Plant Bio Day 5

Secondary Growth produces

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