Transport In Plants Cellular Transport Diffusion Osmosis Facilitated

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

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

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

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