Transport In Plants

Cellular Transport Diffusion Osmosis Facilitated Diffusion Active Transport Proton Pump

Cell Transport

Water Potential The physical property predicting the direction in which water will flow – Solute concentration – Pressure water moves from high water potential to low water potential

Water Potential (a) Left Side – Pure Water = 0 Water Potential Right Side – Negative Water Potential 0 pressure - solute (has solutes) Water moves to the right

Water Potential (b) Left Side – Pure Water = 0 Water Potential Right Side – 0 Water Potential + pressure equal to solute conc. - solute (has solutes) Water is at equilibrium

Water Potential (c) Left Side – Pure Water = 0 Water Potential Right Side – Positive Water Potential + pressure more than solute conc. - solute (has solutes) Water moves to the left

Water Potential (d) Left Side – Pure Water and Negative Tension Right Side – Negative Water Potential 0 pressure - solute (has solutes) Water moves to the left

Plant Cell Water Movement

Water Relationships in Plants Plasmolysis: plasma membrane pulls away from the cell wall Flaccid: limp, no tendency for water to enter Turgid: water moves in and plasma membrane pushes up against cell wall

Aquaporins Specialized proteins that facilitate osmosis water moves into/out of cells quicker than expected across a membrane

Tissue Level Transport

Trans-membrane – across cell wall and cytoplasm Symplastic – across the cytoplasm Apoplastic – across the cell walls

Long Distance Transport Bulk Flow – the movement of a fluid driven by pressure – Only moved up plants by a negative pressure (not solute concentration) Unlike osmosis, moves water and solutes

Absorption of Water and Minerals

– Water and Minerals can move through the epidermis to the cortex in two methods: apoplastic symplastic

Absorption of Water and Minerals – Endodermis is selectively permeable Casparian strip is made of suberin Water and minerals cannot enter through the stele through the apoplastic pathway. It must enter through the symplastic pathway.

Absorption of Water and Minerals Focus on soil --> epidermis --> root cortex -- -> xylem pathway – Once inside the stele, the water and minerals must shift back to the apoplastic pathway because xylem has no protoplast

Absorption of Water and Minerals Focus on soil --> epidermis --> root cortex -- -> xylem pathway (review) – Two pathways 1. Apoplastic --> symplastic--> apoplastic 2. Symplastic --> apoplastic – Water passes into the stele through symplastic route – Water passes into the xylem through apoplastic route

Transport of Xylem Sap Pushing Xylem – Root Pressure caused by active pumping of minerals into the xylem by root cells Guttation: the accumulation of water on the tips of the plant

Transport of Xylem Sap Pulling Xylem – Transpiration the evaporative loss of water from a plant through the stomata

Transport of Xylem Sap Pulling Xylem – Cohesion Water sticking together – Adhesion Water sticking to the cell wall – Surface Tension negative pressure Forms a meniscus (concave shape) – the more concave / the greater the negative pressure

Transport of Xylem Sap

Pulling Xylem – Cohesion: binding together of water molecules pulls sap up plants – Adhesion: Water sticking to the cell wall fights gravity

The Control of Transpiration Guard Cells – turgid - open – flaccid - closed Potassium Ions – active transport of Hydrogen ions out of the cell causes Potassium ions to move in

Stomata Open during the day / Closed at night – first light (blue light receptor) – depletion of Carbon Dioxide – internal clock (circadian rhythms)

Reducing Transpiration Small, thick leaves Thick cuticle Stomata are recessed Lose their leaves C 4 or CAM plants

Phloem Loading

Translocation of Phloem Phloem loading – movement of sugars through apoplastic and symplastic pathways – sugar made in mesophyll cells pass through other cells to seive tube members – bundle sheath cells – parenchyma cells – companion (transfer) cells

Translocation of Phloem Phloem loading – chemiosmotic mechanism used to load sucrose from the apoplast to the symplast pathway – used with high levels of sucrose accumulation

Translocation

Translocation of Phloem Translocation: transport of food – moves from a sugar source to a sugar sink – Reduces water potential inside sieve tube (phloem) and begins to take on water from xylem

Pressure Flow of Phloem Pressure Flow – Water intake generates a hydrostatic pressure near source cell that forces water to lower pressure areas near sink cell – Unloads sugars into sink by active transport which makes cells lose water to relieve pressure – Xylem recycles water