8b Flashcards by Josie Norris

Movement of water through xylem is due to which properties of water?

Cohesion and adhesion

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Cohesion- tension hypothesis: water loss through…

Stomata and cuticle transpiration

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Cohesion- tension hypothesis: related to water potential

At start leaf has potential between 0 and-1MPa
stoma opening results in water loss
cells near stoma reduce water potential
water flows from cells further away toward stoma
results in water gradient

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What does transpiration provide for water movement

The pull

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What works against transpiration?

Gravity

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Gravity gives a ______ water potential

It is more negative at the _____ of the stem than _____ stem

Negative

Top, lower

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Is vertical or lateral movement more difficult?

Vertical movement

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For every 10 meters of height the leaf water potential must be ______ more -ve than root water potential

0.1MPa

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Leaves of a 30m tree must be ____ more - ve than roots

0.3MPa

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Which 3 plant parts are not affected by gravity because they have lateral movement?

Stolons, rhizomes, and vines

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Does cohesion or adhesion resist water movement?

Adhesion

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Water interacts with cell walls Of ________ _________

Vessel elements

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As soil dries its water potential becomes more negative or positive?

More negative

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Leaves lose water faster because the xylem can’t replace it

During night or day?

During the day

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Stomata close and leaves are rehydrated

During night or day?

During night

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Soils water potential varies by what?

Soil type and % moisture

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Roots must have higher or lower water potential than soil to attract water?

Lower

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Roots must have higher Or lower water potential than leaves?

Higher

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What puts plants under stress?

Dry air and soil

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If stomata closes how does transpiration loss still occur?

Through the cuticle

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Tension on the water column can result in

Cavitation

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What is cavitation

The rupture of a water column

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Cavitation can result in

An embolism that can spread

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What is an embolism?

The filling of vessels or tracheids with air or water vapour

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In tracheids what can the bubbles not pass through? And what are they restricted to?

Bubbles can't pass through the pit membranes Restricted to one tracheid

In vessels what does the bubble follow through to empty the whole vessel?

Perforation plates

Transpiration is the: A) flow of water through the xylem B) loss of water Vapor from plants C) absorption of water by roots D) loss of carbon dioxide from leaves

B) loss of water Vapor from plants

Approximately ________ % of the water transpired by a plant is lost through its stomata a) 10 b) 25 c) 60 d) 90

d) 90

Which of the following is NOT consistent with cohesion-tension theory? A) a gradient of water potential exists between the stem and root B) transpiration brings an increased water potential in the leaves C) water in xylem is under tension D) a gradient of water potential provides the driving force for the movement of water from the soil through the plant to the atmosphere

B) transpiration brings an increased water potential in the leaves

In vascular plants, cavitation is the: A) ruputure of water columns B) expulsion of air from water columns C) formation of air bubbles due to particulate matter D) reduction of surface tension at the meniscus spanning pores in the pit membrane

A) ruputure of water columns

What is hydraulic redistribution?

Passive movement of water from Wet to dry soil via roots

hydraulic redistribution: how is water taken up? Soil conditions? how and where is it transferred to?

Water taken up by up roots in moist soil is transferred to dry soil via shallows roots

What does hydraulic redistribution redistribute?

Soil water

When does hydraulic redistribution occur?

At night or during low transpiration periods

Root pressure: when and why does movement of water occur

At night movement of water occurs when ions are secreted into the xylem

Root pressure: ions secreted into the xylem does what to water potential in the xylem and allows water to do what?

Decreases water potential in xylem and allows water to flow

Root pressure: Decreased water potential in the xylem creates what pressure in the xylem and forces water which direction?

Positive pressure, upward

Root pressure: positive pressure in xylem causes what?

Guttation

What is guttation?

Exudation of liquid water from leaves

How are assimilates transported?

From source to sink

What are assimilated carbons?

Carbohydrates in phloem tissue

What is a source

Site from which assimilate solutes are transported

What are sinks

Plant parts unable to meet their own nutritional needs

In spring and summer, what is the predominant source for long-distance phloem transport?

Leaves

Name 2 storage sites when exporting assimilates

Tubers and corms

Sinks are sites that receive transported:

Phloem sap

Name 3 things that can be sinks

Meristems or root tips, developing fruit and seeds, storage tubers and corms

Are the different types of sinks active at the same time?

What is the pressure flow hypothesis?

Assimilates are transported from sources to sinks along a gradient of turgor pressure developed osmotically

pressure flow hypothesis: sugars are loaded into sieve tube-companion cell complexes at a _________

Source

pressure flow hypothesis: water potential of sieve tube is

Decreased

pressure flow hypothesis: water moves into _______ ____ from xylem by osmosis

Sieve tube

pressure flow hypothesis: pressure _________ at the source

Increases

pressure flow hypothesis: removal of sugar from sieve tubes at a _______ increases ___________ _______ of sieve tube

Sink, water potential

pressure flow hypothesis: water moves out by

Osmosis

pressure flow hypothesis: _______ have lower pressure than _________

Sinks, sources

pressure flow hypothesis: sugar molecules are carried passively by water along the _________ ______ from _______ to _______

Concentration gradient Source Sink

Sieve tube elements are

Living cells

Vacuole membrane of sieve tube elements disintegrates and vacuole contents mix with_________ to give__________ ______

Cytoplasm, phloem sap

Vascular bundles vary in ______ and _______ of transfer

Speed and site

Phloem loading is apoplasticc or symplastic?

Can be either

Apoplastic is seen in many _______ plants

Herbaceous

Sugars from mesophyll cells initially follow a ___________ pathway

Symplastic

Sucrose loading involves

Sucrose-proton symport

What is symplastic

Sugars move entirely via plasmodesmata from mesophyll to sieve tubes

Polymer trapping mechanism

Sucrose diffuses from bundle- sheath cells to intermediary cells

Polymer trapping mechanism: sucrose is used to synthesize _________ and _________

Raffinose and stachyose

Polymer trapping mechanism: these polymers cannot diffuse back to the bundle sheath cells but can go into:

Sieve tubes

Passive symplastic loading is seen in:

Many tree species

Sugars produced at high levels in mesophyll diffuse along concentration gradients to ________ ______

Sieve tubes

Phloem unloading: at the _______, sucrose is transported out of sieve terse elements

Sinks

Phloem unloading is apoplastic or symplastic

Can be both

Phloem unloading: transport into sink tissues depends on

metabolic activity

Why don't source cells have a higher water potential?

Sugars are transported at the same rate they are synthesized The sere no loss in water potential in source cells In tubers sucrose leaves the cell at the same rate as starch is depolymerized

Why don't sink cells have a more negative water potential?

Sucrose is depolymerized into starch or cellulose Flow direction is controlled by unknown switch mechanism (pump is regulated) Young leaves switch from sink to source upon maturity

What are 3 components of water potential?

Osmotic, pressure, matric

Which of the potentials measure's waters interaction with dissolved material?

Osmotic potential

What is the water potential of pure water?

Does water potential become more positive or negative as you add solute?

More negative

When water potentials of two cells are in equilibrium is there any net movement of water?

Water moves by osmosis into a plant root because

Water moves towards areas of higher solute concentration

Minerals will more into a root hair cell when:

When solute concentration is lower inside the cell and transport proteins are present