Chapter 18 - Transport System (Part 4)

7/30/2019 Chapter 18 - Transport System (Part 4)

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TRANSPORT SYSTEM

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PREVIOUS LESSON


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LECTURE 4

18.3:

TRANSPORT

IN PLANTS


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OBJECTIVES

At the end of this topic, students should be able to:

Describe water movement via xylem by transpiration-

cohesion-tension mechanism and root pressure.

Describe mineral ion uptake in roots by active transport and

diffusion.

Describe the Pressure Flow Hypothesis in phloem.


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Biology Unit, KMPk 5

FibersFibers

PitPit

TracheidsTracheids

PerforatedPerforated

End WallsEnd Walls

VesselVessel

ElementElement

The Structure of

Xylem


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The Structure of

Xylem

Xylem is a mixture of cell types,

parenchyma and

sclerenchyma fibers (ground tissue)

and two types of conducting cells (allowing water and

dissolved minerals to move)

tracheids; thin with tapered, overlapping ends

joined by pits

vessel elements; The end walls of some vessel

elements are absent, and others have narrow

openings that connect adjacent vessel elements


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Biology Unit, KMPk7

Root pressure

Cohesion

Adhesion

Transpiration pull

Water movement via xylem


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Root pressure

The pressure in xylem sap that

occurs as a result of the active

absorption of mineral ions

Mineral ions that are activelyabsorbed from the soil into the

xylem Lowers the water

potential in roots

Water potential in the soil

became higher

Water moves into roots by

osmosis


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Water accumulate in root

tissues

Produces hydrostatic

pressure

Forces water move up from

soil to root through the

xylem

Root pressure


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Biology Unit, KMPk10

occur in the stem

Is the force of

attraction betweenwater molecules

caused by hydrogen

bonding.

Allow unbroken

column of water to be

pulled up the xylem.

Cohesion


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Attractive force

between water

molecules and thexylem walls

Help to prevent the

water column from

moving down

Wall of

tube

adhesive

force

Cohesive

force

Adhesion


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Transpiration Pull

Water evaporates from the

mesophyll cell into

atmosphere

The loss of water lowersthe water potential of

these cells

Produces tension in thexylem

Creates a force that pulls

water upward.


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Water move

into the

mesophyll cell

by osmosis froman adjacent cell

(high water

potential)

Transpiration Pull


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Mineral ion uptake

in root

The concentration of

ions is lower in the soil

than in the root

The transport of ionsby active transport

(from the soil into the

root) required ATP


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Mineral ion travels in

root via apoplast and

symplast pathway

Mineral ion uptake

in root


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Biology Unit, KMPk 18

Sieve Plate

Sieve-tube

Element

Companion

Cell

Schlerenchyma

Cells

Structure of Phloem


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Phloem is a mixture of cell types,

sclerenchyma,

sieve-tube elements (form the conducting system of

phloem), and companion cells (nourishes sieve-tube elements and

regulates its function)

Structure of Phloem


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Translocation of Phloem

Sap

Translocation:

Movement of organic

solute from the leaves

(source)

to the sieve tubes and

carried to other parts of

the plant (sink)


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Sugar source: sugar

production organ

leaves

Sugar sink: sugar storage

organ

growing roots,

tips,

stems,

fruit

Translocation of Phloem

Sap


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At the source, sucrose

is produced by

photosynthesis

Sucrose is activelytransported from the

source into the sieve

tube

The companion cell

supplied the ATP for

the active transport

PRESSURE FLOW

HYPOTHESIS


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The accumulation of sucrose

(solute) lower the water

potential

Water moves by osmosisfrom the xylem into the

sieve tube.

The entry of water generatesa high hydrostatic pressure

in the sieve tube

PRESSURE FLOW

HYPOTHESIS


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Than create difference

in hydrostatic pressure

between the source and

sink exist

Sucrose is passively

transported to the sieve

tube near to the sink

PRESSURE FLOW

HYPOTHESIS


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At the sieve tube near to the

sink, sucrose is actively

transported into the sink

Energy provided bycompanion cell near the sink

Lowering the hydrostatic

pressure at the sieve tubeWater move from the sieve

tube into the sink by osmosis

PRESSURE FLOW

HYPOTHESIS


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Conclusion

Water movement via xylem


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Conclusion

Translocation ofphloem sap based on

pressure flow

hypothesis


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NEXT LECTURE

CHAPTER 19.0HOMEOSTASIS

Chapter 18 - Transport System (Part 4)

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