Xylem and Stomata

Helpfulness: +1
Set Details Share
created 4 years ago by Jessc_Tegan_Guenter
77 views
3-13-17
updated 4 years ago by Jessc_Tegan_Guenter
show moreless
Page to share:
Embed this setcancel
COPY
code changes based on your size selection
Size:
X
Show:
1

Xylem

Transports water and minerals from
roots to shoots

2

Two types of water-conducting cells

Tracheids-All vascular plants

Vessel elements-Most angiosperms, few gymnosperms and seedless vascular . Cells are dead at maturity. Lignin

3

water and mineral absorption

Occurs near root tips
Root hairs

Modified epidermal cells
Permeable to water
Most of water absorption

4

Epidermis water and mineral absorption

Soil solution drawn into hydrophilic
walls of epidermal cells, passes freely along cell walls and extracellular spaces into cortex

5

Cortex water and mineral absorption

Extensive surface area of cortical cell
membranes enhances uptake of water and selected minerals

6

Concentration of essential minerals is
greater in the ?

in the roots than in the soil because of active transport

7

Transport of water and mineral into the xylem

Endodermis- Innermost layer of cells in the root cortex. Surrounds the vascular cylinder. Last checkpoint for selective
passage of minerals from cortex into vascular tissue
Water can cross the cortex via
the symplast or apoplast
Water and minerals can travel to vascular cylinder through cortex via….
Apoplastic route, Symplastic route, or Transmembrane route

8

Water and minerals in apoplast
must cross the

plasma membrane o fan endodermal cell to enter vascular cylinder

9

Casparian strip

Transverse and radial walls of
endodermal cells
Belt of waxy material (suberin)

Barrier to apoplastic pathway

10

Water and minerals
move from endodermal cell protoplasts into ?

into cellwalls

Diffusion and active transport involved

Water and minerals enter tracheids and vessel elements

11

Bulk flow

transports xylem
sap from roots to leaves

12

Transpiration

Loss of water vapor from a
plant’s surface
Drives xylem sap transport
Transpired water is replaced as
water travels up from the roots

13

Cohesion-tension
hypothesis

Transpiration and
water cohesion pull water from shoots to roots
Xylem sap is normally
under negative pressure (tension)

14

Transpirational pull

Water vapor in leaf air spaces diffuses down water potential gradient and exits via stomata

As water evaporates the air-water interface
▪Retreats farther into mesophyll cell walls
▪Becomes more curved

Curvature creates negative
pressure potential due tohigh surface tension of water

Transpirational pull
Negative pressure pulls
water in xylem into leaf

Pulling effect results
from cohesive bindingbetween watermolecules

Transpirational pull on
xylem sap istransmitted fromleaves to roots

15

Cohesion

Water molecules attracted
to each other
Pulls column of xylem sap

16

Adhesion

Water molecules attracted
to hydrophilic walls ofxylem cell walls
Offsets the force of gravity

17

Thick secondary walls prevent

vessel
elements and tracheids from collapsing undernegative pressure

18

Drought stress or freezing can cause

cavitation, the formation of a water vaporpocket by a break in the chain of watermolecules

19

Bulk flow is
driven by…

Water potential
difference atopposite ends ofxylem tissue

Evaporation -
does not requireenergy

20

Bulk flow differs from diffusion

Driven by differences in (Y)P, not (Y)S

Occurs in hollow dead cells, not membranes of
living cells
Entire solution moves, not just water or solutes

Much faster

21

Stomata

 Allow exchange of CO2 and O2
b/w air surrounding leaf andphotosynthetic cells within leaf
 Route of evaporative loss of water
 Guard cells Specialized epidermal cells Flank pore Regulate the opening and closing of the pore
 Stomatal density under genetic
and environmental control

22

Leaves generally have broad

broad
surface areas and high surface-to-volume ratios
Increase photosynthesisIncrease water loss through
stomata

23

Guard cells

through~95% of water loss occurs
stomata
Balance water conservation with
gas exchange for photosynthesis

24

Changes in turgor pressure

open and close stomata
When turgid, guard cells bow
outward and the pore betweenthem opens

When flaccid, guard cells become
less bowed and the pore closes

25

Stomattal opening and closing

Reversible uptake and loss of K+ ions
causes changes in guard cell turgor pressure
Stomata opening
Guard cells actively pump H+ out K+
absorbed from neighboring epidermalcells  H2O enters cells and becometurgid
Stomata closing
Loss of K+ leading to osmotic loss of
H2O

26

Effects of transpiration of wilting and leaf temp

Large amount of water lost by transpiration
If not replaced, plant will lose water and wilt
Transpiration also results in evaporative
cooling
Lower leaf temperature and prevent protein
denaturation

27

Desert plants

Annuals germinate, grow and reproduce during rainy
season
Perennials that produce leaves during rainy season
Leaf modifications that reduce rate of transpiration▪Xerophytes
▪Reduced or highly modified leaves▪Stems carry out photosynthesis▪Store water in fleshy stems
Crassulacean acid metabolism (CAM)▪Take in CO2 at night and close stomata during the day

28

sugar movement from the sieve-tube elements into the sieve tubes requires....

active transport

29

in the moment that sugar is actively transported into the sieve tube, the water potential of the phloem.....

decrease

30

as water moves into the sieve tube, the pressure within the phloem....

increases

31

water can enter roots through 2 pathways, apoplastic and symplastic route. how do these pathways differ ?

the apoplastic route does not involve transport across a cell membrane, but symplastic route does