Absorption and Transport

Chapter 11

Fig. 11-1, p. 164

H2O

product ofphotosynthesis

(sucrose)

H2O vapor

H2O vapor

H2O vapor

H2O

mineral ions

Fig. 2-6, p. 18

slight negative charge at this end

slight positive charge at this end

but the wholemolecule hasno net charge(+ and – balanceeach other)

Hydrogen bonds in water

Fig. 11-2a, p. 165

water vapor molecules

(1) Diffusion

Fig. 11-2b, p. 165

Differentially permeablemembrane (water goes through, but not starch)

starch solution

waternet flow

(2) Osmosis

Fig. 11-2b, p. 165

(3) Hydrostatic pressure

• Involves osmosis and the cell wall.

Fig. 2-10, p. 22

Polysaccharides:• Cellulose (cellular structure)

- monomer is glucose

- connected in a straight chain

- cellulose molecules bind with each other via hydrogen bonds, resulting in cellulose microfibers

• Starch (energy storage)

- monomer is glucose

- connected in a helix

Fig. 3-7 (a-c), p. 36

PROTOPLAST SOLUTION

Concentration0.3 molar(Isotonic)

Concentration0 molar(Hypotonic)

Concentration0.27 molar

Pressure0.66 megapascals

Concentration0.5 molar(Hypertonic)

Concentration0.3 molar

Pressure0 megapascals

Concentration0.5 molar

Pressure0 megapascals

(3) Hydrostatic pressure in

cells

Turgor pressure is one type of hydrostatic pressure. Turgor pressure is the result of a combination of osmosis and cell wall rigidity.

Fig. 3-7 (d), p. 36

Plasmolyzed cells

Fig. 11-2c, p. 165

force pullingwater along side of tubeair-water interface

capillary tube

water tension inwater column

water moleculesconnected byhydrogen bonds

force pullingthe air-waterinterfacestraight

(4) Capillary forces

(5) Gravity

• Gravity– Takes force to move water upward– Significant factor in tall trees

Transpiration

Fig. 11-5, p. 168

cuticle is relativelyimpermeableto H2O

water-filledxylem in vein

cell wall permeatedwith H2O

air not saturated

water-filledleaf cells

substomatal cavity (intercellular space)

Fig. 11-3, p. 167

thin boundarylayer; steepgradient; fastdiffusion

thick boundarylayer; gentlegradient; slowdiffusion

Boundary layer: an unstirred layer of air close to the leaf

Bulk air: air outside of the boundary layer

Wind stirs up the air close to the leaf and makes the boundary layer thinner. Plants transpire much faster on a windy day than on a still one.

Fig. 11-4, p. 167

sunken stomata

spongyparenchyma

fibers sunken stomata

cuticle stomatalcrypts

Cross section of a yucca leaf

Flow of Water Into Leaves

Fig. 11-6, p. 168

Capillary forces can convert Water loss into a tension within a tracheid.Before evaporation, there is little tension. After evaporation, there is high tension.

Dots: water moleculesShort lines: forces of cohesion and adhesion

Pits

A. B.

Tension in the water pulling the tracheid wall inward.

Capillary forces pulling water into the tracheid

Fig. 4-11, p. 58

pitsin wall

one vesselmember

perforationplate

Tracheary elements comparedVessel members Tracheids

Vessel members join end to end, but they digest out the end walls forming a tube called a vessel.

Tracheids join end to end and along their sides and are connected by bordered pits.

Fig. 11-1, p. 164

H2O

product ofphotosynthesis

(sucrose)

H2O vapor

H2O vapor

H2O vapor

H2O

mineral ions

Fig. 11-7, p. 169

plasmodesma

symplastic flow

apoplastic flow

cell wall

cytoplasm

xylem

epidermis cortex stele

Casparian stripof endodermis

symplastof endodermis

roothair

Symplastic and apoplastic flow through roots

Control of Water Flow

• Environmental factors affecting rate of transpiration– Temperature– Relative humidity of bulk air– Wind speed

Control of Water Flow

• Transpiration– Slow at night– Increases after sun comes up– Peaks middle of day– Decreases to night level over afternoon

• Rate of transpiration directly related to intensity of light on leaves

Fig. 11-8a, p. 170

plasmamembrane

protonpump

starch

malic acid

malate–

ATP

ADP+ Pi

K+

K+

H+

H+

CI

CI

Events leading to the opening of a stoma:

The production of malate and the influx of K+ and Cl- powered by the electrical and pH gradients produced by the proton pump increase the concentration of osmotically active solutes in the guard cells. As a result, water flows into the cells by osmosis.

LIGHT

H+

Fig. 11-9a, p. 170

cells connected

With increased pressure, cell getslonger. Because the outer wall canexpand more readily, cell bowsoutward.

reinforced inner wall

cellulose microfibrils(radial micellation)

How radial micellation and reinforcement of guard cell walls force an expanding cell to bow outward.

Fig. 11-9b, p. 170