Plant Bio Day 5

Secondary growth 1. Vascular cambium 2. Cork cambium Transport 1. Three pathways 2. Water potential 3. Xylem A. Water enters root B. Ascent of sap: mechanism C. Stomate control 4. Phloem

Secondary Growth produces

Wood, Bark

Secondary growth occurs in

Conifers & Woody eudicots

Primary Growth occurs in

All vascular plants (ferns, seed plants)

Cork cambium adds_

Secondary dermal tissue

Vascular Cambium adds_

Secondary xylem (inside) & phloem (outside)

Inside → Outside

* Pith
* Primary xylem
* Secondary Xylem
* Vascular Cambium
* Secondary phloem
* Primary phloem
* Cortex
* Cork Cambium
* Periderm

Vascular cambium produces

1. Secondary xylem to inside (wood)
2. Secondary phloem → outside
3. More VC (increase circumference)
4. Rays - Parenchyma for lateral transport

Xylem (dead or alive?)

Dead

Phloem (dead or alive?)

alive

Fusiform initials (vasc camb) make:

* Tracheids & vessel elements (xylem)
* Sieve elements (phloem)

Ray Initials (vasc camb) make:

Rays (both xylem & Phloem)

Oldest centre

Heartwood

Younger outside

Sapwood

Sap flows thru _

xylem

Lignin

* Deposited in cells walls; fills space & binds cellulose, hemicellulose & pectin

Cork cambium

* New lateral meristem
* Arises from cylinder of cortex cells outside the vascular cambium & secondary phloem

Cork cambium produces what

Periderm: 3 layers

3 layers of periderm

* Phelloderm → inside
* Thin layer living parenchymal cells
* Cork cambium itself
* Cork → outside
* Suberized, dead cells
* Protects woody plant (no more epidermis)

Living phloem + periderm =

bark

Cork cambium + cork =

Periderm

Bark is

all tissues outside vascular cambium

1st law of thermodynamics

* Cannot create / destroy energy, only change

2nd law of thermodynamics

* Energy spontaneously tens to flow only from concentrated→spread out
* Entropy never decreases (entropy = disorder)

2nd law in Life

* Movement of fluid in plants = 2nd law thermodynamics
* Most equitable distribution of entropy
* Osmosis
* Diffusion
* Hydrostatic pressure

3 cell compartment (water movement within a plant)

Cytoplasm, Cytosol, Cellulose

Cytosol

part of cytoplasm excluding organelles

3 transport routes

Trans-membrane

Symplastic

Apoplastic

Water Potential Determines:

* DIRECTION of movement
* Higher → lower water potential

Water potential: 2 components

Solute potential & pressure potential

Loss of water from cell by osmosis

Plasmolysis (cell membrane seperated from cell wall)

Water & minerals travel which direction and where

upwards in xylem

Nonliving continuum outside cytosol

Apoplast (incl. Cell walls, xylem cells, extracellular spaces)

Continuum of cytosol connected by plasmodesmata

Symplast

Stele

* Xylem, Phloem
* Pith
* Pericycle

Material inside endodermis

Casparian strip

* Where primary wall & middle lamella were
* Waterproof & impermeable to ions
* All water & ions entering xylem must pass thru endodermal cells; must cross cell membrane

After Water Enters Root: Pathway of Water & Minerals in a Plant

1. Soil
2. Root Hair
3. Cortex
4. Endodermis
5. Xylem 
6. Atmosphere

Generation of Transpirational Pull

* Negative pressure (tension) at air-water interface in leaf = basis of transpirational pull
* Draws water out of xylem

Water Flow in Xylem: Ascent of sap Steps

* Water evaporates from leaf stomates (transpiration)
* Water potential lowered at air-water interface, causing negative pressure (tension) in xylem
* Hydrogen bonds hold water together (cohesion)
* Xylem under tension gradient: pressure potential (Ψp) lowest (most negative) at top
* Water pulled up by pressure gradient
* Water & minerals enter root by osmosis

Water flow in Xylem: Notes

* Total Path in xylem highest (least -) → Lowest (most -)
* Passive process
* Upwards only

Tracheids & vessel (dead or alive?)

Dead cells

Control of Transpiration by Stomates

Cues to Open at Dawn

* Light, CO2 depletion, Circadian rhythm

What happens in Dry Conditions

Abscisic Acid: Hormone

* Causes K+ to leave guard cells
* Stimulates stomate closure

Phloem transport: what

Sugar in solution & other compounds

Phloem transport: where

Sieve-tube elements

Phloem transport: how

Pressure-flow hypothesis

Transport Within Plants: Keys

Water spontaneously moves high → low water Ep

\

Water Potential energy =

Solute (osmotic) Potential energy (0 or -)

+

Pressure Potential energy (any value)

2 main tissues for transport

* Xylem: sap: tracheids & sometimes vessel elements
* Phloem: sugar water: sieve-tube elements

Xylem (transport cell types) (what is transported?) (direction) (mechanism)

1. Tracheids, vessel
2. Water & minerals
3. Up
4. Transpiration-cohesion-tension

Phloem (transport cell types) (what is transported) (direction) (Mechanism)

1. Sieve-tube elements
2. Sugar water
3. Any
4. Pressure Flow