Transportation In Plants

Moving Materials In Animals• How do most animals move

materials around their body?– Circulatory system – Blood vessels like vein, arteries,

and capillaries • What powers the movement?– Contracting muscles of the heart– Contracting body muscles pinching

veins• What forces work against the

movement?– Thickness of fluid– Gravity

Moving Materials In Plants• How do plants move materials around

their bodies?– Vascular bundle

• Xylem water/ions• Phloem nutrients/hormones

– Narrow tubes made of hollowed out plant cells• Only cell walls remain

• What powers the movement?– Concentration gradients– Gravity– Transpiration

• What forces work against the movement?– Thickness of fluid– Gravity

• Why do plants not require a heart?– Slower metabolism; don’t require a fast

transport of materials

Parts of The Transport System: Roots• Roots designed to absorb water and

minerals from the soil– What minerals do we need?– Nitrates, Phosphates, Mg2+, etc…

• Root cap protective cells to help push through soil

• Root tip mass of rapidly dividing cells so roots can grow

• Epidermal cells outer layer of tissue; have root hairs (thin extensions of outer root cells that absorb water and minerals)

• Cortex stores starch; passes water and minerals to xylem

• Xylem one-way transporting of water/minerals from roots to leaves

• Phloem two-way transporting of sucrose, amino acids, and hormones

Moving Water to the Xylem• How does water get into the

roots?– Absorbed through osmosis by

root hairs• Water must pass through

many layers: epidermis, cortex, endodermis, and pericycle

1) Root hairs Epidermis Cortex: A) Apoplast pathway water passes along space in cell walls B) Symplast pathway water passes through cytoplasm of cells and then through the plasmodemata

Moving Water to the Xylem2) Cortex Endodermis Stele:• Endodermis cells covered in

suberin (waterproof wax); ring forms Casparian strip

• Passage cells cells with no suberin that only allow water through the symplast pathway– Why have this?

• Regulation; filter out unwanted molecules

3) Pericycle Xylem vessels:• Water moves by symplast

pathway towards hollow xylem vessels from the pericycle

• What powers all this movement?– Osmosis

Tissue Layers of Xylem• 4 cell types:1) Vessel elements

– Hollow tubes made from dead plant cells– Coated in lignin (waterproof protein)– Pits non-lignined sections of cell walls; allow

movement of water out by osmosis• Can form unique patterns

2) Tracheids– Primitive vessel elements with tapered ends– Holds water in place by adhesion when

transpiration is slow or stops– Pits help transport water across plant to other

areas3) Fibers

– Dead lignined cells used for support of xylem4) Parenchyma cells

– Living plant cells between vessel elements; support and storage

– Contain no chloroplasts

Parts of The Transport System: Shoots• Shoots designed to support

growing branches/ leafs and transport material

• Vascular bundle main transport system made of phloem, xylem, and cambium

• Cambium produces more phloem/xylem tubes as the diameter of plant grows; supports plant

• Epidermis thin single layer of cells covered with a waxy cuticle to prevent water loss

Parts of The Transport System• Leafs designed to use

water/minerals to do photosynthesis– What is the product of

photosynthesis?• glucose

– Why is glucose changed to sucrose before going to phloem?• Sucrose is more soluble

• Stoma openings in leafs that allow gas exchange– What gases are exchanged?

• O2 and CO2

– What is also lost through the stoma?• Water

Transpiration • Transpiration movement of water from

roots to leaves through the evaporation of water from the leafs– Creates a PULL, or suction

• Where does the strength come from to pull water against gravity?– Hydrogen bonds

• Two forces are needed:1) Cohesion H-bonds between water

molecules; water sticks together2) Adhesion H-bonds between water

molecules and other surfaces; water sticks to xylem vessel

• Mass flow continuous flow of water through xylem– Increases with temp., wind, and

humidity

Pressure Systems• Hydrostatic pressure force pushing

down on top of water in xylem– Reducing this pressure draws xylem

fluid up against gravity– Reduced by the movement of water

out of the xylem into the leaves• Root pressure force of water

flowing into the xylem in the roots– How can roots increase root

pressure?• Raise conc. of solutes in xylem

– Ions are activity transported into the xylem to lower the water potential

– Water moves into xylem from roots by osmosis

Measuring Transpiration• How can we measure

transpiration in plants?1) Measure how much water is

released from plant• Fairly difficult to do

2) Measure how much water is absorbed by plant• Fairly simple to do

• Potometer measures the amount of water absorbed into a plant by the movement of an air bubble a meter– Can expose plant to different

conditions to explore effects of wind, light intensity, temp., and humidity

Transpiration Rate• Plants have constantly monitor

how much H2O is in their leaves. Why?– Need H2O for photosynthesis

• What factors will effect the rate of transpiration?

1) Temperature water evaporation

2) Light intensity increase temp and photosynthesis rate

3) Wind faster evaporation4) Humidity higher % of water in

air means less transpiration

Adapting Transpiration • What environments would cause

the highest transpiration rates?– Hot, dry, and bright areas; deserts

• Xerophytes desert plants1) Smaller leaf surface area less

water loss2) Thick, waxy cuticle less water loss3) Water-storing tissue4) Large root system absorb more

water5) Shiny cuticle reflects sunlight6) Stomata closed during the day

get CO2 at night time

Adapting Transpiration • What environment wouldn’t require

much transpiration regulation?– In or on a body of water

• Hydrophytes grow in or on water1) Few xylem absorb water directly2) No root hairs roots act are anchors3) No cuticle no need to limit water

loss4) Stomata on upper side of leaf5) Air pockets in stem gases diffuse in

water slower, so air pockets increase diffusion rates and can store gases till needed

Adapting Transpiration • What environment is

transpiration most consistent? – Normal temperatures and water

supply• Mesophytes garden plants1) Normal amount of xylem2) Waxy cuticle to lower water loss3) Med. sized root system4) Standard plant adaptations5) Many produce flowers for

pollination

Sap and Water• Sap think sugar solution inside

phloem; used to make syrup – Why is thickness of sap not a

major concern of plants?• Most sap is moving from leafs to

roots and follows with gravity

• Why is the movement of water a major concern for plants?– Must move water upward against

gravity – Only major limit on tree height

• Moss can only grow 1 m tall because it lacks proper xylem

• Giant redwoods 114 m tall!

Moving Nutrients • Translocation transport of soluble

organic substances (assimilates) up and down in a plant

• Phloem tissue:1) Sieve elements2) Companion cells• Transport by mass flow, however it

is an active process• Active loading the moving of

sucrose into sieve elements powered by ATP

• Materials follow a source/sink system:– Source high conc. (leaves)– Sink low conc. (stem/roots)

Phloem Tissue • Sieve elements tube-like cells

similar to xylem but made of living cells– Basic organelles; no nucleus or

ribosomes– Sieve plate porous divider

between each cell that allows free movement of materials

• Companion cells a normal plant cell connected to at least 1 sieve element– Lots of mitochondria and

ribosomes. Why?• Very metabolically active

– Spends ATP to pull in sucrose from other cells; pass on to sieve element through plasmodesmata

Loading Sucrose• Mesophyll cells Companion cells:

– Sucrose is carried by water through symplast pathway or apoplast pathway

• Entering companion cells:– H+ pump uses ATP to push H+ out of

companion cells• Sets up a H+ conc. gradient

– H+ diffuse back in through a co-transport protein; pull sucrose inside with them

• Entering sieve elements:– Sucrose diffuses into sieve elements

through plasmodesmata and join mass flow

• Leaving sieve elements:– Sucrose enters companion cell by

diffusion through plasmodesmata• Entering Root cells:

– Actively pumped into cells and stored in large vacuole is conc. of sucrose is high

Evidence for Loading Sucrose• What characteristics would

you expect to find around the phloem if “active loading” is occurring?

1) Phloem sap has a basic pH (about 8)– H+ pushed out of cell, so inside

becomes more basic2) Electrical potential across the

plasma membrane (-150 mV)– Just like in nerves, high conc. Of

+ ions outside makes electrical potential

3) ATP is high conc.– Need for active transport

Xylem Vs. PhloemCharacteristic Xylem Phloem

Material Transported WaterIons/Minerals

SucroseProteins

Organic Substances Force Powering

TransportTranspiration

CohesionAdhesion

Source/SinkGravity

Direction of Transport Only from roots to leaves

In all directions in plant

Type of Cells In Tissue Mostly dead cells with living cell for support

Only living cells

Reaction To Damage Redirect xylem solution to other xylem

elements

Releases Callose (β 1,3) to clot hole quickly