Also Known As Chapter 36!!

Transpiration + Vascularity

Transport Overview

3 Types of Transport in Vascular Plants

1. Transport of water & solutes by individual cells

2. Short-Distance transport of substances between cells at the tissue level

3. Long-distance transport within the xylem & phloem among the entire plant

From B4

Passive Transport – movement down a gradient Does NOT require energy

Active Transport – Movement against a electrochemical gradient Requires energy

Most solutes must use transport proteins Aquaporin – channel (transport) protein for

water

Proton Pumps

Uses energy from ATP to pump out hydrogen ions from the cell

Establishes a proton gradient with higher [H+] outside the cell The electrical difference is called a

membrane potential Potential energy is therefore created As the H+ ions diffuse back in, they can

do work

Name two processes that used proton pumps.

What is cotransport?

How does it relate in the processes named above?

Water Potential (Ψ)

Water moves from High concentration to Low concentration via osmosis

Equivalently, water moves from high water potential to low water potential

Water potential is the combined effect of Solute Concentration Physical Pressure

Ψ = Ψs + Ψp

Water Potential (Page 2)

Solute potential (Ψs) is proportional to the number of dissolved solute particles Also called Osmotic Potential Ψs of water = 0 Addition of solute Decrease in potential Ψs ≤ 0

Water Potential (Page 3)

Pressure Potential (Ψp) Physical pressure on a solution Can be (+) or (-) Water is usually under a positive pressure

potential Turgor pressure – when cell contents press the

plasma membrane against the cell wall Drying out = Negative pressure potential

Water Potential Examples

Roots & Water Absorption

Root hairs = absorption of water

Root epidermis cortex vascular cylinder To rest of plant via xylem

Mycorrhizae are important for absorption as well

Tonoplast (Vacuolar Membrane)Regulates molecular traffic between the cytosol & vacuolar contents

SymplastCytoplasmic continuum consisting of the cytosol of cells and the plasmodesmata connecting the cytosols. Crosses membrane early in the process

Apoplast Continuum of cell walls + extracellular spaces Only crosses a membrane at endodermis

Casparian Strip

In the endodermis Ensures that any water or

solutes must pass through a plasma membrane before entering xylem

Critical control point Again, plasma membrane

controls what can enter the xylem

Bulk Flow

Water movement from regions of high pressure to regions of low pressure

In xylem, water & minerals travel by bulk flow Called xylem sap

Xylem travels from Roots Stem (xylem) Leaves (exit thru stomata)

1. Root pressure or “push”

2. Transpiration or “pull”

What powers the bulk flow?

VASCULARTRANSPORT

-- Starts with stomatal opening

-- Transpirational Pull

Root Pressure or “push”

Water diffusing into the root cortex = positive pressure

This pressure forces fluid UP the xylem

Weak force – can only propel fluids up a couple of feet

Transpirational Pull

Your book calls this: transpiration-cohesion-tension mechanism

In leaves, water is lost through stomata Why? Lower water pressure in air than in leaves

Water is drawn up in to this area of negative pressure

Water molecules pull up other water molecules Cohesion – water on water action Adhesion – water to cell wall action Via Hydrogen bonds

Transpiration/Cohesion

1 molecule of H2O evaporates due to transpiration, another molecule is drawn from the roots to replace it.

High humidity = DECREASE transpiration Wind = INCREASE transpiration Increasing light intensity = INCREASE

transpiration Close stomata = NO transpiration

Stomata

90% of water lost by plants is through stomata

Stomata account for 1% of leaf surface area

Guard cells control opening & closing of stomata

What causes stomatal opening?1. Depletion of CO2 within air spaces

Photosynthesis consumes CO2 = stomata open IF placed in chamber w/o CO2, stomata open

2. Light

3. An increase in K+ ions Lowers water potential of guard cells Water flows into guard cells stomata

open

What closes stomata?

1. Lack of water – guard cells lose volume & close

2. High Temp. – stimulates cell respiration & CO2 accumulates inside leaf

3. Abscisic Acid – produced in mesophyll cells in response to dehydration

Phloem

Translocation Photosynthetic products leave the leaves

and travel throughout the plant Mechanism is called pressure flow Sieve tube elements carry sugar from

source to sink Source – leaves (net producer of sugar) Sink – roots (net consumer of sugar)

Sucrose is added at the sugar source (leaves)

Electrochemical gradient is created to move sucrose into phloem by cotransport

Decreases water potential in phloem, so creates positive pressure