9.2 Plant Transport9.2 Plant TransportLearning Targets: Explain the process Learning Targets: Explain the process of mineral ion absorption from the soil of mineral ion absorption from the soil into roots. Explain how water is carried into roots. Explain how water is carried by the transpiration stream. State that by the transpiration stream. State that guard cells can regulate transpiration. guard cells can regulate transpiration. Outline the role of phloem in active Outline the role of phloem in active translocation of sugars.translocation of sugars.

Absorption by Roots:Absorption by Roots: Root hairs and mycorrhizae Root hairs and mycorrhizae

(symbiotic associations of roots and (symbiotic associations of roots and fungus) increase surface area for fungus) increase surface area for absorptionabsorption

Water and minerals travel from soil Water and minerals travel from soil epidermis epidermis cortex cortex endodermis endodermis vascular cylinder vascular cylinder

The endodermis protects the The endodermis protects the vascular cylinder, and force vascular cylinder, and force materials to be “screened” by materials to be “screened” by traveling through a cell membranetraveling through a cell membrane

Plant Transport Routes:: Symplastic – solutes move through Symplastic – solutes move through

plasmodesmata (cytoplasm channels) plasmodesmata (cytoplasm channels) between cellsbetween cells

Apoplastic – solutes move through cell Apoplastic – solutes move through cell walls and extracellular spacewalls and extracellular space

Root hairs and mycorrhizaeRoot hairs and mycorrhizae

Mineral Ion TransportMineral Ion Transport Mineral ions are needed by plants Mineral ions are needed by plants

and enter through three main and enter through three main processes:processes:

Carried through soil by the mass flow Carried through soil by the mass flow of water, and diffuse into root cellsof water, and diffuse into root cells

Absorbed into symbiotic fungi Absorbed into symbiotic fungi (mycorrhizae) and passed to root (mycorrhizae) and passed to root cellscells

Active transport into root cells Active transport into root cells (requires ATP)(requires ATP) If the concentration of a mineral is If the concentration of a mineral is

higher inside plant cells than in the soilhigher inside plant cells than in the soil If ions cannot cross the cell membraneIf ions cannot cross the cell membrane

SupportSupport To allow terrestrial plants to grow To allow terrestrial plants to grow

tall, strong support is needed:tall, strong support is needed: Cell walls made of thickened Cell walls made of thickened

cellulosecellulose Xylem vessels reinforced with ligninXylem vessels reinforced with lignin Turgor pressure - Supportive Turgor pressure - Supportive

pressure of the water inside cellspressure of the water inside cells

Xylem TransportXylem Transport xylem sap (water and dissolved xylem sap (water and dissolved

minerals) rises against gravityminerals) rises against gravity the “push” comes from the “push” comes from root root

pressurepressure: since there is a higher : since there is a higher concentration of minerals in the concentration of minerals in the vascular cylinder, water moves in vascular cylinder, water moves in through osmosisthrough osmosis

the “pull” comes from the “pull” comes from transpiration, transpiration, cohesion, and adhesion cohesion, and adhesion (due to H-(due to H-bonding) bonding)

Xylem Transport water evaporates and diffuses out of stomatawater evaporates and diffuses out of stomata the surface tension of the water film in the air the surface tension of the water film in the air

spaces pulls water out of the xylemspaces pulls water out of the xylem this pull is transmitted down the column of this pull is transmitted down the column of

water in a xylem vesselwater in a xylem vessel adhesion to cell walls (hydrophilic cellulose) adhesion to cell walls (hydrophilic cellulose)

helps resist gravityhelps resist gravity

TranspirationTranspiration – the loss of water – the loss of water vapor from leaves and other aerial vapor from leaves and other aerial parts of the plant.parts of the plant.

How is the flow How is the flow of water of water through xylem through xylem vessels solar vessels solar powered?powered?

Evaporation of Evaporation of water from air water from air spaces in spaces in leaves is leaves is driven by the driven by the sunsun

Control of TranspirationControl of Transpiration guard cells control the size of stomataguard cells control the size of stomata stomata let CO2 diffuse in, and O2 and stomata let CO2 diffuse in, and O2 and

H2O diffuse outH2O diffuse out generally, stomata are open during the generally, stomata are open during the

daytime, and closed at nightdaytime, and closed at night

Control of TranspirationControl of Transpiration opening: guard cells accumulate K+ opening: guard cells accumulate K+

water enters by osmosis water enters by osmosis guard cells guard cells swell swell stoma opens stoma opens

closing: guard cells lose K+ closing: guard cells lose K+ water water leaves by osmosis leaves by osmosis guard cells collapse guard cells collapse stoma closes stoma closes

K+ transport is stimulated by:K+ transport is stimulated by: LightLight CO2 depletionCO2 depletion Internal clock (circadian rhythm)Internal clock (circadian rhythm) Abscisic acid – a plant hormone Abscisic acid – a plant hormone

produced by roots in dry conditions produced by roots in dry conditions (drought)(drought)

Xerophytes – plants adapted for water Xerophytes – plants adapted for water scarce conditionsscarce conditions

What are some plant adaptations that could What are some plant adaptations that could limit water loss?limit water loss?

Small leaves, deep roots, waxy cuticles, Small leaves, deep roots, waxy cuticles, fewer stomatafewer stomata

C4 photosynthesis – CO2 is stored as a 4 C4 photosynthesis – CO2 is stored as a 4 carbon sugar and the Calvin cycle occurs carbon sugar and the Calvin cycle occurs in bundle sheath cellsin bundle sheath cells

CAM photosynthesis – stomata open at CAM photosynthesis – stomata open at night and CO2 is stored for use during the night and CO2 is stored for use during the day when stomata are closed day when stomata are closed

Phloem Sap TransportPhloem Sap Transport phloem sap (water and organic phloem sap (water and organic

products of photosynthesis) flows products of photosynthesis) flows from sugar sources to sugar sinksfrom sugar sources to sugar sinks

What are some possible examples of What are some possible examples of sugar sources and sinks?sugar sources and sinks?

Sources – mature leaves, roots (early Sources – mature leaves, roots (early in growing season)in growing season)

Sinks – growing roots, shoots, flowers Sinks – growing roots, shoots, flowers or fruitsor fruits

Phloem Sap TransportPhloem Sap Transport sugar enters/leaves phloem through sugar enters/leaves phloem through

diffusion or active transportdiffusion or active transport the “push” comes from water pressurethe “push” comes from water pressure high solute concentrations at sugar high solute concentrations at sugar

sources lead to water pressure from sources lead to water pressure from osmosisosmosis

low solute concentration at sugar sinks low solute concentration at sugar sinks leads to water loss by osmosis and leads to water loss by osmosis and reduced pressure reduced pressure