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

Absorption by Roots: Root hairs and mycorrhizae (symbiotic associations of roots and fungus) increase surface area for absorption Root hairs and mycorrhizae (symbiotic associations of roots and fungus) increase surface area for absorption Water and minerals travel from soil  epidermis  cortex  endodermis  vascular cylinder Water and minerals travel from soil  epidermis  cortex  endodermis  vascular cylinder The endodermis protects the vascular cylinder, and force materials to be “screened” by traveling through a cell membrane The endodermis protects the vascular cylinder, and force materials to be “screened” by traveling through a cell membrane

Plant Transport RoutesPlant Transport Routes: Plant Transport Routes Symplastic – solutes move through plasmodesmata (cytoplasm channels) between cells Symplastic – solutes move through plasmodesmata (cytoplasm channels) between cells Apoplastic – solutes move through cell walls and extracellular space Apoplastic – solutes move through cell walls and extracellular space

Root hairs and mycorrhizae

Mineral Ion Transport Mineral ions are needed by plants and enter through three main processes: Mineral ions are needed by plants and enter through three main processes: Carried through soil by the mass flow of water, and diffuse into root cells Carried through soil by the mass flow of water, and diffuse into root cells Absorbed into symbiotic fungi (mycorrhizae) and passed to root cells Absorbed into symbiotic fungi (mycorrhizae) and passed to root cells

Active transport into root cells (requires ATP) Active transport into root cells (requires ATP) If the concentration of a mineral is higher inside plant cells than in the soil If the concentration of a mineral is higher inside plant cells than in the soil If ions cannot cross the cell membrane If ions cannot cross the cell membrane

Support To allow terrestrial plants to grow tall, strong support is needed: To allow terrestrial plants to grow tall, strong support is needed: Cell walls made of thickened cellulose Cell walls made of thickened cellulose Xylem vessels reinforced with lignin Xylem vessels reinforced with lignin Turgor pressure - Supportive pressure of the water inside cells Turgor pressure - Supportive pressure of the water inside cells

Xylem Transport xylem sap (water and dissolved minerals) rises against gravity xylem sap (water and dissolved minerals) rises against gravity the “push” comes from root pressure: since there is a higher concentration of minerals in the vascular cylinder, water moves in through osmosis the “push” comes from root pressure: since there is a higher concentration of minerals in the vascular cylinder, water moves in through osmosis the “pull” comes from transpiration, cohesion, and adhesion (due to H- bonding) the “pull” comes from transpiration, cohesion, and adhesion (due to H- bonding)

Xylem Transport Xylem Transport water evaporates and diffuses out of stomata water evaporates and diffuses out of stomata the surface tension of the water film in the air spaces pulls water out of the xylem the surface tension of the water film in the air spaces pulls water out of the xylem this pull is transmitted down the column of water in a xylem vessel this pull is transmitted down the column of water in a xylem vessel adhesion to cell walls (hydrophilic cellulose) helps resist gravity adhesion to cell walls (hydrophilic cellulose) helps resist gravity

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

How is the flow of water through xylem vessels solar powered? Evaporation of water from air spaces in leaves is driven by the sun

Control of Transpiration guard cells control the size of stomata guard cells control the size of stomata stomata let CO2 diffuse in, and O2 and H2O diffuse out stomata let CO2 diffuse in, and O2 and H2O diffuse out generally, stomata are open during the daytime, and closed at night generally, stomata are open during the daytime, and closed at night

Control of Transpiration opening: guard cells accumulate K+  water enters by osmosis  guard cells swell  stoma opens opening: guard cells accumulate K+  water enters by osmosis  guard cells swell  stoma opens closing: guard cells lose K+  water leaves by osmosis  guard cells collapse  stoma closes closing: guard cells lose K+  water leaves by osmosis  guard cells collapse  stoma closes

K+ transport is stimulated by: K+ transport is stimulated by: Light Light CO2 depletion CO2 depletion Internal clock (circadian rhythm) Internal clock (circadian rhythm) Abscisic acid – a plant hormone produced by roots in dry conditions (drought) Abscisic acid – a plant hormone produced by roots in dry conditions (drought)

Xerophytes – plants adapted for water scarce conditions What are some plant adaptations that could limit water loss? Small leaves, deep roots, waxy cuticles, fewer stomata Small leaves, deep roots, waxy cuticles, fewer stomata C4 photosynthesis – CO2 is stored as a 4 carbon sugar and the Calvin cycle occurs in bundle sheath cells C4 photosynthesis – CO2 is stored as a 4 carbon sugar and the Calvin cycle occurs in bundle sheath cells CAM photosynthesis – stomata open at night and CO2 is stored for use during the day when stomata are closed CAM photosynthesis – stomata open at night and CO2 is stored for use during the day when stomata are closed

Phloem Sap Transport phloem sap (water and organic products of photosynthesis) flows from sugar sources to sugar sinks phloem sap (water and organic products of photosynthesis) flows from sugar sources to sugar sinks What are some possible examples of sugar sources and sinks? Sources – mature leaves, roots (early in growing season) Sources – mature leaves, roots (early in growing season) Sinks – growing roots, shoots, flowers or fruits Sinks – growing roots, shoots, flowers or fruits

Phloem Sap Transport sugar enters/leaves phloem through diffusion or active transport sugar enters/leaves phloem through diffusion or active transport the “push” comes from water pressure the “push” comes from water pressure high solute concentrations at sugar sources lead to water pressure from osmosis high solute concentrations at sugar sources lead to water pressure from osmosis low solute concentration at sugar sinks leads to water loss by osmosis and reduced pressure low solute concentration at sugar sinks leads to water loss by osmosis and reduced pressure