9.1 TransportintheXylemofPlants

PlantStructure

Labelthediagramoftheleaftissueofaplant

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Explainthelocationofthemesophyll(palisadeandspongy)andvascularbundlewithintheleaf

PalisadeMesophyll:…………………………………………………………………………………………………………………………

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VascularBundle:……………………………………………………………………………………………………………………………..

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Identifythefollowingplanttissues(monocotvsdicot;rootvsstem)

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Vascular bundle

Xylem

Phloem

Epidermis (lower)

Waxy cuticle

Guard cell

Stoma

Palisade mesophyll

Spongy mesophyll

On the upper surface of the leaf, the cells are packed tight and rich in chloroplasts

This increases light absorption for photosynthesis

On the lower surface of the leaf, the cells are interspersed by space and near stomata

This increases gas exchange for photosynthesis

Vascular bundles exist centrally between the two layers (allowing equal access)

Have xylem for water transport to leaf & phloem for food transport from leaf

Monocot root Monocot stem Dicot root Dicot stem

XylemStructure

Describethestructureofthexylem

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Drawthestructureofprimaryxylemvesselsinstems

Transpiration

Definetranspiration

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Differentiatebetweenfibrousandtaprootsystems

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Tap:………………………………………………………………………………………………………………………………………………...

Xylem Phloem

Lignin Meta Proto Pit Cellwall

Xylem Phloem

MICROSCOPE DRAWING

Inner lining is composed of dead cells that have fused into a continuous tube

These cells lack a cell membrane, allowing water to enter the xylem freely

The cell walls have thickened cellulose and are reinforced with lignin (annular or spiral)

The outer layer is perforated (has pores), enabling water movement out of xylem

Transpiration is the loss of water vapour from the leaves and stems of the plant

Fibrous roots are thin and very spread out

Tap roots penetrate deeply (for stability) and have many connected lateral branches

Explaintheuptakeofmineralionsintotherootbydirectandindirectactivetransport

DirectActiveTransport

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IndirectActiveTransport

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Outlinetheroleofstomatainregulatingthelevelofevaporationfromtheleaf

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Definecohesionandadhesion

Cohesion:………………………………………………………………………………………………………………………………………..

Adhesion:………………………………………………………………………………………………………………………………………..

Explainhowwateristransportedaroundtheplantviaatranspirationstream

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Protein pumps use ATP to translocate ions against their concentration gradient

Proton pumps expel H+ ions into the soil, displacing the cationic minerals from clay

Displaced minerals will passively diffuse into the root (along a concentration gradient)

Anionic minerals may bind to the H+ ions and be reabsorbed with the proton

The transpiration rate can be regulated by the guard cells

which flank the stomata

Guard cells occlude the opening when flaccid

Guard cell turgor is regulated by abscisic acid

Water molecules stick together (by H-bonding)

Water molecules form polar associations with the wall of the xylem vessel

Some of the light energy absorbed by leaves changes into heat, converting water to vapour

The vapour diffuses out and is evaporated, creating a negative pressure gradient in leaves

New water is drawn via the xylem from roots (which enters from soil via osmotic uptake)

Water rises up (against gravity) through xylem vessels via mass flow due to cohesion and adhesion

The flow of water from the roots to the leaf (via the xylem) is called the transpiration stream

Explainhowabioticfactorsaffecttherateoftranspirationinatypicalterrestrialplant

Light:………………………………………………………………………………………………………………………………………………

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Temperature:………………………………………………………………………………………………………………………………….

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Wind:……………………………………………………………………………………………………………………………………………...

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Humidity:………………………………………………………………………………………………………………………………………..

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Identifyfouradaptationsinxerophytesandhalophytesthathelpreduceorincreasetranspiration

Xerophyte Halophyte

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Issue

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Adaptations

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Listthreewayswatertransportcanbemodelledinxylem

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Describehowpotometerscanbeusedtomeasuretranspirationrates

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Increasing ambient temperature causes an increase in the rate of transpiration

Higher temperatures lead to an increase in the rate of evaporation within the mesophyll

Increasing the light intensity to which a plant is exposed increases the rate of transpiration

Increasing light exposure causes more stomata to open to facilitate photosynthetic gas exchange

Increasing the level of wind exposure causes an increase in the rate of transpiration

Wind / air circulation removes water vapour from near the leaf, effectively reducing proximal humidity

Increasing the humidity is predicted to cause a decrease in the rate of transpiration

Less vapour will diffuse from the leaf if there is more vapour in the air

Arid / dry and high temperatures Saline (salty soil / water)

Increased water loss via evaporation

Reduced water uptake via roots

Reduced water uptake due to hypertonic

soil conditions (+ high levels of salt uptake)

Reduced leaves (⬇ evaporation)

Thick cuticles (prevents water loss)

Stomata in pits (traps water vapour)

CAM physiology (open stomata at night)

Cellular sequestration (salt in vacuoles)

Tissue partitioning (leaf abscission)

Salt excretion (active salt removal)

Root level exclusion (avoid salt uptake)

Capillary tubing

Porous pots

Filter paper

Potometers estimate transpiration rate by measuring the rate of water loss or uptake by a plant

They record the distance moved by an air bubble or meniscus to indicate the rate of water uptake