration gradient for diffusion of water vapour between air spaces and atmosphere: more/less steep

Question 30

how does light affect transpiration rate

Answer 30

light intensity incr = transpiration incr - stomata closed in dark; incr LI = open stomata, water escapes - photons provide energy for evaporation

Question 31

how does wind affect transpiration rate

Answer 31

wind velocity incr = transpiration incr - low wind = incr humidity = decr water vapour conc gradient = decr transpiration

Question 32

using a porous pot, how is cohesion-tension due to evaporation demonstated via a model

Answer 32

- water saturates the porous pot, evaporates into surrounding air - cohesion tension extends down tubing into beaker, water drawn up

Question 33

using filter paper, how is cohesion-tension due to capillary action demonstated via a model

Answer 33

cohesion of water + adhesion to cellulose fibres in paper draws water up

Question 34

what are potometers used for

Answer 34

indirect measurement of water loss = rate of transpiration measurement of water uptake via water level/ movement of air bubbles

Question 35

measuring transpiration rates using mass

Answer 35

measuring decr in mass from plant in sealed container - BUT does not account for mass incr due to photosynthesis

Question 36

struture of stomata

Answer 36

- structure: 2 elongated guard cells, attached to epidermal cells - pore appears when they seperate

Question 37

how do stomata open and close

Answer 37

due to turgor pressure of guard cells water absorbed by guard cells = push epidermal cells beside them = pore develops - closes when water is lost and guard cells become flaccid

Question 38

what are root hairs

Answer 38

extensions of individual epidermal cells, relatively short lived

Question 39

3 possible routes for water movement thru plant cells and tissues

Answer 39

1. mass flow (apoplast pathway) - occurs thru interconnecting free spaces betw cellulose fibres of cell walls (incl xylem) 2. diffusion (symplast pathway) - occurs thru cytoplasm and via cytoplasmic connections betw cells (organelles = resistance) 3. osmosis - from vacuole to vacuole, driven by osmotic pressure gradient - AT of mineral ions in roots = absorption of water via osmosis - not as significant pathway for across plant transport

Question 40

how active uptake is achieved -- movement of water and ions from roots to xylem by structure

Answer 40

1. vascular tissue in roots contained by endodermis 2. Casparian strip at endodermis: waxy strip in radial walls -- blocks water passage momentarily 3. water passes thru endodermis via osmosis 4. HENCE cytoplasm of endodermal cells AT ions from cortex to endodermis

Question 41

outline ion uptake

Answer 41

- by active transport - highly selective process -- reflects needs of the plant - involves protein pumps -- needs ATP + specific

Question 42

how do ions reach the cell membranes during active uptake of ions in roots

Answer 42

1. mass flow of water thru free spaces = delivers fresh soil solution to root hair cell plasma membranes 2. active uptake of selected ions 3. ions diffuse from higher conc outside apoplast --> lower conc adjacent to protein pumps 3. mutualistic r/s with soil-inhabiting fungi: fungal hyphae receive supply of sugar from plant root cells, in exchange they release ions + death & decay also releases ions

Question 43

active uptake of ions in soil but mnore chemistry

Answer 43

- neg charged clay particles -- pos charge ions attach - minerals needed: Mg2+, nitrates, Na+, K+, PO43- - AT uploading into roots - root cells have protein pumps -- expel H+ ions into soil = displaces pos mineral ions